Gas Transport

Question 1

Describe how oxygen is transport in the blood?

Answer 1

Physically dissolved in plasma (2%) and combined with haemoglobin (98%)

Question 2

Describe why only a small amount of blood is physically dissolved in plasma

Answer 2

At 37 degrees, the solubility of oxygen in plasma is poor (0.03) and the partial pressure of oxygen in arterial blood is 100mmHg so only 3ml oxygen per litre of blood can be transported. Much less than our bodies consume.

Question 3

Describe the structure oh haemoglobin

Answer 3

Tetramer with four O2-binding heme groups. Consists of two alpha and two beta chains. Each heme group consists of a porphyrin ring surrounding an iron ion.

Question 4

How can oxygen bind to iron

Answer 4

Only in ferrous state

Question 5

Describe how haemoglobin structure changes with oxygenation

Answer 5

Deoxygenated Hb exists in a tensed state. In this state strong ionic bonds form between the 4 polypeptide chains which means Fe lies deeper in the pocket and cannot bind O2. Where as oxygenated Hb is in a relaxed state, this occurs because when oxygen binds the ionic bonds break so Fe moves to plane of porphyrin ring. Colour of blood changes from dark red to bright red.

Question 6

What accounts for the shape of the O2-Hb dissociation curve?

Answer 6

Cooperatively (haem-haem interaction). This means that the binding of one O2 molecules makes it easier for subsequent ones to attach

Question 7

With quite respiration how much oxygen does haemoglobin deposit?

Answer 7

47ml/L of blood. This will increase if undergoing exercise

Question 8

What is oxygen capacity and what does it depend on?

Answer 8

The amount oxygen/L of blood attached to Hb at full saturation. It depends on Hb concentration in blood

Question 9

Each gram of Hb can carry how much oxygen?

Answer 9

1.35ml

Question 10

Describe the effects of myoglobin and foetal haemoglobin?

Answer 10

They shift the curve to the left

Question 11

What is the difference between adult and foetal haemoglobin

Answer 11

Foetal - 2 alpha and 2 gamma chains. This means foetal haemoglobin has a higher affinity for oxygen than adult due to the special properties of the gamma chains

Question 12

What causes the haemoglobin oxygen dissociation curve to shift to the left and what does this mean and where does this commonly occur

Answer 12

• Increase in pH, a decrease in PCO2, decrease in temperature and a decrease in 2,3 DPG. This means the haemoglobin has a high affinity for oxygen, this occurs in pulmonary capillaries

Question 13

What causes the haemoglobin oxygen dissociation curve to shift to the right and what does this mean and where does this commonly occur

Answer 13

• Decrease in pH and an increase in PCO2, temp and 2,3-DPG. This means Hb has a low affinity for oxygen, occurs in systemic capillaries

Question 14

Describe what factors account for the bohr effect

Answer 14

pH accounts for most of it.

Temperature will affect O2 capacity of Hb.

Hypocapnia as CO2 combines with unprotonated amino group on Hb forming carbamino haemoglobin.

2,3 Diphosphoglycerate - By product of glycolysis, if there is a decrease in PO2, RBCs stimulate glycolysis resulting in increased levels of 2,3 DPG

Question 15

Describe the effects of carbon monoxide on Hb affinity for oxygen

Answer 15

CO has a 200 fold greater affinity for Hb than oxygen so maximal oxygen capacity falls to the extend that CO binds. However it also increases oxygen affinity of Hb, shifting dissociation curve to the left (meaning Hb doesn’t release oxygen when it gets to tissue).

Question 16

How much CO2 does the metabolism produce and then how will it be transported?

Answer 16

• At rest 200ml co2/min.
  It is then transported via two ways:
• In plasma as it is physically dissolved, combined with plasma proteins and as bicarbonate ions.
• In RBCs, combined with Hb and as bicarbonate ions.

Question 17

What preortion of carbon dioxide is transported via each method

Answer 17

As bicarbonate ions - 70%.

Dissolved in plasma - 10%

Carbaminohaemoglobin -20%

Question 18

Describe the release of carbon dioxide from blood into lungs

Answer 18

• Partial pressure gradients for oxygen and carbon dioxide reverse.
• High PO2 causes H+ to dissociate from Hb, the H+ then combines with bicarbonate ions to form CO2 and H2O.
• Bicarbonate ions can also reenter RBCs and combine with hydrogen ions to form H2CO3 (carbonic acid) which dissociates to release CO2 and H2O.

Question 19

Carriage of CO2 in blood depends on what?

Answer 19

PCO2, plasma pH and PO2

Question 20

What is the oxygen consumption in adults?

Answer 20

250 ml/min, rising to 4L/min in heavy exercise