Oxygen transport

Question 1

oxygen systemic arterial partial pressure

Answer 1

between 75mmHg- 100mmHg, 14kPa

Question 2

how is oxygen carried in the blood?

Answer 2

small volume dissolves in blood, other becomes bound to haemoglobin

Question 3

what is haemoglobin?

Answer 3

protein of a molecular weight of 64,500

4 globin subunits, 2 alpha and 2 beta chains, each 16KDa

one haem structure in each chain that binds to oxygen

Question 4

explain haem structure

Answer 4

four pyrrole rings held together by methane bridges

centre of the pyrrole rings is a bivalent iron ion, held together by two ionic and two covalent bonds

oxygen binds reversibly to the iron ion with no change in valency, so the reaction is called oxygenation and not oxidation

Question 5

haemoglobin function

Answer 5

carries 4 oxygen molecules to form oxyhemoglobin

Question 6

O2 carrying capacity definition

Answer 6

the maximum amount of oxygen that can be combined with Hb which is limited by the number of binding sites and whether they are available

Question 7

2 measurements of bound oxygen

Answer 7

oxygen concentration as ml O2/100ml of blood

percentage saturation of maximal oxygen capacity

Question 8

what process occurs during the binding of oxygen atoms

Answer 8

positive cooperativity

Question 9

explain positive cooperativity

Answer 9

binding of each oxygen molecule to the tetramer facilitates the binding of the next molecule which results in a sigmoidal dissociation curve

1. first oxygen difficult to bind
2. once first binds, conformation change occurs bringing forward the pyrrole groups, makes it easier for the next 2 to bind
3. last one more difficult, as smaller chance that it binds to an unoccupied binding site

Question 10

what does the curve facilitate?

Answer 10

unloading of oxygen at tissues where partial pressure is low

loading at the lungs where partial pressure is high

Question 11

curved S shape advantages

Answer 11

flat upper portion means that if PO2 falls slightly that loading is hardly affected

central steep part of the curve means that peripheral tissues can withdraw large amounts of oxygen for only a small drop in capillary partial pressure

Question 12

oxhaemoglobin saturation definition

Answer 12

haemoglobin is said to be saturated with oxygen when all four binding sites are occupied

Question 13

factors affecting oxygen binding to haemoglobin

Answer 13

1. increase in H+
2. increase in PCO2
3. temperature
4. increase in 2,3 diphosphoglycerate

Question 14

explain the resulting shift of the curve

Answer 14

rightward shift

favour unloading the oxygen, with more oxygen unloaded at a given partial pressure of oxygen within the tissue capillary

Question 15

what is a name for this + definition?

Answer 15

Bohr Effect

shifting to the right due to the collective effect of partial carbon dioxide pressure and decrease in pH

allosteric binding of carbon dioxide

increase in H+ ions, protonate various amino acid residues, such as histidine allowing them to form ion pairs that stabilise the deoxyhaemoglobin in the T state

bohR Right

Question 16

explain 2,3-diphosphoglycerate effect

Answer 16

2,3-DPG is produced by red blood cells during glycolysis and binds to Hb

this reduces the affinity for oxygen and favours unloading

2,3-DPG concentrations increase during hypoxic conditions, favouring the delivery of oxygen to tissues

heteroallosteric effector of haemoglobin that lowers its affinity for oxygen by binding preferentially to deoxyhaemoglobin, thus favouring the formation of T haemoglobin

Question 17

explain the temperature effect

Answer 17

increases in temperature begin to denature the haemoglobin, weakening the bonds between iron and oxygen

with an increase in temperature there is also an increase in partial oxygen pressure, so for a lessen haemoglobin saturation there is a higher partial pressure of oxygen

Question 18

what is methemogloinaemia ?

Answer 18

a form of abnormal haemoglobin where the iron centre has been oxidised from +2 to +3, causing a leftward shift of the curve as the ions are unable to unload the bound oxygen into the tissues, as +3 impairs cooperativity

thereby increasing its affinity for oxygen

Question 19

what can methemoglobin be used for?

Answer 19

has an increased affinity for cyanide

administration of a nitrite will oxidise the haemoglobin to raise methemoglobin levels so that they can bind to cyanide and remove it

Question 20

inadequate oxygen uptake of tissues causes

Answer 20

1. hypoxaemia- low arterial partial pressure and percentage arterial saturation due to low inspired oxygen, diffusing capacity of V/Q mismatch, Not enough oxygen
2. stagnant hypoxia- low perfusion, cardiac failure. blood oxygenated, but not enough of it.
3. anaemic hypoxia, low Hb, carbon monoxide poisoning. There is enough oxygen but the body cannot carry it
4. histotoxic hypoxia, high venous pressure and saturation due to inability of tissues to use oxygen, cyanide poisoning . There is enough oxygen but the body cannot use it

Question 21

how does cyanide poison?

Answer 21

acts as an inhibitor of enzyme cytochrome C oxidase in the electron transport chain by attaching to the iron

prevents the transport of electrons from cytochrome C to oxygen and thus causes histotoxic hypoxia

Question 22

hypoxia definition

Answer 22

a condition in which the body or region of the body is deprived of adequate oxygen supply at the tissue level

Question 23

hypoxemia definition

Answer 23

an abnormally low level of oxygen in the blood

Question 24

body’s oxygen stores

Answer 24

lungs, blood, tissue fluid, muscle myoglobin

Question 25

what affinity does carbon monoxide have for Hb?

Answer 25

240x that of oxygen

Question 26

What does the saturation curve look like for carbon monoxide?

Answer 26

identical in shape but the PCO acts is greatly compressed due to better binding at lower partial pressures

Question 27

Why is CO bad?

Answer 27

binds irreversible to form carboxyhaemoglobin which shifts the oxygen curve to the left and interferes with the unloading of oxygen