Does the human abdominal cavity use pressure to maintain posture?

Does the human abdominal cavity use pressure to maintain posture?

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Several of my PT friends have referenced a physical therapist p who has studied breathing named Mary Massery. In her articles, she has referenced the idea of "intra-abdominal pressure"

See page 2

If I am understanding her correctly, she is basically saying that

  • an unopened soda can is sealed and hard because of the pressure inside the canister
  • the human trunk tries to support itself upright. In this sense it is rigid. Therefore, it too must be using an internal pressure to create the rigidify necessary for uprightness. This is what she calls "intra-abdominal pressure."

My Question

Given what is known about the mechanics of human breathing, do the pressures of the abdominal cavity actually behave this way? Does the abdominal cavity rigidity itself using some sort of pressure? If so, how does this pressure mechanism relate to the mechanisms used during respiration?

If I am understanding her model correctly, I am extremely skeptical. A soda can is really not similar at all physically to the abdominal cavity.

I found this review which can help to clarify this notion of intra-abdominal pressure : Intensive Care Med. 2009 Jun;35(6):969-76. What is normal intra-abdominal pressure and how is it affected by positioning, body mass and positive end-expiratory pressure? De Keulenaer BL1, De Waele JJ, Powell B, Malbrain ML. The authors mention that there is indeed a positive pressure in the normal subject. This IAP is contributed by gravity, uniform compression (abdominal contraction, diaphragmatic contraction, mechanical ventilation, rib cage excursions) and shear deformation, this last one depending on the intrinsic stabilty of the tissue. The authors conclude that "the abdomen behaves as a hydraulic system with normal IAP of about 5-7 mmHg… ". Kind of a can of soda, without the bubbles… Pathologies affecting this pressure are named "abdominal compartment syndrome) and result from multiple etiologies (obesity, trauma… ,).

Does the human abdominal cavity use pressure to maintain posture? - Biology

António M. Lopes 1 , 2 , , Andreia Nunes 2 , Maria M. R. E. Niza 3 , António Dourado 1

1 University of Coimbra – Department of Informatics Engineering, Center for Informatics and Systems of the University of Coimbra (CISUC), Polo II University of Coimbra, 3030-290 Coimbra, Portugal

2 University Lusofona – Faculty of Veterinary Medicine, Avenida do Campo Grande, 3761749-024 Lisboa, Portugal

3 University of Lisbon - Faculty of Veterinary Medicine, Avenida da Universidade Técnica, 1300-477 Lisboa, Portugal


Background: Increased intra-abdominal pressure (IAP) is a complication related to physio pathological changes with high rates of mortality and morbidity. Abdominal surgery is consider one of the risk factors that can increased IAP. Measurement can be done by direct or indirect methods, being the most used the transurethral (TM). However this method continues to generate some controversy. This study tries to clarify the doubts of the effect of body position when we use different methods to measure IAP. Methodology: Study realized an anatomical model in order to eliminate the described variables that influence IAP: abdominal and gastric contraction, micturition reflex and breathing. IAP was measured, directly, via microsensor and, indirectly, by TM and intragastric manometry, in five different body positions. The study population consists in a population of 29 anatomical model, 14 males and 15 females, with an average weight of 12.04 ± 5.67 kilograms (Kg). The inclusion criteria consisted in the absence of abdominal disease that would. Principal Findings: IAP determination by direct method showed no differences in the five body positions (P=0.765). The indirect method with better correlation with the direct was TM (cc0.87). Indirect methods revealed statistically significant differences with the direct, only in the Trendelenburg and reverse Trendelenburg. Conclusions: The clinical impact of this study is to decrease the doubts in the measurements of IAP. This study improves the knowledge of the application of the direct and indirect methods to accesses IAP. IAP is not affected by body position and the direct pressure value measured in all positions is constant. Only if the indirect methods are used, in Trendelenburg and reverse Trendelenburg positions, they may underestimate or overestimate IAP value. For the first time it was explained why this phenomenon occurs.

Keywords: Abdominal surgery, Intra-abdominal pressure, transurethral method, intragastric manometry, body position

Copyright © 2016 Science and Education Publishing. All Rights Reserved.

Cite this article:

  • António M. Lopes, Andreia Nunes, Maria M. R. E. Niza, António Dourado. Intra-abdominal Pressure is Influenced by Body Position?. American Journal of Clinical Medicine Research. Vol. 4, No. 1, 2016, pp 11-18.
  • Lopes, António M., et al. "Intra-abdominal Pressure is Influenced by Body Position?." American Journal of Clinical Medicine Research 4.1 (2016): 11-18.
  • Lopes, A. M. , Nunes, A. , Niza, M. M. R. E. , & Dourado, A. (2016). Intra-abdominal Pressure is Influenced by Body Position?. American Journal of Clinical Medicine Research, 4(1), 11-18.
  • Lopes, António M., Andreia Nunes, Maria M. R. E. Niza, and António Dourado. "Intra-abdominal Pressure is Influenced by Body Position?." American Journal of Clinical Medicine Research 4, no. 1 (2016): 11-18.

At a glance: Figures

1. Introduction

Increased intra-abdominal pressure (IAP) is a complication related to physio pathological changes in cardiac, respiratory, renal, gastrointestinal, liver and nervous systems. Increased IAP may originate pathological changes, causing abdominal compartment syndrome [1, 2, 3, 4] . These alterations influence vital functions of the patient, which lead to a high mortality and morbidity [3, 5, 6, 7, 8] . One of the main risk factors, is the diminished abdominal wall compliance caused by abdominal surgery [7, 9, 10] . Hernia and its surgical repair are also linked with elevated IAP [11, 12, 13] .

The measurement of IAP may be performed through direct or indirect methods. Direct measurement of IAP is used as a reference to indirect methods [14, 15] and can be measured with a solid microtranducer placed in the abdominal cavity [16] . The use of indirect methods has advantages due to it being less invasive, more cost efficient, and easier to use [17, 18] . The transurethral method (TM) is the most commonly used for measuring IAP and it is considered the gold standard [17, 19, 20, 21] . This method has already been clinically validated [22] . However, the measurement of IAP by TM continues to generate some controversy due to the large number of variables that can affect it, questioning its reproducibility [17, 23, 24, 25, 26, 27, 28] . Intragastric manometry (IGM) is other indirect method used to measure IAP by means of a nasogastric or gastrostomy tube when TM cannot be used. IGM also has already clinically validated [15, 20, 29] . Davies and co-workers compared the indirect methods, TM and IGM, with direct measurements via peritoneal dialysis catheter and conclude that the TM achieved better correlation coefficients in comparison with IGM [30] . There are also several studies comparing IAP measurement methods using animal models of rabbits, pigs and dogs [18, 31, 32] . Although the above studies show similar findings, they have poor experimental design and cannot fully explain the divergent results obtained in clinical practice.

Most patients in intensive care unit (ICU) are nursed with an head-of-bed elevation to reduce the risk of ventilator-associated pneumonia and pressure ulcers (33). Measuring IAP via the bladder in the supine position is still the accepted standard method but sometimes these measurements are made with head-of-bed elevation (34). Several studies describe that the patient´s position influence the measurement of IAP [26, 35, 36, 37] .

The role of TM as the gold standard for IAP has become a matter of debate but in our days continues to be the most used to access IAP in clinical patients and experimental study´s worldwide [17, 20] . The incorrect use and interpretation of TM can influence the IAP measurements. This study tries to clarify the doubts of the effect of body position when we use different methods to measure IAP. The value of IAP is also used to determine abdominal perfusion pressure (APP) which is an accurate predictor of visceral perfusion in patients. APP and IAP are booth clinical parameters used to classify the degree of abdominal hypertension. The accurate measurement of IAP is clinically relevant to not influence practician in the wrong way.

2. Materials and Methods

The methodology used in this study was chosen because of the difficulty of eradicating some of the variables that influence the method and all the ethical issues linked to experimentation. Using an analytical approach of breaking a problem down into smaller problems the study was realized in a cadaver anatomical model of the abdominal cavity. Like this, the large number of variables that affects IAP was reduced to a single variable: influence of body positon. The anatomic model of the abdominal cavity allowed the eradication of the described variables that influence IAP: abdominal and gastric contraction, micturition reflex and breathing [23, 37, 38, 39, 40, 41, 42, 43] . The model of the abdominal cavity used was from dog, to maintain the similarity of the anatomical biology. To avoid changes in tissue tension and elasticity of the cavity´s the study was performed immediately after cadaver´s entry into the service of pathological anatomy.

The study population consists in a population of 29 dog cadavers, 14 males and 15 females, with an average weight of 12.04 ± 5.67 kilograms (Kg), received for necropsy at the Department of Pathology, Faculty of Veterinary Medicine. None of the animals used in this study were euthanized for this purpose. The inclusion criteria consisted in the absence of abdominal disease that would affect the abdominal cavity and its organs, which was confirmed by necropsy. All cadavers showing marked alterations of tension and elasticity of the abdominal cavity and its organs were eliminated from the study.

The IAP was measured by three methods - Direct, TM and IGM (Figure 1) - in five different positions – lateral, ventral and dorsal recumbency, Trendelenburg and reverse Trendelenburg (45 degrees angle). All measurements were performed before the necropsy and all the determinations were carried out in the framework of normal necropsy.

IAP measurement was held directly through an intra-peritoneal catheter of 16 G. The insertion of the catheter was performed at the midline near the umbilicus scar. Two sites of increased resistance were noted during cannula placement: the peritoneal aponeurosis and the peritoneal serosa. Once in the peritoneal cavity, the CODMAN sensor (Codman, Johnson & Johnson) was inserted inside the catheter, until it entered into the abdominal cavity [16] . Readings were carried out after the stabilization of the pressure [3] . Before introducing the catheter into the abdomen, the sensor was calibrated according to the manufacturer's instructions and the reference was adjusted to zero, the reference being atmospheric pressure [16] .

2.2. Indirect IAP Measurements

The existing indirect methods to measure IAP are mostly based on the use of a water column metrically divided [17] . Indirect systems such as TM and IGM allow the connection between organic structures and a water column by urinary and gastric medical disposable catheters, extensions and three-way stopcock. Both systems allow IAP measurement after allowing, by means of the three-way stopcock, the dynamic balance between the water column and the fluid restrained in the bladder or stomach, respectively (Figure 1). The conversion to mmHg was done by multiplying by 0.736 [16] .

The TM was originally described by Kron and co-workers [44, 45] , but suffered some modifications [17] . One of the most commonly used modifications is the closed technique, proposed by Cheathman and co-workers [46] . This technique has some advantages over the initial method for which it was applied in this study [17] . IAP was measured via a transurethral bladder catheter. The bladder was emptied and a standard volume of sterile saline solution, 0.5 to 1 ml/kg of 0.9% saline, was instilled into the bladder to slightly distend it (too much saline in the bladder would elevate IAP) [19] . A three-way stopcock was connected to the transurethral bladder catheter and the other entrance was connected to a column of water, filled with sterile saline solution, to create a closed system. Once saline was instilled into the bladder, the three way stopcock was turned on, to allow the connection between the animal’s bladder and the fluid column contained in the extension set. This led to the decrease in height of the fluid column, until its pressure was balanced with the pressure inside the bladder. The equilibrium point was considered to be the IAP. Its numerical value was obtained considering the zero point of the metric scale to be the level of the patient’s symphysis pubis [19, 47] .

The IGM is similar to the TM, but the water column is connected to the stomach instead of the bladder. IAP pressure was measured via a standard nasogastric tube, which is positioned in the stomach. In this procedure, the volume of fluids instilled in the stomach was 50 ml per animal. We then allowed the connection between the fluid contained in the stomach and the water column, as to reach the equilibrium point. This point was considered to be IAP [17, 32] .

Consecutive measurements were carried out by indirect and direct methods in the five positions: lateral, ventral and dorsal recumbency, Trendelenburg and reverse Trendelenburg (Figure 2 - 45 degrees angle). All values were recorded in a database. Finally, necropsy was performed to confirm if the direct measurement catheter was inside the abdominal cavity and if the indirect catheters were in the bladder and stomach. It was also confirmed the non-existence of pathological alterations of the abdominal cavity. All dogs which revealed disease affecting the cavity and its organs were excluded.

The data was analysed using the SPSS program (Statistical Package for the Social Sciences, 2010 version), which made a comparison between all variables. Analysis of variance (ANOVA) was used to identify significant differences between the averages of the groups. The Pearson coefficient correlation test was used to analyse relationships between the various pressures. Values are expressed as mean ± standard deviation and statistical tests of mean comparisons differences were considered statistically significant when P <0.05.

3. Results

The pressure measurements by direct sensor showed very constant readings in all positions. In lateral recumbency average, pressures were 3.1 ± 3.0 mmHg in ventral recumbency, 2.3 ± 3.4 mmHg in the dorsal recumbency, 1.9 ± 3.4 mmHg in Trendelenburg position, 2.4 ± 3.2 mmHg finally, in reverse Trendelenburg position, 2.2 ± 3.3 mmHg (Table 1).

Table 1. Average IAP of the measured values by direct method in mmHg

The comparison of the direct values of IAP in the various positions did not reveal statistically significant differences (P = 0.765).

The pressure measurements by TM showed stable readings in lateral, ventral and dorsal recumbency, but some differences in the Trendelenburg and reverse Trendelenburg position. In lateral recumbency, mean pressures were 4.5 ± 3.1 mmHg in ventral recumbency, 3.6 ± 2.9 mmHg in dorsal recumbency, 3.4 ± 3.4 mmHg in Trendelenburg position, 2.6 ± 3.1 mmHg in reverse Trendelenburg position, 4.6 ± 2.9 mmHg (Table 2).

Table 2. Average IAP of the measured values by transurethral method in mmHg

The comparison between the values of IAP obtained by TM in the various positions did not show statistically significant differences (P = 0.091).

The pressure measurements by IGM showed variable readings, with considerably different values in Trendelenburg and reverse Trendelenburg position. In lateral recumbency, mean pressures were 4.7 ± 2.2 mmHg in ventral recumbency, 3.0 ± 1.6 mmHg in dorsal recumbency, 2.6 ± 1.9 mmHg in Trendelenburg position, 7.1 ± 2.7 mmHg in reverse Trendelenburg position, 0.1 ± 0.3 mmHg (Table 3).

Table 3. Average IAP of the measured values by intra-gastric manometry method in mmHg

The comparison between values of IAP obtained by IGM in the various positions revealed statistically significant differences (P = 0.0001).

3.4. Comparison of Methods

The measurements obtained by the three methods were subsequently compared with each other to see if there were differences between methods.

Table 4. Level of significance between the measurements made by the three methods, in the five positions

It was observed that lateral, ventral and dorsal positions showed no statistically significant differences between them (P >0.05), with identical mean values obtained with through methods (Table 4). As for the efficacy of the direct IAP sensor, significant correlation coefficients (cc) were observed between the IAP measurements obtained directly versus indirectly: direct versus TM, cc. 0.87 direct versus IGM, cc. 0.28 TM versus IGM, cc. 0.25.

Regarding Trendelenburg and reverse Trendelenburg position, the IAP values obtained by the three methods showed statistically significant differences between groups (P< 0.05).

4. Discussion

The measurement of IAP can be useful for detecting early changes, such as intra-abdominal hypertension or alterations in APP. When IAP values are greater than 12 mmHg it is symptomatic of intra-abdominal hypertension, and compartment syndrome is generally considered when IAP values are greater than this in combination with at least one end-organ failure [4, 48, 49] . Abdominal compartment syndrome is the pathophysiological consequence of raised IAP, including reduction in perfusion, ventilation deficit, oliguria and other renal problems, and increased intra-cranial pressure [3, 5, 48, 50] . Abdominal surgery is consider one of the risk factors that can increased IAP [7, 21, 31, 50, 51] . It is documented that hernioplasty and changes of anatomic stuctures in hernia´s are also responsible of IAP alterations [7, 11, 12] .

Although there are several doubts regarding the measurements of IAP, the indirect methods used for determination of IAP are considered the most accurate to evaluate this parameter [17] . The choice of method usually points to the TM, since it is consider the gold standard [17, 19, 20, 21] . In our study, we used the modified technique of Kron, proposed by Cheatham and Safcsak [17, 46] . This technique minimizes the risk of urinary tract infections and sepsis, contrary to the original technique proposed, allowing the possibility of repeated measurements and reduced costs [17] . We also used the MIG to determine IAP since it is usually the alternative, when the TM cannot be used (urinary tract infection, pelvic trauma and cistotomy). This technique is also very cost efficient, it doesn’t interfere with urine output and the risk of infection is absent, making this technique perfect to screening IAP, comparing its costs to the results [17] .

The direct measurement through Codman´s micro sensor, micro miniature silicon strain gauge type sensor, was first used by Pracca and co-workers [16] . They concluded that these sensors allow continuous monitoring, without urinary tract manipulation, are simple to use and to calibrate and are minimally invasive. The problem with this sensor is its cost, for which it should be reserved for patients where standard techniques cannot be used [16] .

The MT is widely used in ICU and scientific studies and sometimes the findings may be influenced by the method. In the literature there are several studies about the variables that affect IAP but none of them study each variable singly. In these studies all the variables that affect the IAP are always present. The type of methodology used in this study was chosen because three reasons: 1 - The difficulties linked to human experimentation and ethical issues (is not ethical rotate a patient to five positions, and measure IAP by three methods at the same time point) 2 - The difficulty of creating an artificial model of the abdominal cavity and 3- The difficulty of eradicating some of the variables described that influence the measurement of IAP. Using an analytical approach of breaking a problem down into smaller problems, the study was realized in an animal anatomical model of the abdominal cavity. Like this we have an anatomical model of the abdominal cavity with scale and similarities to humans. The principal difference between the abdominal cavity of dogs and humans is the orientation of the organs because animals walk in prone position. This fact can influence abdominal compliance which affects IAP. These and other differences lead to different values of IAP between species. However the type of cavity, the anatomical constituents and the definition of abdominal pressure is similar. This type of study has many advantages, since it allows the elimination of variables that are identified in the literature as being liable for influencing IAP measurement [38-43] [38] . For this reason, the following variables will not be present: abdominal and gastric contraction, micturition reflex and breathing [23, 37, 38, 39, 40, 41, 42, 43] . Therefore we have a better explanation of the methods used, whilst maintaining the ethics of the study. Like this we only experiment the variable under study: the effect of body position.

The normal values in humans for IAP are 0.2-12.2 mmHg [1, 7] and the normal interval in dogs is between 0 and 3.75 mmHg, however, in animals submitted to ovariohysterectomy, IAP values can reach up to 11.25 mmHg, without symptoms of hypertension [7, 19, 47] . Recently Way and co-workers (2014) found in dogs higher average IAP values (5.9 ± 1.0 mmHg) than those previously described [52] . Although the present study was performed in cadavers, IAP values established are within the limits defined for the species, as shown in Table 1, Table 2 and Table 3. The fact that IAP values in cadavers are similar to live animals is directly linked with the definition of IAP, which is nothing more than a pressure state. The pressure state of the abdominal cavity is determined by body mass index, posture, muscular activity of the wall and breath [48, 50, 53] . This definition of IAP is precisely the reason why we decided to carry out a cadaver study. Nevertheless the IAP values obtained can be considered low. Lower values of IAP in this study can be due to loss of tissue tension, the non-existence of respiratory movements and a complete absence of abdominal muscles contraction. It is documented that only the variable muscle contraction may lead to a decrease in 25% of IAP if exists neuromuscular blocking in abdominal surgery [54] . The effect of respiratory movements in IAP was studied by Wilson (1933) and he concluded that there is a rise in IAP during inspiration proportional to the depth of inspiration [55] . He also concluded that no rise of IAP occurs in normal expiration [55] . As in this study there are no respiratory movements will be no change in IAP, independently of the physiological mechanism.

In this study, it was concluded that IAP measurement through the bladder, using urethral or intra-gastric catheter, is, in both cases, an accurate method for measuring IAP in lateral, ventral and dorsal positions in dogs. In these body positions, the three methods showed no statistically significant differences between them (P <0.05), with identical average values obtained with both methods (Table 4). As for the efficacy of the direct IAP sensor, significant correlation coefficients (cc) were observed between the IAP measurements obtained directly versus indirectly: direct versus TM, cc. 0.87 direct versus IGM, cc. 0.28 TM versus IGM, cc. 0.25. The correlation coefficients found for the different methods are in accordance with the literature, although showing lower values [32] . In the study of Engum and co-workers the objective was to compare gastric tonometry with direct IAP in a canine model with simulated abdominal compartmentalization syndrome. The dogs were submitted to laparotomy and a bag of fluid was positioned inside the abdomen. The issue occurred with the anaesthetic protocol. They induced the dogs with thiopental and the anaesthesia was maintained with isoflurane. In the experimental design of this study, the animals were without any analgesia when undergoing laparotomy. This means that the animals could demonstrate pain and, consequently, there could have been abdominal contraction, which is one of the factors that may result in IAP increase [38, 40] . This fact can explain the differences between the correlation values of our study and Engum work. Another fact that may explain the difference between the correlation coefficients is the absence of contraction by abdominal muscles [54] . Despite these small differences, this study demonstrates that the best indirect method for measuring IAP in dogs is the TM, similar to what happens in humans [30, 56] .

The IAP values obtained by direct method were quite constant in all the positions studied and no statistically significant differences were obtained (P = 0.765). This presupposes that there is no difference in IAP when body position is altered. This fact is contrary to what is described in the literature, which contradicts the previously described [26, 36, 37] . These studies conclude that IAP values are different depending of the body position. However, all IAP values were determined by indirect methods, namely the TM. We mustn’t forget that TM is based on fluids mechanic and in the principles of hydrostatic. The pressure value obtained depends on the dynamic balance between columns of water, between the bladder and the stomach (17). This type of system has some disadvantages linked to being a fluid-filled system. The displacement of the fluid from an upper pressure to a lower pressure influences the system, as observed in this work. We believe that this fact explains why these studies refer that IAP is influenced by body position. In our work, statistically significant differences were demonstrated between direct measurements and IAP values obtained by indirect methods (TM and IGM) in the Trendelenburg and reverse Trendelenburg position. We believe this to be directly related to the dynamic equilibrium of the fluid column pressures. In such positions, the patient is placed in an inclined plane leading to fluid movement as Figure 2 illustrates. In our study, although measurements are being collected simultaneously by the three methods, we observed that the water in both columns (TM and IGM) demonstrates several alterations when we change the body position, with the direct measurement remaining equal. Thus, in the Trendelenburg position, the TM tends to have values close to zero, since the water column will move in the cranial direction, with the average values decreasing by 50%, 2.6 ± 3.1 mmHg, when compared with the average in lateral, ventral and dorsal recumbency. On the other hand, IGM rises whit a gain of approximately 40%, 7.1 ± 2.7 mmHg. The fluid column, due to the inclination, tends to move anteriorly. Hence, the IAP will be underestimated by TM and overestimated by IGM. In the reverse Trendelenburg position, the opposite occurs, because, as the slope is the opposite, the fluid column movement will be as well, presenting a direction of the fluid flow. Thus, the IAP value reflected a decrease of average values close to zero, 0.1 ± 0.3 mmHg in IGM. Similarly, the movement of the fluid column in this position led to an increase in the IAP value for TM, to mean 4.6 ± 2.9 mmHg. This fact had already been described by De Keulenaer and co-workers when observed that patients with the head of the bed elevated to 30 and 45 degrees had IAP increased [36] . Therefore, in reverse Trendelenburg position, IAP by IGM will be underestimated and by TM will be overestimated. This type of change is not linked to the type of patient (human, dog or cat) or if the study was realized in a living or non-living animal model. This change is directly related to the TM and the principles of fluid mechanics and is going to happen in all species and in any type of model.

There are, however, some indirect systems that accomplish the IAP measurement with an air-pouch localized in the stomach. These systems use air and not liquid, eliminating the disadvantages related with the water column [17, 20, 25] . The problem of this systems is that are not indicated to screening, but is best for continuous fully automated monitoring for a long period of time [17, 20] .

Abdominal perfusion pressure has been demonstrated to be an accurate predictor of visceral perfusion and an end-point for resuscitation [5, 48, 49, 57] . The calculation of the APP is performed by subtracting the value of IAP to the mean arterial pressure (MAP) [48, 49, 57] . As the most widely used method for measuring the IAP is the MT, when the patient is inclined, measurement may be erroneous leading to false judgments of APP. This false assumption can lead the practician to wrong therapeutic decisions.

The clinical impact of this study is improves the knowledge in the measurements of IAP in ICU and surgery blocks allowing proper use of the direct and indirect methods. Direct and both indirect methods to measure IAP in humans and animals have been validated clinically and they are used worldwide in ICUs [15, 16, 19, 20, 22, 29, 37] . Although this study was conducted in a non-living animal model, results provide a better explanation of the IAP. Only a study with this experimental design allows eradicate the variables described of influence the measurements and maintain the ethics of the study. The use of a non-living animal model to realize the study and measure IAP may be controversial. However, the IAP measurements obtained have similar values in live dogs and the physical definition of pressure was not changed.

5. Conclusions

For the first time, is given the explanation why body position can influence the measurement of IAP. The measurements of IAP via the bladder through a urethral catheter, and the measurement via intra-gastric catheter, are both accurate methods for measuring IAP in lateral, ventral and dorsal position. All measurements carried out in Trendelenburg and reverse Trendelenburg position by indirect methods show differences regarding the direct method. This fact can be explained by the movement of the water column, which is the base of the indirect methods.

The values obtained from direct method measurements in different positions (lateral, ventral, dorsal, Trendelenburg and reverse Trendelenburg) have no statistically significant differences. This fact assumes that there are no differences of IAP in different body positions. In the literature it is described that position can alter the IAP because in these studies they use indirect methods based in water manometers. Therefore, in Trendelenburg position the IAP by TM will be underestimated and overestimated by IGM, and in reverse Trendelenburg position the IAP by IGM will be underestimated and the TM will be overestimated.

The indirect methods to obtain IAP are valid methods that give valid information to the practician. However the clinician must know the variables that affect the method to obtain the most reliable information.


The author(s) declare(s) that there is no conflict of interest.

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.


The abdomen is also called the belly, tummy, midriff, or stomach. It is the part of the body between the thorax and pelvis in every human and in other vertebrates. The abdomen is the front part of the abdominal segment of the trunk. The abdominal cavity is the area that is occupied by the abdomen. In the arthropods, the abdomen is the posterior tagma of the body and it follows the thorax or the cephalothorax.

In human beings, the abdomen is between the thorax at the thoracic diaphragm and the pelvis at the pelvic brim. The space above the pelvis inlet and under the thoracic diaphragm is termed the abdominal cavity. The boundary of the abdominal cavity is nothing but the abdominal wall which is in the front and the peritoneal surface at the rear.

In all the vertebrates, the abdomen is a large body cavity that is enclosed by the abdominal muscles at the front and to the sides and by the part of the vertebral column at the back. The ventral and the lateral walls are also enclosed by the lower ribs. The abdominal cavity is very continuous with and above the pelvic cavity. The abdominal cavity is attached to the thoracic cavity by the diaphragm. Through the diaphragm, many structures such as the aorta, inferior vena cava, and the esophagus pass through. A serous membrane line known as the parietal peritoneum lines both the abdominal and pelvic cavities. This membrane is known to be continuous with the visceral peritoneum which lines the organs. The abdomen is known to have many organs such as the digestive system, urinary system, and muscular system.

In this article, we are going to give information about the abdomen, its layers of muscles, functions, various diseases related to the abdomen, and also a few frequently asked questions will also be answered.

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About Abdomen

The abdomen which is commonly known as the belly is the body space found between the thorax and the pelvis. The upper surface of the abdomen is formed by the diaphragm. At the level of the pelvis bones, the abdomen is found to end and the pelvis initially begins.

The abdomen is found to contain all the important organs such as the stomach, small intestines, and the large intestine, the liver, the pancreas, and the gallbladder. All these organs are held together loosely by the connecting tissues which allow them to expand and slide against each other. The kidneys and spleen are also found to be contained within the abdomen. The uterus, urinary bladder, fallopian tubes, and ovaries may be seen as either the pelvic organs or the abdominal organs. The abdomen also contains an extensive membrane known as the peritoneum. An initial fold of the peritoneum is found to completely cover certain organs, whereas it may also cover only one side of the organs that usually lie closer to the abdominal wall, this is called the retroperitoneum. The ureters and the kidneys are known as the retroperitoneal organs.

Muscles of the Abdomen

The abdominal wall is made up of three layers of muscles. External oblique, internal oblique, and transverse abdominal are the three types, from outside to within. Around the vertebral spine, the lower ribs, the iliac crest, and the pubis of the hip are the first three layers. Their fibres both converge at the midline and form a sheath around the rectus abdominis before entering on the opposite side at the linea alba.

The external oblique, which runs downward and forward, the internal oblique, which runs upward and forward, and the transverse abdominal, which runs horizontally forward, provide power.

The fibres of the transverse abdominal muscle run horizontally and are smooth and triangular. It's located between the internal oblique and the transverse fascia underneath it. Poupart's ligament, the inner lip of the ilium, the lumbar fascia, and the inner surface of the six lower rib cartilages are all sources. It goes behind the rectus abdominis and into the linea alba.

The muscles of the rectus abdominis are long and smooth. The tendinous intersections are three fibrous bands that cross the muscle. The rectus abdominis is encased in a dense sheath made up of fibres from each of the three lateral abdominal wall muscles. They start at the pubis bone, run up the abdomen on both sides of the linea alba, and insert into the fifth, sixth, and seventh rib cartilages.

The inguinal canal which is located in the groin region is a passageway between the layers. The testes will fall through the wall here, and the fibrous cord from the female uterus passes through it. This is also where inguinal hernias can develop due to weakness. The pyramidalis muscle is very small and triangular in shape. It is located in the lower abdomen which is in front of the rectus abdominis. The pyramidalis muscle originates at the pubic bone and is inserted into the linea alba halfway up to the navel.

Abdomen Functions

The primary functions of the abdomen consist of breathing, digestion, posture, and balance as well as movement. All the major organs that are located in the abdomen are associated with digestion. The abdomen is very important for breathing via the accessory muscles of respiration. These muscles are also involved in postural support, balance, movement, coughing, urination, vomiting, singing, defecation, and childbirth. A detailed explanation of the function with which the abdomen is associated is given below.


Under steady-state conditions, the diaphragm is known to control respiration, the accessory muscles of respiration help in respiration when a greater effort is required for breathing. The scalene and the sternocleidomastoid muscles are the muscles that serve to raise the ribcage. Whenever these muscles are engaged, it is a sign of respiratory distress, such as the one that is observed during an asthma attack.

Movement and Posture

To maintain the posture, the balance of the body, and the movement, the abdominal muscles are required. The internal obliques and the abdominis muscle greatly affects the posture by providing spinal support during rotation and lateral flexion and also stabilize the spine when a person is in a standing position. Both of these muscles are situated deep in the abdomen. The external oblique muscles are also known to support the lateral flexion and stabilize the spine when standing. The rectus abdominis main function is to help the spine bend in the forward position.

Abdomen Conditions

Here are a few of the abdominal conditions that everyone should be aware of:

Peritonitis: It is the inflammation of the covering of the abdominal structures. This causes the abdominal wall to get rigid and also causes immense pain. This condition is usually caused by ruptured or infected abdominal organs.

Appendicitis: It is caused due to the inflammation of the appendix in the lower right colon. The only treatment of this condition is to remove the inflamed colon with the help of surgery.

Cholecystitis: It is the inflammation of the gallbladder and it causes immense pain in the right side of the abdomen. Many cases have been found to suggest that a gallstone blocking the duct exiting the gallbladder could be the main reason behind this condition.

Dyspepsia: It is the feeling of an upset stomach or indigestion and it is believed that Dyspepsia could be caused by benign or any other series of conditions.

Constipation: A person who has less than three bowel movements per week might be suffering from this condition. It could be caused due to an inappropriate diet or not doing enough exercise.

Gastritis: In this condition, there is an inflammation of the stomach which often causes nausea and pain. Gastritis can also be caused due to the consumption of alcohol, NSAIDs, H. pylori infection, or other factors.

Peptic Ulcer Disease: It is a condition where there are ulcers in the stomach and the duodenum. It is usually caused due to an infection with H. pylori or by taking any anti-inflammatory medications like ibuprofen.

Intestinal obstruction may occur in a particular region of the small or large intestine, or the whole intestine may quit functioning. Symptoms include nausea and stomach distension.

Gastroparesis is a disorder in which the stomach empties painfully as a result of nerve damage caused by diabetes or other disorders. Symptoms include nausea and vomiting.

Pancreatitis is a condition in which the pancreas is inflamed. The two frequent causes of pancreatitis are alcohol and gallstones. Other factors include medications and trauma about 10% to 15% of cases are caused by unexplained factors.

Hepatitis is an inflammation of the liver caused by a virus. Hepatitis can also be caused by drugs, alcohol, or immune system issues.

An abdominal hernia occurs when the abdominal fascia weakens or a void opens, allowing a portion of the intestine to protrude.

Abdominal distension is the swelling of the belly caused by an excess of intestinal gas.

An aortic aneurysm is a balloon-like extension of the vessel caused by a fracturing of the aorta's wall that expands with time. Aortic aneurysms in the abdomen can burst if they develop large enough.

Cirrhosis is a condition in which the liver scars as a result of chronic inflammation. The most prevalent causes are over alcohol or untreated hepatitis.

Cirrhosis is a common cause of ascites, which is an accumulation of fluid in the abdomen. Ascites can make the abdomen protrude noticeably.

Abdomen Treatments

There are many treatments that will help in treating the various conditions related to the abdomen, a few of them are listed below.

Abdominal surgery is done when there are a series of abdominal conditions like cholecystitis, appendicitis, colon or stomach cancer, or an aneurysm.

Histamine(H2) Blockers: Histamine in our body is known to increase stomach acid secretion which causes many complications in our body. Blocking the histamine will evidently reduce the acid production and the GERD symptoms.

Proton Pump Inhibitors: These are the medicines that will directly inhibit the acid pumps in the stomach. They are prescribed in such a way that they should be consumed every day.

Motility Agents: These are the medicines or the drugs that will increase the contractions in the stomach and the intestines. These drugs are used in the management of intestinal motility disorders which include cholinergic agonists, prokinetic agents, opioid antagonists, and antibiotics. These are used to improve the symptoms of constipation.

Antibiotics: Antibiotics can help in curing many infections of the stomach. These antibiotics can be taken with other medicines to help heal the stomach.

Intro to Human Body 46 Bi

The human body begins to take shape during the earliest stages of embryonic development. While the embryo is a tiny hallow ball of dividing cells, it begins forming the tissues and organs that compose the human body. By the end of its third week, human embryo has bilateral symmetry (a body plan in which the left and right sides mirror each other) and is developing vertebrate characteristics that will support an upright body.

OBJECTIVES: Define Anatomy and Physiology, and explain how they are related. List and describe the major characteristics of life. Define homeostasis, and explain its importance to survival. Describe a Homeostatic Mechanism.List and describe the four types of tissues that make up the human body. Explain how tissues, organs, and organ systems are organized. Summarize the functions of the primary organ systems in the human body. Name and locate four human body cavities, and describe the organs that each contain. Properly use terms that describe relative positions, body sections, and body regions.

1. The human body is a precisely structured container of Chemical Reactions.

2. Biology is the Study of Living Things including the Study of the Human Body.

3. The Study of BODY STRUCTURE, which includes Size, Shape, Composition, and perhaps even Coloration, is called ANATOMY.

4. The Study of HOW the BODY FUNCTIONS is called PHYSIOLOGY.

5. The purpose of this course is to enable you to gain an understanding of Anatomy and Physiology with the emphasis on Normal Structure and Function. You will examine the anatomy and physiology of the major body systems.

A. The Chemicals that make up the body may be divided into TWO major categories: INORGANIC AND ORGANIC.

B. INORGANIC CHEMICALS are usually simple molecules made of one or more elements other than CARBON. Examples: Water, Oxygen, Carbon Dioxide (an exception), and Minerals such as iron, calcium, and sodium.

C. ORGANIC CHEMICALS are often VERY Complex and ALWAYS CONTAIN THE ELEMENTS CARBON AND HYDROGEN. Examples: Carbohydrates, Fats, Proteins, and Nucleic Acids.


B. Cells are the smallest living subunits of a multicellular organism such as a human being.

C. There are many different types of cells each is made of chemicals and carries out specific chemical reactions.

A. A Tissue is a group of cells with similar structure and function.

B. There are FOUR Groups of Tissue.

C. EPITHELIAL TISSUE – Cover or line body surfaces some are capable of producing secretions with specific functions. The outer layer of the Skin and Sweat Glands are examples of Epithelial Tissue.

D. CONNECTIVE TISSUE – Connects and supports parts of the body some transport or store materials. Blood, Bone, and Adipose Tissue (Fat) are examples.

E. MUSCLE TISSUE – Specialized for CONTRACTION, which brings about movement. Our Skeleton Muscles and the Heart are examples.

F. NERVE TISSUE – Specialized to generate and transmit Electrochemical Impulses that regulate body functions. The Brain and Optic Nerves are examples.

A. An Organ is a group of TWO or more different types of Tissues precisely arranged so as to accomplish Specific Functions and usually have recognizable shape.

B. Heart, Brain, Kidneys, Liver, Lungs are Examples.

5. ORGAN SYSTEMS (System Level)

A. An Organ System is a group of organs that all contribute to a Particular Function.

B. Examples are the Circulatory, Respiratory, and Digestive Systems.

C. Each organ system carries out its own specific function, but for the organism to survive the organ systems must work together- this is called INTEGRATION OF ORGAN SYSTEM.

B. ALL the Organ Systems of the body functioning with one another constitute the TOTAL ORGANISM – ONE LIVING INDIVIDUAL.


1. All living organisms carry on certain processes that set them apart from nonliving things.

2. The Following are Several of the more important life processes of Humans:

A. METABOLISM is the sum of all the chemical reactions that occur in the body. One phase of Metabolism called CATABOLISM provides the ENERGY needed to sustain life by BREAKING DOWN substances such as food molecules. The other phase called ANABOLISM uses the energy from catabolism to MAKE various substances that form body structures and enable them to function.

B. ASSIMILATION is the changing of Absorbed substances into forms that are chemically different from those that entered body fluids.

C. REPONSIVNESS is the ability to Detect and Respond to changes Outside or Inside the Body. Seeking Water to quench thirst is a response to water loss from body tissue.

D. MOVEMENT includes motion of the whole body, individual organs, single cells, or even structures inside cells.

E. GROWTH refers to an Increase in Body Size. It may be due to an increase in the size of existing cells, the number of cells, or the amount of substance surrounding cells. It occurs whenever an organism produces new body materials faster than old ones are worn out or replaced.

F. DIFFERENTIATION is the process whereby unspecialized cells become specialized cells. Specialized Cells differ in Structure and Function from the cells from which they originated.

G. REPRODUCTION refers either to the formation of new cells for Growth, Repair, or Replacement or to the making of a New Individual.

H. Others Include:
Respiration – obtaining Oxygen.
Digestion – Chemically and Mechanically breaking down food substances.
Absorption – The passage of substances through certain membranes.
Circulation – the movement of substances within the body in Body Fluids.
Excretion – Removal of wastes that the body produces.


1. The structures and functions of almost all body parts help maintain the Life of the Organism. The ONLY Exceptions are an Organisms Reproductive Structures, which ensure that its species will continue into the future.

2. Life requires certain Environmental Factors, including the Following:

A. WATER – this is the most abundant chemical in the body and it is required for many Metabolic Processes and provides the environment in which Most of them take place. Water also transports substances within the organism and is important in regulating body temperature.

B. FOOD – the Substances that provide the body with necessary Chemicals (Nutrients) in addition to Water. Food is used for Energy, supply the raw materials for building new living matter, and still others help regulate vital chemical reactions.

C. OXYGEN – It is required to release Energy from food substances. This energy, in turn, drives metabolic processes. Approximately 20% of the air be breathe is oxygen.

D. HEAT (BODY TEMPERATURE) – a form of energy, it is a product of Metabolic Reactions. Normal Body Temperature is around 37 C or 98 F. both low or high body temperatures are dangerous to the organism.

E. PRESSURE (ATMOSPHERIC) – Necessary for our Breathing.



A. The Skin and Structures derived from it, such as hair, nails, and sweat and oil glands.

B. Is a barrier to pathogens and chemicals (Protects the body), Helps regulate body temperature, Eliminates waste, Helps synthesize vitamin D, and receives certain stimuli such as Temperature, Pressure, and Pain.

A. All the Bones of the body (206), their associated Cartilage, and the Joints of the Body.

B. Bones Support and Protect the body, assist in body movement, They also house cells that produce blood cells, and they store minerals.

A. Specifically refers to Skeletal Muscle Tissue and Tendons.

B. Participates in bringing about movement, maintaining posture, and produces heat.


A. The Heart, Blood and Blood Vessels.

B. Transports oxygen and nutrients to tissues and removes waste.

5. LYMPHATIC SYSTEM- Sometimes included with the Immune System or Circulatory System becuase it works closely with Both Systems.

A. The Lymph, Lymphatic Vessels, and Structures or Organs (Spleen and Lymph Nodes) containing Lymph Tissue.

B. Cleans and Returns tissue fluid to the blood and destroys pathogens that enter the body.

A. The Brain, Spinal Cord, Nerves, and Sense Organs, such as the eye and ear.

B. Interprets sensory information, Regulates body functions such as movement by means of Electrochemical Impulses.

A. ALL Hormone producing Glands and Cells such as the Pituitary Gland, Thyroid Gland, and Pancreas.

B. Regulates body functions by means of Hormones.


A. The Lungs and a series of associated passageways such as the Pharynx (Throat), Larynx (Voice Box), Trachea (Windpipe), and Bronchial Tubes leading into and out of them.

B. Exchange oxygen and carbon dioxide between the air and blood.

A. A long tube called the Gastrointestinal (GI) Tract and associated organs such as the Salivary Glands, Liver, Gallbladder, and Pancreas.

B. Breaks down and absorbs food for use by cells and eliminates solid and other waste.


A. The Kidneys, Urinary Bladder, and Urethra that together produce, store, and eliminate Urine.

B. Removes waste products from the blood and regulates volume and pH of blood.

A. The Immune System Consists of Several Organs, as well as White Blood Cells in the Blood and Lymph.
Includes the Lymph Nodes, Spleen, Lymph Vessels,Blood Vessels, Bone Marrow, and White Blood Cells (Lymphocytes).

B. Provides protection against Infection and Disease.


A. Organs that produce, store, and transport reproductive cells (Sperm and Eggs).

B. Produces eggs and sperm, in women, provides a site for the developing embryo-fetus.

Pressure Associated with the Lungs

The pressure inside the lungs increases and decreases with each breath. The pressure drops to below atmospheric pressure (negative gauge pressure) when you inhale, causing air to flow into the lungs. It increases above atmospheric pressure (positive gauge pressure) when you exhale, forcing air out. Lung pressure is controlled by several mechanisms. Muscle action in the diaphragm and rib cage is necessary for inhalation this muscle action increases the volume of the lungs thereby reducing the pressure within them Figure 3. Surface tension in the alveoli creates a positive pressure opposing inhalation. (See Cohesion and Adhesion in Liquids: Surface Tension and Capillary Action.) You can exhale without muscle action by letting surface tension in the alveoli create its own positive pressure. Muscle action can add to this positive pressure to produce forced exhalation, such as when you blow up a balloon, blow out a candle, or cough. The lungs, in fact, would collapse due to the surface tension in the alveoli, if they were not attached to the inside of the chest wall by liquid adhesion. The gauge pressure in the liquid attaching the lungs to the inside of the chest wall is thus negative, ranging from −4 to −8 mm Hg during exhalation and inhalation, respectively. If air is allowed to enter the chest cavity, it breaks the attachment, and one or both lungs may collapse. Suction is applied to the chest cavity of surgery patients and trauma victims to reestablish negative pressure and inflate the lungs.

Figure 3. (a) During inhalation, muscles expand the chest, and the diaphragm moves downward, reducing pressure inside the lungs to less than atmospheric (negative gauge pressure). Pressure between the lungs and chest wall is even lower to overcome the positive pressure created by surface tension in the lungs. (b) During gentle exhalation, the muscles simply relax and surface tension in the alveoli creates a positive pressure inside the lungs, forcing air out. Pressure between the chest wall and lungs remains negative to keep them attached to the chest wall, but it is less negative than during inhalation.

Abdomen Anatomy

The abdomen is comprised primarily of the digestive tract and other accessory organs which assist in digestion, the urinary system, spleen, and the abdominal muscles (shown below). The majority of these organs are encased in a protective membrane termed the peritoneum. While the digestive organs and assessor organs are located within the peritoneum, the kidneys, ureters and urinary bladder are located outsider of the peritoneum, and thus, are considered by some scientists to be pelvic organs.

Digestive Tract

The organs of the digestive tract consist of the small and large intestines, the stomach, cecum, and the appendix. The stomach is located between the esophagus and the small intestine in the upper left region of the abdomen. The stomach is responsible for the secretion of digestive enzymes and gastric acid required to digest food products. The small intestine is situated between the stomach and large intestine and consists of the three segments (duodenum, jejunum, and ileum), each exhibiting distinct functional properties. The duodenum is situated around the top of the pancreas and receives the digested stomach contents known as gastric chyme. The duodenum functions to neutralize the acid contained in the gastric chyme, as well as break down proteins and fat via enzymes and bile. The jejunum is the middle segment of the small intestine and is responsible for the absorption of sugar, amino acids, and fatty acids into the bloodstream. The final segment of the small intestine is the ileum, which connects to the large intestine. The ileum is responsible for the absorption of vitamin B12, as well as any remaining nutrients. The large intestine consists of the cecum, colon, rectum, and anus and stretches the entire width of the abdominal cavity. The primary function of the large intestine is to absorb water and store the remaining food material as feces until it can be excreted from the body via defecation.

Accessory Digestive Organs

The organs which assist in digestion consist of the pancreas, liver, and gallbladder. These organs secrete various hormones (i.e., insulin), enzymes, and bile via specialized ducts to aid in digestion. In particular, the pancreas functions as an endocrine organ which secretes a variety of digestive enzymes as well as hormones which aid in the digestion of food passing through the digestive tract. The pancreas is located behind the stomach. The liver is located in the upper right quadrant of the abdomen and functions to produce bile, which is responsible for breaking down fats. The liver also functions to produce hormones, regulate the storage of glycogen, and detoxification of the blood. The gallbladder is responsible for the storage of bile produced by the liver until it is released into the small intestine. The gallbladder is situated in the abdomen just under the right lobe of the liver.


The spleen functions as a secondary lymphoid organ and is responsible for the removal of red blood cells via active filtration. The spleen also acts as a reservoir of red blood cells and metabolizes hemoglobin obtained from old red blood cells. The spleen is located in the upper left quadrant of the abdomen.

Urinary System

Abdominal cavity

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Abdominal cavity, largest hollow space of the body. Its upper boundary is the diaphragm, a sheet of muscle and connective tissue that separates it from the chest cavity its lower boundary is the upper plane of the pelvic cavity. Vertically it is enclosed by the vertebral column and the abdominal and other muscles. The abdominal cavity contains the greater part of the digestive tract, the liver and pancreas, the spleen, the kidneys, and the adrenal glands located above the kidneys.

The abdominal cavity is lined by the peritoneum, a membrane that covers not only the inside wall of the cavity (parietal peritoneum) but also every organ or structure contained in it (visceral peritoneum). The space between the visceral and parietal peritoneum, the peritoneal cavity, normally contains a small amount of serous fluid that permits free movement of the viscera, particularly of the gastrointestinal tract, inside the peritoneal cavity. The peritoneum, by connecting the visceral with the parietal portions, assists in the support and fixation of the abdominal organs. The diverse attachments of the peritoneum divide the abdominal cavity into several compartments.

Some of the viscera are attached to the abdominal walls by broad areas of the peritoneum, as is the pancreas. Others, such as the liver, are attached by folds of the peritoneum and ligaments, usually poorly supplied by blood vessels.

The peritoneal ligaments are actually rather strong peritoneal folds, usually connecting viscera to viscera or viscera to the abdominal wall their name usually derives from the structures connected by them (e.g., the gastrocolic ligament, connecting the stomach and the colon the splenocolic ligament, connecting the spleen and the colon) or from their shape (e.g., round ligament, triangular ligament).

The mesentery is a band of peritoneum that is attached to the wall of the abdomen and encloses the viscera. It extends from the pancreas, over the small intestine, and down over the colon and upper rectum. It helps to hold the organs in place and is richly supplied with vessels that carry blood to or from the organs it enfolds.

The omenta are folds of peritoneum enclosing nerves, blood vessels, lymph channels, and fatty and connective tissue. There are two omenta: the greater omentum hangs down from the transverse colon of the large intestine like an apron the lesser omentum is much smaller and extends between the stomach and the liver.

Common afflictions of the abdominal cavity include the presence of fluid in the peritoneal cavity ( ascites) and peritonitis, an inflammation of the peritoneum.

This article was most recently revised and updated by Kara Rogers, Senior Editor.

Functional Core Movements:

The anti-movement resists movement, or activates the core while not changing the length of the muscles. Some of our favorite movements include anti-rotation movements and anti-lateral flexion movements. Movement variations of the pallof press (anti-rotation) and farmers carries (anti-lateral flexion) are regularly programmed into our prenatal fitness programming. This movements strength the core without involving any abdominal flexion or extension, so would be safe for pregnancy and early postpartum.

Axial Muscles of the Abdominal Wall, and Thorax

It is a complex job to balance the body on two feet and walk upright. The muscles of the vertebral column, thorax, and abdominal wall extend, flex, and stabilize different parts of the body’s trunk. The deep muscles of the core of the body help maintain posture as well as carry out other functions. The brain sends out electrical impulses to these various muscle groups to control posture by alternate contraction and relaxation. This is necessary so that no single muscle group becomes fatigued too quickly. If any one group fails to function, body posture will be compromised.

Muscles of the Abdomen

There are four pairs of abdominal muscles that cover the anterior and lateral abdominal region and meet at the anterior midline. These muscles of the anterolateral abdominal wall can be divided into four groups: the external obliques, the internal obliques, the transversus abdominis, and the rectus abdominis ((Figure) and (Figure)).

Muscles of the Abdomen
Movement Target Target motion direction Prime mover Origin Insertion
Twisting at waist also bending to the side Vertebral column Supination lateral flexion External obliques internal obliques Ribs 5–12 ilium Ribs 7–10 linea alba ilium
Squeezing abdomen during forceful exhalations, defecation, urination, and childbirth Abdominal cavity Compression Transversus abdominus Ilium ribs 5–10 Sternum linea alba pubis
Sitting up Vertebral column Flexion Rectus abdominis Pubis Sternum ribs 5 and 7
Bending to the side Vertebral column Lateral flexion Quadratus lumborum Ilium ribs 5–10 Rib 12 vertebrae L1–L4

There are three flat skeletal muscles in the antero-lateral wall of the abdomen. The external oblique , closest to the surface, extend inferiorly and medially, in the direction of sliding one’s four fingers into pants pockets. Perpendicular to it is the intermediate internal oblique , extending superiorly and medially, the direction the thumbs usually go when the other fingers are in the pants pocket. The deep muscle, the transversus abdominis , is arranged transversely around the abdomen, similar to the front of a belt on a pair of pants. This arrangement of three bands of muscles in different orientations allows various movements and rotations of the trunk. The three layers of muscle also help to protect the internal abdominal organs in an area where there is no bone.

The linea alba is a white, fibrous band that is made of the bilateral rectus sheaths that join at the anterior midline of the body. These enclose the rectus abdominis muscles (a pair of long, linear muscles, commonly called the “sit-up” muscles) that originate at the pubic crest and symphysis, and extend the length of the body’s trunk. Each muscle is segmented by three transverse bands of collagen fibers called the tendinous intersections . This results in the look of “six-pack abs,” as each segment hypertrophies on individuals at the gym who do many sit-ups.

The posterior abdominal wall is formed by the lumbar vertebrae, parts of the ilia of the hip bones, psoas major and iliacus muscles, and quadratus lumborum muscle. This part of the core plays a key role in stabilizing the rest of the body and maintaining posture.

Physical Therapists Those who have a muscle or joint injury will most likely be sent to a physical therapist (PT) after seeing their regular doctor. PTs have a master’s degree or doctorate, and are highly trained experts in the mechanics of body movements. Many PTs also specialize in sports injuries.

If you injured your shoulder while you were kayaking, the first thing a physical therapist would do during your first visit is to assess the functionality of the joint. The range of motion of a particular joint refers to the normal movements the joint performs. The PT will ask you to abduct and adduct, circumduct, and flex and extend the arm. The PT will note the shoulder’s degree of function, and based on the assessment of the injury, will create an appropriate physical therapy plan.

The first step in physical therapy will probably be applying a heat pack to the injured site, which acts much like a warm-up to draw blood to the area, to enhance healing. You will be instructed to do a series of exercises to continue the therapy at home, followed by icing, to decrease inflammation and swelling, which will continue for several weeks. When physical therapy is complete, the PT will do an exit exam and send a detailed report on the improved range of motion and return of normal limb function to your doctor. Gradually, as the injury heals, the shoulder will begin to function correctly. A PT works closely with patients to help them get back to their normal level of physical activity.

Muscles of the Thorax

The muscles of the chest serve to facilitate breathing by changing the size of the thoracic cavity ((Figure)). When you inhale, your chest rises because the cavity expands. Alternately, when you exhale, your chest falls because the thoracic cavity decreases in size.

Muscles of the Thorax
Movement Target Target motion direction Prime mover Origin Insertion
Inhalation exhalation Thoracic cavity Compression expansion Diaphragm Sternum ribs 6–12 lumbar vertebrae Central tendon
Inhalationexhalation Ribs Elevation (expands thoracic cavity) External intercostals Rib superior to each intercostal muscle Rib inferior to each intercostal muscle
Forced exhalation Ribs Movement along superior/inferior axis to bring ribs closer together Internal intercostals Rib inferior to each intercostal muscle Rib superior to each intercostal muscle

The Diaphragm

The change in volume of the thoracic cavity during breathing is due to the alternate contraction and relaxation of the diaphragm ((Figure)). It separates the thoracic and abdominal cavities, and is dome-shaped at rest. The superior surface of the diaphragm is convex, creating the elevated floor of the thoracic cavity. The inferior surface is concave, creating the curved roof of the abdominal cavity.

Defecating, urination, and even childbirth involve cooperation between the diaphragm and abdominal muscles (this cooperation is referred to as the “Valsalva maneuver”). You hold your breath by a steady contraction of the diaphragm this stabilizes the volume and pressure of the peritoneal cavity. When the abdominal muscles contract, the pressure cannot push the diaphragm up, so it increases pressure on the intestinal tract (defecation), urinary tract (urination), or reproductive tract (childbirth).

The inferior surface of the pericardial sac and the inferior surfaces of the pleural membranes (parietal pleura) fuse onto the central tendon of the diaphragm. To the sides of the tendon are the skeletal muscle portions of the diaphragm, which insert into the tendon while having a number of origins including the xiphoid process of the sternum anteriorly, the inferior six ribs and their cartilages laterally, and the lumbar vertebrae and 12th ribs posteriorly.

The diaphragm also includes three openings for the passage of structures between the thorax and the abdomen. The inferior vena cava passes through the caval opening , and the esophagus and attached nerves pass through the esophageal hiatus. The aorta, thoracic duct, and azygous vein pass through the aortic hiatus of the posterior diaphragm.

The Intercostal Muscles

There are three sets of muscles, called intercostal muscles , which span each of the intercostal spaces. The principal role of the intercostal muscles is to assist in breathing by changing the dimensions of the rib cage ((Figure)).

The 11 pairs of superficial external intercostal muscles aid in inspiration of air during breathing because when they contract, they raise the rib cage, which expands it. The 11 pairs of internal intercostal muscles, just under the externals, are used for expiration because they draw the ribs together to constrict the rib cage. The innermost intercostal muscles are the deepest, and they act as synergists for the action of the internal intercostals.

Muscles of the Pelvic Floor and Perineum

The pelvic floor is a muscular sheet that defines the inferior portion of the pelvic cavity. The pelvic diaphragm , spanning anteriorly to posteriorly from the pubis to the coccyx, comprises the levator ani and the ischiococcygeus. Its openings include the anal canal and urethra, and the vagina in women.

The large levator ani consists of two skeletal muscles, the pubococcygeus and the iliococcygeus ((Figure)). The levator ani is considered the most important muscle of the pelvic floor because it supports the pelvic viscera. It resists the pressure produced by contraction of the abdominal muscles so that the pressure is applied to the colon to aid in defecation and to the uterus to aid in childbirth (assisted by the ischiococcygeus , which pulls the coccyx anteriorly). This muscle also creates skeletal muscle sphincters at the urethra and anus.

The perineum is the diamond-shaped space between the pubic symphysis (anteriorly), the coccyx (posteriorly), and the ischial tuberosities (laterally), lying just inferior to the pelvic diaphragm (levator ani and coccygeus). Divided transversely into triangles, the anterior is the urogenital triangle , which includes the external genitals. The posterior is the anal triangle , which contains the anus ((Figure)). The perineum is also divided into superficial and deep layers with some of the muscles common to men and women ((Figure)). Women also have the compressor urethrae and the sphincter urethrovaginalis , which function to close the vagina. In men, there is the deep transverse perineal muscle that plays a role in ejaculation.

Chapter Review

Made of skin, fascia, and four pairs of muscle, the anterior abdominal wall protects the organs located in the abdomen and moves the vertebral column. These muscles include the rectus abdominis, which extends through the entire length of the trunk, the external oblique, the internal oblique, and the transversus abdominus. The quadratus lumborum forms the posterior abdominal wall.

The muscles of the thorax play a large role in breathing, especially the dome-shaped diaphragm. When it contracts and flattens, the volume inside the pleural cavities increases, which decreases the pressure within them. As a result, air will flow into the lungs. The external and internal intercostal muscles span the space between the ribs and help change the shape of the rib cage and the volume-pressure ratio inside the pleural cavities during inspiration and expiration.

The perineum muscles play roles in urination in both sexes, ejaculation in men, and vaginal contraction in women. The pelvic floor muscles support the pelvic organs, resist intra-abdominal pressure, and work as sphincters for the urethra, rectum, and vagina.

Review Questions

Which of the following abdominal muscles is not a part of the anterior abdominal wall?

  1. quadratus lumborum
  2. rectus abdominis
  3. interior oblique
  4. exterior oblique

Which muscle pair plays a role in respiration?

  1. intertransversarii, interspinales
  2. semispinalis cervicis, semispinalis thoracis
  3. trapezius, rhomboids
  4. diaphragm, scalene
  1. a small muscle that helps with compression of the abdominal organs
  2. a long tendon that runs down the middle of the rectus abdominis
  3. a long band of collagen fibers that connects the hip to the knee
  4. another name for the tendinous inscription

Critical Thinking Questions

Describe the fascicle arrangement in the muscles of the abdominal wall. How do they relate to each other?

Arranged into layers, the muscles of the abdominal wall are the internal and external obliques, which run on diagonals, the rectus abdominis, which runs straight down the midline of the body, and the transversus abdominis, which wraps across the trunk of the body.

What are some similarities and differences between the diaphragm and the pelvic diaphragm?

Both diaphragms are thin sheets of skeletal muscle that horizontally span areas of the trunk. The diaphragm separating the thoracic and abdominal cavities is the primary muscle of breathing. The pelvic diaphragm, consisting of two paired muscles, the coccygeus and the levator ani, forms the pelvic floor at the inferior end of the trunk.


43.3 Human Reproductive Anatomy and Gametogenesis

As animals became more complex, specific organs and organ systems developed to support specific functions for the organism. The reproductive structures that evolved in land animals allow males and females to mate, fertilize internally, and support the growth and development of offspring.

Human Reproductive Anatomy

The reproductive tissues of male and female humans develop similarly in utero until a low level of the hormone testosterone is released from male gonads. Testosterone causes the undeveloped tissues to differentiate into male sexual organs. When testosterone is absent, the tissues develop into female sexual tissues. Primitive gonads become testes or ovaries. Tissues that produce a penis in males produce a clitoris in females. The tissue that will become the scrotum in a male becomes the labia in a female that is, they are homologous structures.

Male Reproductive Anatomy

In the male reproductive system, the scrotum houses the testicles or testes (singular: testis), including providing passage for blood vessels, nerves, and muscles related to testicular function. The testes are a pair of male reproductive organs that produce sperm and some reproductive hormones. Each testis is approximately 2.5 by 3.8 cm (1.5 by 1 in) in size and divided into wedge-shaped lobules by connective tissue called septa. Coiled in each wedge are seminiferous tubules that produce sperm.

Sperm are immobile at body temperature therefore, the scrotum and penis are external to the body, as illustrated in Figure 43.8 so that a proper temperature is maintained for motility. In land mammals, the pair of testes must be suspended outside the body at about 2 ° C lower than body temperature to produce viable sperm. Infertility can occur in land mammals when the testes do not descend through the abdominal cavity during fetal development.

Visual Connection

Which of the following statements about the male reproductive system is false?

  1. The vas deferens carries sperm from the testes to the penis.
  2. Sperm mature in seminiferous tubules in the testes.
  3. Both the prostate and the bulbourethral glands produce components of the semen.
  4. The prostate gland is located in the testes.

Sperm mature in seminiferous tubules that are coiled inside the testes, as illustrated in Figure 43.8. The walls of the seminiferous tubules are made up of the developing sperm cells, with the least developed sperm at the periphery of the tubule and the fully developed sperm in the lumen. The sperm cells are mixed with “nursemaid” cells called Sertoli cells which protect the germ cells and promote their development. Other cells mixed in the wall of the tubules are the interstitial cells of Leydig. These cells produce high levels of testosterone once the male reaches adolescence.

When the sperm have developed flagella and are nearly mature, they leave the testicles and enter the epididymis, shown in Figure 43.8. This structure resembles a comma and lies along the top and posterior portion of the testes it is the site of sperm maturation. The sperm leave the epididymis and enter the vas deferens (or ductus deferens), which carries the sperm, behind the bladder, and forms the ejaculatory duct with the duct from the seminal vesicles. During a vasectomy, a section of the vas deferens is removed, preventing sperm from being passed out of the body during ejaculation and preventing fertilization.

Semen is a mixture of sperm and spermatic duct secretions (about 10 percent of the total) and fluids from accessory glands that contribute most of the semen’s volume. Sperm are haploid cells, consisting of a flagellum as a tail, a neck that contains the cell’s energy-producing mitochondria, and a head that contains the genetic material. Figure 43.9 shows a micrograph of human sperm as well as a diagram of the parts of the sperm. An acrosome is found at the top of the head of the sperm. This structure contains lysosomal enzymes that can digest the protective coverings that surround the egg to help the sperm penetrate and fertilize the egg. An ejaculate will contain from two to five milliliters of fluid with from 50–120 million sperm per milliliter.

The bulk of the semen comes from the accessory glands associated with the male reproductive system. These are the seminal vesicles, the prostate gland, and the bulbourethral gland, all of which are illustrated in Figure 43.8. The seminal vesicles are a pair of glands that lie along the posterior border of the urinary bladder. The glands make a solution that is thick, yellowish, and alkaline. As sperm are only motile in an alkaline environment, a basic pH is important to reverse the acidity of the vaginal environment. The solution also contains mucus, fructose (a sperm mitochondrial nutrient), a coagulating enzyme, ascorbic acid, and local-acting hormones called prostaglandins. The seminal vesicle glands account for 60 percent of the bulk of semen.

The penis , illustrated in Figure 43.8, is an organ that drains urine from the renal bladder and functions as a copulatory organ during intercourse. The penis contains three tubes of erectile tissue running through the length of the organ. These consist of a pair of tubes on the dorsal side, called the corpus cavernosum, and a single tube of tissue on the ventral side, called the corpus spongiosum. This tissue will become engorged with blood, becoming erect and hard, in preparation for intercourse. The organ is inserted into the vagina culminating with an ejaculation. During intercourse, the smooth muscle sphincters at the opening to the renal bladder close and prevent urine from entering the penis. An orgasm is a two-stage process: first, glands and accessory organs connected to the testes contract, then semen (containing sperm) is expelled through the urethra during ejaculation. After intercourse, the blood drains from the erectile tissue and the penis becomes flaccid.

The walnut-shaped prostate gland surrounds the urethra, the connection to the urinary bladder. It has a series of short ducts that directly connect to the urethra. The gland is a mixture of smooth muscle and glandular tissue. The muscle provides much of the force needed for ejaculation to occur. The glandular tissue makes a thin, milky fluid that contains citrate (a nutrient), enzymes, and prostate specific antigen (PSA). PSA is a proteolytic enzyme that helps to liquefy the ejaculate several minutes after release from the male. Prostate gland secretions account for about 30 percent of the bulk of semen.

The bulbourethral gland , or Cowper’s gland, releases its secretion prior to the release of the bulk of the semen. It neutralizes any acid residue in the urethra left over from urine. This usually accounts for a couple of drops of fluid in the total ejaculate and may contain a few sperm. Withdrawal of the penis from the vagina before ejaculation to prevent pregnancy may not work if sperm are present in the bulbourethral gland secretions. The location and functions of the male reproductive organs are summarized in Table 43.1.

Male Reproductive Anatomy
Organ Location Function
Scrotum External Carry and support testes
Penis External Deliver urine, copulating organ
Testes Internal Produce sperm and male hormones
Seminal Vesicles Internal Contribute to semen production
Prostate Gland Internal Contribute to semen production
Bulbourethral Glands Internal Clean urethra at ejaculation

Female Reproductive Anatomy

A number of reproductive structures are exterior to the female’s body. These include the breasts and the vulva, which consists of the mons pubis, clitoris, labia majora, labia minora, and the vestibular glands, all illustrated in Figure 43.10. The location and functions of the female reproductive organs are summarized in Table 43.2. The vulva is an area associated with the vestibule which includes the structures found in the inguinal (groin) area of women. The mons pubis is a round, fatty area that overlies the pubic symphysis. The clitoris is a structure with erectile tissue that contains a large number of sensory nerves and serves as a source of stimulation during intercourse. The labia majora are a pair of elongated folds of tissue that run posterior from the mons pubis and enclose the other components of the vulva. The labia majora derive from the same tissue that produces the scrotum in a male. The labia minora are thin folds of tissue centrally located within the labia majora. These labia protect the openings to the vagina and urethra. The mons pubis and the anterior portion of the labia majora become covered with hair during adolescence the labia minora is hairless. The greater vestibular glands are found at the sides of the vaginal opening and provide lubrication during intercourse.

Female Reproductive Anatomy
Organ Location Function
Clitoris External Sensory organ
Mons pubis External Fatty area overlying pubic bone
Labia majora External Covers labia minora
Labia minora External Covers vestibule
Greater vestibular glands External Secrete mucus lubricate vagina
Breast External Produce and deliver milk
Ovaries Internal Carry and develop eggs
Oviducts (Fallopian tubes) Internal Transport egg to uterus
Uterus Internal Support developing embryo
Vagina Internal Common tube for intercourse, birth canal, passing menstrual flow

The breasts consist of mammary glands and fat. The size of the breast is determined by the amount of fat deposited behind the gland. Each gland consists of 15 to 25 lobes that have ducts that empty at the nipple and that supply the nursing child with nutrient- and antibody-rich milk to aid development and protect the child.

Internal female reproductive structures include ovaries, oviducts, the uterus , and the vagina, shown in Figure 43.10. The pair of ovaries is held in place in the abdominal cavity by a system of ligaments. Ovaries consist of a medulla and cortex: the medulla contains nerves and blood vessels to supply the cortex with nutrients and remove waste. The outer layers of cells of the cortex are the functional parts of the ovaries. The cortex is made up of follicular cells that surround eggs that develop during fetal development in utero. During the menstrual period, a batch of follicular cells develops and prepares the eggs for release. At ovulation, one follicle ruptures and one egg is released, as illustrated in Figure 43.11a.

The oviducts , or fallopian tubes, extend from the uterus in the lower abdominal cavity to the ovaries, but they are not in contact with the ovaries. The lateral ends of the oviducts flare out into a trumpet-like structure and have a fringe of finger-like projections called fimbriae, illustrated in Figure 43.10b. When an egg is released at ovulation, the fimbrae help the non-motile egg enter into the tube and passage to the uterus. The walls of the oviducts are ciliated and are made up mostly of smooth muscle. The cilia beat toward the middle, and the smooth muscle contracts in the same direction, moving the egg toward the uterus. Fertilization usually takes place within the oviducts and the developing embryo is moved toward the uterus for development. It usually takes the egg or embryo a week to travel through the oviduct. Sterilization in women is called a tubal ligation it is analogous to a vasectomy in males in that the oviducts are severed and sealed.

The uterus is a structure about the size of a woman’s fist. This is lined with an endometrium rich in blood vessels and mucus glands. The uterus supports the developing embryo and fetus during gestation. The thickest portion of the wall of the uterus is made of smooth muscle. Contractions of the smooth muscle in the uterus aid in passing the baby through the vagina during labor. A portion of the lining of the uterus sloughs off during each menstrual period, and then builds up again in preparation for an implantation. Part of the uterus, called the cervix, protrudes into the top of the vagina. The cervix functions as the birth canal.

The vagina is a muscular tube that serves several purposes. It allows menstrual flow to leave the body. It is the receptacle for the penis during intercourse and the vessel for the delivery of offspring. It is lined by stratified squamous epithelial cells to protect the underlying tissue.

Sexual Response during Intercourse

The sexual response in humans is both psychological and physiological. Both sexes experience sexual arousal through psychological and physical stimulation. There are four phases of the sexual response. During phase one, called excitement, vasodilation leads to vasocongestion in erectile tissues in both men and women. The nipples, clitoris, labia, and penis engorge with blood and become enlarged. Vaginal secretions are released to lubricate the vagina to facilitate intercourse. During the second phase, called the plateau, stimulation continues, the outer third of the vaginal wall enlarges with blood, and breathing and heart rate increase.

During phase three, or orgasm, rhythmic, involuntary contractions of muscles occur in both sexes. In the male, the reproductive accessory glands and tubules constrict placing semen in the urethra, then the urethra contracts expelling the semen through the penis. In women, the uterus and vaginal muscles contract in waves that may last slightly less than a second each. During phase four, or resolution, the processes described in the first three phases reverse themselves and return to their normal state. Men experience a refractory period in which they cannot maintain an erection or ejaculate for a period of time ranging from minutes to hours.

Gametogenesis (Spermatogenesis and Oogenesis)

Gametogenesis, the production of sperm and eggs, takes place through the process of meiosis. During meiosis, two cell divisions separate the paired chromosomes in the nucleus and then separate the chromatids that were made during an earlier stage of the cell’s life cycle. Meiosis produces haploid cells with half of each pair of chromosomes normally found in diploid cells. The production of sperm is called spermatogenesis and the production of eggs is called oogenesis .


Spermatogenesis, illustrated in Figure 43.12, occurs in the wall of the seminiferous tubules (Figure 43.8), with stem cells at the periphery of the tube and the spermatozoa at the lumen of the tube. Immediately under the capsule of the tubule are diploid, undifferentiated cells. These stem cells, called spermatogonia (singular: spermatagonium), go through mitosis with one offspring going on to differentiate into a sperm cell and the other giving rise to the next generation of sperm.

Meiosis starts with a cell called a primary spermatocyte. At the end of the first meiotic division, a haploid cell is produced called a secondary spermatocyte. This cell is haploid and must go through another meiotic cell division. The cell produced at the end of meiosis is called a spermatid and when it reaches the lumen of the tubule and grows a flagellum, it is called a sperm cell. Four sperm result from each primary spermatocyte that goes through meiosis.

Stem cells are deposited during gestation and are present at birth through the beginning of adolescence, but in an inactive state. During adolescence, gonadotropic hormones from the anterior pituitary cause the activation of these cells and the production of viable sperm. This continues into old age.

Link to Learning

Visit this site to see the process of spermatogenesis.


Oogenesis, illustrated in Figure 43.13, occurs in the outermost layers of the ovaries. As with sperm production, oogenesis starts with a germ cell, called an oogonium (plural: oogonia), but this cell undergoes mitosis to increase in number, eventually resulting in up to about one to two million cells in the embryo.

The cell starting meiosis is called a primary oocyte, as shown in Figure 43.13. This cell will start the first meiotic division and be arrested in its progress in the first prophase stage. At the time of birth, all future eggs are in the prophase stage. At adolescence, anterior pituitary hormones cause the development of a number of follicles in an ovary. This results in the primary oocyte finishing the first meiotic division. The cell divides unequally, with most of the cellular material and organelles going to one cell, called a secondary oocyte, and only one set of chromosomes and a small amount of cytoplasm going to the other cell. This second cell is called a polar body and usually dies. A secondary meiotic arrest occurs, this time at the metaphase II stage. At ovulation, this secondary oocyte will be released and travel toward the uterus through the oviduct. If the secondary oocyte is fertilized, the cell continues through the meiosis II, producing a second polar body and a fertilized egg containing all 46 chromosomes of a human being, half of them coming from the sperm.

Egg production begins before birth, is arrested during meiosis until puberty, and then individual cells continue through at each menstrual cycle. One egg is produced from each meiotic process, with the extra chromosomes and chromatids going into polar bodies that degenerate and are reabsorbed by the body.

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    • Authors: Connie Rye, Robert Wise, Vladimir Jurukovski, Jean DeSaix, Jung Choi, Yael Avissar
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