Respiratory 6: Transport of O2 and CO2

Question 1

Where is haemoglobin blood.

Answer 1

It is kept in a RBC, because it can be concentrated without affecting viscosity of the blood.

Question 2

What are the ways that O2 is transported in blood and which is the majority

Answer 2

1. Binds with haemoglobin (majority)

2. Dissolves in solution

Question 3

How does haemoglobin molecule bind O2

Answer 3

Haemoglobin has an 4 x a and B polypeptide chains containing a haem (fe2+) moiety in a chain.
The binding of O2 has cooperative allosteric effect where it twists the haem moiety to make next site more exposed to O2 for binding. (Speeds up as more O2 binds)

Question 4

What does the Oxygen dissociation curve tell us about the binding of haemoglobin. What are the main features of the graph

Answer 4

Main features :
% oxygen saturation: (4 O2 = 100%) on the y. and partial pressure of O2 on the x.
There is a sigmoidal relationship due to cooperative binding

Question 5

In the systemic veins, what is the PO2 and what does this mean for saturation of Haem compared to when its in the systemic arteries.

Answer 5

In Systemic veins the PO2 is low: 40 mmHg. This means that Haem has less affinity to take up O2. This encourages release

In the Systemic arteries/ alveoli
PO2 is high: 100 mmHG.
This means haem has higher affinity for binding O2.
This encourages O2 uptake

Question 6

Why does Hb Affinity for O2 change as you go from Lungs to Veins

Answer 6

The tissues are more acidic because there is more CO2 going to Carbonic acid-> H+. This means that Hb has less affinity.

Whereas at lungs there is less CO2, so higher pH and O2 and is taken up and its max affinity restored.

Question 7

What is the ratio of Carbon dioxide transported as bicarbonate in the plasma vs in red blood cells.
Where does the majority of bicarbonate come from in plasma vs RBC

Answer 7

70% transported in plasma to 30% RBC

• Majority of the bicarbonate in plasma (60%) has originated from the RBC by help of enzyme then diffused out.
• Majority in RBC (20%) is the rapidly forming bicarbonate

Question 8

What is the difference between saturation and content of oxygen in blood

Answer 8

Saturation refers to the amount of O2 that the Hb can carry (1-4). It is not affected by volume of blood.
However the content of oxygen in the blood is affected by the amount of Hb present (volume of blood) and the saturation of that Hb as well.

Question 9

What is the Bohr shift and what causes it

Answer 9

This is a shift in the oxygen dissociation curve to the right, meaning that Hb’s affinity for O2 is reduced for the same PO2, therefore promoting O2 release.
This is caused by increased metabolism products (at tissues)
: CO2, [H+] DPG, temperature.

Question 10

What is the “opposite” Bohr shift and what causes it

Answer 10

This is a shift of the oxygen disassociation curve to the left, meaning the affinity for O2 is increased for the same PO2.
It is caused by : Decreased CO2, [H+], temperature, DPG. By making the Haem hs a higher affinity for O2. This sigmoidal relationship is moving depends on location of RBC

Question 11

What shift does Fetal haemoglobin have on the oxygen dissociation curve and why is this important

Answer 11

Shift is to the left because it has higher affinity per PO2. This is important to help move O2 across the placenta from the mother’s haemoglobin to the foetus.

Question 12

What shift does Myoglobin have on the oxygen dissociation curve and why is this important

Answer 12

It has big shift to the left, meaning that it has high affinity for O2 over a large range of PO2 and it only rlly dissociates when PO2 is really low so its a good storage of O2 for muscle.

Question 13

What are the ways that CO2 is transported in blood - by most to least

Answer 13

1. Transported mainly in HCO3- (bicarbonate)
2. Combines to amine groups (on the heme molecule)
3. CO2 is dissolved in solution
4. Transported as H2CO3 and Co3- ions

(CO2 20x more soluble than O2 in blood )

Question 14

How bicarbonate formed and what is the difference between rapidly and slowly forming.

Answer 14

CO2 + H2O is the limiting step -> forming carbonic acid which dissociates into bicarbonate and H+.
Rate limiting step makes rapid with carbonic anhydrase (in RBC) or slow without it.

Question 15

How does CO2 associate with amine groups on Hb

Answer 15

CO2 + R-NH2 -> R- NHCOO- + H+

Amine group loses an H to let COO join on.

Question 16

What determines whether O2 is being taken up and CO2 being released by RBC or versa

Answer 16

The concentration of H+ which changes Hbs affinity for O2.

Question 17

What is the chloride shift

Answer 17

During the process of CO2 entering the RBC to be converted to Bicarbonate, Chloride shift is how Cl- moves in the opposite direction to bicarbonate ion(-) as it moves in or out of RBC to maintain the electroneutrality.

Question 18

How does Haemoglobin help to make a buffer in RBCs

Answer 18

Haemoglobins bind to H+ produced by the carbonic acid to stop the pH increasing and in doing so, reduces its affinity for O2, leading to release of O2.

Question 19

What is the Haldane effect

Answer 19

This is the difference between the affinity of Hb for transporting CO2 in the venous blood vs the arterial blood.

There is an increase in Hb affinity for CO2 in venous blood which enhances the uptake of CO2 from tissues. Compared to PO2, if there is lower PO2 there will be a greater Hb affinity for CO2

Question 20

Compare Hypoxia to Anoxia and Asphyxia

Answer 20

Hypoxia: low levels of O2
Anoxia: No O2
Asphyxia: Deprived of O2

Question 21

How does blood gas levels control the rate and depth of breathing

Answer 21

Chemoreceptors detect the levels of gas (O2 and CO2) in the blood and send signals to the brain to control breathing

Question 22

What 7 things stimulates peripheral chemoreceptors?

Answer 22

1. Hypoxia
2. Hypercapnia
3. combo of 1&2
4. Haemorrhage
5. Acidosis
6. Increased sympathetic activity
7. NaCn -> mimics removal of O2 by switching off ETC

Question 23

Compare the response time of the peripheral chemoreceptors

vs central chemoreceptors

Answer 23

Peripheral has fast response time: within a breath

Central: has slow response time because the rate of producing H+ from CO2 is slow in CSF because not many carbonic anhydrase: `30 s

Question 24

What stimulates central chemoreceptors to stimulate breathing

Answer 24

Increase of CO2 in the brain capillaries, is detected by nerves in the medulla oblongata by CO2 crossing the blood brain barrier into the Cerebrospinal fluid.
and forming bicarbonate (with limited carbonic anhydrase present compared to in RBC). The H+ ions from this reaction in the cerebrospinal fluid stimulate the central chemoreceptors in the medulla

Question 25

Describe the main stages of the ventilatory response to Hypoxia (stimulated by addition of N2 to inhaled gas)

(peripheral chemoreceptors only)

Answer 25

As the PO2 is decreased, ventilation will reach 1. peak ventilatory response then

2. Depression in ventilation because in order to conserve O2 brainstem neural activity is reduced-> slowing of breathing
3. Apnoea: where there is last attempt to get O2 through gasp to auto resuscitate.

Question 26

Describe features of the Ventilatory response to Hypercapnia. (both receptors) What contribution does receptors do

Answer 26

With only slight increase in PCO2 there is a very steep increase in minute ventilation.
Central does 80%, Peripheral 20%

Question 27

What keeps you breathing through sleep

Answer 27

Central chemoreceptors provide a stimulus to breath and they are sensitive to CO2. This is Ondine curse.

Question 28

The partial pressure of a gas (O2, CO2) is higher when the concentration of the gas in the blood is:

Why

Answer 28

higher. Ie PO2 is higher in the arteries than veins.

This is because the gas moves from a place of higher pressure to low pressure

Question 29

What are the main features of the CO2 dissociation curve

Answer 29

It has ml/ L blood of CO2 on the y and PCO2 on the x.
The curve depends on the PCO2 and is linear over the physiological range, there is no measure of saturation as CO@ is very soluble in plasma.

Question 30

What is hyper and hypo. What is capnia and ventilate

Answer 30

Hyper: high
Hypo: low
Capnia: CO2
Ventilate: breathing

Question 31

What is Apnoea vs Dyspnoea

Answer 31

Apnoea : no breathing

Dyspnoea: sensation of breathlessness

Question 32

What is the location and projection of peripheral chemoreceptor vs central chemoreceptor

Answer 32

Peripheral: is located in the bifucation of the carotid artery (carotid body).
Projection: Sinus nerve that joins with the glossopharyngeal 9th cranial nerve to the medulla

Central: 3 chemosensitive regions on the ventral surface of medulla oblongata.

Question 33

What cannot cross the Blood brain barrier

Answer 33

charged ions ie H+