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SMP - Cardiopulmonary Exam 1 > Lecture 14 - Elements of Vascular and Microvascular Function > Flashcards

Lecture 14 - Elements of Vascular and Microvascular Function Flashcards

1
Q

In what vessels is the highest resistance?

A

Arterioles

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2
Q

What are the 3 active functions of smooth muscle cells? Describe each.

A
  1. Contractile function to induce changes in capacitance and resistance of vessels
  2. Plasticity, meaning they can undergo hypertrophy, proliferate, and undergo phenotypic changes in vascular disease and during development
  3. Secretory function: during vascular disease they can form and release matrix, growth factors, and proteases
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3
Q

What determines vascular smooth muscle tone?

A

Free intracellular [Ca++]

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4
Q

Are smooth muscle cells electrically or chemically induced to contract?

A

BOTH

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5
Q

How does muscle contraction in smooth muscle compare to that in skeletal/cardiac muscle?

A

Process is much slower because of series of reactions (involving MLCK) and decreased myosin ATPase activity

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6
Q

Definition of microcirculation?

A

Circulation made of vessels in the 10-200 micron range in diameter

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7
Q

Describe the smooth muscle of metarterioles.

A

Discontinuous smooth muscle surrounding them

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8
Q

When can vessels of the microcirculation collapse?

A

Below a critical opening pressure

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9
Q

Other name for critical opening pressure?

A

Critical closing pressure

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10
Q

What is rarefaction?

A

Reduced density of patent vessels as a result of a collapse of vessels of the microcirculation

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11
Q

Describe the smooth muscle of arterioles.

A

Continuous smooth muscle surrounding them

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12
Q

What do we find between arterioles/metarterioles and capillaries? Purpose?

A

Precapillary sphincters = band of smooth muscle at the arteriolar end of capillaries

Purpose = band of smooth muscle that determines local resistance thus blood flow to the given capillary bed

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13
Q

How do precapillary sphincters respond to local conditions?

A

They are exposed to the same environment as the tissues the capillaries are supplying so can regulate blood flow based on secretions by these cells

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14
Q

For what 2 reasons are arteries not designed to regulate blood flow to tissues?

A
  1. They have a lot of smooth muscle, but not enough to truly regulate their size efficiently
  2. They are not in the local environment of the tissues being supplied so cannot respond to changes in the environment
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15
Q

What is the modern view of the endothelium?

A

Dynamic tissue that will have a varying structure depending on what tissue it’s in

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16
Q

What are the 4 types of compounds secreted by endothelial cells? Give examples for each type.

A
  1. Endothelial derived vasodilators: NO, prostacyclin (PGI2)
  2. Endothelial-derived vasoconstrictors: endothelin
  3. Anti-thrombogenic/aggregatory factors for platelets
  4. Anti-mitogenic factors for vascular smooth muscle to maintain their structure
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17
Q

Describe 2 metabolic functions of endothelial cells.

A

Processing of vasoactive factors:

  1. Production of angiotensin II from angiotensin I by angiotensin-converting enzyme (ACE)
  2. Breakdown of bradykinin by angiotensin-converting enzyme (ACE)
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18
Q

In what circumstances do endothelial undergo angiogenesis?

A
  1. In response to injury and ischemia
  2. Embryonic development
  3. Tumorigenesis
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19
Q

3 active functions of endothelial cells?

A
  1. Secretory function
  2. Metabolic function
  3. Plasticity
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20
Q

What are the 2 methods for causing either vasoconstriction or vasodilation of smooth muscles of vessels? Describe each briefly.

A
  1. Endothelium-dependent: ligand binding to endothelium receptors => production of endothelial relaxing or constricting factors which diffuse to smooth muscle
  2. Endothelium independent: direct binding to receptor on smooth muscle
21
Q

What are 5 examples of an endothelium independent vasoconstrictors?

A
  1. Vasopressin (AVP)
  2. NE
  3. EPI
  4. Angiotensin II (but requires ACE in endothelium to go from angiotensin I to II)
  5. Endothelin
22
Q

What are 4 example of an endothelium independent vasodilator?

A
  1. Atrial natriuretic peptide (ANP)
  2. NO
  3. PGI2
  4. EDHF
23
Q

What are 6 examples of an endothelium dependent vasodilator? What do they cause the endothelium to release?

A
  1. Histamine
  2. ACh
  3. Bradykinin
  4. Purinergics (e.g. adenosine)
  5. Serotonin
  6. Shear stress

=> endothelium releases NO, PGI2, and EDHF

24
Q

What is shear stress? What is directly related to?

A

A frictional force tangential to the direction of a flowing fluid, the force of which is directly related to the fluid’s viscosity and the pressure gradient

25
Q

What are 2 examples of an endothelium dependent vasoconstriction? What do they cause the endothelium to release?

A
  1. Pulmonary HT
  2. Vessel injury

=> endothelium releases endothelin

26
Q

What are the steps of the mechanism of endothelium-dependent vasodilation with NO?

A
  1. Ligands/shear stress on endothelial cell increase intracellular Ca++
  2. Activation of eNOS = NO synthase (Ca++ dependent)
  3. eNOS: O2 + L-arginine => NO + L-citrulline
  4. NO diffuses to smooth muscle cell and acts on soluble guanylate cyclase to activate it
  5. GC: cGTP => cGMP
  6. cGMP decreases free Ca++ in smooth muscle cell => RELAXATION
27
Q

What is the half life of NO? What does this mean?

A

6 s => only affects nearby cells despite the fact is diffuses readily = potent LOCAL vasodilator

28
Q

CAN NO REGULATE BP? Why?

A

NOPE

Because of very short half-life

29
Q

What kind of molecule is NO?

A

Free radical gas

30
Q

Is NO lipid or water soluble?

A

Lipid

31
Q

What kind of enzyme is eNOS? What does this mean?

A

Constitutive enzyme => produced in constant amounts without regard to the physiological demand

32
Q

What is iNOS?

A

Inducible NO synthase

33
Q

Other than activating eNOS, what else can free intracellular Ca++ induce in endothelial cells? Describe the mechanism.

A

Increase conversion of arachodonic acid to prostacyclin (PGI2) by COX => activates AC in smooth muscle: ATP => cAMP => decrease of Ca++ in smooth muscle cells => RELAXATION

34
Q

How long does PGI2 lasts?

A

1 circulation through the body, also a short-lived vasodilator

35
Q

Which is the more important vasodilator: NO or PGI2?

A

NO

36
Q

What are the 3 endothelium-dependent relaxation mechanisms?

A
  1. NO secretion by endothelium
  2. PGI2 secretion by endothelium
  3. EDHF secretion by endothelium
37
Q

What does EDHF stand for?

A

Endothelium-dependent hyperpolarizing factor

38
Q

Describe how EDHF works.

A

The endothelium releases EDHF which causes hyperpolarization of smooth muscle cells by causing K+ outflow => relaxation

39
Q

What effect would the endothelium dependent vasodilators have without the presence of an endothelium? Purpose?

A

They would cause constriction by direct actions on vascular smooth muscle

Ligands having direct access to the smooth muscle means that something is wrong with the endothelium (like damage), and flow should not be increased to this part of the vessel - this is an inappropriate response when the damage is due to HT of arteriosclerosis because it just makes the situation worse

40
Q

What could cause dysfunctional endothelium?

A

Arteriosclerosis or other vascular diseases

41
Q

Do blood vessels receive parasympathetic innervation?

A

NOPE, except for GIT and sex organs

42
Q

How do platelets react with the endothelium?

A
  1. Healthy endothelium: platelets cannot stick because they make NO and prostacyclins. If they do stick, they will release ADP and serotonin, which will further relax the smooth muscle cell
  2. Unhealthy/damaged endothelium: platelets are activated by tissue below endothelium and aggregate on smooth muscle cells and secrete serotonin and thromboxane A2 (which also causes further platelet aggregation via + feedback) to contract them
43
Q

What are the 2 lymphatic ducts? % drainage in each?

A
  1. Thoracic duct (75%)

2. Right lymphatic duct (25%)

44
Q

What forces cause exchange of molecules at capillaries?

A

Starling forces:

  1. Net filtration at arteriolar end
  2. Net reabsorption at venular end
45
Q

Which of the Starling forces is responsible for lymph fluid flow?

A

Pressure gradient between interstitial hydrostatic pressure and lymphatic capillary hydrostatic pressure

46
Q

Describe the resistance in the capillaries.

A

They have an intrinsic resistance that decreases throughout the capillaries

47
Q

What determines the tone of a vessel?

A

Free intracellular Ca++

48
Q

Other name for NO?

A

Endothelium dependent relaxing factor

SMP - Cardiopulmonary Exam 1 (28 decks)

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