Chapter 37

Question 1

Pulmonary gas exchange

Answer 1

Pulmonary gas exchange refers to the exchange of gases in the lungs which takes place between the alveolar air and the blood flowing through the lung capillaries

Question 2

The amount of CO2 that diffuses into the blood can be affected by:

Answer 2

The oxygen pressure gradient between alveolar air and blood
The total functional surface area of the respiratory membrane
The respiratory minute volume (ml of air moved per minute)
Alveolar ventilation (volume of inspired air that reaches the alveoli) & alveolar function

Question 3

Structural facts that facilitate oxygen diffusion from the alveolar air to the blood:

Answer 3

The walls of the alveoli and capillaries form only a very thin barrier for gases to cross
The alveolar and capillary surfaces are large
The blood is distributed through the capillaries in a thin layer so that each red blood cell comes close to alveolar air

Question 4

Pulmonary gas exchange occurs via

Answer 4

diffusion due to the pressure gradient of O2 & CO2 between blood and lung capillaries surrounding alveoli
O2 will follow its concentration gradient from an area of
high to an area of low concentration
CO2 will diffuse in the opposite direction

Question 5

Exchange of gases in lungs

Answer 5

O2 moves from alveoli into lung capillaries
Hemoglobin combines with O2 oxyhemoglobin
Carbaminohemoglobin breaks down  CO2 + hemoglobin
CO2 moves out of lung capillary blood into alveolar air and out of body in expired air

Question 6

Exchange of gases

Answer 6

Occurs due to the pressure gradient of O2 & CO2 between the tissue capillaries and the tissue cells
Exchange of gases between blood in tissue capillaries and the body cells = internal respiration
Oxyhemoglobin breaks down into O2 and hemoglobin

O2 moves out of tissue capillary blood IF tissue cells
CO2 moves from tissue cells  IF tissue capillary blood
Hemoglobin combines with CO2 carbamino-hemoglobin

Question 7

Blood transportation of gases

Answer 7

O2 & CO2 are transported in the blood either in a dissolved state or combined with other chemicals

Dissolved O2 & CO2 rapidly form a chemical union with some other molecule (e.g. hemoglobin) because fluids (such as blood) can only hold small amounts of gas in solution

Once O2 & CO2 are bound to another molecule, their plasma concentration (partial pressure – PO2 or PCO2) decreases and more gas can diffuse into the plasma allowing comparatively large volumes of these gases to be transported

Question 8

Transport of oxygen

Answer 8

The majority of O2 transported by blood is in the form of oxyhemoglobin (O2 + hemoglobin). Only 1.5% as dissolved O2

Hemoglobin molecules = large proteins containing 4 iron-containing heme components, each capable of combining with an O2 molecule

Hemoglobin combines with O2 very rapidly. 97% of hemoglobin is combined with O2 . (this is the oxygenated blood/’red’ blood in systemic arteries and pulmonary veins)

‘deoxygenated’ blood is about 75% saturated with oxygen and is found in the systemic veins and pulmonary arteries
the difference in O2 saturation results in the release of O2 from oxyhemoglobin to supply the body cells with O2 (the chemical ‘bond’ between O2 and hemoglobin is reversible)

SUMMARY:
There are two forms of O2 in the blood
dissolved O2
oxyhemoglobin (vast majority)

Question 9

CO2

Answer 9

by-product of cellular metabolism
contributes to the pH of body fluids
excesses can be toxic and are eliminated from the body (enters alveoli and is expelled during expiration)

Question 10

In order to expel CO2 via expiration it must be transported in the blood to the lungs as either:

Answer 10

Dissolved CO2
10% of total CO2 transported in blood
Produces PCO2 of blood plasma

2. Carbaminohemoglobin
   CO2 + hemoglobin + other plasma proteins
   20% of total CO2 transported in blood
   Formation is accelerated by an increase in PCO2 and slowed down by a decrease in PCO2
3. Bicarbonate ions (HCO3-)
   70% of total CO2 transported in blood