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Cardio > Microcirculation > Flashcards

Microcirculation Flashcards

1
Q

What are the 2 functions of microcirculation?

A
  • Exchange of molecules from the blood to cells and vice versa, via DIFFUSION
  • Regulation of blood volume by altering the distribution of fluid between the interstitial and vascular compartments, via FILTRATION from or ABSORPTION into capillaries
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2
Q

Do capillaries have smooth muscle cells?

A

NO! just endothelial cells

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3
Q

What controls the blood flow into capillary beds?

A

As the metarterioles give off capillaries, the junction is surrounded by precapillary sphincters that regulate the blood flow into the capillary bed and venules.

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4
Q

Where are precapillary sphincters most abundant?

A

mesenteric circulation

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5
Q

What molecules can cross capillaries via diffusion?

A

Oxygen and Carbon dioxide

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6
Q

What molecules can diffuse through clefts?

A

water and small solutes

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7
Q

How are proteins transported across capillaries?

A

1) Fenestrations (in liver)

2) taken up by endocytosis and transported across endothelial cells via exocytosis! (very low flux thorugh this system)

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8
Q

Can proteins usually cross capillaries?

A

NO

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9
Q

What is the equation for osmotic pressure?

A

Osmotic pressure π=RTσΔc

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10
Q

What is the reflection coefficient related to?

A

σ =1 - permeability coefficient

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11
Q

What is the reflection coefficient of proteins?

A

Albumin and Hemoglobin have permeability coefficient of around 0, so they are almost completely reflected (.999)! This means that they generate a significant osmotic pressure.

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12
Q

What is the reflection coefficient of water?

A

Water has permeability coefficient of 1, so it is NOT reflected (0)

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13
Q

What can change the refection coefficient of proteins?

A

The reflection coefficients of proteins can decrease significantly during inflammatory conditions (like burns)

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14
Q

What is the Starling Equation?

A

Jv = Kf [(Pc - Pi ) – (Πc – Πi) ]

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15
Q

What does Jv stand for?

A

transcapillary flow

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16
Q

What does a positive Jv mean?

A

(+) when flow is outward, filtration

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17
Q

What does a negative Jv mean?

A

(-) when flow is inward, reabsorption

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18
Q

What does Kf stand for?

A

filtration coefficient (hydraulic conductance)- equal to inverse of resistance

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19
Q

What regulates Kf?

A
  • Regulated by precapillary sphincters that can block flow into capillaries and shunt blood around them
  • Regulated by capillary type (fenestrated (high) v. continuous (low))
  • Regulated by inflammation (which will increase capillary permeability and raise Kf)
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20
Q

What is [(Pc - Pi ) – (Πc – Πi) ] ?

A

Net transcapillary pressure

21
Q

What is (Pc - Pi )?

A

capillary - interstitial hydrostatic pressure

22
Q

Is hydrostatic pressure negative or positive?

A

+ PRESSURE- forces water OUT

23
Q

What is (Πc – Πi)?

A

oncotic pressure: capillary - interstitial colloid osmotic pressure

24
Q

Is oncotic pressure negative or positive?

A
  • PRESSURE- high protein content within plasma pulls water IN from interstitium
25
Q

Increasing Pc will do what to filtration?

A

INCREASE IT! (water is forced out of capillaries)

26
Q

Decreased arteriolar hydrostatic RESISTANCE will have what effect?

A

increase blood flow and increase pressure in capillary

27
Q

Increasing the venous hydrostatic pressure will have what effect on pressure in the capillary?

A

decreases blood flow and increases capillary pressure

28
Q

What is the only factor in the Starling equation that changes from the arteriole to the venous side?

A

Pc is the only variable that really changes (DECREASES), because pressure as lost with forward movement of fluid

29
Q

Is the net filtration or absorption on the arteriole side of the capillary?

A

net filtration

30
Q

Is the net filtration or absorption on the venuole side of the capillary?

A

net absorption

31
Q

What controls Pi?

A

Depends on interstitial fluid volume (fluid flowing in from the capillaries vs fluid flowing out via lymphatics ). Usually a vacuum!

32
Q

A higher Pi says what about lymph flow?

A

HIGHER

33
Q

Πc depends on what?

A

plasma protein concentration

34
Q

What decreases plasma protein concentration (and decreases Πc)?

A

liver disease, starvation, kidney disease, transient dilution (IV infusion and fluid shifts)→ increased filtration

35
Q

What increases plasma protein concentration (and increase Πc)?

A

lowering liquid component via dehydration, diarrhea, vomiting, prolonged sweating→increased absorption to replace fluid

36
Q

Πi is regulated by what?

A

input (protein entering from capillaries)- output (protein leaving via lymphatic drainage)

37
Q

Increased lymph flow does what to the interstitial protein concentration?

A

lowers it! flushes it out!

38
Q

What opens flap valves?

A

increased interstitial pressure

39
Q

What creates negative pressure (suction) that can pull fluid into the lymphatic vessel?

A

smooth muscle around lymph vessels

40
Q

What is the most simplistic way to explain edema?

A

fluid entry is greater than fluid removal

41
Q

List the edema safety factors.

A
  1. increase in lymph flow as interstitial fluid pressure increases (to a certain point)
42
Q

How does increase in interstitial fluid pressure act as a safety factor to edema?

A

Negative interstitial pressure and Low compliance: flow will resist swelling until it is around 0mmHg (get about 5mm Hg of safety)

increase in interstitial volume → increase in Pi (goes from negative to more positive)→ decrease in (Pc – Pi) → reduce any further increase in interstitial volume

43
Q

How does lymph flow act as a safety factor to edema?

A

Get around 7 mmHg of safety due to increasing lymph flow as interstitial fluid pressure increases

44
Q

List the causes of edema.

A 
Capillary pressure
Interstitial pressure
Plasma oncotic pressure
Interstitial oncotic pressure
Permeability – inflammation
45
Q

What can increase capillary pressure?

A

heart failure; venous obstruction, inflammation (local vasodilation)

46
Q

What can change interstitial pressure and lead to edema?

A

pulmonary– restrictive lung disease

47
Q

What can decrease plasma oncotic pressure?

A

liver disease and malnutrition (reduced production), kidney disease (loss)

48
Q

What can increase interstitial oncotic pressure?

A

lymphatic obstruction (only way for protein to get back into circulation is via lymphatics), inflammation (increased permeability)

Cardio (24 decks)

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