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CV physiology (from notes) > Microcirculation > Flashcards

Microcirculation Flashcards

1
Q

What does the blood flow through

A

True capillary or thoroughfare channel

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2
Q

What sort of walls do arterioles have

A

Muscular walls

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3
Q

What sort of walls do metarterioles have

A

SM fibres encircle the vessel at intermediate points

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4
Q

What is a pre-capillary sphincter

A

Junction of metarteriole and true capillary

Opens and closes entrance to capillary

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5
Q

Proximity of metarterioles and pre-capillary sphincters to tissues they serve

A

Very close proximity

Metabolic status of tissue can alter radius of metarteriole

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6
Q

At rest, what proportion of capillaries in a tissue are open at any one time

A

25%

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7
Q

What is the blood flow like in capillaries

A

Non-pulsatile

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8
Q

What is the average length of a capillary

A

0.1 cm

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9
Q

What is blood flow velocity in a capillary at rest

A

0.05 cm/s

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10
Q

How long does it take blood cells to traverse capillary

A

2s - TRANSIT TIME

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11
Q

Effect of arteriolar dilation on capillary

A

Diameter of capillary does not change

Blood cell velocity increases

Blood cell transit time can be decreased to 1s - sufficient time for adequate diffusion of gases and nutrients across capillary wall

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12
Q

What are arteriovenous anastomoses

Where are they found

A

Direct flow of blood from arterial to venous circulation, w/o passing through capillaries

Found in skin - blood flow involved in thermoregulation

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13
Q

What is the structure of capillaries

What is the thin wall of capillaries called and how does a capillary withstand high pressure

A

Devoid of SM - incapable of active constriction

Endothelium - capillary can withstand high pressure due to narrow lumen (7-8 um)

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14
Q

Law of Laplace

A

T = Pr/w

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15
Q

P in aorta vs capillary

A

100 mmHg vs 25 mmHg

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16
Q

Why does a capillary not burst

A

Wall tension is low

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17
Q

Total thickness of wall of capillary

A

0.5 um

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18
Q

What is located at the junction of 2 endothelial cells

A

Cleft/pore (6-7nm diameter)

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19
Q

What is special about the junction between endothelial cells in the brain

A

Very small - TIGHT JUNCTIONS

  • allows movement of only small molecules into the brain

BBB

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20
Q

In what organ are clefts large

A

Liver

Allows movement of plasma proteins into IS space

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21
Q

What is vesicular transport

A

Molecules move across the capillary wall in membrane-bound pockets called VESICLES - slow

22
Q

Where does lipid soluble diffusion occur

A

Through cells

23
Q

Where does water soluble diffusion occur

A

Through pores/clefts

glucose, Na+, Cl-, H2O

24
Q

Diff rate for H20 vs rate of plasma flow

A

Diffusion rate for H2O is 40x faster than rate of plasma flow through capillary

Considerable exchange of small water-soluble molecules between capillary and IS fluid is possible

lower RMM increases permeability

higher RMM decreases permeability - Hb, myoglobin, albumin

25
How does fluid move from capillary to IS fluid
// BULK FLOW * Ultrafiltration - capillary -\> IS space * Reabsorption - IS space -\> capillary
26
How much fluid is ultrafiltered daily
20 L (5L of blood)
27
How much fluid is reabsorbed (from ultrafiltration)
90%
28
How much fluid returns to circulation via lymphatic system (from ultrafiltration)
2L or 10%
29
Driving F for ultrafiltration
Difference in hydrostatic pressure across capillary wall * Pc (capillary) * Pif (interstitial fluid)
30
Capillary hydrostatic P @: 1. Arteriolar end 2. Venular end
1. 32 mmHg 2. 15 mmHg
31
What is the driving force for reabsorption
Difference in colloid osmotic pressures * COP plasma (COPp) * COP IS fluid (COPip)
32
What is colloid osmotic P What is its value along full capillary length
Proteins are the only dissolved substances in plasma and interstitial fluids that do not readily diffuse through the capillary wall Plasma proteins thus exert an osmotic P (COP) which is linked to their concentrations 25 mmHg
33
Which is higher at arteriolar end - hydrostatic P or COP
HP =\> Ultrafiltration is higher
34
Which is higher at venular end - hydrostatic P or COP
COP =\> reabsorption is increased
35
Effect of vasoconstriction on balance between ultrafiltration and reabsorption in capillary
Arteriolar vasoconstriction causes an increase in P upstream and a decrease in P downstream in capillary COP is unchanged COP will exert a greater effect =\> greater re-absorption will occur Fluid will move from interstitial to vascular space
36
Effect of arterolar vasodilation on balance between ultrafiltration and reabsorption in capillary
Vasodilation causes an increase in pressure downstream P will exert a greater effect - greater ultrafiltration will occur Fluid will move from vascular space -\> IS space
37
What happens to substances with an increased RMM
Cannot be reabsorbed, so enter lymphatic capillary IS fluid -\> lymph
38
Lymph protein conc
Relatively high
39
Where is 70% of lymph
Liver and GIT
40
What tissue does NOT have lymphatic channels
Bone
41
What do lymphatics do
Drain excess fluid directly from IS space
42
Where does lymph from the lower part of the body (including legs) flow up through
Thoracic duct
43
Where does lymph empty, after the thoracic duct
Venous system @ junction of internal jugular and subclavian veins
44
What structure allows production of lymph from IS fluid
A 1 way valve @ junction of endothelial cells
45
What is total lymph flow @ rest
120 ml/hr very low in comparison t oexchange between plasma and IS fluid
46
What is rate of lymph flow determined by (3)
1. IS hydrostatic P 2. Activity of lymphatic pump 3. External compression
47
What is interstitial hydrostatic P @ rest
SUB-ATMOSPHERIC Increasing IHP increases lymph flow
48
Factors that increase IHP (4)
* Pc * COPp * IS fluid protein conc * permeability of capillaries (Increases of above)
49
What happens when IHP rises above atm P
Lymph flow rises dramatically At peak, P causes compression of lymph vessels so flow cannot rise further
50
P generated by large lymphatic vessels
25-30 mmHg
51
What happens if ultrafiltration is excessive
Vol of IS fluid increases Rate of lymph production is exceeded Fluid accumulate in IS space - OEDEMA
52
What is oedema induced by
Increase in venous P Decrease in COPp

CV physiology (from notes) (10 decks)

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