Gas Transport

Question 1

Respiratory and circulatory systems function together to transport gasses around the body. What gasses do they transport and where?

Answer 1

• CO2 from tissues to the lungs

- O2 from the lungs to tissues

Question 2

The movement of gasses throughout the respiratory system occurs via what process?

Answer 2

Diffusion

Question 3

The respiratory and circulatory systems contain unique anatomical and physiological properties to facilitate gas diffusion. What are these?

Answer 3

1. Large surface area for gas exchange
2. Large partial pressure gradients
3. Gasses with advantageous diffusion properties
4. Specialised mechanisms for transporting O2 and CO2 between lungs and tissues

Question 4

O2 is carried in 2 forms. What are these?

Answer 4

• Dissolved in the plasma

- Bound to haemoglobin

Question 5

Dissolved O2 is measured clinically in an arterial blood sample PaO2. How much O2 in the blood is in the dissolved form?

Answer 5

• Only a small percentage
• Amount of dissolved O2 in the blood is proportional to the partial pressure
• For each mmHg of PO2 there is 0.003mlO2/100ml of blood (so oxygen is not very soluble)

Question 6

Is the transport of O2 in the dissolved form adequate for the body’s requirements (even at rest)?

Answer 6

NO, which is why there is a second O2 transport system in place: haemoglobin

Question 7

What is haemoglobin?

Answer 7

A major transport molecule for O2 found in RBC’s

Question 8

What is the structure of haemoglobin?

Answer 8

• Four haem groups joined to globin protein (2 alpha and 2 beta chains)
• Each haem group contains iron in the reduces ferrous form, which is the site of O2 binding

Question 9

How many haem groups are found in a single molecule of haemoglobin?

Answer 9

4

Question 10

Why is it necessary for binding and dissociation of O2 with Hb to occur in milliseconds to facilitate transport?

Answer 10

Because RBC’s are in capillaries for 1 second only

Question 11

Does oxygen bind to haemoglobin more at higher or lower temperatures?

Answer 11

Lower temperatures

Question 12

Does oxygen bind to haemoglobin more in acidic or alkaline conditions?

Answer 12

Alkaline conditions

Question 13

Is O2 binding to haemoglobin reversible or irreversible?

Answer 13

Reversible

Question 14

How many O2 atoms can bind to one Hb molecule?

Answer 14

Up to 4

Question 15

What does oxygen saturation refer to?

Answer 15

The amount of O2 bound to Hb relative to the maximal amount that can bind
- 100% saturation means all haem groups of Hb molecules are fully saturated with O2

Question 16

What is the total oxygen capacity in mls O2/1L of blood?

Answer 16

211mls O2/1L of blood

Question 17

What device is used in the clinic to measure O2 saturation?

Answer 17

• Pulse oximeters

- Measures the ratio of absorption of red and infrared light by oxyHb and deoxyHb

Question 18

In a healthy human being how much CO2 is produced in a minute?

Answer 18

200mls

Question 19

What is the ration of CO2 expired by the lung compared to the amount of O2 molecules that enter

Answer 19

• 80 molecules of CO2 expired for every 100 molecules of O2 that enter

Question 20

What is meant by the respiratory exchange ration?

Answer 20

The ratio of expired CO2 to O2 uptake

- In normal conditions, the respiratory exchange ratio = 0.8 (80 CO2 to 100 O2)

Question 21

What are the 3 different forms in which CO2 is carried in the blood?

Answer 21

1. Dissolved
2. Bound to haemoglobin
3. As bicarbonate

Question 22

Bicarbonate concentrations can be used to stabilise the Ph of blood. What kind of reaction is this?

Answer 22

A buffer reaction

- The high bicarbonate concentration makes buffering reaction strong

Question 23

What shape is the O2-dissociation curve?

Answer 23

S-shaped