Lecture 14: Elements of Vascular and Microvascular Circulation

Question 1

Where is the resistance highest in regional circulation?

Answer 1

arterioles

Question 2

Does the structure of vessel walls vary with the type and size of vessels?

Answer 2

yes = wall structure (3 layers or less/orientation) reflects function

Question 3

Do arteries have proportionately higher tunica externa (collagen, elastin) and tunica media (smooth muscle) than veins?

Answer 3

Yes.

Question 4

Are capillaries made of a single layer of endothelial cells (tunica interna)?

Answer 4

Yes.

Question 5

Smooth muscles have what 3 active functions?

Answer 5

1, contractile(relaxation and contraction)

2. plasticity (hypertrophy, proliferate and change phenotype)
3. secretory (release matrix, growth factors, proteases)

Question 6

What is the smooth muscle excitation-contraction coupling function of vascular cells?

Answer 6

Contraction can be initiated either:

1. chemically (ligand e.g. NE) OR
2. electrically (depolarization)

Free Ca2+ ultimately determines vascular smooth muscle tone

Question 7

What is a precapillary sphincter?

Answer 7

a band of smooth muscle where capillary arises from an arteriole

Question 8

What 2 things regulate local blood flow?

Answer 8

1. smooth muscle of arterioles
2. precapillary sphincter (well positioned to control flow into capillaries)

Both are well positioned to respond to local conditions

Question 9

what is rarefaction?

Answer 9

reduced density of patent vessels as a result of such collapse

Question 10

Can microcirculation vessels may collapse below a critical opening pressure (critical closing pressure)?

Answer 10

Yes.

Question 11

What are the 2 types of regulation of vascular smooth muscle tone?

Answer 11

1. Endothelium-INDEPENDENT: Vasopressin constricts smooth muscle
2. Endothelium-DEPENDENT contraction:
   When you have Pulmonary Hypertension = vessels are hypertrophied so have high BP–>endothelium can release ENDOTHELIN (Peptide) that acts on smooth muscle and causes constriction in response to this–> smooth muscle constriction

Question 12

Endothelial cells release what type of relaxing factors?

Answer 12

1. uses nitric oxide synthase to make Nitric Oxide = vasodilator (NO effects only important for local flow NOT overall bp)
2. PGI2 = prostacyclin
3. EDHF = enzyme dependent hyperpolarizing factor

Endothelium + NO or PGI2 = vasodilation and inhibit platelet aggregation

No Endothelium = No vasodilation instead CONSTRICTION

Question 13

What do endothelial cells secrete to constrict blood vessels?

Answer 13

ENDOTHELIN