Transport of O2 and CO2 in blood

Question 1

Gas movement through the conducting airways occurs by convection. but gas exchange across the blood-gas barrier in the alveolus occurs by what?

Answer 1

Diffusion

Fick’s law

Question 2

What is Fick’s law?

Answer 2

The rate of diffusion oxygen is equal to “Krogh’s Oxygen Permeation Coefficient” (3.3x10-8cm-2.min-1.mmHg-1)-the rate at which oxygen naturally diffuses through humidified gas in the alveolus

Question 3

Why is maintaining a thin blood gas barrier more desired?

Answer 3

Optimal gas diffusion

Question 4

Oxygen is transported in two forms of blood. What are they?

Answer 4

Physical and Chemical

Question 5

What does the physical form of blood mean?

Answer 5

Plasma soluble O2 (2%)

Question 6

What does the chemical form of blood mean?

Answer 6

O2 bound to haemoglobin (98%) -Most common

Rapid and reversible reaction between oxygen and heam

Question 7

How much oxygen us carried by haemoglobin?

Answer 7

1g Hb binds 1.34 O2
15Hb/100ml total blood
O2 carrying capacity of hb=1.34x15=20mls O2/100ml

Question 8

What is the total arterial blood oxygen content (CaO2)?

Answer 8

O2 carrying capacity of Hb (20mlsO2/100ml0+plasma soluble O2 (0.3mlsO2/100mls)
=20.3mlsO2/100ml total blood

Question 9

What is the total venous blood oxygen content (CvO2)?

Answer 9

O2 carrying capacity of Hb (15mlsO2/100mls) + Plasma soluble O2 (0.28mlsO2/100mls)
=15.28mlsO2/100ml total blood

Question 10

What is the difference between onxygen content and saturation?

Answer 10

Content- Determined by amount of Hb and O2 in blood

Saturation (usually SaO2)- proportion (%)

Question 11

What is the calculation for SaO2?

Answer 11

Oxyhemoglobin/O2 carrying capacity of Hb

Question 12

What can remain the same even if O2 content of blood differs?

Answer 12

Saturation

Question 13

What is sued to view the oxygen uptake from the alveolus?

Answer 13

Oxyhemoglobin Dissociation Curve

Question 14

P50 value gives what?

Answer 14

PO2 required fro half maximal Hb saturation

Question 15

Venous blood enters the alveolus at what? This equilibrates to alveolar PO2 of what?

Answer 15

40mmHg, 75% saturation

100mmHg, 97% saturation

Question 16

Arterial plateau phase ensures what?

Answer 16

Maximal HbO2 saturation even if alveolar PO2 is below the normal (normoxic) oxygen tension

Question 17

What does the steep phase of the curve favour?

Answer 17

Off-load of arterial oxygen to tissues. Greater HbO2 diassociation for small xhanges in tissue PO2

Question 18

Normal P50 = 27mmHg at pH 7.4 and PCO2 of 40mmHg. What happens to these numbers if there is a left or right shift?

Answer 18

Left= Increased Hb-O2 affinity and reduced O2 offloading to tissues (eg fetal Hb)

Right=Decreased Hb-O2 affinity and raised O2 offloading to tissues (eg high altitude)

Question 19

What are factors that cause a right shift in the axyhemoglobin dissociation curve?

Answer 19

-Acidosis (pH down)
-Increase in PCO2
These are both Bohr effect

• Fever
• Hypoxic glycolysis

Question 20

What is the Bohr effect?

Answer 20

pH alters the ability of oxygen to bind to haemoglobin

Question 21

In the Bohr effect, increased blood pCO2 releases O2 from Hb in two ways. What are these two ways?

Answer 21

1) Production of carbonic acid in red cell
2) Carbamate reaction at N-terminal Amino Groups on Hb a-subunit

These both lead to acid stabilisation of a-b Hb subunit interaction and low Hb affinity for O2

Question 22

What is the physical and chemical ways that CO2 is transported in the blood. Three ways

Answer 22

Physical- Plasma soluble CO2

1) Soluble CO2 gas
2) Bicarbonate ion

Chemical 3)Carbamate reaction at N-terminal amino group of Hb a subunit

Question 23

In the red blood cell, what enables CO2 carriage as bicarbonate anion?

Answer 23

Carbonic Anhydrase

Question 24

What are the 3 forms that CO2 is carried within the blood?

Answer 24

Hypoxia
Venous
Alveolar

Question 25

What is the haldane effect?

Answer 25

Low tissue O2 favours CO2 carriage by blood

Question 26

What reaction reeuces HbO2 affinity?

Answer 26

Carbamate

Question 27

Oxygen equilibrates from alveolus to blood
CO2 equilibrates from blood to alveolus?
true or false

Answer 27

True

Question 28

What is the equation for measuring the alveolar PO2 (pAO2)?

Answer 28

pAO2=proportion of oxygen in inhales gas - the partial pressure of CO2 (measured as arterial pCO2) x rate of O2 consumption by metabolism

Question 29

In high altitude environments, how can you adapt to conserve pAO2?

Answer 29

• Increase breathing frequency
• High carb diet
• Climb when barometric pressure is high

Question 30

Poor ventilation and large blood flow requires what and why?

Answer 30

Perfusion needs to be reduced due to hypoxia constricting pulmonary arterioles

Question 31

Good ventilation and poor blood flow requires what and why?

Answer 31

A reduction in ventilation because low CO2 contrcits bronchioles

Question 32

What does hypoxia mean?

Answer 32

Constricts pulmonary arteries to increase pulmonary transit time of blood

Question 33

In the event of a collapsed lung what happens to the flow of blood?

Answer 33

Re-directed to well ventilated area of the lung

Question 34

In the event of a blood clot and there is an obstruction which causes low CO2 what happens to the bronchioles and what happens to the air flow?

Answer 34

• Constricts bronchioles to area of vascular obstruction

- Re-directs air flow in lungs away from obstruction