Respiratory Physiology 3.2- Diffusion of gases between alveoli and blood

Question 1

What is the function of the pulmonary artery?

Answer 1

Pulmonary artery carries deoxygenated blood AWAY from the heart to the lungs.

Question 2

What is the function of the pulmonary vein?

Answer 2

Pulmonary vein carries oxygenated blood TOWARDS the heart from the lungs.

Question 2

How is pulmonary circulation different to systemic circulation?

Answer 2

Pulmonary circulation is opposite from systemic circulation in function!
It delivers CO2 to the lungs and picks up O2.
Whereas systemic circulation is about picking up carbon dioxide from the tissues and delivering oxygen to the tissues.

Question 3

What is bronchial circulation?

Answer 3

branch of the systemic circulation that delivers nutritive blood supply to the lungs.
Delivering oxygen, nutrients, enzymes and hormones to lungs and removing waste products.

Question 4

Describe bronchial circulation (nutritive)?

Answer 4

supplied via the bronchial arteries arising from systemic circulation to supply oxygenated blood to lung tissues.

Comprises 2% of left heart output.

Blood from the bronchial veins (systemic veins) (deoxygenated as oxygen delivered to tissues) drains to left atrium via pulmonary veins.
(dilates down a little of the oxygenated blood that’s normally in pulmonary veins)

Question 5

What is main difference between pulmonary and bronchial circulation?

Answer 5

bronchial circulation- concerned with a nutritive supply- in supplying oxygen, nutrients, enzymes, hormones

pulmonary circulation- collecting oxygen and delivering carbon dioxide

Question 6

Describe pulmonary circulation?

Answer 6

Pulmonary circulation (gas exchange) consists of L & R pulmonary arteries originating from the right ventricle. Entire cardiac output from RV. Supplies the dense capillary network surrounding the alveoli and returns oxygenated blood to the left atrium via the pulmonary vein.

Question 7

Compare pressure in pulmonary circulation compared to the pressure in systemic circulation?

Answer 7

pulmonary- systolic over diastolic pressure is 25/10mm/Hg

systemic- 120/80 mm/Hg

Pressure that is driving flow in the pulmonary circulation is much lower than the pressure that is driving flow in the systemic circulation

Question 8

What about the difference in pressure between the pulmonary artery and the pulmonary vein?

Answer 8

very low pressure gradient driving blood from the right side of the heart to the left side of the heart. Much lower than there is between the left side of the heart and the right side of the heart through systemic circulation.

Question 9

Where is gas exchange taking place?

Answer 9

at the level of the alveoli and pulmonary circulation
at level of tissues with systemic circulation

Question 10

How does partial pressure of gas in alveoli compare to partial pressure of gas in systemic arteries?

Answer 10

the same if have healthy lungs

Question 11

What is the partial pressure of oxygen in the alveoli and partial pressure of carbon dioxide?

Answer 11

oxygen- 100mm/Hg
carbon dioxide- 40mm/Hg
and as long as diffusion is working as normal , see same partial pressure in our systemic arterial blood

Question 12

What is the partial pressure of oxygen in our peripheral tissues?

Answer 12

40mm Hg- big partial pressure gradient that effectively sucks oxygen out of arterial blood and into our peripheral tissues

Question 13

What happens when oxygen goes to peripheral tissues?

Answer 13

cells metabolise oxygen and produce carbon dioxide as a waste product.
Constant production of carbon dioxide means we always have more carbon dioxide in cells than in our veins.

Question 14

What happens to carbon dioxide in cells?

Answer 14

carbon dioxide moves down a partial pressure gradient from 46mm Hg into venous blood (PCO2 is 40 mmHg).
And so venous blood has same partial pressure as what is found in resting, metabolising peripheral tissues.

Question 15

What does systemic artery partial pressure reflect?

Answer 15

reflects what’s happening in the alveoli

Question 16

What does venous blood partial pressure in systemic circulation reflect?

Answer 16

what’s happening in our peripheral tissues

Question 17

What happens to systemic venous blood?

Answer 17

Systemic venous blood goes back to the right side of the heart.
Comes out of pulmonary artery and travels to alveoli.
Partial pressures in pulmonary artery are the same as partial pressures in systemic veins.

Question 18

What does capital A define?

Answer 18

alveolar

Question 19

What does a little a define?

Answer 19

arterial blood

Question 20

What does a little v define?

Answer 20

mixed venous blood
e.g. pulmonary artery or large veins of the body

Question 21

What is PaO2 referring to?

Answer 21

partial pressure of oxygen in arterial blood

Question 22

What is PACO2 referring to?

Answer 22

partial pressure of carbon dioxide in alveolar air

Question 23

What is the rule of simple diffusion for gases?

Answer 23

gas will move across a membrane that is permeable to that gas, down it’s partial pressure (similar to concentration) gradient, and will continue to do so until equilibrium is reached.

Question 24

What are the factors for the rate of diffusion across membrane?

Answer 24

directly proportional to the partial pressure gradient. (bigger the gradient, faster the gas will move)

directly proportional to gas solubility (gas needs to be in solution)

directly proportional to the available surface area

inversely proportional to the thickness of the membrane

most rapid over short distances.

Question 25

What are the partial pressures of oxygen and carbon dioxide in pulmonary arterial blood (venous blood) and alveoli?

Answer 25

For venous blood:
PCO2 =46 mmHg
PO2= 40mmHg

For alveoli:
PCO2= 40mmHg
PO2= 100mm Hg

partial pressure gradient that is driving the diffusion of oxygen is 10 times greater than partial pressure gradient driving diffusion of carbon dioxide

Question 26

Why does carbon dioxide diffuse faster than oxygen?

Answer 26

carbon dioxide is more soluble in water