Gas Exchange and Gas Transport

Question 1

where and in what way does gas exchange occur

Answer 1

at capillaries in lungs (capillary beds at avioli) and at tissue capillary level

by diffusion oxygen and carbon dioxide down their partial pressure gradients

Question 2

what is partial pressure and what is it typically at sea level

Answer 2

pressure exerted by a single gas or liquid on their own

basically when we breathe in we create a lower partial pressure than sea level in our avioli (by creating space), so that higher pressured gases can travel to it

typically 760 mm Hg varies with temperature and humidity

Question 3

what is henry’s law

Answer 3

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

Question 4

PO2 and PCO2 of deoxy blood going to the lungs

Answer 4

P02 = 40 mm Hg
PCO2 = 45 mm Hg

Question 5

PO2 and PCO2 of oxygenated blood in alveoli vs atmospheric air
why the difference

Answer 5

atmospheric - 160 mm Hg of O2, 0.3 mm Hg of CO2
alveoli - 104 mm Hg O2 (more like 100), 40 mm Hg CO2

in alveoli there is the partial pressure of water vapour and CO2 which reduces the P of oxygen (as the volume is not fixed)

Question 6

PO2 and PCO2 of blood leaving the lungs

Answer 6

100 mm Hg O2 (more like 96)
40 mm Hg CO2

(notice all figures have higher oxygen difference, however with oxygen and carbon di end up with the same concentration of about 80%, as co2 has a higher solubility coefficient due to its polarity)

Question 7

PO2 and PCO2 in interstitial fluid (blood after tissues have used oxygen and given off CO2)

Answer 7

less than 40 mm Hg O2

greater than 45 mm Hg CO2

Question 8

what accounts for the difference between alveolar blood PO2 and the PO2 of the blood leaving lungs about to enter tissue capillaries

Answer 8

(there is no gas diffusion during the travel of the blood)
so this is due to anatomical right to left shunts (also physiological shunting in asthmatic people) (heart and bronchial tree veins) drain straight into left ventricles diluting oxygenated blood and hence oxygen partial pressure

Question 9

factors other than partial pressure of gases that affect their diffusion

Answer 9

SA
thickness of membrane / travel distance
diffusion coefficient

Question 10

what can increase the thickness of membranes

Answer 10

fluid build up or PULMONARY OEDEMA - high altitude pulmonary oedema for eg when you’re high up in the mountain. pulmonary arteries constrict creating pressure build up and fluid leaking into membranes

PNEUMONIA eg. COVID, infection and fluid build up in alveoli increased thickness of epithelium of bronchioles, reducing air flow

scar tissue can cause Pulmonary fibrosis, thickening of membrane

Question 11

what is the diffusion coefficient connected to

Answer 11

solubility of a gas and its molecular weight

CO2 heavier and more polar so diffusion coefficient is about 20 X that of O2

Question 12

how much oxygen is purely dissolved in blood and how much is otherwise transported by …

Answer 12

by haemoglobin is 98.5%

1.5% is dissolved

Question 13

how many global chains does Hb have and what’s inside each

Answer 13

4
inside each Heme molecule which has an Fe2+ that binds to one oxygen molecule
so overall a Hb molecules only carries four oxygen molecules
once it carries 4 its considered fully saturated

Question 14

what determines the saturation of a haemoglobin molecule

Answer 14

the partial pressure of O2

Question 15

PO2 in systemic vs pulmonary capillaries and the correlating Hb saturation

Answer 15

sys - 40 mm Hg correlates to 75% sat
! 25% of carried oxygen from pulmonary circuit will be offloaded into the tissue, remaining 75% bonded to Hb will stay bonded to it

pul - 100 mm Hg t 100% sat

Question 16

explain Bohr’s effect in relation to the change in relationship between haemoglobin saturation and PO2

Answer 16

Bohr’s effect is the influence of Co2 and acid (H+) on the release of O2.
both Co2 and H+ combine with Hb reversibly at site other than the O2, changing its structure and reducing its affinity for O2.
AKA presence of CO2 and H+ increases the release of O2 molecules

this is important for working muscles which also produce heat

Question 17

difference in fetus oxygen uptake in relation to haemoglobin

Answer 17

fetus gets oxygen from placenta which is tissue and has an PO2 of 40 mm Hg.
(less o2 released)
the foetus actually has a structurally different haemoglobin molecule
unloading of O2 occurs at placenta, offloading occurs at about 20 mm Hg

Question 18

normal blood values for haemoglobin, oxygen carrying capacity, O2 content of arterial and venous blood

Answer 18

15 g Hb / 100 mL

20 mL O2 / 100 mL (15 X 1.34mL)

same as above at 100% Hb saturation at 100 mm Hg

15 mL o2 / 100 mL
75% at 40 mm Hg

Question 19

anaemic blood values

Answer 19

7.5 g Hb / 100 mL

10 mL O2 / 100 mL (15 X 1.34mL)

same as above at 100% Hb saturation at 100 mm Hg

7.5 mL o2 / 100 mL
75% at 40 mm Hg

Question 20

4 locations CO2 can travel to when being excreted from tissue cells into systemic circulation

Answer 20

1. dissolved in plasma
2. in intracellular fluid of red blood cells
3. bound to the globin chains of haemoglobin molecules
4. binds to water molecules and in the presence of carbonic anhydrase forms carbonic acid which dissolved into hydrogen ions and bicarbonate (HCO3)
   the H+ binds to globin chain so it doesn’t change the pH of the intracellular fluid of red blood cells

bicarb molecules get transported out of cell, for each one out a chlorine ion goes in (majority of CO2 produced gets transformed and transported out as HCO3-)

Question 21

locations CO2 can travel to when being excreted from tissue cells into pulmonary circulation

Answer 21

1. in alveoli which have a lower pp of CO2, by first dissolving in plasma (some stays there)
2. reverse reaction of it binding with water and globin chains

Question 22

how much co2 is dissolved in plasma and what reaction occurs with some of it

Answer 22

5%
5% reacts with water to form H2Co3 then HCO3- and H+ THIS ACIDIFIED BLOOD, so if you don’t breathe out your blood becomes acidic - respiratory acidosis
conversely if you hyperventilate, result is respiratory alkalosis

Question 23

what is a body response to combat respiratory acidosis/alkalosis
(assuming you’re in respiratory failure)

Answer 23

changing the amount of bicarb in the plasma, bicarb is produced by kidneys and excreted into urine for instance (renal compensation). increasing HCO3- concentration increases pH and vice versa

(davenport’s diagram)

Question 24

what is Haldane’s effect

Answer 24

globin chains increase their affinity for co2 molecules and hydrogen ions if the haemoglobin molecules have just offloaded oxygen

works in synchrony with Bohr effect for efficient gas transport