Lecture 17 - O2 and CO2 transport

Question 1

How can oxygen be transported in the body?

Answer 1

Dissolved in plasma or combined with haemoglobin.

Question 2

Why do we rely on O2 in Haemoglobin more than O2 dissolved in plasma?

Answer 2

We have very little oxygen dissolved in plasma (3ml of O2 per litre) as it dissolves very slowly. As dissolved O2 is not enough on its own, we have the utilisation of haemoglobin for oxygen transport

Question 3

What is the rate of O2 need in the body

Answer 3

We need about 250 ml O2 /min

Question 4

What is Haemoglobin (Hb)?

Answer 4

Haemoglobin is a protein complex made up of 4 subunits (globin’s). Attached on each globin subunit is a haem group. Within these haem groups we have iron, an atom where oxygen binds readily.

Question 5

Why is the structure of Haem important in oxygen transport?

Answer 5

As we have 4 haem groups in haemoglobin, we can bind 4 oxygen molecules. As a result, it is easy for oxygen to reversibly bind to Hb to form an oxyhaemoglobin.

Question 6

What does the binding of oxygen to Hb depend on?

Answer 6

PO2

Question 7

What determines blood colour?

Answer 7

The colour of blood is due to the saturation of O2. When Hb is saturated, iron gives the molecule a red colour

Question 8

What does Hb saturation refer to?

Answer 8

Haemoglobin saturation refers to the amount of haemoglobin that has oxygen bound

Question 9

What happens to partial pressure of oxygen as we deliver oxygen around the body?

Answer 9

As we deliver oxygen around the body, the partial pressure in the blood decreases, meaning less oxygen is bound to Hb.

Question 10

What happens to PO2 during exercise and why?

Answer 10

When we exercise PO2 decreases, meaning oxygen is more readily released.

Question 11

What shape is the Oxygen-haemoglobin dissociation curve?

Answer 11

Sigmoidal

Question 12

What does the steep part of the oxygen-haemoglobin dissociation curve allow for?

Answer 12

In places of lower PO2, slight changes in PO2 will have drastic effects in Hb saturation.
This steeper part in the curve helps with the loading of Hb in the lungs as well as the unloading of oxygen in the lungs.
- Occurs around systemic venous PO2 of around 40

Question 13

What does the upper flat part of the oxygen-haemoglobin dissociation curve allow for?

Answer 13

In higher PO2 like in the arteries, when there are slight changes in PO2, haemoglobin saturation stays relatively the same to allow for a more constant saturation of oxygen - some reserve capacity

Question 14

Where can the oxygen-haemoglobin dissociation curve shift?

Answer 14

Left or Right

Question 15

What happens when the O2-Hb dissociation curve shifts to the right?

Answer 15

When the curve shifts to the right, the PO2 where 50% of HB is saturated increases and oxygen affinity decreases. This shift to the right favours the release of O2 from the Hb to the tissues (offloading) and naturally occurs as blood flows through the tissue capillaries (where there is a high metabolic demand).
- Right shift improves delivery of oxygen by Hb

Question 16

How can the O2-Hb dissociation curve shift to the right?

Answer 16

The curve can shift to the right from an increase in PCO2, H+, temp, or 2,3-BPG. During exercise these factors increase which means the curve is shifted to the right.

Question 17

What happens when the O2-Hb dissociation curve shifts to the left?

Answer 17

When the curve shifts to the left, the PO2 where 50% of HB is saturated decreases and oxygen affinity increases. This shift to the left favours the binding of O2 to Hb (onloading) and naturally occurs as blood flows through the lung capillaries (where we have the uptake of oxygen).
- Left shift improves loading of oxygen by Hb

Question 18

How can the O2-Hb dissociation curve shift to the left?

Answer 18

The curve can shift to the left from a decrease in PCO2, H+, temp, or 2,3-BPG.

Question 19

What does the Bohr effect explain?

Answer 19

How the oxygen-haemoglobin dissociation curve can shift left or right

Question 20

What is O2 carrying capacity

Answer 20

The O2 carrying capacity describes how much O2 the blood could carry. The O2 carrying capacity is defined by the maximal amount of O2 carried where Hb is 100% saturated.

Question 21

What is the normal O2 carrying capacity in blood?

Answer 21

In normal blood, we have about 150g Hb/L. Each gram of Hb can carry approx. 1.34ml of O2. This means that O2 capacity generally sits at around 200ml per L of blood.

Question 22

What is O2 content?

Answer 22

O2 content describes how much O2 the blood is actually carrying. O2 content is determined by O2 capacity and saturation (+dissolved O2).

Question 23

How can we measure O2 capacity?

Answer 23

O2 capacity = 1.34 x Hb x Sat/100

Question 24

How can we measure O2 content?

Answer 24

O2 content = O2 capacity x saturation ( + dissolved)

Question 25

What is O2 content in arteries?

Answer 25

In the arteries where saturation is high, O2 content is near O2 capacity

Question 26

Compare O2 content of venous blood to arteries

Answer 26

In the veins where saturation is lower, the O2 content is decreased.

Question 27

How can we measure the amount of O2 extracted by the tissues?

Answer 27

The difference in O2 content of the arteries and veins = the amount of O2 extracted by the tissues.

Question 28

MCQ: If a person has a haemoglobin concentration of 150 g per litre of blood, then (ignoring any dissolved oxygen) the oxygen content of this person’s blood at P50 will be closest to:

Answer 28

100 ml O2 per litre of blood.

Question 29

What happens to a-v O2 difference during excercise and why?

Answer 29

During excercise the a-v O2 difference will increase. This is due to the saturation curve having the capacity to provide extra O2 extraction

Question 30

What is the affect of anaemia on excercise and a-v difference?

Answer 30

In anaemia, the level of Hb is lower but the saturation curve stays the same. This means that O2 content is reduced which can lead to problems in exercise due to lower a-v difference.

Question 31

What is the affect of CO on O2 content in the blood?

Answer 31

CO has a high affinity to Hb which means as CO concentration increases, there will be a decrease in how much O2 can be bound. This increase in CO will also shift the curve to the right. This means O2 will only be released in to the tissues at very low PO2

Question 32

What does smoking do to arterial CO concentration?

Answer 32

Increase

Question 33

How can CO2 be transported?

Answer 33

CO2 can be transported in 3 different forms, dissolved in plasma (10%), as a bicarbonate (70%), or combined with proteins as carbamino compounds (20%).

Question 34

Describe how CO2 transported as a bicarbonate

Answer 34

After CO2 dissolves in plasma, carbonic hydrase binds it with water to form carbonic acid (H2CO3). Carbonic acid then immediately dissociates into hydrogen and bicarbonate ions.

Question 35

Describe the difference in dissolving between O2 and CO2

Answer 35

Unlike O2, CO2 can easily dissolve in plasma - 20 x more soluble

Question 36

What does the Haldane effect describe?

Answer 36

The Haldane effect describes how the CO2-Blood curve is able to shift up or down

Question 37

What does an upward shift of CO2-blood dissociation curve mean?

Answer 37

CO2 and H+ bind more readily to globin chain when the heme contains less O2 i.e., as arterial blood flows through the tissue capillaries losing O2, the change in molecular configuration of Hb favours the onloading of CO2 onto the globin chain

Question 38

What does an downward shift of CO2-blood dissociation curve mean?

Answer 38

CO2 and H+ bind less readily to globin chain when the heme contains more O2 i.e., as venous blood flows through the lung capillaries gaining O2, the change in molecular configuration of Hb to promote the release of CO2 in the alveoli