L72: Gas Transport

Question 1

In what direction do gases move in blood circulation?

Answer 1

Down pressure gradients

Question 2

What direction do gases move in the pulmonary circuit?

Answer 2

O2 enters, CO2 leaves blood

Question 3

What direction do gases move in the systemic circuit?

Answer 3

CO2 enters, O2 leaves blood

Question 4

What are the partial pressures of O2 and CO2 in the alveoli?

Answer 4

PO2 (alveolar air) > PO2 (venous blood), 100:40;

PCO2 (alveolar air) < PCO2 (venous blood), 40:46

Question 5

What are the partial pressures of O2 and CO2 in the tissues?

Answer 5

PO2 (tissues) < PO2 (venous blood) 40:100;

PCO2 (tissues) > PCO2 (venous blood), 46:40

Question 6

Why are pressure gradients for O2 much larger than those of CO2?

Answer 6

CO2 is more diffusible

Question 7

What is the process of gas transport in the respiratory system?

Answer 7

Diffusion

Question 8

How is the respiratory system specialised to facilitate gas transport?

Answer 8

• Large surface area;
• Large partial pressure gradients;
• Gases with advantageous diffusion properties.

Question 9

What is total pressure?

Answer 9

The sum of partial pressures within a system e.g. total sum of gases (i.e. total pressure) in the circulatory system = pp (O2) + pp (CO2) etc.)

Question 10

How is O2 transported around the body?

Answer 10

• Dissolved;

- Bound to haemoglobin (Hb).

Question 11

What is the primary transport system for oxygen around the body?

Answer 11

Haemoglobin

Question 12

How much oxygen is transported that is dissolved in the blood?

Answer 12

• A very small percentage that is not an adequate supply alone;
• For each mmHg of PO2, 0.003mL O2/100mL;
• Amount of dissolved is proportional to pp;
• In arterial blood, ppO2: 100mmHg;
• Arterial blood: 0.3mL O2/ 100mL of blood.

(3mL/ 1L of blood)

Question 13

Explain the structure of haemoglobin:

Answer 13

• Transport molecule found in rbc;
• 4 heme groups (iron porphyrin compounds) bound to a globin protein (2 x a and 1 x b polypeptide chains);
• Each heme group contains iron in the reduced ferrous form (Fe3+).

Question 14

How many Hb molecules are there per rbc?

Answer 14

280 million

Question 15

O2 binding to heme is a reversible process, explain the effect of pH on the oxyhemoglobin dissociation curve:

Answer 15

• A decrease in pH shifts the standard curve to the right;
• An increase in pH shifts it to the left;
• A shift to the right indicates less O2 affinity to Hb, and more O2 available in the tissues;
• A shift to the left indicates a higher affinity of O2 to Hb, and less O2 available to the tissues.

Question 16

O2 binding to heme is a reversible process, explain the effect of temperature on the oxyhemoglobin dissociation curve:

Answer 16

• An increase in temperature shifts the standard curve to the right;
• An decrease in temperature shifts it to the left;
• A shift to the right indicates less O2 affinity to Hb, and more O2 available to the tissues;
• A shift to the left indicates a higher affinity of O2 to Hb, and less O2 available to the tissues.

Question 17

What does the flat portion of the oxyhemoglobin dissociation curve represent?

Answer 17

A drop in PO2 from 100 to 60 mmHg has minimal effect on Hb saturation

Question 18

What does the steep portion of the oxyhemoglobin dissociation curve represent?

Answer 18

A small drop in PO2 (if <60) leads to a large release from Hb, facilitated to supply tissues

Question 19

How many molecules of O2 can one heme group bind to?

Answer 19

Up to 4

Question 20

What is oxygen saturation (SaO2)?

Answer 20

The amount go O2 bound to Hb, relative to the maximal amount that can bind

Question 21

What is the primary transport mechanism of oxygen?

Answer 21

Haemoglobin. (~20.8mL O2/100mL of blood vs. 0.3mL O2/100mL blood [dissolved])

Question 22

How is SaO2 measured clinically?

Answer 22

Pulse oximeters

Question 23

What is a healthy rate of CO2 production in the body?

Answer 23

200mL/min

Question 24

What is the Respiratory Exchange Rate (RER)?

Answer 24

Ratio of expired CO2 to O2 uptake

Question 25

What is RER in normal conditions?

Answer 25

0.8 (80 CO2 to 100 O2)

Question 26

How is CO2 transported around the body?

Answer 26

• Dissolved;
• Bound to haemoglobin;
• As bicarbonate.

Question 27

Bicarbonate is a major buffer in the body, what is the equation of equilibrium and what determines this?

Answer 27

• H2O + CO2 = H2CO3 = H+ + HCO3- ;

- Concentration gradients.

Question 28

What two physiological processes regulate blood pH?

Answer 28

• Acidity can be regulated through ventilation, to adjust PCO2;
• OR by using the kidneys to regulate bicarbonate concentration.

Question 29

What term is used to describe the general shape of the O2-dissociation curve?

Answer 29

S-shaped

Question 30

What is the primary transport system for carbon dioxide around the body?

Answer 30

In rbc, in the form of HCO3-