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A Physiology > 2.7A. Functional organization of microcirculation and its control. > Flashcards

2.7A. Functional organization of microcirculation and its control. Flashcards

1
Q

I. Basics
1. What is microcirculation?

A

Refers to circulation of the blood in the smallest blood vessels in the human body (ex: terminal arterioles, capillaries, metarterioles and venules), which separate the arterial and venous system

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2
Q

I. Basics
2. Route of microcirculation

A

Arterioles (input) ↔ capillaries ↔ venules (output)

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3
Q

I. Basics
3. Function of microcirculation

A

exchange of products

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4
Q

II. Functional organization of microcirculation
1. What are 6 components of microcirculation?

A
  1. Terminal arterioles (<20μm)
  2. Metarterioles
  3. Precapillary sphincters
  4. Capillaries
  5. (postcapillary) venules
  6. AV-shunt
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5
Q

II. Functional organization of microcirculation
2. Characteristics of Terminal arterioles (<20μm)

A
  • the vessel on the arterial side of the microcirculation
  • composed of (1) single layer of SMCs (2) thin adventitia layer (3) endothelium
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6
Q

II. Functional organization of microcirculation
3. Characteristics of Metarterioles

A
  • SMCs are discontinuous and NOT innervated
  • Capillaries originate from here
    -> Exchange of H2O and other solutes
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7
Q

II. Functional organization of microcirculation
4. Characteristics of Precapillary sphincters

A
  • 1 smooth muscle cell
  • Are responsible to local tissue conditions
    -> Relaxation/contraction of precapillary sphincter modulate tissue blood flow (which capillaries are open/closed)
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8
Q

II. Functional organization of microcirculation
5. Characteristics of Capillaries

A
  • Smallest blood vessels in human body
  • Receives arterial blood from terminal arterioles
  • Exchange site of nutrients and cellular waste product
    between blood and tissues
  • Site of fluid exchange between vascular and interstitial
    compartments
  • No smooth muscle – only endothelial cell
    -> Basal membrane
    -> Have pores – filled with H2O
    -> Total surface of capillaries in body = 5000 – 7000 m2
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9
Q

II. Functional organization of microcirculation
6. Characteristics of (postcapillary) venules

A
  • Carry blood back into the vein
  • Have a discontinuous SMC layer that allows for control of local blood flow
  • They may also exchange some solute across their walls
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10
Q

II. Functional organization of microcirculation
7. Characteristics of AV-shunt

A
  • Direct link with arteriole and venule
  • NO CAPILLARIES
  • A lot of SMCs -> SYM control
    -> Only in skin circulation (responsible for thermoregulation)
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11
Q

III. Types of capillaries
1. What are the 4 types of capillaries

A

1) Continuous capillaries
2) Fenestrated capillaries
3) Sinusoidal (discontinuous) capillaries
4) Tight capillary

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12
Q

III. Types of capillaries
2. Characteristics of Continuous capillaries

A
  • Most abundant (ex: muscle, fat, nervous tissue)
  • Cells are joined by tight junctions
  • Has small pores
  • Pinocytotic vessel -> pinocytotic channel (permeability of wall for H2O and other soluble particles)
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13
Q

III. Types of capillaries
3. Characteristics of Fenestrated capillaries

A
  • Found in GI-tract, endocrine + exocrine glands, kidney
  • Has fenestrae (intracellular perforations)
    -> increased pore diameter
    -> increased capillary permeability = more permeable than continuous type
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14
Q

III. Types of capillaries
4. Characteristics of Sinusoidal (discontinuous) capillaries

A
  • Found in liver, spleen, bone marrow
  • Have open spaces between endothelial cells
    -> very permeable (cells cross easily)
  • Sometime permits passage of blood cells
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15
Q

III. Types of capillaries
5. Characteristics of Tight capillary

A
  • Found in brain and retina
  • No pores, no H2O-filled structures
  • Allows only highly-regulated transcellular transport (ex: BBB)
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16
Q

IV. Autoregulation
1. Characteristics of autoregulation

A
  • Intrinsic ability of a body part to maintain a constant blood flow despite changes in perfusion pressure
  • A passive process that occurs in absence of neural and hormonal influences
  • Tendency of vascular smooth muscles to contract when stretched
17
Q

IV. Autoregulation
2. Mechanism of autoregulation

A

Tendency of vascular smooth muscles to contract when stretched:
- Stretch induces opening of stretch-activated, non-selective cation channels in the VSCMs
-> depolarization
-> L-type Ca2+-channel activation
-> [Ca2+]↑
-> muscle contraction (myogenic response)
-> vasoconstriction

18
Q

V. Vasomotion
1. What is Vasomotion?

A
  • Vascular SM in arterioles undergoes cyclic contractions and relaxations (oscillations)
19
Q

V. Vasomotion
2. What is mechanism of Vasomotion?

A

Mechanism: the cyclic change of Ca2+-signal, synchronized across the SM in the arteriole wall
- This improves flow in the periphery
-> giving blood a little push
-> makes flow through the periphery more efficient
- Oscillations also prevents a ‘’latch state’’, which is otherwise common in smooth muscle due to having low levels of ATP

20
Q

VI. Plug and bolus flow
1. What are characteristics of Plug and bolus flow

A
  • Capillaries have a smaller diameter than RBC (cap: 6μm, RBC: 7μm)
  • The RBCs undergo severe deformation while they travel though the capillary
  • Each RBC is a ‘’plug’’ followed by a plasma ‘’bolus’’ between another RBC
  • RBC does not ever come into contact with the wall, because of the wall’s glycocalyx layer, which covers the internal surface of the endothelium:
    +) If glycocalyx is present, hematocrit is lower (less RBC’s out of overall layer)
    +) If glycocalyx is absent, hematocrit goes up
21
Q

VI. Plug and bolus flow
2. Why doesn’t RBC come into contact with the capillary wall>

A

RBC does not ever come into contact with the wall, because of the wall’s glycocalyx layer, which covers the internal surface of the endothelium:
- If glycocalyx is present, hematocrit is lower (less RBC’s out of overall layer)
- If glycocalyx is absent, hematocrit goes up

22
Q

VII. Flow: impact of WBCs
- How can WBCs impact the blood flow in capillaries?

A
  • WBCs are even larger than RBCs, but still make it pass through the capillaries
  • Slower flow, frequently blocks in the capillary that has to build up a pressure gradient to push it through

A Physiology (88 decks)

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