B2 W1 - Gas Transport - Oxygen

Question 1

What is the role of oxygen in cellular respiration?

Answer 1

Oxygen is the ultimate electron acceptor in the electron transport chain, where it is reduced to water.

Question 2

Why is simply dissolving oxygen in blood plasma insufficient for oxygen transport?

Answer 2

Oxygen has poor solubility in water, requiring an unrealistically high cardiac output of over 80 litres per minute to meet the body’s oxygen needs.

Question 3

What is the primary function of haemoglobin?

Answer 3

Haemoglobin is a protein in red blood cells that binds to oxygen, enabling efficient transport of oxygen throughout the body.

Question 4

Describe the structure of a haem group.

Answer 4

A haem group is a planar porphyrin ring with a ferrous iron ion (Fe2+) at its centre, to which oxygen can bind.

Question 5

What is the structure of haemoglobin?

Answer 5

Haemoglobin is a tetramer consisting of four polypeptide chains (two alpha and two beta chains), each with an associated haem group.

Question 6

What are the two conformational states of haemoglobin?

Answer 6

Haemoglobin exists in either a relaxed state with high oxygen affinity or a tense state with low oxygen affinity.

Question 7

How does the binding of oxygen to one haemoglobin subunit affect the other subunits?

Answer 7

Binding of oxygen to one subunit induces a conformational change in the entire tetramer, increasing the oxygen affinity of the remaining subunits, a phenomenon called cooperativity.

Question 8

What is the significance of the shape of the oxygen dissociation curve?

Answer 8

The sigmoid shape of the curve reflects the cooperative binding of oxygen to haemoglobin.

Question 9

How does the partial pressure of oxygen affect haemoglobin saturation?

Answer 9

Haemoglobin saturation increases as the partial pressure of oxygen rises, reaching near saturation at the partial pressure found in the lungs.

Question 10

How does haemoglobin offload oxygen in the tissues?

Answer 10

The lower partial pressure of oxygen in the tissues causes haemoglobin to release oxygen, with approximately 30% of bound oxygen being offloaded under resting conditions.

Question 11

What is the oxygen reserve?

Answer 11

The oxygen reserve refers to the additional oxygen that haemoglobin can release if tissue oxygen tension drops further.

Question 12

What factors can shift the oxygen dissociation curve to the right?

Answer 12

Increased acidity (low pH), increased temperature, elevated carbon dioxide levels, and increased 2,3-diphosphoglycerate (DPG) concentration all shift the curve rightward.

Question 13

What adaptive responses occur in response to chronic hypoxia?

Answer 13

Chronic hypoxia triggers responses such as increased erythropoietin production, increased tissue capillary density, elevated DPG levels, and increased ventilation rate.

Question 14

Why is a rapidly reversible reaction with oxygen important for an oxygen-carrying molecule?

Answer 14

It allows for efficient uptake of oxygen in the lungs (where partial pressure is high) and release of oxygen in the tissues (where partial pressure is low).

Question 15

How does the histidine side chain contribute to conformational changes in haemoglobin?

Answer 15

When oxygen binds to the haem group, it pulls on a histidine side chain attached to the iron ion. This pull is transmitted to the polypeptide chain, inducing a conformational change in the haemoglobin subunit and ultimately affecting the entire tetramer.

Question 16

How does capillary density affect tissue oxygenation?

Answer 16

Higher capillary density means shorter diffusion distances and a larger surface area for oxygen to move from the blood into the cells. This allows tissues to better maintain oxygen supply even with lower partial pressure in the extracellular space.

Question 17

What is the physiological significance of the steep region of the oxygen dissociation curve?

Answer 17

This region corresponds to the typical partial pressure of oxygen found in tissues. Small changes in partial pressure in this range lead to significant changes in the amount of oxygen released from haemoglobin, making oxygen delivery highly responsive to tissue needs.

Question 18

Why might increased erythropoietin production not always resolve hypoxia?

Answer 18

Erythropoietin signals for the production of red blood cells, but other factors are necessary for this process, such as adequate iron for haemoglobin synthesis. Deficiencies in these factors can limit the effectiveness of increased erythropoietin.

Question 19

What is the difference between the partial pressure of oxygen in the lungs and the tissues, and how does this affect oxygen binding to haemoglobin?

Answer 19

The partial pressure of oxygen is higher in the lungs (around 13 kPa) compared to the tissues (around 6 kPa at rest). This difference in partial pressure drives the binding of oxygen to haemoglobin in the lungs (high saturation) and the release of oxygen from haemoglobin in the tissues (lower saturation).

Question 20

How much oxygen is typically offloaded from haemoglobin in resting tissues?

Answer 20

Under normal resting conditions, haemoglobin offloads approximately 30% of its bound oxygen in the tissues.

Question 21

What is the effect of acidity, temperature, carbon dioxide, and 2,3-diphosphoglycerate on the oxygen dissociation curve?

Answer 21

These factors, often found in higher concentrations in metabolising tissues, shift the curve to the right, decreasing haemoglobin’s affinity for oxygen. This promotes a greater release of oxygen into the tissues where it is needed most.

Question 22

What is meant by “oxygen tension,” and how does it relate to oxygen movement?

Answer 22

Oxygen tension is another term for the partial pressure of oxygen. It determines the direction of oxygen movement, with oxygen flowing from areas of higher tension to areas of lower tension. This principle governs oxygen uptake in the lungs and release in the tissues.

Question 23

Explain the concept of dynamic equilibrium in oxygen binding to haemoglobin.

Answer 23

Oxygen binding to haemoglobin is a dynamic process where the amount of oxygen bound constantly adjusts to match the surrounding oxygen tension. When haemoglobin encounters a lower oxygen tension, it releases oxygen to re-establish equilibrium. This dynamic process ensures that tissues receive oxygen according to their needs.

Question 24

How does oxygen delivery change during exercise, considering the principles of oxygen tension and haemoglobin saturation?

Answer 24

During exercise, working muscles demand more oxygen, leading to a decrease in tissue oxygen tension. This lower tension causes haemoglobin to release a greater proportion of its bound oxygen to meet the increased demand.

Question 25

Why is it essential to maintain a sufficient oxygen tension gradient between the extracellular space and the intracellular space within tissues?

Answer 25

While a low extracellular oxygen tension favours offloading from haemoglobin, it shouldn’t be so low that it hinders diffusion into cells. Maintaining a sufficient gradient ensures oxygen can move from capillaries, through the extracellular space, and into cells for respiration.

Question 26

What is the significance of the 0.6 Angstrom shift described in the source?

Answer 26

This tiny shift, caused by oxygen binding to the haem group and pulling on a histidine side chain, highlights how small molecular changes can significantly impact protein function. This seemingly minor shift leads to conformational changes throughout the haemoglobin tetramer, affecting its overall oxygen affinity.

Question 27

What is the difference between the tense and relaxed states of haemoglobin?

Answer 27

The relaxed state has a higher affinity for oxygen, making it more receptive to binding oxygen. The tense state has a much lower affinity, making it more likely to release oxygen.

Question 28

What conditions favour the tense state of haemoglobin?

Answer 28

Low pH (acidic conditions), increased temperature, increased carbon dioxide, and increased 2,3-diphosphoglycerate all favor the tense state. These conditions are usually found in metabolically active tissues, promoting the release of oxygen where it’s most needed.

Question 29

What is the relationship between the colour of haemoglobin and its oxygen saturation?

Answer 29

Haemoglobin appears bright red when fully saturated with oxygen and takes on a more purplish hue when deoxygenated. This difference is why arterial blood (oxygen-rich) is brighter red than venous blood (oxygen-poor).

Question 30

Why is having a tetrameric structure beneficial for haemoglobin’s function?

Answer 30

The tetrameric structure (four subunits) allows for cooperativity in oxygen binding. The binding of oxygen to one subunit makes it easier for subsequent oxygen molecules to bind to other subunits. This results in the characteristic sigmoidal shape of the oxygen dissociation curve, enabling efficient loading and unloading of oxygen.

Question 31

Apart from increased red blood cell production, what are some other adaptive responses to chronic hypoxia?

Answer 31

Other adaptations include increased tissue capillary density (to improve oxygen delivery), increased 2,3-diphosphoglycerate levels (to promote oxygen unloading), and increased ventilation (to increase oxygen intake).