gas transport in the blood 1 (R4)

Question 1

what happens to O2 picked up by blood at the lungs

Answer 1

it must be transported to the tissues for cellular use

Question 2

what happens to CO2 produced at tissues

Answer 2

it must be transported to the lungs for removal

Question 3

oxygen partial pressures around the respiratory system

Answer 3

PO2 (kPa) decreases as you go from atomsphere to the tissues

Question 4

effect of partial pressure on gas solubility

Answer 4

(due to henry’s law)
-if the partial pressure in the gas phase is increased the concentration of the gas in the liquid phase would increase proportionally

Question 5

henry’s law

Answer 5

-the amount of given gas dissolved in a given type and volume of liquid (eg. blood) at a constant temperature is; proportional to the partial pressure of the gas in equilibrium with the gas

Question 6

partial pressure of a gas in solution

Answer 6

= its partial pressure in the gas mixture which it is in equilibrium

Question 7

amount of O2 dissolved in blood

Answer 7

-proportional to the partial pressure (henry’s law)

-

Question 8

volume of O2 per litre of blood

Answer 8

3ml (at a PO2 of 13.3 kPa)

Question 9

volume of O2 taken to tissues as dissolved O2 under resting conditions (CO= 5L/min)

Answer 9

15ml/min

Question 10

cardiac output (CO) under resting conditions

Answer 10

5L/min

Question 11

volume of O2 taken to tissues as dissolved O2 during strenuous exercise (CO=30L/min)

Answer 11

90ml/min

Question 12

resting O2 consumption of body cells

Answer 12

250ml/min

-may increase up to 25 folds during strenuous exercise

Question 13

how is oxygen transported in the blood

Answer 13

-most O2 in the blood is transported bound to haemoglobin in the red blood cells

Question 14

normal O2 concentration in arterial blood

Answer 14

• 20ml/100ml (200ml per L)
• > at a normal arterial PO2 of 13.3 kPa
• > and a normal haemoglobin concentration of 15 grams/100ml

Question 15

normal arterial PO2

Answer 15

13.3 kPa

Question 16

normal haemoglobin concentration in arterial blood

Answer 16

15 grams/100ml

Question 17

% of O2 bound to haemoglobin

Answer 17

98.5%

Question 18

% of O2 carried in the dissolved form

Answer 18

1.5% (3ml per litre at a PO2 of 13.3 kPa)

Question 19

what are the two forms that O2 is present in the blood

Answer 19

• bound to haemoglobin

- physically dissolved (very little O2)

Question 20

how does oxygen bind to haemoglobin

Answer 20

• haemoglobin can form a reversible combination with O2
• Each Hb molecule (made up of alpha and beta chains) contains 4 haem groups (each haem group contains an iron, Fe++, molecule which is responsible for the binding to O2)
• each haem group reversibly binds to one O2 molecule
• the binding of one O2 to Hb increases the affinity of Hb for O2 (co operativity causing sigmoid curve in oxygen haemoglobin dissociation curve)

Question 21

when is haemoglobin considered fully saturated

Answer 21

when all the Hb present is carrying its maximum O2 load

Question 22

what is the primary factor which determines % saturation of haemoglobin with O2

Answer 22

the PO2

Question 23

oxygen haemoglobin dissociation curve explained

Answer 23

• the main determinant of % saturation of haemoglobin with O2 is the PO2, therefore as PO2 increases as does the O2 concentration and therefore %haemoglobin saturation
• as O2 concentration increases the haemoglobin becomes mores saturated with oxygen as more haem groups are filled up/bound to oxygen
• this eventually levels out when haemoglobin is completely saturated (100%) and there are no more haem groups that can bind to O2 therefore total O2 curve is greater than the O2 bound to Hb curve
• sigmoid curve produced due to cooperativity of haemoglobin (binding of one O2 to Hb increases affinity of Hb for O2)
• curve flattens when all sites are becoming occupied
• flat upper portions of curve means that moderate fall in alveolar PO2 will not affect oxygen loading greatly
• steep lower part of curve means that the peripheral tissues get a lot of oxygen for a small drop in capillary PO2 (all because PO2 determines haemoglobin saturation with oxygen)
• at low PO2, oxygen release occurs as it is not bound to Hb

Question 24

DO2I

Answer 24

• oxygen delivery index (ml/min/metre squared)
• DO2I=CaO2 x CI
• (CaO2= oxygen content of arterial blood (ml/L))
• (CI=cardiac index (L/min/metre squared))

Question 25

what is oxygen delivery to the tissues a function of

Answer 25

oxygen content of arterial blood and the cardiac output | DO2I= CaO2 x CI

Question 26

CaO2

Answer 26

-oxygen content of arterial blood (ml/L) -determined by the haemoglobin concentration [Hb] and the saturation of Hb with O2 =1.34 x [Hb] x SaO2 ->1 gram of Hb carries 1.34ml of O2 when fully saturated ->[Hb] = haemoglobin concentration (gram/L) -> SaO2 = % Hb saturated with O2, remember this is determined by PO2

Question 27

CI

Answer 27

- cardiac index - (L/min/metre squared) - cardiac index relates the cardiac output to the body surface area (ie. the size of the individual) - normal range for CI= 2.4 - 4.2 L/min/metre squared

Question 28

PO2

Answer 28

- (partial pressure of oxygen) - reflects the amount of oxygen gas dissolved in the blood. - It primarily measures the effectiveness of the lungs in pulling oxygen into the blood stream from the atmosphere

Question 29

average resting PO2 at systematic capillaries

Answer 29

5.3kPa

Question 30

normal PO2 at pulmonary capillaries

Answer 30

13.3kPa

Question 31

volume of O2 carried by 1 gram of Hb when fully saturated

Answer 31

1.34ml

Question 32

[Hb]

Answer 32

-haemoglobin concentration (gram/L)

Question 33

SaO2

Answer 33

- %Hb saturated with O2 | - determined by PO2

Question 34

what can impair oxygen delivery to the tissues

Answer 34

- respiratory disease - heart failure - anaemia

Question 35

cooperativity of Hb

Answer 35

- binding of one O2 to Hb increases affinity of Hb for O2 | - produces sigmoid curve of oxygen haemoglobin dissociation curve

Question 36

bohr effect

Answer 36

- states that hemoglobin's oxygen binding affinity is inversely related both to acidity and to the concentration of carbon dioxide. - shifts the oxygen haemoglobin dissociated curve to the right, therefore conditions at the tissues causes an increased release of O2 from haemoglobin (conditions: increase in PCO2, increased H+/acidity, increased temperature, increased 2,3-biphosphoglycerate)

Question 37

off loading of O2 at tissues

Answer 37

- tissue O2 tension and arterial O2 tension decrease (PO2) therefore % saturation of haemoglobin with O2, releasing O2 from haem groups - arterial and tissue conditions also differ and tissue conditions cause a shift in curve to the right (bohr effect), furthermore 'off loading' O2

Question 38

structure of haemoglobin/Hb

Answer 38

made up of 2 beta chains/subunits and 2 alpha chains/subunits which contain haem groups (iron, Fe++, is contained within haem group which is responsible for the binding of oxygen)

Question 39

foetal haemoglobin

Answer 39

- (HbF) - differs from adult haemoglobin in structure as HbF has 2 alpha and 2 gamma subunits (instead of 2 alpha and 2 beta) - interacts less with 2,3-biphosphoglycerate in red blood cells, therefore HbF has a higher affinity for O2 compared to HbA/adult haemoglobin), this means that O2-Hb dissociation curve is shifted to the left for HbF - this would allow more O2 to transfer from mother to foetus even if the PO2 is low - foetal Hb is usually replaced with adult Hb within a few months after birth and oxygen dissociated curve shifts back to normal position

Question 40

HbF

Answer 40

foetal haemoglobin

Question 41

2,3- biphosphoglycerate

Answer 41

an isomeric ester of diphosphoglyceric acid that occurs in human red blood cells and facilitates release of oxygen by decreasing the oxygen affinity of haemoglobin

Question 42

HbA

Answer 42

adult haemoglobin

Question 43

why does HbF/foetal haemoglobin shift oxygen haemoglobin dissociation curve to the left

Answer 43

- interacts less with 2,3-biphosphoglycerate in red blood cells, therefore HbF has a higher affinity for O2 compared to HbA/adult haemoglobin), this means that O2-Hb dissociation curve is shifted to the left for HbF - this would allow more O2 to transfer from mother to foetus even if the PO2 is low

Question 44

myoglobin (Mb)

Answer 44

- present in skeletal and cardiac muscle - has one haem group per myoglobin molecule - no cooperative binding of O2 as a result of this - has a hyperbolic dissociation curve - releases O2 at very low PO2 - provides a short term storage of O2 for anaerobic conditions - presence of myoglobin in blood indicates muscle damage

Question 45

what does the presence of myoglobin in blood indicate

Answer 45

muscle damage

Question 46

oxygen myoglobin dissociation curve

Answer 46

- hyperbolic | - levels off very quickly as myoglobin only has one haem group therefore is very quickly saturated

Question 47

how many haem groups do each myoglobin molecule have

Answer 47

1