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respiratory physiology > gas transport in the blood 1 (R4) > Flashcards

gas transport in the blood 1 (R4) Flashcards

1
Q

what happens to O2 picked up by blood at the lungs

A

it must be transported to the tissues for cellular use

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2
Q

what happens to CO2 produced at tissues

A

it must be transported to the lungs for removal

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3
Q

oxygen partial pressures around the respiratory system

A

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

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4
Q

effect of partial pressure on gas solubility

A

(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

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5
Q

henry’s law

A

-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

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6
Q

partial pressure of a gas in solution

A

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

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7
Q

amount of O2 dissolved in blood

A

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

-

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8
Q

volume of O2 per litre of blood

A

3ml (at a PO2 of 13.3 kPa)

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9
Q

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

A

15ml/min

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10
Q

cardiac output (CO) under resting conditions

A

5L/min

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11
Q

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

A

90ml/min

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12
Q

resting O2 consumption of body cells

A

250ml/min

-may increase up to 25 folds during strenuous exercise

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13
Q

how is oxygen transported in the blood

A

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

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14
Q

normal O2 concentration in arterial blood

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

normal arterial PO2

A

13.3 kPa

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16
Q

normal haemoglobin concentration in arterial blood

A

15 grams/100ml

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17
Q

% of O2 bound to haemoglobin

A

98.5%

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18
Q

% of O2 carried in the dissolved form

A

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

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19
Q

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

A
  • bound to haemoglobin

- physically dissolved (very little O2)

20
Q

how does oxygen bind to haemoglobin

A
  • 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)
21
Q

when is haemoglobin considered fully saturated

A

when all the Hb present is carrying its maximum O2 load

22
Q

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

A

the PO2

23
Q

oxygen haemoglobin dissociation curve explained

A
  • 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
24
Q

DO2I

A
  • 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))
25
Q

what is oxygen delivery to the tissues a function of

A

oxygen content of arterial blood and the cardiac output

DO2I= CaO2 x CI

26
Q

CaO2

A

-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

27
Q

CI

A
  • 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
28
Q

PO2

A
  • (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
29
Q

average resting PO2 at systematic capillaries

A

5.3kPa

30
Q

normal PO2 at pulmonary capillaries

A

13.3kPa

31
Q

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

A

1.34ml

32
Q

[Hb]

A

-haemoglobin concentration (gram/L)

33
Q

SaO2

A
  • %Hb saturated with O2

- determined by PO2

34
Q

what can impair oxygen delivery to the tissues

A
  • respiratory disease
  • heart failure
  • anaemia
35
Q

cooperativity of Hb

A
  • binding of one O2 to Hb increases affinity of Hb for O2

- produces sigmoid curve of oxygen haemoglobin dissociation curve

36
Q

bohr effect

A
  • 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)
37
Q

off loading of O2 at tissues

A
  • 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
38
Q

structure of haemoglobin/Hb

A

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)

39
Q

foetal haemoglobin

A
  • (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
40
Q

HbF

A

foetal haemoglobin

41
Q

2,3- biphosphoglycerate

A

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

42
Q

HbA

A

adult haemoglobin

43
Q

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

A
  • 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
44
Q

myoglobin (Mb)

A
  • 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
45
Q

what does the presence of myoglobin in blood indicate

A

muscle damage

46
Q

oxygen myoglobin dissociation curve

A
  • hyperbolic

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

47
Q

how many haem groups do each myoglobin molecule have

A

1

respiratory physiology (7 decks)

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