Lecture 13: Microcirculation and Coronary Circulation Flashcards
Clefts in the capillaries allow passage of what kind of substances across the capillary wall?
Glucose and electrolytes
Compare the size of the capillary clefts in the brain vs. liver/gut?
Brain = very small
Liver/gut = very large
How do lipid soluble substances move through capillary wall?
Free to diffuse right through (O2 and CO2)
How do larger molecules pass through the capillary wall?
Some may use vesicles
What are the two types of Starling Forces?
1) Hydrostatic (P)
2) Osmotic (π)
What is the starling equation?
= Kf [(Pc - Pi) - (πc - πi)]
What does a positive Starling force indicate?
A net driving force out of the capillary (filtration)
What does a negative Starling force indicate?
A net driving force into the capillary? (absorption)
Typically fluid moves which way toward the arteriolar end of the capillary?
Usually leaves the capillary (filtration)
Typically fluid moves which way toward the venous end of the capillary?
Usually returns into the capillary (absorption)
Any extra fluid taken into the interstitium will be taken up by?
The lymphatic system
Heart failure can affect which Starling force at what end; lead to?
Pc by elevated venous pressure; edema
Pi is a force that opposes what?
Filtration (movement out of capillary)
πc can be decreased how; lead to?
Decrease in albumin (starvation or liver failure); edema
πi favors movement in which direction; and is determined by?
Filtration; determined by interstitial protein concentration (usually small)
What can alter Pi and πi leading to edema?
Restricted lymphatic flow, causing more protein and fluid to be stuck in the interstitial space.
How does excess fluid and proteins enter the lymphatics?
Via one-way valved channels
Lymph flow back to the thoracic duct is promoted by which 2 forces?
1) Smooth muscle contraction within lymph vessels
2) Compression of these vessels by surrounding skeletal muscle
What causes edema?
When the volume of interstitial fluid exceeds the ability of the lymphatics to return it to circulation
What is Kf?
Water permeability of the capillary wall
Local control is exerted through the direct action of?
Local metabolites on arteriolar resistance
What is autoregulation?
Maintenance of a constant blood flow to an organ in the face of changing arterial pressure
If arterial pressure in a coronary artery suddenly decreases, how will auto-regulation attempt to fix the problem?
Immediate compensatory vasodilation of the coronary arterioles, decreasing the resistance
Active hyperemia results from increasing interstitial concentrations of what?
Co2, H+, K+, lactate and adenosine
Reactive hyperemia is what?
An increase in blood flow in response to or reacting to a prior period of decreased blood flow (i.e an occlusion)
What does active hyperemia illustrate about blood flow and metabolic activity?
Blood flow to an organ is proportional to its metabolic activity.
How does shear stress increase flow?
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
When is local vs. metabolic control active in skeletal muscle?
Local = during exercise
Sympathetic = at rest (α1 and β2 receptors
What helps to regulate body temperature through the skin?
Dense sympathetic innervation, which can alter blood flow
What 2 things do histamine and bradykinin lead to?
1) Arteriolar vasodilation and constriction of venules (increases Pc)
2) Increases Kf allowing escape of large molecules (edema)
What affect does serotonin have during tissue damage?
Vasoconstriction
Angiotensin II and vasopressin (ADH) are powerful?
Vasocontrictors
Coronary circulation is largely under what kind of control; most important metabolic factors?
- Metabolic (local)
- Hypoxia and adenosine
An unusual feature of the coronary circulation is the effect of?
Mechanical compression of the blood vessels during systole.
What does mechanical compression during systole lead to?
Reactive hyperemia to increase blood flow and O2 delivery, repaying O2 debt that incurred during the compression
Cerebral circulation is controlled almost entirely by; most important ones?
- Local metabolites
- CO2 and H+
An increase in cerebral PCO2, producing an increase in H+, causes what?
Vasodilation of cerebral arterioles, increasing blood flow to assist in removal of the excess CO2
Hypoxia in pulmonary circulation leads to?
Vasoconstriction, shunting blood away from poorly ventilated areas where the blood flow would be “wasted.”
What is the predominate sympathetic response in skeletal muscle; why?
- Vasoconstriction
- NE released stimulated primarily α1 receptors
When is epinephrine released to act on skeletal muscle; receptor?
During fight or flight response; β2 receptors (vasodilate)
The vasodilator substances in skeletal muscle during exercise are?
Lactate, adenosine, and K+
What happens to the sympathetic centers controlling blood flow to the skin during exercise/temp increase?
They are inhibited
What happens when sympathetic centers controlling blood flow to the skin are inhibited during exercise?
Causes vasodilation so that warm blood from the body core is shunted to skin surface for dissipation
