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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
Q

How does fluid move from capillary to IS fluid

A

// BULK FLOW

  • Ultrafiltration
  • capillary -> IS space
  • Reabsorption
  • IS space -> capillary
26
Q

How much fluid is ultrafiltered daily

A

20 L (5L of blood)

27
Q

How much fluid is reabsorbed (from ultrafiltration)

A

90%

28
Q

How much fluid returns to circulation via lymphatic system (from ultrafiltration)

A

2L or 10%

29
Q

Driving F for ultrafiltration

A

Difference in hydrostatic pressure across capillary wall

  • Pc (capillary)
  • Pif (interstitial fluid)
30
Q

Capillary hydrostatic P @:

  1. Arteriolar end
  2. Venular end
A
  1. 32 mmHg
  2. 15 mmHg
31
Q

What is the driving force for reabsorption

A

Difference in colloid osmotic pressures

  • COP plasma (COPp)
  • COP IS fluid (COPip)
32
Q

What is colloid osmotic P

What is its value along full capillary length

A

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
Q

Which is higher at arteriolar end - hydrostatic P or COP

A

HP

=> Ultrafiltration is higher

34
Q

Which is higher at venular end - hydrostatic P or COP

A

COP

=> reabsorption is increased

35
Q

Effect of vasoconstriction on balance between ultrafiltration and reabsorption in capillary

A

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
Q

Effect of arterolar vasodilation on balance between ultrafiltration and reabsorption in capillary

A

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
Q

What happens to substances with an increased RMM

A

Cannot be reabsorbed, so enter lymphatic capillary

IS fluid -> lymph

38
Q

Lymph protein conc

A

Relatively high

39
Q

Where is 70% of lymph

A

Liver and GIT

40
Q

What tissue does NOT have lymphatic channels

A

Bone

41
Q

What do lymphatics do

A

Drain excess fluid directly from IS space

42
Q

Where does lymph from the lower part of the body (including legs) flow up through

A

Thoracic duct

43
Q

Where does lymph empty, after the thoracic duct

A

Venous system @ junction of internal jugular and subclavian veins

44
Q

What structure allows production of lymph from IS fluid

A

A 1 way valve @ junction of endothelial cells

45
Q

What is total lymph flow @ rest

A

120 ml/hr

very low in comparison t oexchange between plasma and IS fluid

46
Q

What is rate of lymph flow determined by (3)

A
  1. IS hydrostatic P
  2. Activity of lymphatic pump
  3. External compression
47
Q

What is interstitial hydrostatic P @ rest

A

SUB-ATMOSPHERIC

Increasing IHP increases lymph flow

48
Q

Factors that increase IHP (4)

A
  • Pc
  • COPp
  • IS fluid protein conc
  • permeability of capillaries

(Increases of above)

49
Q

What happens when IHP rises above atm P

A

Lymph flow rises dramatically

At peak, P causes compression of lymph vessels so flow cannot rise further

50
Q

P generated by large lymphatic vessels

A

25-30 mmHg

51
Q

What happens if ultrafiltration is excessive

A

Vol of IS fluid increases

Rate of lymph production is exceeded

Fluid accumulate in IS space - OEDEMA

52
Q

What is oedema induced by

A

Increase in venous P

Decrease in COPp

CV physiology (from notes) (10 decks)

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