w1 gas transport and blood gases

Question 1

What are the different ways that gases can be carried in the human body?

Answer 1

Dissolved in plasma
Chemically bonded to haemoglobin
Converted into a different molecule.

Question 2

What is meant by external respiration in the human body?

Answer 2

Gas exchange across the blood gas barrier in the lungs at the alveoli.
Lungs contain air from the external world.

Question 3

What causes the movement of gases in both internal and external respiration?

Answer 3

Gases move down a partial pressure gradient by diffusion.
Until an equilibrium is reached

Question 4

What factors influence the rate of external respiration?

Answer 4

1. Surface area and structure of the respiratory membrane
2. Partial pressure gradients
3. Matching the rate of alveolar air flow to pulmonary capillary blood flow (maintain concentration gradient).

Question 5

What is meant by internal respiration in the human body?
What different factors influence the rate of internal respiration?

Answer 5

Diffusion of O2 and CO2 between the capillaries and respiring tissue down a partial pressure gradient
Rate influenced by:
Available surface area
Partial pressure gradients
Rate of blood flow

Question 6

What cells rely on internal respiration to receive oxygen?

Answer 6

Myofibres
Adipocytes
Epithelial cells
Immune cells.

Question 7

Where are partial pressure gradients observed for gas exchange in the human body?

Answer 7

Surrounding the whole capillay network.

Question 8

What are gas laws in the human body?

Answer 8

Gases diffuse along their partial pressure gradient from regions of high to low partial pressure until an equilibrium is established.

Question 9

Compare the proportion of oxygen found in haemoglobing v dissolved in plasma.

Answer 9

Plasma - 1.5% of O2
Haemoglobin - 98.5% of O2.

Question 10

What is the structure of haemoglobin?
How does this relate to its function?

Answer 10

Four polypeptide chains
Hence has a quarternary protein structure
Made of two alpha and two beta chains.
Each chain contains a heme group that has an Fe2+ iron that can bind to oxygen.
This allows hemaglobin to be fully saturated when 4 O2 are bound and partially saturated when fewer O2 bound or unsaturated when no O2 are bound.

Question 11

Is the binding of oxygen to hemaglobin reversible?

Answer 11

Yes

Question 12

How does partial pressure of oxygen affect haemoglobin affinity for oxygen?

Answer 12

Higher partial pressure for oxygen = higher affinity for oxygen, so more associates and less dissociates.

Question 13

What is oxyhaemoglobin?

Answer 13

Haemoglobin saturated with oxygen

Question 14

What are some advantages of the S shaped extension curve of oxygen association with haemoglobin?

Answer 14

At high partial pressures of oxygen the curve plateaus - in the lungs a small drop in PO2 will still allow for high affinity hence lots of association of O2 with Hb.
At low partial pressures of oxygen the steep curve - means that even a small decrease in pO2 at respiring tissue will allow a large dissociation of oxygen from Hb to provide cells with plentiful oxygen to meet respiratory demand.

Question 15

When might humans Hb need a higher affinity for oxygen?

Answer 15

At high altitudes - lower pO2
Fetal Hb - higher affinity than mother Hb to take oxygen from mother Hb as cant inspire/expire

Question 16

What happens to the affinity for oxygen in Hb during exercise?
Why?

Answer 16

Hb affinity for oxygen decreases as lower pO2, at 20mmHg around 35% of Hb is saturated.
Allows oxygen to dissociate and supply respiring cells to continue to meet energy demands.

Question 17

What happens in the oxygen dissociation curve shift to the left?
What might cause this?

Answer 17

Shift left = Hb affinty for oxygen increases so more oxygen associates and less oxygen dissociates.
Less oxygen is provided to respiring muscles
Caused by decrease pCO2, decreased BPG or increase pH.
Useful in areas with lower pO2 such as high altitudes.

Question 18

What happens when the oxygen dissociation curve shifts to the right?
What might cause this?

Answer 18

This is a bohr shift, increase in CO2 decreases Hb affinity for oxygen by slightly altering Hb tertiary structure.
This causes a decrease in Hb affinity for oxygen, this means more oxygen dissociates and less oxygen associates.
This is useful during exercise to help supply respiring muscles with more O2 to fulfil their oxygen demand.
Causes:
Increased CO2
Decreased H+
Increase BPG

Question 19

What is BPG?

Answer 19

Stabilises the deoxygenated form of Hb.
Increases the probability of oxygen release from Hb.

Question 20

How does a higher temperature influence the oxygen dissociation curve?

Answer 20

Higher temperature can be caused by a higher rate of respiration in cells
Causes a Bohr shift to the right, causing a decrease in Hb affinity for O2.
Causes more oxygen to dissociate and less oxygen to associate with Hb.

Question 21

How does a decreased temperature influence the oxygen dissociation curve?

Answer 21

Decreased temperature causes a Bohr shift to the left so increased Hb affinity for Hb.
More oxygen associates with Hb, less oxygen dissociates.

Question 22

How does carbon monoxide affect O2 transport?

Answer 22

Hb Affinity for carbon monoxide is 240 times higher than O2
So CO replaces O2 bound to Hb, acts as a competitive inhibitor
Carboxyhaemoglobin causes a curve shift to the left, so oxygens affinity for Hb increases so more oxygen associates and less oxygen dissociates.
Leads to severe hypoxia

Question 23

How is CO2 transported in the blood?

Answer 23

CO2 is twenty times more soluble than oxygen in blood plasma, so is often carried as a solute.
48% vol of C02 in arterial blood
52% vol of CO2 in venous blood
Each time CO2 passes through the body 4% of its volume is removed from the tissues and removed by the lungs.

Question 24

What proportion of CO2 is transported in each form?

Answer 24

5% of physically dissolved in blood plasma*
90% is dissolved as a bicarbonate ion*
23% is combines with Hb.
* in arterial blood.

Question 25

What is meant by carboxyhaemoglobin?
Is its formation reversible?

Answer 25

CO2 is bound to the globin portion of Hb molecule.
Formation of Carbahaemoglobin is reversible, dissociates at low CO2 such as in the lungs.

Question 26

Write equations to show how carbon dioxide can cause acidic conditions in the body?

Answer 26

CO2 plus H2O makes H2CO3
This dissociates into H+ and HCO3-.

Question 27

What are the two ways that oxygen can be transported in the body?

Answer 27

Dissolved in the plasma
Bound to Hb as oxyhaemoglobin.

Question 28

What is meant by the co-operative nature of the binding of oxygen to haemoglobin?

Answer 28

Links to the s shaped curve
Difficult for the first oxygen to bind to haemoglobin
After binding of first, it changes the tertiary structure of Hb so it is easier for following oxygens to binds
However, probability of fourth oxygen binding is lower as majority of oxygen binding sites are occupied.