Gas exchange in humans

Option H6

H.6.1: Partial pressure explained

Partial pressure explained

H.6.2: The oxygen dissociation curves of adult hemoglobin, fetal hemoglobin and myoglobin

Adult oxygen-hemoglobin dissociation curve

The graph belows illustrates the relationship between oxygen and hemoglobin. Each hemoglobin molecule can carried 4 oxygen molecules within its structure. The important heme group contains the iron atom which allows the oxygen to bind to hemoglobin. On the y-axis can be seen the how the number of oxygen molecules bound to hemoglobin (i.e., percent saturation) changes depending on the partial pressure (PO2) of the tissue surrounding the capillaries. In the lungs the initial uptake of one oxygen molecule by hemoglobin facilitates the further uptake of oxygen molecules thus increasing the affinity for oxygen by hemoglobin. Whereas in respiring tissue the initial release of one oxygen molecule by hemoglobin facilitates the subsequent release of oxygen molecules thus decreasing hemoglobin affinity for oxygen.

Placing your cursor over numbers 1 to 7 on the graph will display information regarding the dissociation curve.


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Oxygen Dissociation Curves for adult and fetal hemoglobin and myoglobin

The graph below outlines the differences between adult (red curve) and fetal (green curve) hemoglobin and myoglobin (blue curve) and adult hemoglobin (red curve).

Myoglobin and Hemoglobin

H.6.3: Transport of Carbon Dioxide in the Blood

Carbon dioxide produced in the respiring cells of the body must be taken from the tissues to the lungs. The diagram below outlines how carbon dioxide is carried in three forms in the blood (shown as numbers i, ii and iii). Also shown is the importance of carbonic anhydrase (iv) and the chloride shift (v) that occurs between the red blood cell and the blood plasma.

Carbon dioxide transport

Key Points

Place your cursor on numbers i to v below for information regarding carbon dioxide transport in the blood for each corresponding number in the diagram above.

Close the popup window clicking on the x in the corner or it will stay open.

Click on i Click on ii Click on iii Click on iv Click on v

H.6.4: The Bohr Effect

The Bohr Effect causes the oxygen-hemoglobin dissociation curve to shift to the right. The key point to understand is that the Bohr effect ensures a readily available supply of oxygen to respiring cells.

Bohr effect graph

H.6.5: How and why ventilation rate varies with exercise.?

Breathing changes during exercise

Can you explain the changes in breathing rate and volume during exercise?

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Breathing changes during exercise explained

H.6.6: Causes of asthma and its effects on the gas exchange system

Asthma is a chronic inflammation of the airway. It causes the airway smooth muscle to be hyperresponsive and contract strongly when an individual exercises, is under emotional stress, is exposed to cold air, cigarette smoke, or inhaled irritants. Shown below is the diagram of a normal bronchiole in the human lung, put your cursor onto the diagram to see the difference of a asthmatic bronchiole.

normal bronchiole

What are the Effects of Asthma on Gas Exchange?

Compare the two bronchioles and then click on Show the Effects of Asthma below the diagram to see asthma's effects on the bronchioles.

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Effects of Asthma

H.6.7: Effects of High Altitude on Gas Exchange

A person living at high altitude has to deal with a number of challenges regarding gas exchange in the lungs. One of the main problems is the change in atmospheric pressure as you go higher in altitude. As shown in Table 1 below going from 0 m (sea level) to 9000 m, although the air still contains 21% oxygen by volume, both the total atmospheric pressure and the partial pressure of oxygen decrease. The effect of this reduced pressure is decreased alveolar and arterial partial pressure for oxygen which causes hemoglobin to be not fully saturated with oxygen and this leads to decreased oxygen for respiring tissues and cells. This leads to what is known as Mountain Sickness.

Table 1: Air Pressure at different altitudes

Altitude (m) Total Pressure (mmHg) Percent Oxygen Partial Pressure Oxygen (mmHg)
0 (sea level) 760 21 160
9000 253 21 53

Can you think of ways in which the body acclimatizes to the decrease alveolar PO2 due to an increase in altitude?

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How the body acclimatizes to altitude
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