Session 4 - Blood Gas Carriage

Question 1

What is the typical partial pressure of oxygen in the lungs?

Answer 1

13.3 kPa

Question 2

What is the typical partial pressure of oxygen in the tissues?

Answer 2

Around 5 kPa

Question 3

What is the effect on the Hb-oxygen dissociation curve of a fall in pH?

Answer 3

• Promotes T-state of Hb
• Extra oxygen is given up
• Curve shifts right
• important in metabolically active tissues where pH is lowER

Question 4

What is the effect on the Hb-oxygen dissociation curve of a rise in temperature?

Answer 4

• Promotes T-state of Hb
• Extra oxygen is given up
• Curve shifts right
• Important in metabolically active tissues where temp is slightly higher

Question 5

What is the effect on the Hb-oxygen dissociation curve of an increase in levels of 2,3-DPG?

Answer 5

• Curve shifts right

- Important as anaemic and those at altitude have higher levels of 2,3-DPG

Question 6

What properties of Hb facilitate oxygen transport?

Answer 6

• 4 tetramers allow lots of oxygen to transported quickly
• Has two states a high and low affinity allowing co-operative binding
• Allows oxygen to dissociate at the tissues readily

Question 7

Define Cyanosis

Answer 7

A bluish discolouration of the skin due to poor circulation or inadequate oxygenation of the blood

Question 8

How may peripheral cyanosis present?

Answer 8

Bluish discolouration in the hands and feet due to poor circulation

Question 9

How may systemic cyanosis present?

Answer 9

Bluish discolouration of the mouth, lips and tongue due to poorly saturated blood in the systemic circulation.

Question 10

List the three reactions of carbon dioxide in the blood.

Answer 10

1. Dissolves in the Blood
2. Reacts with water
3. Binds directly to proteins

Question 11

Give the reaction that occurs when carbon dioxide reacts with water (Ignore intermediate step)

Answer 11

Carbon Dioxide + Water Hydrogen Ions + Hydrogen Carbonate Ions

Question 12

Give the Henderson-Hasselbalch equation.

Answer 12

pH = 6.1 + Log(Hydrogen Carbonate ions conc / (pCO2 x 0.23))

Question 13

Why is the reaction of carbon dioxide with water slower in plasma compared to inside the RBC’s?

Answer 13

There is little Carbonic anhydrase present and hence the reaction proceeds at a slower rate

Question 14

How is the reversible reaction between Carbon dioxide and water driven in the forwards direction?

Answer 14

There is an anti porter which transports the hydrogen carbonate into the plasma and the hydrogen ions bind to Hb meaning that the reaction is forced in the forwards direction

Question 15

State the normal content of carbon dioxide in arterial blood.

Answer 15

21.5 mmol/L

Question 16

State the normal content of carbon dioxide in venous blood.

Answer 16

23.5 mmol/ L

Question 17

How are the kidneys involved in controlling the pH of the blood?

Answer 17

It determines how much of the hydrogen carbonate is excreted and hence the pH of the blood

Question 18

What proportions of Carbon dioxide are transported by each of the forms in which it travels in the blood?

Answer 18

As Hydrogen Carbonate = 60%
As Carbamino compounds = 30%
As dissolved Carbon Dioxie = 10%