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22.18: Gas Pressure and Respiration - Biology

22.18: Gas Pressure and Respiration - Biology


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The respiratory process can be better understood by examining the properties of gases. Gases move freely, but gas particles are constantly hitting the walls of their vessel, thereby producing gas pressure.

Air is a mixture of gases, primarily nitrogen (N2; 78.6 percent), oxygen (O2; 20.9 percent), water vapor (H2O; 0.5 percent), and carbon dioxide (CO2; 0.04 percent). Each gas component of that mixture exerts a pressure. The pressure for an individual gas in the mixture is the partial pressure of that gas. Approximately 21 percent of atmospheric gas is oxygen. Carbon dioxide, however, is found in relatively small amounts, 0.04 percent. The partial pressure for oxygen is much greater than that of carbon dioxide. The partial pressure of any gas can be calculated by:

[ ext{P}_{ ext{atm}}]

The pressure of the atmosphere at sea level is 760 mm Hg. Therefore, the partial pressure of oxygen is:

and for carbon dioxide:

At high altitudes, decreases, but concentration does not change; the partial pressure decrease is due to the reduction in .

When the air mixture reaches the lung, it has been humidified. The pressure of the water vapor in the lung does not change the pressure of the air, but it must be included in the partial pressure equation. For this calculation, the water pressure (47 mm Hg) is subtracted from the atmospheric pressure:

and the partial pressure of oxygen is:

These partial pressures determine the rate of gas exchange, or the flow of gas, in the system. Oxygen and carbon dioxide will flow according to their pressure gradient from high to low. Therefore, understanding the partial pressure of each gas will aid in understanding how gases move in the respiratory system.


MAP 6 - Respiratory System

Part A - Hemoglobin Saturation.
Focus your attention on the graph shown, from the left side of the Focus Figure. The percent of O2O2 saturation of hemoglobin is plotted (on the y-axis) against PO2PO2 (mm Hg) (on the x-axis). Use this graph to complete Parts A-C below. On this graph, the y-axis (the vertical edge) tells you how much O2O2 is bound to hemoglobin (Hb). At 100%, each Hb molecule has four bound oxygen molecules. The x-axis (the horizontal edge) tells you the relative amount (partial pressure) of O2O2 dissolved in the fluid surrounding the Hb.

In blood with a PO2PO2 of 30 mm Hg, the average saturation of all hemoglobin proteins is 60%.

Focus your attention on the graph shown, from the top right box, "In the lungs," of the Focus Figure.

100 mm Hg.
The saturation of hemoglobin in the lungs at sea level is

100 mm Hg.
The saturation of hemoglobin in the lungs at high altitude of PO2

95% O2 saturation.
The saturation of hemoglobin in the lungs at an altitude representing PO2


Lung Volumes and Capacities

Different animals have different lung capacities based on their activities. Cheetahs have evolved a much higher lung capacity than humans it helps provide oxygen to all the muscles in the body and allows them to run very fast. Elephants also have a high lung capacity. In this case, it is not because they run fast but because they have a large body and must be able to take up oxygen in accordance with their body size.

Human lung size is determined by genetics, gender, and height. At maximal capacity, an average lung can hold almost six liters of air, but lungs do not usually operate at maximal capacity. Air in the lungs is measured in terms of lung volumes and lung capacities (Figure 20.12 and Table 20.1). Volume measures the amount of air for one function (such as inhalation or exhalation). Capacity is any two or more volumes (for example, how much can be inhaled from the end of a maximal exhalation).

Figure 20.12.
Human lung volumes and capacities are shown. The total lung capacity of the adult male is six liters. Tidal volume is the volume of air inhaled in a single, normal breath. Inspiratory capacity is the amount of air taken in during a deep breath, and residual volume is the amount of air left in the lungs after forceful respiration.

The volume in the lung can be divided into four units: tidal volume, expiratory reserve volume, inspiratory reserve volume, and residual volume. Tidal volume (TV) measures the amount of air that is inspired and expired during a normal breath. On average, this volume is around one-half liter, which is a little less than the capacity of a 20-ounce drink bottle. The expiratory reserve volume (ERV) is the additional amount of air that can be exhaled after a normal exhalation. It is the reserve amount that can be exhaled beyond what is normal. Conversely, the inspiratory reserve volume (IRV) is the additional amount of air that can be inhaled after a normal inhalation. The residual volume (RV) is the amount of air that is left after expiratory reserve volume is exhaled. The lungs are never completely empty: There is always some air left in the lungs after a maximal exhalation. If this residual volume did not exist and the lungs emptied completely, the lung tissues would stick together and the energy necessary to re-inflate the lung could be too great to overcome. Therefore, there is always some air remaining in the lungs. Residual volume is also important for preventing large fluctuations in respiratory gases (O2 and CO2). The residual volume is the only lung volume that cannot be measured directly because it is impossible to completely empty the lung of air. This volume can only be calculated rather than measured.

Capacities are measurements of two or more volumes. The vital capacity (VC) measures the maximum amount of air that can be inhaled or exhaled during a respiratory cycle. It is the sum of the expiratory reserve volume, tidal volume, and inspiratory reserve volume. The inspiratory capacity (IC) is the amount of air that can be inhaled after the end of a normal expiration. It is, therefore, the sum of the tidal volume and inspiratory reserve volume. The functional residual capacity (FRC) includes the expiratory reserve volume and the residual volume. The FRC measures the amount of additional air that can be exhaled after a normal exhalation. Lastly, the total lung capacity (TLC) is a measurement of the total amount of air that the lung can hold. It is the sum of the residual volume, expiratory reserve volume, tidal volume, and inspiratory reserve volume.

Lung volumes are measured by a technique called spirometry . An important measurement taken during spirometry is the forced expiratory volume (FEV) , which measures how much air can be forced out of the lung over a specific period, usually one second (FEV1). In addition, the forced vital capacity (FVC), which is the total amount of air that can be forcibly exhaled, is measured. The ratio of these values ( FEV1/FVC ratio ) is used to diagnose lung diseases including asthma, emphysema, and fibrosis. If the FEV1/FVC ratio is high, the lungs are not compliant (meaning they are stiff and unable to bend properly), and the patient most likely has lung fibrosis. Patients exhale most of the lung volume very quickly. Conversely, when the FEV1/FVC ratio is low, there is resistance in the lung that is characteristic of asthma. In this instance, it is hard for the patient to get the air out of his or her lungs, and it takes a long time to reach the maximal exhalation volume. In either case, breathing is difficult and complications arise.


Respiration lab - Heart and breathing rate during activity

The body needs energy for all kind of activities. When the body is resting, it needs lower amount of energy. But the more demanding activities we are doing, the more energy is needed.

The main source of energy is carbohydrate and fat. The fat and carbohydrates are transformed by the ‘citric acid cycle’ into energy. The chemical energy is transferred to a substance that is called ATP (adenosine triphosphate). The ATP is a small package of energy that is used by the cells. In aerobic respiration oxygen is needed. The waste products are water, carbon dioxide and heat.

The oxygen (O2) and carbon dioxide (CO2) is transported to/from the cells by the hemoglobin in the blood from/to the lungs. It is in the lungs, in the border between the capillaries and the alveoli, where the gases are exchanged by diffusion. The heart is the pump which makes the blood circulate in the body. And our breathing enables new air (with O2) to enter the lungs by inhaling and get rid of the old air (with CO2) by exhaling.

Therefore with more demanding exercises (eg. running) more energy is needed and therefore also more oxygen is needed (in the citric acid cycle) and more carbon dioxide is produced. Therefore the heart and breathing rate is becoming higher to enable the transportation of carbon dioxide and oxygen.

Normal resting heart rate for an untrained man is 70 - 75 bpm. And it's lower for people that are well trained, it can be low as 25 bpm. And for old people it is higher. Normal breathing rate/min is 13 - 16

With this lab I want to find out how activities affect the heart and breathing rate in humans.

Hypothesis:I think that the heart and breathing rate will increase during activity.


Procedure:
Our activity was to jump on the same place for 15s (seconds).

  1. I measured the testpersons heart rate by putting a finger on the neck and controlling how many times the heart beats in 15s.
  2. I measured the testpersons breathing rate by counting how many times they exhaled in 15s by holding a hand in front of the persons mouth (around 20 cm away).
  3. The testpersons jumped on the place for 15s.
  4. I measure the heart rate as in 1
  5. I measured the breathing rate as in 2.
  6. I multiplied all results that I measured in 15s by 4, so I got the results per minute (60s) instead.


Results:

The aim of this lab was to find out how activities affect the heart and breathing rate in a human. In my lab, I can easily see that the heart and breathing rate become higher during activity.

My data isn't 100% reliable because that measurement that I used wasn’t so good, eg. I measured for 15s and then I multiplied it by 4. If I would make a more accurate lab, I would measure in 60s. Or if even more correct, I could measure for 120s and divide by 2. It would be more accurate if I did like this, because when I measured for 15s and multiplied it by 4, it might be up to 2 heartbeats wrong when I started to measure and up to 2 heartbeats wrong in the end, then I multiply it by 4, so I could get up to 16 heartbeats wrong per minute. But if I measure for 60s, it could be up to 2 wrong in the beginning and up to 2 wrong in the end, which would mean that I would only get up to 4 heartbeats wrong per minute. Eg. if the accurate heartbeat/min is 70, it would be somewhere between 54 bpm and 86 bpm if I measured in 15s, if I measured in 60s it would be somewhere between 66bpm and 74bpm (which is much more reliable).
If I would do the lab even more accurate, I could use a professional pulse and breathing meter and have a treadmill for the testpersons to run on, so the testpersons would make exact the same activity.

In this lab the resting heart rate and the resting breathing rate were much higher than normal. The reason for this was probably that I didn’t measured the real resting rate for pulse and breathing. The persons was probably not relaxed. So in next lab I would make sure that the persons are relaxing.

It would be interesting to measure the heart and breathing rate on a smoker or a person that has certain health problems as eg. asthma, or a person that lives in a place where the environment is polluted, and how they respond to exercise, and compare to my results.

In these persons, the gas exchange is slower, and smoking also has that negative effect that the hemoglobin can bind less oxygen because of it is occupied of carbon monoxide (CO). So if I would make a new study with persons in this group, I would probably get the results that their heart will beat faster and they will have much harder to make exercices.

According to the literature obesity, alcohol and drugs can affect a person’s heart and breathing rate. For example alcohol depresses both heart and breathing rate, which makes it harder to make exercices. Some drugs (medicines) can change the heart rate or make it easier to breath, eg. asthma drugs (eg. ventolin) make the muscles around the bronchi relax so that the tubes open and it is easier to breathe. Other drugs as nitroglycerine is used in angina pectoris and it makes the arteries around the heart becoming broader and let more blood pass to the heart and lower the heart rate.

When we don’t use the energy sources (fat, carbohydrates and proteins) that we eat, they get stored as glycogen and fat. If there is too big excess of energy sources, one become fat. Fat people have more mass and weighs more than not fat people, so they also need more energy and oxygen to do activities. Too much fat in the diet stops muscle cells to take up glucose from the blood and makes the cells to slow down the release of needed energy.


Henry’s Law

Henry’s law states that the amount of a gas that dissolves in a liquid is directly proportional to the partial pressure of that gas.

Learning Objectives

Explain the way in which Henry’s law relates to gas exchange in the respiratory system

Key Takeaways

Key Points

  • At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.
  • Gasses with a higher solubility will have more dissolved molecules than gasses with a lower solubility if they have the same partial pressure.
  • Henry’s law explains how gasses dissolve across the alveoli – capillary barrier.
  • Henry’s law predicts how gasses behave during gas exchange based on
    the partial pressure gradients and solubility of oxygen and carbon
    dioxide.

Key Terms

  • Henry’s law: At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.
  • partial pressure gradient: The difference between the partial pressures (and thus concentration) of gasses between gaseous and dissolved forms.

Examples

An everyday example of Henry’s law is given by carbonated soft drinks. Before the bottle or can is opened, the gas above the drink is almost pure carbon dioxide at a pressure slightly higher than atmospheric pressure. The drink itself contains dissolved carbon dioxide. When the bottle or can is opened, some of this gas escapes, giving the characteristic hiss (or pop in the case of a sparkling wine bottle). Because the pressure above the liquid is now lower, some of the dissolved carbon dioxide comes out of solution as bubbles. If a glass of the drink is left in the open, the concentration of carbon dioxide in solution will come into equilibrium with the carbon dioxide in the air, and the drink will go flat.

Henry’s law states that at a constant temperature, the amount of a gas that dissolves in a liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid. It was formulated by William Henry in 1803.

Henry’s law: Henry’s law states that when a gas is in contact with the surface of a liquid, the amount of the gas which will go into solution is proportional to the partial pressure of that gas.

The practical description for the law is that the solubility (i.e., equilibrium) of a gas in a liquid is directly proportional to the partial pressure of that gas. In addition, the partial pressure is able to predict the tendency to dissolve simply because the gasses with higher partial pressures have more molecules and will bounce into the solution they can dissolve into more often than gasses with lower partial pressures.

Henry’s law also applies to the solubility of other substances that aren’t gaseous, such as the equilibrium of organic pollutants in water being based on the relative concentration of that pollutant in the media its suspended in.

Henry’s law can be put into mathematical terms (at constant temperature):

Where p is the partial pressure of the solute in the gas above the solution, c is the concentration of the solute, the solubility of the substance is k, and the Henry’s law constant (H), which depends on the solute, the solvent, and the
temperature.

The solubility captures the tendency of a substance to go towards equilibrium in a solution, which explains why gasses that have the same partial pressure may have different tendencies to dissolve.

Henry’s Law in Respiration

The main application of Henry’s law in respiratory physiology is to predict how gasses will dissolve in the alveoli and bloodstream during gas exchange. The amount of oxygen that dissolves into the bloodstream is directly proportional to the partial pressure of oxygen in alveolar air.

The partial pressure of oxygen is greater in alveolar air than in deoxygenated blood, so oxygen has a high tendency to dissolve into deoxygenated blood. Conversely the opposite is true for carbon dioxide, which has a greater partial pressure in deoxygenated blood than in the alveolar air, so it will diffuse out of the solution and back into gaseous form.

Recall that the difference in partial pressures between the bloodstream and alveoli (the partial pressure gradient) are much smaller for carbon dioxide compared to oxygen. Carbon dioxide has much higher solubility in the plasma of blood than oxygen (roughly 22 times greater), so more carbon dioxide molecules are able to diffuse across the small pressure gradient of the capillary and alveoli.

Oxygen has a larger partial pressure gradient to diffuse into the bloodstream, so it’s lower solubility in blood doesn’t hinder it during gas exchange. Therefore, based on the properties of Henry’s law, both the partial pressure and solubility of the oxygen and carbon dioxide determine how they will behave during gas exchange.


22.4 Gas Exchange

The purpose of the respiratory system is to perform gas exchange. Pulmonary ventilation provides air to the alveoli for this gas exchange process. At the respiratory membrane, where the alveolar and capillary walls meet, gases move across the membranes, with oxygen entering the bloodstream and carbon dioxide exiting. It is through this mechanism that blood is oxygenated and carbon dioxide, the waste product of cellular respiration, is removed from the body.

Gas Exchange

In order to understand the mechanisms of gas exchange in the lung, it is important to understand the underlying principles of gases and their behavior. In addition to Boyle’s law, several other gas laws help to describe the behavior of gases.

Gas Laws and Air Composition

Gas molecules exert force on the surfaces with which they are in contact this force is called pressure. In natural systems, gases are normally present as a mixture of different types of molecules. For example, the atmosphere consists of oxygen, nitrogen, carbon dioxide, and other gaseous molecules, and this gaseous mixture exerts a certain pressure referred to as atmospheric pressure (Table 22.2). Partial pressure (Px) is the pressure of a single type of gas in a mixture of gases. For example, in the atmosphere, oxygen exerts a partial pressure, and nitrogen exerts another partial pressure, independent of the partial pressure of oxygen (Figure 22.21). Total pressure is the sum of all the partial pressures of a gaseous mixture. Dalton’s law describes the behavior of nonreactive gases in a gaseous mixture and states that a specific gas type in a mixture exerts its own pressure thus, the total pressure exerted by a mixture of gases is the sum of the partial pressures of the gases in the mixture.

Gas Percent of total composition Partial pressure
(mm Hg)
Nitrogen (N2) 78.6 597.4
Oxygen (O2) 20.9 158.8
Water (H2O) 0.4 3.0
Carbon dioxide (CO2) 0.04 0.3
Others 0.06 0.5
Total composition/total atmospheric pressure 100% 760.0

Partial pressure is extremely important in predicting the movement of gases. Recall that gases tend to equalize their pressure in two regions that are connected. A gas will move from an area where its partial pressure is higher to an area where its partial pressure is lower. In addition, the greater the partial pressure difference between the two areas, the more rapid is the movement of gases.

Solubility of Gases in Liquids

Henry’s law describes the behavior of gases when they come into contact with a liquid, such as blood. Henry’s law states that the concentration of gas in a liquid is directly proportional to the solubility and partial pressure of that gas. The greater the partial pressure of the gas, the greater the number of gas molecules that will dissolve in the liquid. The concentration of the gas in a liquid is also dependent on the solubility of the gas in the liquid. For example, although nitrogen is present in the atmosphere, very little nitrogen dissolves into the blood, because the solubility of nitrogen in blood is very low. The exception to this occurs in scuba divers the composition of the compressed air that divers breathe causes nitrogen to have a higher partial pressure than normal, causing it to dissolve in the blood in greater amounts than normal. Too much nitrogen in the bloodstream results in a serious condition that can be fatal if not corrected. Gas molecules establish an equilibrium between those molecules dissolved in liquid and those in air.

The composition of air in the atmosphere and in the alveoli differs. In both cases, the relative concentration of gases is nitrogen > oxygen > water vapor > carbon dioxide. The amount of water vapor present in alveolar air is greater than that in atmospheric air (Table 22.3). Recall that the respiratory system works to humidify incoming air, thereby causing the air present in the alveoli to have a greater amount of water vapor than atmospheric air. In addition, alveolar air contains a greater amount of carbon dioxide and less oxygen than atmospheric air. This is no surprise, as gas exchange removes oxygen from and adds carbon dioxide to alveolar air. Both deep and forced breathing cause the alveolar air composition to be changed more rapidly than during quiet breathing. As a result, the partial pressures of oxygen and carbon dioxide change, affecting the diffusion process that moves these materials across the membrane. This will cause oxygen to enter and carbon dioxide to leave the blood more quickly.

Gas Percent of total composition Partial pressure
(mm Hg)
Nitrogen (N2) 74.9 569
Oxygen (O2) 13.7 104
Water (H2O) 6.2 40
Carbon dioxide (CO2) 5.2 47
Total composition/total alveolar pressure 100% 760.0

Ventilation and Perfusion

Two important aspects of gas exchange in the lung are ventilation and perfusion. Ventilation is the movement of air into and out of the lungs, and perfusion is the flow of blood in the pulmonary capillaries. For gas exchange to be efficient, the volumes involved in ventilation and perfusion should be compatible. However, factors such as regional gravity effects on blood, blocked alveolar ducts, or disease can cause ventilation and perfusion to be imbalanced.

The partial pressure of oxygen in alveolar air is about 104 mm Hg, whereas the partial pressure of oxygenated blood in pulmonary veins is about 100 mm Hg. When ventilation is sufficient, oxygen enters the alveoli at a high rate, and the partial pressure of oxygen in the alveoli remains high. In contrast, when ventilation is insufficient, the partial pressure of oxygen in the alveoli drops. Without the large difference in partial pressure between the alveoli and the blood, oxygen does not diffuse efficiently across the respiratory membrane. The body has mechanisms that counteract this problem. In cases when ventilation is not sufficient for an alveolus, the body redirects blood flow to alveoli that are receiving sufficient ventilation. This is achieved by constricting the pulmonary arterioles that serves the dysfunctional alveolus, which redirects blood to other alveoli that have sufficient ventilation. At the same time, the pulmonary arterioles that serve alveoli receiving sufficient ventilation vasodilate, which brings in greater blood flow. Factors such as carbon dioxide, oxygen, and pH levels can all serve as stimuli for adjusting blood flow in the capillary networks associated with the alveoli.

Ventilation is regulated by the diameter of the airways, whereas perfusion is regulated by the diameter of the blood vessels. The diameter of the bronchioles is sensitive to the partial pressure of carbon dioxide in the alveoli. A greater partial pressure of carbon dioxide in the alveoli causes the bronchioles to increase their diameter as will a decreased level of oxygen in the blood supply, allowing carbon dioxide to be exhaled from the body at a greater rate. As mentioned above, a greater partial pressure of oxygen in the alveoli causes the pulmonary arterioles to dilate, increasing blood flow.

Gas Exchange

Gas exchange occurs at two sites in the body: in the lungs, where oxygen is picked up and carbon dioxide is released at the respiratory membrane, and at the tissues, where oxygen is released and carbon dioxide is picked up. External respiration is the exchange of gases with the external environment, and occurs in the alveoli of the lungs. Internal respiration is the exchange of gases with the internal environment, and occurs in the tissues. The actual exchange of gases occurs due to simple diffusion. Energy is not required to move oxygen or carbon dioxide across membranes. Instead, these gases follow pressure gradients that allow them to diffuse. The anatomy of the lung maximizes the diffusion of gases: The respiratory membrane is highly permeable to gases the respiratory and blood capillary membranes are very thin and there is a large surface area throughout the lungs.

External Respiration

The pulmonary artery carries deoxygenated blood into the lungs from the heart, where it branches and eventually becomes the capillary network composed of pulmonary capillaries. These pulmonary capillaries create the respiratory membrane with the alveoli (Figure 22.22). As the blood is pumped through this capillary network, gas exchange occurs. Although a small amount of the oxygen is able to dissolve directly into plasma from the alveoli, most of the oxygen is picked up by erythrocytes (red blood cells) and binds to a protein called hemoglobin, a process described later in this chapter. Oxygenated hemoglobin is red, causing the overall appearance of bright red oxygenated blood, which returns to the heart through the pulmonary veins. Carbon dioxide is released in the opposite direction of oxygen, from the blood to the alveoli. Some of the carbon dioxide is returned on hemoglobin, but can also be dissolved in plasma or is present as a converted form, also explained in greater detail later in this chapter.

External respiration occurs as a function of partial pressure differences in oxygen and carbon dioxide between the alveoli and the blood in the pulmonary capillaries.

Although the solubility of oxygen in blood is not high, there is a drastic difference in the partial pressure of oxygen in the alveoli versus in the blood of the pulmonary capillaries. This difference is about 64 mm Hg: The partial pressure of oxygen in the alveoli is about 104 mm Hg, whereas its partial pressure in the blood of the capillary is about 40 mm Hg. This large difference in partial pressure creates a very strong pressure gradient that causes oxygen to rapidly cross the respiratory membrane from the alveoli into the blood.

The partial pressure of carbon dioxide is also different between the alveolar air and the blood of the capillary. However, the partial pressure difference is less than that of oxygen, about 5 mm Hg. The partial pressure of carbon dioxide in the blood of the capillary is about 45 mm Hg, whereas its partial pressure in the alveoli is about 40 mm Hg. However, the solubility of carbon dioxide is much greater than that of oxygen—by a factor of about 20—in both blood and alveolar fluids. As a result, the relative concentrations of oxygen and carbon dioxide that diffuse across the respiratory membrane are similar.

Internal Respiration

Internal respiration is gas exchange that occurs at the level of body tissues (Figure 22.23). Similar to external respiration, internal respiration also occurs as simple diffusion due to a partial pressure gradient. However, the partial pressure gradients are opposite of those present at the respiratory membrane. The partial pressure of oxygen in tissues is low, about 40 mm Hg, because oxygen is continuously used for cellular respiration. In contrast, the partial pressure of oxygen in the blood is about 100 mm Hg. This creates a pressure gradient that causes oxygen to dissociate from hemoglobin, diffuse out of the blood, cross the interstitial space, and enter the tissue. Hemoglobin that has little oxygen bound to it loses much of its brightness, so that blood returning to the heart is more burgundy in color.

Considering that cellular respiration continuously produces carbon dioxide, the partial pressure of carbon dioxide is lower in the blood than it is in the tissue, causing carbon dioxide to diffuse out of the tissue, cross the interstitial fluid, and enter the blood. It is then carried back to the lungs either bound to hemoglobin, dissolved in plasma, or in a converted form. By the time blood returns to the heart, the partial pressure of oxygen has returned to about 40 mm Hg, and the partial pressure of carbon dioxide has returned to about 45 mm Hg. The blood is then pumped back to the lungs to be oxygenated once again during external respiration.

Everyday Connection

Hyperbaric Chamber Treatment

A type of device used in some areas of medicine that exploits the behavior of gases is hyperbaric chamber treatment. A hyperbaric chamber is a unit that can be sealed and expose a patient to either 100 percent oxygen with increased pressure or a mixture of gases that includes a higher concentration of oxygen than normal atmospheric air, also at a higher partial pressure than the atmosphere. There are two major types of chambers: monoplace and multiplace. Monoplace chambers are typically for one patient, and the staff tending to the patient observes the patient from outside of the chamber (Figure 22.24). Some facilities have special monoplace hyperbaric chambers that allow multiple patients to be treated at once, usually in a sitting or reclining position, to help ease feelings of isolation or claustrophobia. Multiplace chambers are large enough for multiple patients to be treated at one time, and the staff attending these patients is present inside the chamber. In a multiplace chamber, patients are often treated with air via a mask or hood, and the chamber is pressurized.

Hyperbaric chamber treatment is based on the behavior of gases. As you recall, gases move from a region of higher partial pressure to a region of lower partial pressure. In a hyperbaric chamber, the atmospheric pressure is increased, causing a greater amount of oxygen than normal to diffuse into the bloodstream of the patient. Hyperbaric chamber therapy is used to treat a variety of medical problems, such as wound and graft healing, anaerobic bacterial infections, and carbon monoxide poisoning. Exposure to and poisoning by carbon monoxide is difficult to reverse, because hemoglobin’s affinity for carbon monoxide is much stronger than its affinity for oxygen, causing carbon monoxide to replace oxygen in the blood. Hyperbaric chamber therapy can treat carbon monoxide poisoning, because the increased atmospheric pressure causes more oxygen to diffuse into the bloodstream. At this increased pressure and increased concentration of oxygen, carbon monoxide is displaced from hemoglobin. Another example is the treatment of anaerobic bacterial infections, which are created by bacteria that cannot or prefer not to live in the presence of oxygen. An increase in blood and tissue levels of oxygen helps to kill the anaerobic bacteria that are responsible for the infection, as oxygen is toxic to anaerobic bacteria. For wounds and grafts, the chamber stimulates the healing process by increasing energy production needed for repair. Increasing oxygen transport allows cells to ramp up cellular respiration and thus ATP production, the energy needed to build new structures.


Measuring Respiration of Germinating and Non-germinating Peas

Living cells require transfusions of energy from outside sources to perform their many tasks – for example, assembling polymers, pumping substances across membranes, moving, and reproducing (Campbell, and Reece 162). Heterotrophs obtains its energy for its cells by eating plants that makes it own food (Autotrophs) some animals feed on other organisms that eat plants. The most beneficial catabolic pathway in an organism is cellular respiration, in which oxygen and glucose are consumed and where carbon and water become the waste products. The purpose of cellular respiration is to convert glucose into ATP(energy) for the organism. Respiration consists of glycolysis, the Krebs Cycle, and the oxidative phosphorylation. Glycolysis, which occurs in the cytosol, breaks the six carbon glucose molecule into two pyruvates. During this stage two ATP and two NADH molecules are made. The next step in respiration is the Krebs cycle. The Krebs cycle uses the two pyruvates made during glycolysis and converts them to Acetyl-CoA and carbon dioxide to make three NADH, one FADH2, and two CO2 through redox reactions, and goes to the Electron Transport Chain. ATP is also formed during the Krebs cycle (Campbell, and Reece 166). Since two pyruvates are made during glycolysis, the Krebs cycle repeats two times to produce four CO2, six NADH, two FADH2, and two ATP (Campbell, and Reese 166). The last stage in cellular respiration is the Oxidative phosphorylation Electron Transport. The Oxidative phosphorylation occurs in the inner membrane of the mitochondria. The electron transport chain is powered by electrons from electron carrier molecules NADH and FADH2 (Campbell, and Reese 166). As the electrons flow through the electron chain, the loss of energy by the electrons is used to power the pumping of electrons across the inner membrane. At the end of the electron transport chain, the electrons from the inner membrane bind to two flowing hydrogen ions to form water molecules. The protons, outside the inner membrane, flow down the ATP gradient and make a total of thirty two ATP (Campbell, and Reese 166).

In this experiment, an apparatus called a respirometer is used. A respirometer is a tool used to observe exactly how much oxygen was consumed by the peas and the glass beads. Since the carbon dioxide produced is removed by reaction with potassium hydroxide (Forming K2CO3 + H2O as shown below), as oxygen is used by cellular respiration the volume of gas in the respirometer will decrease. As the volume of gas decreases, water will move into the pipet. This decrease of volume, as read from the scale printed on the pipet, will be measured as the rate of cellular respiration (Cell Respiration).

The purpose of this lab was to measure the rate of cellular respiration. There are three ways to measure the rate of cellular respiration. These three ways are by measuring the consumption of oxygen gas, by measuring the production of carbon dioxide, or by measuring the release of energy during cellular respiration (Respiration). In order to measure the gases, the general gas law must be understood. The general gas law state: PV=nRT where P is the pressure of the gas, V is the volume of the gas, n is the number of molecules of gas, R is the gas constant, and T is the temperature of the gas (Respiration). The rate of respiration of germinating and non-germinating peas in this experiment was determined by the consumption of oxygen. Potassium Hydroxide (KOH) was used to alter the equilibrium. KOH removed the carbon dioxide and oxygen was used by cellular respiration thus decreasing the gas in the respirometer. The rate of respiration in germinating peas was compared to the rate of the non-geminating peas. These peas were placed in two different temperatures: 10ºC and 23ºC.

The hypothesis of this lab states that if the peas are germinated then the rate of cellular respiration will be higher in both room temperature and cold temperature. If the temperature of water is cooler than room temperature, then the process of cellular respiration of the peas will decline.

v Room-Temperature Water Bath Nonabsorbent Cotton

v Cold Water Bath 15% Potassium Hydroxide (KOH) Solution

v Container of Ice Dropping Pipets

v Paper (White or Lined) Forceps

v Germinating Peas Stopwatch (Timer or Clock)

v Nongerminating Peas Calculators (Optional)

v Glass Beads Absorbent Cotton Balls

v Respirometers Graduated Tube

Setup of Respirometers and Water Baths

There are two water baths (trays of water) to buffer the respirometers against temperature change and to provide two temperatures for testing: room temperature and a colder temperature (Approx. 10°C). Place of sheet of paper in the bottom of each water bath. This will make the graduated pipet easier to read. Next, place a thermometer in each tray. If necessary, add ice to the cold-temperature tray to further cool the water to get it as close to 10°C as possible. While waiting for the cold- water temperature to stabilize at 10°C, prepare the three respirometers to test at room temperature, and prepare an identical set of three respirometers to test at the colder temperature.

Prepare Peas and Glass Beads

Respirometer 1: Put 25 mL of H2O in your 50-mL graduated plastic tube. Drop in 25 germinating peas. Determine the volume of water that is displaced (equivalent to the volume of peas). Record the volume of the 25 germinating peas. Remove these peas and place them on a paper towel.

Respirometer 2: Refill the graduated tube to 25 mL with H2O. Drop 25 dry, nongerminating peas into the graduated cylinder. Next, add enough glass beads to equal the volume of the germinating peas. Remove the nongerminating peas and beads and place them on a paper towel.

Respirometer 3: Refill the graduated tube to 25 mL with of H2O. Add enough glass beads to equal the volume of the germinating peas. Remove these beads and place them on a paper towel.

The independent variable is the type of peas (Germinated or Nongerminated) and the temperature (Room or Cold Temperature). The dependent variable is the consumption of oxygen from all 6 respirometers. The control group is respirometer three from both temperatures that consists of only glass beads.

Respirometer Assembly

This requires three respirometers for room-temperature testing and three respirometers for cold-temperature testing.

To assemble a respirometer, place an absorbent cotton ball in the bottom of each respirometer vial. Use a dropping pipet to saturate the cotton with 2 mL of 15% KOH. (Caution: Avoid skin contact with KOH. Be certain that the respirometer vials are dry on the inside. Do not get KOH on the sides of the respirometer.) Place a small wad of dry, nonabsorbent cotton on top of the KOH- soaked absorbent cotton. The nonabsorbent cotton will prevent the KOH solution from contacting the peas. It is important that the amount of cotton and KOH solution be the same for each respirometer.

  • Place 25 germinating peas in the respirometer vial(s) 1.
  • Place 25 dry peas and beads in your respirometer vial(s) 2.
  • Place beads only in your respirometer vial(s) 3.

Insert stopper fitted with a calibrated pipet into each respirometer vial. The stopper must fit tightly. If the respirometers leak during the experiment, you will have to start over.

Placement of Respirometers in Water Baths

Place a set of respirometers (1, 2, and 3) in each water bath with their pipet tips resting on lip of the tray. Wait five minutes before proceeding. This is to allow time for the respirometers to reach thermal equilibrium with the water. If any of the respirometers begins to fill with water, the experiment will have to restarted.

After the equilibrium period, immerse all respirometers (including pipet tips) in the water bath. Position the respirometers so that it’s easy to read the scales on the pipets. The paper should be under the pipets to make reading them easier. Do not put anything else into the water bath or take anything out until all readings have been completed.

Allow the respirometers to equilibrate for another five minutes. Then, observe the initial volume reading on the scale to the nearest 0.01 mL. Record the data in Table 1 for Time 0. Also, observe and record the temperature. Repeat your observations and record them every five minutes for 20 minutes.


Dissolved Carbon Dioxide

Although carbon dioxide is not considered to be highly soluble in blood, a small fraction—about 7 to 10 percent—of the carbon dioxide that diffuses into the blood from the tissues dissolves in plasma. The dissolved carbon dioxide then travels in the bloodstream and when the blood reaches the pulmonary capillaries, the dissolved carbon dioxide diffuses across the respiratory membrane into the alveoli, where it is then exhaled during pulmonary ventilation.


13 C content of ecosystem respiration is linked to precipitation and vapor pressure deficit

Variation in the carbon isotopic composition of ecosystem respiration (δ 13 CR) was studied for 3 years along a precipitation gradient in western Oregon, USA, using the Keeling plot approach. Study sites included six coniferous forests, dominated by Picea sitchensis, Tsuga heterophylla, Pseudotsuga menziesii, Pinus ponderosa, and Juniperus occidentalis, and ranged in location from the Pacific coast to the eastern side of the Cascade Mountains (a 250-km transect). Mean annual precipitation across these sites ranged from 227 to 2,760 mm. Overall δ 13 CR varied from -23.1 to -33.1‰, and within a single forest, it varied in magnitude by 3.5-8.5‰. Mean annual δ 13 CR differed significantly in the forests and was strongly correlated with mean annual precipitation. The carbon isotope ratio of carbon stocks (leaves, fine roots, litter, and soil organic matter) varied similarly with mean precipitation (more positive at the drier sites). There was a strong link between δ 13 CR and the vapor saturation deficit of air (vpd) 5-10 days earlier, both across and within sites. This relationship is consistent with stomatal regulation of gas exchange and associated changes in photosynthetic carbon isotope discrimination. Recent freeze events caused significant deviation from the δ 13 CR versus vpd relationship, resulting in higher than expected δ 13 CR values.

Keywords: Coniferous forest Isotope OTTER Oregon transect Precipitation transect.


Effects of sitting position and applied positive end-expiratory pressure on respiratory mechanics of critically ill obese patients receiving mechanical ventilation*

Objective: To evaluate the extent to which sitting position and applied positive end-expiratory pressure improve respiratory mechanics of severely obese patients under mechanical ventilation.

Design: Prospective cohort study.

Settings: A 15-bed ICU of a tertiary hospital.

Participants: Fifteen consecutive critically ill patients with a body mass index (the weight in kilograms divided by the square of the height in meters) above 35 were compared to 15 controls with body mass index less than 30.

Interventions: Respiratory mechanics was first assessed in the supine position, at zero end-expiratory pressure, and then at positive end-expiratory pressure set at the level of auto-positive endexpiratory pressure. Second, all measures were repeated in the sitting position.

Measurements and main results: Assessment of respiratory mechanics included plateau pressure, auto-positive end-expiratory pressure, and flow-limited volume during manual compression of the abdomen, expressed as percentage of tidal volume to evaluate expiratory flow limitation. In supine position at zero end-expiratory pressure, all critically ill obese patients demonstrated expiratory flow limitation (flow-limited volume, 59.4% [51.3-81.4%] vs 0% [0-0%] in controls p < 0.0001) and greater auto-positive end-expiratory pressure (10 [5-12.5] vs 0.7 [0.4-1.25] cm H2O in controls p < 0.0001). Applied positive end-expiratory pressure reverses expiratory flow limitation (flow-limited volume, 0% [0-21%] vs 59.4% [51-81.4%] at zero end-expiratory pressure p < 0.001) in almost all the obese patients, without increasing plateau pressure (24 [19-25] vs 22 [18-24] cm H2O at zero end-expiratory pressure p = 0.94). Sitting position not only reverses partially or completely expiratory flow limitation at zero end-expiratory pressure (flow-limited volume, 0% [0-58%] vs 59.4% [51-81.4%] in supine obese patients p < 0.001) but also results in a significant drop in auto-positive end-expiratory pressure (1.2 [0.6-4] vs 10 [5-12.5] cm H2O in supine obese patients p < 0.001) and plateau pressure (15.6 [14-17] vs 22 [18-24] cm H2O in supine obese patients p < 0.001).

Conclusions: In critically ill obese patients under mechanical ventilation, sitting position constantly and significantly relieved expiratory flow limitation and auto-positive end-expiratory pressure resulting in a dramatic drop in alveolar pressures. Combining sitting position and applied positive end-expiratory pressure provides the best strategy.