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Anatomy and Physiology > Lecture 14-Capillary Exchange > Flashcards

Lecture 14-Capillary Exchange Flashcards

1
Q

How do the capillaries provide a short distance for diffusion

A

thin walls-Thin walls (1µm)
Small diameter (8µm)
Close proximity to cells

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2
Q

why does blood flow slowly in capillaries

A

large cross-sectional area of capillary network

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3
Q

how does the capillary have a large surface area for exchange

A

10+ billion capillaries
600m^2

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4
Q

what are the 3 types of capillaries

A

continuous
fenestrated
sinusoid

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5
Q

which is the most common capillary

A

continuous

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6
Q

where are fenestrated capillaries found

A

endocrine organs, intestine and kidneys

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7
Q

features of fenestrated capillaries

A

water-filled pores to allow rapid change of water and solutes

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8
Q

where are sinusoid capillaries found

A

endocrine organs, liver, bone marrow, spleen

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9
Q

features of sinusoid capillaries

A

large clefts between endothelial cells and incomplete BM to allow free exchange of water and larger solutes e.g. plasma proteins

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10
Q

what are the transport mechanisms in capillary exchange

A

diffusion (down conc gradient)
bulk flow (down pressure gradient)
transcytosis (by vesicular transport; through endothelial cells)

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11
Q

what substances travel through endothelial cells via diffusion in capillary exchange

A

-lipid soluble gases and molecules e.g. O2, CO2, Fatty Acids
-ions e.g. Na+, K+, Ca2+,Cl- (via ion channels in the ECs)

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12
Q

what substances travel between endothelial cells in capillary exchange

A

small water-soluble molecules e.g water, ions, glucose, urea, amino acids

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13
Q

what substances travel via transcytosis in capillary exchange

A

macromolecules e.g glycoproteins in vesicles

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14
Q

where does bulk flow occur during capillary exchange

A

down pressure gradients between gaps and pores

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15
Q

what is bulk flow associated with in capillary exchange

A

filtration and reabsorption

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16
Q

what determines bulk flow between capillaries and interstitial fluid

A

the net pressure difference across capillary walls

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17
Q

what 4 forces influence fluid and solute movement

A

-capillary hydrostatic pressure
-interstitial fluid hydrostatic pressure
-blood colloid osmotic pressure
-interstitial fluid colloid osmotic pressure

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18
Q

capillary hydrostatic pressure

A

the blood pressure exerted on capillary walls ‘pushing’ fluid out

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19
Q

interstitial fluid hydrostatic pressure

A

the pressure exerted on the outer capillary walls by the IF pushing fluid in

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20
Q

blood colloid osmotic pressure

A

the plasma osmotic pressure pulling the fluid in

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21
Q

interstitial fluid colloid osmotic pressure

A

the osmotic pressure of the interstitial fluid pulling fluid out

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22
Q

net filtration pressure formula

A

net filtration pressure= net hydrostatic pressure - net osmotic pressure

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23
Q

net hydrostatic pressure formula

A

capillary hydrostatic pressure (decreases along capillary) - interstitial fluid hydrostatic pressure (generally negligible- 0)

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24
Q

what does net hydrostatic pressure favour

A

favours pushing fluid from capillary to IF

25
Q

net osmotic pressure

A

blood colloid osmotic pressure - interstitial fluid colloid osmotic pressure

26
Q

what is blood colloid osmotic pressure affected by

A

blood volume

27
Q

why is interstitial fluid colloid osmotic pressure generally negligible

A

IF has few plasma proteins in suspension

28
Q

what does a positive net filtration pressure lead to

A

filtration

29
Q

what does a negative net filtration pressure result in

A

reabsorption

30
Q

what are the values of capillary hydrostatic pressure from the arterial to the venous end

A

35 -> 18mmHg

31
Q

what is the value of blood colloid oncotic pressure along the capillary

A

25mmHg

32
Q

what gets filtered out of the capillaries

A

nutrients to tissues

33
Q

what gets absorbed into the capillary

A

waste from tissues

34
Q

what volume of substance is filtered per day

A

24L/day

35
Q

how many litres of filtration is delivered to the lymphatic system

A

3.6 L/day

36
Q

how many liters of filtration gets reabsorbed

A

20.4L/day

37
Q

max filtration pressure is greater than…

A

max absorption pressure

38
Q

transition point

A

filtration is equal to absorption

39
Q

where is the transition point in capillary exchange located

A

towards the venous end

40
Q

what is the effect of hypertension on net filtration pressure

A

-increased capillary
-hydrostatic pressure
-increased net filtration
-fluid collects in extremities
-systemic oedema

41
Q

effect of severe hemorrhage on net filtration pressure

A

-lower CHP
-decreased net filtration pressure
-increased reabsorption
-fluid recalled from tissue into the bloodstream
-increased BP and CO

42
Q

effect of dehydration on net filtration pressure

A

-increased blood colloid oncotic pressure
-reduced net filtration pressure
-fluid recalled from tissue into bloodstream
-delays onset of symptoms

43
Q

effect of tissue damage on net filtration pressure

A

-increased ICOP as plasma proteins leak into IF
-increased net filtration pressure
-local swelling (oedema)

44
Q

in pulmonary circulation, what occurs when O2 level falls? How does this differ to other organ vessels

A

-arterioles constrict in regions of low O2 to shunt blood flow to O2 rich areas
-Enhances O2 absorption

-in other organs, vessels dilate when oxygen levels fall (enhances o2 delivery)

45
Q

how many alveoli does pulmonary circulation supply

A

Pulmonary circulation supplies >300 million alveoli

46
Q

why is pulmonary vascular resistance very low

A

Arterioles are shorter, wider and have thinner walls

47
Q

CHP in pulmonary circulation compared to systemic circulation

A

10 mmHg rather than 35 mmHg

48
Q

why are arteries more distensible in pulmonary circulation

A

Can accommodate increased CO with little increase in pressure

49
Q

what happens if pulmonary CHP exceeds 25mmHg

A

fluid leaks into alveoli impacting respiration causing pulmonary oedema

50
Q

what does SNS/ adrenaline cause in the coronary circulation? How does this differ to other organs?

A

promotes coronary artery vasodilation increasing coronary flow
-in other organs, this would cause vasoconstriction

51
Q

why is coronary blood flow restricted during systole

A

due to compression of the left coronary artery

52
Q

when is coronary flow the highest in the cardiac cycle

A

during diastole, enabled by arterial elastic recoil

53
Q

how does coronary circulation compensate for loss of blood flow during systole

A

Cardiomyocytes have high O2 reserves
The myocardium has high capillary density → increases O2 extraction

54
Q

in neural emergencies does vasodilation or vasoconstriction occur in cerebral vessels

A

vasodilation

55
Q

how much co2 does the brain consume for 2% body mass

A

12%

56
Q

flow rate of the brain

A

750ml/min

57
Q

do neurons have good or bad metabolic reserves

A

bad

58
Q

how many arteries are used to supply the brain

A

4 arteries that anastomose inside the cranium to maintain flow is there is a disruption

59
Q
A

Anatomy and Physiology (14 decks)

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