Carriage of Oxygen

Question 1

3 ways in which oxygen is transported in the body

Answer 1

Physically dissolved in plasma (~3 %)
combined with Hb as carbamino-haemoglobin (HbCO2) (3%)
Chemically bound to the haemoglobin molecule (Hb) in the red blood cells (RBC) (~92 %)

Question 2

why is the percentage of oxygen dissolved in plasma so low

Answer 2

poor solubility of oxygen in plasma

Question 3

what is haemoglobin Hb

Answer 3

heterotetramer consisting of 4 subunits (2 α and 2 β chains)

Each haemmolecule contains one ironatom

Question 4

when oxygen is bound to haemoglobin what does it form

Answer 4

binds with iron to form oxyhaemoglobin

Question 5

why is oxygens reversibility to being to bound to haemoglobin useful

Answer 5

allows O2 to be carried from the respiratory organs and released to the rest of the body

Question 6

how many oxygen molecules can bind to Hb

Answer 6

4

Question 7

allosteric affect of oxygen

Answer 7

Hb conformation from atensestate (loweraffinityfor oxygen) to arelaxed state(higheraffinityfor O2).

Question 8

colour of oxygenated Hb, HboO2

Answer 8

Bright red (normal arterial blood

Question 9

colour of deoxygenated Hb

Answer 9

dark red, blue

Question 10

colour of carboxyhaemoglobin COHb

Answer 10

cherry red

Question 11

oxygen content of blood

Answer 11

the amount of O2 in the blood (sum of both forms, dissolved and bound to Hb)
blood.

Question 12

in a typical ml O2 per 100ml of blood name its oxygen content

Answer 12

(or volume %) = 0.3 ml (plasma) + 19.5 ml (RBC) = 19.8 ml/100 ml blood.

Question 13

how do we calculate O2 blood content in tissue

Answer 13

Arterial O2 blood content - venous O2 blood content

Question 14

oxygen carrying capacity of the blood

Answer 14

the maximum amount of O2 that can be carried by Hb. Each gram of Hb, when fully saturated, can combine with 1.34 ml of oxygen.

Question 15

% saturation calculation

Answer 15

O2 content / O2 capacity

Question 16

tool used to measure % saturation

Answer 16

pulse oximeter

Question 17

how are arterial blood gas pressures measured

Answer 17

arterial blood samples and a blood gas analyser

Question 18

P50 is the partial pressure of

Answer 18

oxygen

Question 19

relationship of % saturation and PO2is a

Answer 19

sigmoid shape

plateau when percentage saturation is closest to 100%

Question 20

why is it important that there is a plateau near 100% saturation

Answer 20

this is a protection against altitude and respiratory disease

Question 21

cons of the plateau in sigmoid shape

Answer 21

however, the plateau reduces the usefulness of hyperventilation and O2 therapy

Question 22

benefits of steep portion at start of graph reflecting in % saturation and PO2

Answer 22

allows for O2 unloading in the tissues

Question 23

under what conditions can the increased affinity for O2 and there the left shift of the sigmoid shape occur

Answer 23

decrease in pCO2 partial pressure
decrease hydrogen ions
decrease 2,3 DPG 
decrease temp
HbR

Question 24

under what conditions can the decreased affinity for O2 and there the right shift of the sigmoid shape occur

Answer 24

increase in pCO2 partial pressure
increase hydrogen ions
increase 2,3 DPG
increase temp

Question 25

bohr effect

Answer 25

in the tissues, the increase in PCO2 and H+ causes the haemoglobin to release more O2, the Bohr effect that haemoglobin’s oxygen binding affinity is inversely related to both acidity and PCO2

Question 26

what does the Bohr effect facilitate

Answer 26

O2 release from Hb at tissues (curve shifts right due to increased PCO2)

Question 27

how does the bohr effect apply to 2,3 DPG

Answer 27

by an increase in temperature and 2,3-diphosphoglycerate

Question 28

Where is DPG diphosphoglycerate

Answer 28

formed in the RBC and binds to the beta chains of haemoglobin causing O2 release

Question 29

when is 2,3 DPG increased

Answer 29

increased in exercise, altitude, anaemia and respiratory disease and is reduced in stored blood

Question 30

which haemoglobin binds to O2 better and why haemoglobin F or haemoglobin A

Answer 30

haemoglobin F (fetal) binds O2 better than haemoglobin A (adult) because 2,3-DPG binds poorly to the gamma chains of haemoglobin F - improves O2 transfer across placenta

Question 31

where is myoglobin found and does it have a higher or lower affinity for O2 than Hb

Answer 31

myoglobin is found in skeletal and cardiac muscle. It has a higher O2 affinity than Hb and acts as a tissue store of O2

Question 32

how is Hb saturation affected in anemia

Answer 32

not affected

Question 33

how is arterial content reduced and why

Answer 33

but the arterial content of blood is reduced because the decreased amount of Hb per 100 ml blood decreases the O2 carrying capacity of the blood

Question 34

in what direction does the CO shift the oxyhaemoglobin dissociation curve

Answer 34

to the left

Question 35

what condition can CO lead to

Answer 35

severe tissue hypoxia

Question 36

signs of cyanosis

Answer 36

blue colouration of the skin and mucous membranes, especially the tongue, mouth, lips and nail beds

Question 37

when does cyanosis

Answer 37

it occurs when the arterial blood is 85% saturated (PO2=50 mmHg or 6.7 kPa) or when the capillary blood is 70% saturated (37.5 mmHg or 5 kPa) central cyanosis is due to arterial blood desaturation

Question 38

what causes cyanosis

Answer 38

due to reduced tissue blood flow due to vasoconstriction (exposure to cold, Raynaud’s disease etc.), vascular obstruction or decreased cardiac output (heart failure, shock etc.)

Question 39

right shift in oxyhaemoglobin dissociation shift mean

Answer 39

increased oxygen unloading

Question 40

chloride shift at tissue

Answer 40

CO2 diffuses in rbc -> bicarbonate in rbc then into plasma because of permeability of cell membrane to negative ions Cell membranes. impermeable to charged ions - rbc can exchange bicarbonate w/ Cl wi/ an anion exchanger protein Band 3 rbc - positive charge - neutralised by entering Cl- ions

Question 41

benefits of chloride shift at tissue

Answer 41

ensures ionic and electrical stability  | during the transport of carbon dioxide

Question 42

reverse chloride shift

Answer 42

O2 diffuses in rbc and CO2 diffuses out O2 binds to haemoglobin and causes release of hydrogen fall in RBC pH -> converts bicarbonate to CO2 and water conc of bicarbonate falls -> bicarbonate exchanged w/ chloride

Question 43

haldane effect

Answer 43

the deoxygenation of blood increases its ability to carry CO2 the loss of O2 allows Hb to bind more CO2 and H+ so more CO2 is carried as carbamino compounds and as HCO3-

Question 44

how does haldane effect affect pH

Answer 44

the pH falls from 7.4 in the arterial blood to 7.35 in the venous blood

Question 45

conc of paCO2 during hyperventilation

Answer 45

“overbreathing” i.e. the PaCO2 is less than 40 mmHg | respiratory alkalosis

Question 46

conc of PaCO2 during hypoventilation

Answer 46

means that the PaCO2 is greater than 40 mmHg