Gas exchange and transport

Question 1

Gas Exchange

Answer 1

Gas exchange at both the pulmonary- capillary and the tissue-capillary levels involves simple passive diffusion of O2 and CO2 down partial pressure gradients.

Question 2

total atmospheric pressure

Answer 2

760 mm Hg

600 mg of N2, 160 mg of O2

Question 3

Henry’s law

Answer 3

At a given temperature, the amount of a particular gas in solution is directly proportional to the partial pressure of that gas

Question 4

Factors other than the partial pressure that influence the rate of gas transfer:

Answer 4

Surface area
Thickness of the
membrane
diffusion coefficient

Question 5

Increased thickness of membrane due to

Answer 5

pulmonary oedema
pulmonary fibrosis
pneumonia

Question 6

Diffusion Coefficient

Answer 6

The rate of gas transfer is directly proportional to the diffusion coefficient (D), a constant value related to the solubility of a particular gas in the lung tissue and to its molecular weight.

D for CO2 is 20 times that of O2 because CO2 is much more soluble in body tissues than O2 is.

The rate of CO2 diffusion across the respiratory membrane is therefore 20 times more rapid than that of O2.

The difference in D is offset by the difference in partial pressure. Normally equal amounts of O2 and CO2 are exchanged.

Question 7

Gas Transport: O2 and CO2

Answer 7

Only 1.5 % of the O2 in the blood is dissolved; the remaining 98.5% is transported in combination with Haemoglobin (Hb).
The majority of CO2 is transported in the blood as bicarbonate

Question 8

gas dissolved

Answer 8

The amount of a gas dissolved depends on its solubility
Pair = Pwater
No net diffusion when Pair= Pwater

Question 9

normal blood

Answer 9

15 g Hb/100 ml blood

Question 10

Anemic blood

Answer 10

7.5 g Hb/100 ml blood

Question 11

Myoglobin

Answer 11

(monomer with one heme) stores oxygen in aerobic muscle and may facilitate diffusion from the blood to the mitochondria.

Question 12

Neuroglobin

Answer 12

is found in neurons. The function of this oxygen-binding protein is unknown.

Question 13

Bohr effect

Answer 13

The influence of CO2 and acid on the release of O2 is known as The Bohr effect.
Both CO2 and H+ component of acids can combine reversibly with Hb at sites other than the O2-binding sites. The result is a change in the molecular structureof Hb that reduces the affinity for O2.
The % Hb saturation refers only to the extent to which Hb is combined with O2, not the extent to which it is bound with CO2, H+, or other molecules. Indeed, the % Hb saturation decreases when CO2 and H+ bind with Hb, because their presence on Hb facilitates increased release of O2 from Hb.

Question 14

Bohr effect 2

Answer 14

CO2 picked up at the tissue level is transported in the blood to the lungs in three ways: physically dissolved, bound to Hb, and as bicarbonate ion. Hb is present only in RBCs, as
is carbonic anhydrase, the
enzyme that catalyses the
production of HCO3-. The
H+ generated during the production of HCO3- also binds to Hb. HCO3- moves by facilitated diffusion down its concentration gradient out of the RBC into plasma, and CL- moves by the means of the same passive carrier into the RBC down the electrical gradient created by the outward diffusion of HCO3-. The reactions that occur at the tissue level are being reversed at the pulmonary level, where CO2 diffuses out of the blood to enter the alveoli.

Question 15

Haldane effect

Answer 15

Oxygenation of blood in the lungs displaces carbon dioxide from hemoglobin which increases the removal of carbon dioxide.

Because only free, dissolved H+ contributes to the acidity of a solution, the venous blood would be considerably more acidic than the arterial blood if Hb did not mop up most of the H+ generated at the tissue level.

Question 16

Bohr effect and Haldane effect work in synchrony

Answer 16

Bohr effect and Haldane effect work in synchrony to facilitate O2 liberation and the uptake of CO2 and CO2-generated H+ at the tissue level. Increased CO2 and H+ cause increased O2 release by the Bohr effect; increased O2 release from Hb in turn causes increased CO2 and H+ uptake by Hb through the Haldane effect. The entire process is very efficient. Reduced Hb must be carried back to the lungs to refill on O2 anyway. Meanwhile, after O2 is released, Hb picks up new passengers – CO2 and H+ - that are going in the same direction to the lungs.

Question 17

When we go deep-sea diving…

Answer 17

Nitrogen narcosis (“raptures of the deep”) is believed to result from a reduction in the excitability of neurons because of the highly lipid-soluble N2.

• High-pressure neurological syndrome (HPNS) occurs below 200m. Mounting pressure results in tremors and convulsion.
• Decompression sickness (“the bends”) occurs during sudden ascent to the surface, the rapid reduction in pressure causes N2 to quickly come out of solution and form bubbles of gaseous N2 in the body, particularly in joints.

Question 18

Adaptations of deep-diving mammals

Answer 18

Elimination of blood flow to most organs, except heart, brain and adrenal gland
Reduction of body temperature by up to 3°C Bradycardia (2-6 beats/min)
Exhalation before dive, reduces buoyancy
Smaller lungs with special airways to store remaining gases after the lungs collapse below 40m that prevent the gases to enter the circulation

Question 19

Sudden decompression of an aircraft cabin at 9000m altitude

Answer 19

Oxygen is less than 30% of that at sea level.
Drastically reduced Hb saturation with O2.
O2 deprivation of the brain results in unconsciousness.
Death from hypoxia

Question 20

Adaptation of high-fliers, eg the bar-headed goose, who can reach an altitude of 9000m

Answer 20

A very low P50 of 10mmHg!
Counter-current perfused flow- through lungs
Increased Myoglobin?