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CVB by Minnie- 2024 Update > SM 118a - Microcirculation > Flashcards

SM 118a - Microcirculation Flashcards

1
Q

Which mechanisms govern water soluble solvent transfer in and out of capillaries?

A
  • Small molecules
    • ​Diffusion through endothelial junctions
      • Must pass through a gauntlet of fiber matrix
        • Glycocalyx
        • Protein constituents
  • Larger molecules (plasma proteins)
    • Vesicular transport via transcytosis (active transport)
      • This mechanism dominates
    • Diffusion through fenestrations in fenestrated capillaries or gaps in discontinuous capillaries
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2
Q

What is the Starling Equation?

What does it predict?

A

The Starling Equation predicts the net absorption into or filtration out of a capillary

  • Note:
    • Fluid out of the capillary is (+)
    • Fluid into the capillary is (-)
    • P = Hydrostatic pressure (pushes fluid out due to volume)
    • Pi = Oncotic pressure (sucks water toward it due to osmosis)
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3
Q

What is the reversal point of a capillary?

A

The point in the capillary where net filtration ends and net absorption begins.

  • Predicted by the Starling Equation
  • Filtration is early to deliver nutrients along their concentration gradient
  • Absorption is later to remove waste products, also along their concentration gradient
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4
Q

Describe the sequence of lymphatic flow from capillaries

A

Increased interstitial pressure initiates movement into lymphatics

  • Expansion phase
    • P(interstitium) is greater than P(lymph), forcing fluid into the lymphatics
    • 1-way microvalves open
  • Compression phase
    • Fluid flow into the lymphatics raises P(lymph) above P(interstitium)
    • The 1-way microvalves close (this prevents flow back into the interstitium)
    • Secondary lymph valves open, allowing the lymph to enter the thoracic duct
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5
Q

What prevents flow from the lymphatics to the interstitial spaces?

A

1-way valves that only allow for flow from the interstitium to the lymph

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6
Q

List the two systemic and three local mechanisms for control of blood flow

A

Systemic

  • Neural
  • Hormonal

Local

  • Myogenic
  • Metabolic
  • Endothelial
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7
Q

Describe neural control of blood flow

A

Systemic, controlled by the sympathetic nervous system

  • Vasoconstrictor nerves secrete norepinephrine
    • Activates alpha-1 adrenergic receptors on smooth muscle
      • Vasoconstriction in nonessential muscles
  • Adrenal medulla secretes epinephrine
    • Activates beta-2 adrenergic receptors in skeletal muscle/smooth muscle endothelium that carries blood to exerscising muscles
      • Vasodilation in excercising muscle
    • Activates alpha-1 adrenergic receptors on smooth muscle that is not needed for exercise
      • Vasoconstriction in nonessential muscles
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8
Q

In neural control of blood flow, what determines whether there is net vasodilation or net vasoconstriction in a given tissue?

A
  • Relative alpha-1 and beta-2 receptors in a given tissue
  • Mixture of epinephrine and norepinephrine released
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9
Q

Describe hormonal control of blood flow in response to trauma

A

Systemic

  • Trauma
  • -> Histamine Release
  • -> Arteriole dilation and venule constriction
  • -> Increased pressure in the capillaries
  • -> Increased filtration out of the capillaries, due to increased hydrostatic pressure in the capillary
  • -> Local edema
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10
Q

Describe myogenic control of blood flow

A

Local

  • Increased local blood flow
  • -> Stretch in vascular smooth muscle
  • -> Response mediated by stretch receptors
  • Reflex constriction
  • Increased local resistance
  • Local blood flow returns to normal
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11
Q

Describe metabolic control of blood flow

A
  • Metabolically active tissue generate vasodilator metabolites
    • Lactate
    • Adenosine (breakdown of ATP)
    • K+; if cells lyse, K+ in the blood goes up
    • H+ (more acidic)
    • CO2
  • Also sense interstitial concentrations of…
    • Decreased pO2
    • Increased pCO2
    • Decreased interstitial pH
  • All of the above trigger increased blood flow
    • Wash away waste products (and deliver more oxygen)
    • Re-establish equilibrium
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12
Q

Describe endothelial control of blood flow

A
  • Endothelial cells make certain substances
  • Vasodilators
    • Nitric Oxide
      • Generated by endothelial NO synthase (eNOS)
      • Converts arginine to NO
    • Prostaglandins
  • Vasoconstrictors
    • Endothelin (ET) = vasoconstrictor
      • Binds ET receptors on vascular smooth muscle
        • Increases cytosolic Ca2+
        • Released by endothelial cells in response to hypoxia and other stimuli
    • Thromboxanes
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13
Q

What is the effect of prostaglandin on local blood flow?

A

Protsaglandin is a vasodilator: increases local blood flow

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14
Q

What is the effect of thromboxane on local blood flow?

A

Thromboxane is a vasoconstrictor: decreases local blood flow

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15
Q

Describe autoregulation of blood flow

A
  • MAP can increase or decrease to keep blood flow to an area constant
  • Works in a broad range
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16
Q

This graph shows which pattern of blood flow regulation?

A

Autoregulation

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17
Q

Describe active hyperemia

A
  • Organ blood flow increases in response to increased metabolic rate
  • Blood flow increases to match the metabolic demands of a tissue
  • Local metabolic mechanisms are responsible
18
Q

Which mechanism of blood flow regulation is responsible for active hyperemia?

A

Metabolic (local)

19
Q

This graph shows which pattern of blood flow regulation?

A

Active Hyperemia

20
Q

This graph shows which pattern of blood flow regulation?

A

Reactive Hyperemia

21
Q

Describe reactive hyperemia

A
  • Organ blood flow responds to a period of arrested blood flow
  • Blood flow increases after insufficient blood flow
  • Flushes away toxins
  • Local metabolic and myogenic mechanisms are responsible
22
Q

Which mechanisms of blood flow regulation are responsible for reactive hyperemia?

A
  • Metabolic (Local)
  • Myogenic (Local)
23
Q

Which mechanism of blood flow regulation relies on the baroreceptor reflex?

A

Myogenic

24
Q

Which pattern of blood flow regulation is likely to dominate during exercise?

A

Active hyperemia, regulated by metabolic mechanisms

25
Q

Which pattern of blood flow regulation is likely to dominate after anginal pain has subsided?

A

Reactive hyperemia, regulated by metabolic and myogenic mechanisms

26
Q

Which mechanism of blood flow regulation dominates in the coronary arteries?

A
  • Metabolic (local)
    • Sensitive to hypoxia and adenosine
27
Q

Which metabolic conditions is the coronary circulation most sensitive to?

A
  • Hypoxia
  • Adenosine (breakdown of ATP)
28
Q

Which mechanism of blood flow regulation dominates in the cerebral circulation?

A
  • Metabolic (local)
    • Sensitive to ischemia
29
Q

Which metabolic condition is the cerebral circulation most sensitive to?

A

Ischemia

30
Q

What physiologic response is activated in response to increased intracranial pressure?

A
  • Cushing reflex
    • Increased intracranial pressure -> decreased blood flow
    • Cushing reflex increases systemic pressure above intracranial pressure to maintain blood flow to the brain
31
Q

Which mechanism of blood flow regulation dominates in the pulmonary circulation?

A
  • Metabolic (local)
    • Sensitive to changes in pO2
32
Q

Which metabolic condition is the pulmonary circulation most sensitive to?

A

Changes in pO2

33
Q

In the pulmonary circulation, what is the response to hypoxia?

Why does this make physiologic sense?

A
  • In the pulmonary circulation, hypoxia leads to vasoconstriction
  • Paradoxically, this further restricts blood flow and oxygen delivery
  • However, this makes sense in the lungs:
    • If a tissue is ineffective for gas exchange (ex: filled with mucus or not working), it is a “waste of circulation” to perfuse it
34
Q

Which mechanism of blood flow regulation dominates in the skeletal muscle?

A
  • Metabolic (local)
  • Sympathetic (systemic)
35
Q

Which metabolic condition is the skeletal muscle circulation most sensitive to?

A

Increases in…

  • Lactate
  • Adenosine
  • K+
  • Epinephrine acting on beta-2 receptors

All cause vasodilation

36
Q

What system in the body is responsible for determining TPR?

A

Skeletal Muscle

37
Q

What percentage of the total body circulation goes to skeletal muscle at rest?

A

80%

(More during exercise)

38
Q

What percentage of the total body circulation goes to the coronary arteries at rest?

A

5%

(More during exercise)

39
Q

What is the muscle pump that is sometimes referred to as the “2nd heart?”

A

The skeletal muscle surrounding veins

Contractions in a pumping pattern increase venous return

40
Q

What are glomus bodies? Where are they found? What do they do?

A

Glomus bodies are arterio-venous anastomoses in apical skin that are under sympathetic control.

  • They function to control heat conservation or dissipation in apical skin
  • If there is a decrease in core temperature, norepinephrine secreted by sympathetic neurons acts on alpha-1 receptors in glomus bodies, causing constriction
    • Decreased blood flow -> decreased heat loss
  • If there is an increase in core temperature, sympathetic tone is withdrawn
    • Glomus bodies dilate
    • Increased blood flow -> increased heat dissipation
41
Q

What regulates blood flow in apical skin in response to core temperature changes?

A

Glomus bodies

  • They constrict in response to decreased core temperature, due to sympathetic input
    • Heat conservation
  • They dilate in response to increased core temperature, due to decreased sympathetic tone
    • Heat dissipation
42
Q

In non-apical skin, how does blood flow change in response to acetylcholine release by neurons?

A

Blood flow increases due to vasodilation

CVB by Minnie- 2024 Update (43 decks)

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