SCT II - Local Regulation of Circulation

Question 1

What are the types of local control of blood flow?

Answer 1

1. Metabolic factors
2. Active hyperemia
3. Reactive hyperemia
4. Myogenic autoregulation
5. Functions of endothelium

Question 2

What is the local control of blood flow via metabolic factors?

Answer 2

Vasodilator effect
- Hypercapnia
- Hypoxia
- pH (Acidosis)
- Adenosine
- Lactic acid
- K+
- Mg2+
- High temperature

Question 3

What is the local control of blood flow via active hyperemia?

Answer 3

Hyperemia = excess blood

Metabolism INC
Blood flow INC

Question 4

What is the local control of blood flow via reactive hyperemia?

Answer 4

Reactive Hyperemia = Reaction to low blood flow

due to obstruction, compensation via excess blood

Question 5

What is the local control of blood flow via myogenic autoregulation?

Answer 5

Happens only during the autoregulatory range.

Increase in pressure will result in increase in resistance to cancel out the change, and keep flow constant

AIM - MAINTAINING CONSTANT FLOW

Question 6

Bayliss Effect of myogenic autoregulation

Answer 6

MAP INC
↓
Stretch of vessel wall
↓
Stretch-Activated Channels
↓
Depolarization + [Ca2+]i INC
↓
Vasoconstriction
↓
Resistance INC
↓
Unchanged Q (resistance combats map increase)

Question 7

Mention the crucial role of endothelium

Answer 7

1. Hemostatic (pro/anti-coagulant)
2. Growth
3. Barrier
4. Enzymatic metabolites
5. Immunity & immune response
6. REGULATION OF VASCULAR TONE (how contracted/relaxed a vessel is)

Question 8

What stimulate the release of endothelin-1?

Answer 8

1. Angiotensin-II
2. ADH
3. Thrombin
4. Cytokines
5. ROS
6. Damage to endothelium

Question 9

What happens when there is shear stress on the blood vessel?

Answer 9

Blood vessel wants to relax. How:

NO production
NO causes vasodilation in smooth m.

Question 10

How does Bradykinin have dual function?

Answer 10

Endothelium present
Causes vasodilation

Endothelium not present
Causes contraction

Question 11

What is the function of adrenomedullin?

Answer 11

Vasodilator

Binds to endothelium
Endothelium secretes NO & CO
NO & CO relaxes smooth muscle

Question 12

What is the function of acetylcholine

Answer 12

PRESENCE OF ENDOTHELIUM
VASODILATOR
Binds to endothelium
Endothelium secretes NO
NO relaxes smooth m.

ABSENCE OF ENDOTHELIUM
CONTRACTOR
Binds to smooth m. directly
Causes contraction

Question 13

What are the 4 substances that are able to induce vasodilation via endothelium but contraction of smooth muscle via absence of endothelium?

Answer 13

Acetylcholine
Histamine
Bradykinin
Serotonin

Question 14

What’s the alias of serotonin?

Answer 14

5-Hydroxytryptamine

Question 15

What’s the function of serotonin

Answer 15

SMALL CONC
Binds to endothelium
Endothelium release NO
NO causes vasodilation

BIG CONC
Binds directly to smooth m
Causes contraction (vasoconstriction)

Question 16

What’s the function of thromboxane (TXA2)?

Answer 16

Vasoconstrictor, immediately binds to smooth muscle cells (bypass endothelium)

Question 17

How does the heart receive blood during diastole?

Answer 17

During systole the heart muscles are contracted and compress the vessels.

During diastole the heart muscles are relaxed and blood is able to reach the heart

Question 18

What tone is dominant in the coronaries?

Answer 18

Basal tone

Question 19

Munroe-Kaillie’s Law

Answer 19

Vskull = Vbrain + Vblood + Vcsf

CONSTANT

Question 20

Equation of cerebral perfusion pressure

Answer 20

CPP = MAP - ICP (~ 70-80 mmHg)

Question 21

What tone is dominant in the brain?

Answer 21

Basal tone

Question 22

What is the role of astrocytes?

Answer 22

Supporting cells of the brain neurons, are able to release vasodilative metabolites

Question 23

What is the role of PNS in the meninges?

Answer 23

Induces vasodilation

Question 24

How is stroke prevented via the SNS?

Answer 24

Sudden MAP increase induces SNS activation, which constricts blood vessels

Question 25

How does the lung prevent pulmonary edema?

Answer 25

Ratio of absorption is greater than that of filtration, unlike systemic circulation, where filtration is 2/3 and absorption is 1/3

Question 26

Hormones that effect pulmonary circulation and why they are special

Answer 26

OPPOSITE Histamine - Usually VD, VC in lungs Serotonin - Usually VD, VC in lungs Catecholamines - Usually VD, VC in lungs VIP, NO, ANP - Vasodilation

Question 27

Metabolite differences in pulmonary circulation

Answer 27

P[O2] **DEC** P[CO2] **INC** Acidosis OPPOSITE TO SYSTEMIC - DO VASOCONSTRICTION

Question 28

Why is the reaction to metabolites different in pulmonary circulation?

Answer 28

Body assumes there's an obstruction of an alveoli, redirecting blood to healthier alveoli, in order to be supplied with metabolites

Question 29

Explain the difference in ventilation and perfusion in the three zones of the lung

Answer 29

Zone I: V ↑ + Q ↓ Q ↑ from Zone I - III

Question 30

Which zone do bacteria prefer and why?

Answer 30

Zone I as it has lots of free oxygen

Question 31

Which zone is the lung in whilst lying-down?

Answer 31

Zone III

Question 32

Which zone should be absent in a healthy human?

Answer 32

Zone I

Question 33

What is deadspace? What is a shunt?

Answer 33

Deadspace = Good ventilation, bad perfusion Shunt = Bad ventilation, good perfusion Perfusion is flow

Question 34

Which tone is dominant in skeletal muscles?

Answer 34

Both basal tone and constrictor (reflex) tone

Question 35

Which tone is dominant in acral skin (thick)?

Answer 35

Only constrictor (reflex) tone - Has extensive capillary networks - Countercurrent flow - Sympathetic innervation

Question 36

Which tone is dominant in non-acral skin (thin)

Answer 36

Both basal tone and constrictor tone

Question 37

Which tone is dominant in kidneys?

Answer 37

Basal tone Autoregulation - Maintaining flow Nervous - SNS for VC for redistribution Humoral - both VC and VD agents

Question 38

Which tone is dominant in splanchnic organs?

Answer 38

Sympathetic VC to redistribute blood