Lecture 13: Microcirculation and Coronary Circulation

Question 1

Clefts in the capillaries allow passage of what kind of substances across the capillary wall?

Answer 1

Glucose and electrolytes

Question 2

Compare the size of the capillary clefts in the brain vs. liver/gut?

Answer 2

Brain = very small

Liver/gut = very large

Question 3

How do lipid soluble substances move through capillary wall?

Answer 3

Free to diffuse right through (O2 and CO2)

Question 4

How do larger molecules pass through the capillary wall?

Answer 4

Some may use vesicles

Question 5

What are the two types of Starling Forces?

Answer 5

1) Hydrostatic (P)

2) Osmotic (π)

Question 6

What is the starling equation?

Answer 6

= Kf [(Pc - Pi) - (πc - πi)]

Question 7

What does a positive Starling force indicate?

Answer 7

A net driving force out of the capillary (filtration)

Question 8

What does a negative Starling force indicate?

Answer 8

A net driving force into the capillary? (absorption)

Question 9

Typically fluid moves which way toward the arteriolar end of the capillary?

Answer 9

Usually leaves the capillary (filtration)

Question 10

Typically fluid moves which way toward the venous end of the capillary?

Answer 10

Usually returns into the capillary (absorption)

Question 11

Any extra fluid taken into the interstitium will be taken up by?

Answer 11

The lymphatic system

Question 12

Heart failure can affect which Starling force at what end; lead to?

Answer 12

Pc by elevated venous pressure; edema

Question 13

Pi is a force that opposes what?

Answer 13

Filtration (movement out of capillary)

Question 14

πc can be decreased how; lead to?

Answer 14

Decrease in albumin (starvation or liver failure); edema

Question 15

πi favors movement in which direction; and is determined by?

Answer 15

Filtration; determined by interstitial protein concentration (usually small)

Question 16

What can alter Pi and πi leading to edema?

Answer 16

Restricted lymphatic flow, causing more protein and fluid to be stuck in the interstitial space.

Question 17

How does excess fluid and proteins enter the lymphatics?

Answer 17

Via one-way valved channels

Question 18

Lymph flow back to the thoracic duct is promoted by which 2 forces?

Answer 18

1) Smooth muscle contraction within lymph vessels

2) Compression of these vessels by surrounding skeletal muscle

Question 19

What causes edema?

Answer 19

When the volume of interstitial fluid exceeds the ability of the lymphatics to return it to circulation

Question 20

What is Kf?

Answer 20

Water permeability of the capillary wall

Question 21

Local control is exerted through the direct action of?

Answer 21

Local metabolites on arteriolar resistance

Question 22

What is autoregulation?

Answer 22

Maintenance of a constant blood flow to an organ in the face of changing arterial pressure

Question 23

If arterial pressure in a coronary artery suddenly decreases, how will auto-regulation attempt to fix the problem?

Answer 23

Immediate compensatory vasodilation of the coronary arterioles, decreasing the resistance

Question 24

Active hyperemia results from increasing interstitial concentrations of what?

Answer 24

Co2, H+, K+, lactate and adenosine

Question 25

Reactive hyperemia is what?

Answer 25

An increase in blood flow in response to or reacting to a prior period of decreased blood flow (i.e an occlusion)

Question 26

What does active hyperemia illustrate about blood flow and metabolic activity?

Answer 26

Blood flow to an organ is proportional to its metabolic activity.

Question 27

How does shear stress increase flow?

Answer 27

Increased flow downstream would increase the amount of shear on the walls upstream, releasing NO, causing vasodilation and helping to make the downstream effect greater

Question 28

When is local vs. metabolic control active in skeletal muscle?

Answer 28

Local = during exercise

Sympathetic = at rest (α1 and β2 receptors

Question 29

What helps to regulate body temperature through the skin?

Answer 29

Dense sympathetic innervation, which can alter blood flow

Question 30

What 2 things do histamine and bradykinin lead to?

Answer 30

1) Arteriolar vasodilation and constriction of venules (increases Pc)
2) Increases Kf allowing escape of large molecules (edema)

Question 31

What affect does serotonin have during tissue damage?

Answer 31

Vasoconstriction

Question 32

Angiotensin II and vasopressin (ADH) are powerful?

Answer 32

Vasocontrictors

Question 33

Coronary circulation is largely under what kind of control; most important metabolic factors?

Answer 33

• Metabolic (local)

- Hypoxia and adenosine

Question 34

An unusual feature of the coronary circulation is the effect of?

Answer 34

Mechanical compression of the blood vessels during systole.

Question 35

What does mechanical compression during systole lead to?

Answer 35

Reactive hyperemia to increase blood flow and O2 delivery, repaying O2 debt that incurred during the compression

Question 36

Cerebral circulation is controlled almost entirely by; most important ones?

Answer 36

• Local metabolites

- CO2 and H+

Question 37

An increase in cerebral PCO2, producing an increase in H+, causes what?

Answer 37

Vasodilation of cerebral arterioles, increasing blood flow to assist in removal of the excess CO2

Question 38

Hypoxia in pulmonary circulation leads to?

Answer 38

Vasoconstriction, shunting blood away from poorly ventilated areas where the blood flow would be “wasted.”

Question 39

What is the predominate sympathetic response in skeletal muscle; why?

Answer 39

• Vasoconstriction

- NE released stimulated primarily α1 receptors

Question 40

When is epinephrine released to act on skeletal muscle; receptor?

Answer 40

During fight or flight response; β2 receptors (vasodilate)

Question 41

The vasodilator substances in skeletal muscle during exercise are?

Answer 41

Lactate, adenosine, and K+

Question 42

What happens to the sympathetic centers controlling blood flow to the skin during exercise/temp increase?

Answer 42

They are inhibited

Question 43

What happens when sympathetic centers controlling blood flow to the skin are inhibited during exercise?

Answer 43

Causes vasodilation so that warm blood from the body core is shunted to skin surface for dissipation