Lecture 23: Circulation and Hemodynamics Part II Flashcards
What vessels are important for microcirculation/local circulation control? What do they have that make them important?
Arterioles (lots of smooth muscle walls)
Metarterioles (limited smooth muscle walls)
Capillaries (precapillary sphincters)
What allows substance exchange across capillary walls? Where are they found the most?
Clefts that allow water soluble substances to pass through
Liver and gut
What does the starling equation calculate?
Positive value means? Negative value means?
Net H2O flow in and out of the capillary
Positive: net force pushes fluid out of the capillary
Negative: net force pushes fluid in the capillary
What is the Starling equation? What does each term mean?
Flow = Kf (Pc + Oi) - (Pi+Oc)
Pc + Oi = net forces pulling fluid out
Pi + Oc = net forces pulling fluid in
What can alter these values significantly? Pc Pi Oc Oi
- elevated venous pressure as in heart failure
- lymphatic restriction or increased driving force out of capillary
- decrease albumin (as in starvation or liver failure)
- lymphatic restriction or inflammation
What do lymphatic vessels do?
Collect fluid flowing out of capillary and returns it to venous circulation
How does myogenic control exert local influence on vasculature? Why?
- vasoconstricts the vasculature to impede blood flow and reduce the blood flowing through that system
- Responds to high BP because it means more force squeezing blood through increasing blood flow than necessary.
How does metabolic control exert local influence on vasculature? Why?
Vasodilates vasculature
Detects buildup of metabolic products and decrease in O2
What is active hyperemia? What is reactive hyperemia?
- vasodilation due to increased metabolic demand which increases metabolites
- vasodilation due to obstruction which increases metabolites
How does shear control influence local vasculature? Why?
Downstream vasodilation causes increase in upstream flow in arterioles increasing the shear force. This causes NO release which also vasodilates the upstream vessels. Overall lowering of the metabolites due to vasodilation.
How does histamine affect vasculature?
How does serotonin affect vasculature?
How does prostaglandin affect vasculature?
- increases Kf = vasodilates = swelling
- vasoconstriction
- mixed
How is coronary circulation controlled?
Metabolically. Ignores sympathetic innervation since you don’t want to constrict blood flow to the heart every time your BP is low
How is cerebral circulation controlled?
Metabolically and not that responsive to ANS control just like the heart
Is pressure in the pulmonary circulation lower or higher than the systemic circulation? How about resistance?
- Lower. Highest at the RV and Pulmonary A. and tapers off
- Also lower, since pressure is lower.
How is pulmonary vasculature regulated?
Little sympathetic control but increased compliance compared to systemic vasculature
What event can vasoconstrict the pulmonary circulation?
Hypoxia restricts flow to the lungs, so body shunts blood away from there since lungs aren’t functional anyway
How is skin vasculature controlled during …
BP control?
Temp control?
- vasoconstriction
- bypassing capillary beds and vasodilating to let fluid flow from vessels to sweat glands
Shunting blood from right to left means
Shunting blood from left to right means
- Venous to systemic, bypassing pulmonary circulation
- systemic to venous, bypassing the capillary bed
Which systems are largely controlled by central ANS mechanisms?
Which systems are largely controlled by local mechanisms?
- skin, gut and inactive muscle
- heart, brain, active muscle, lung vasculature during hypoxia
What is Hc dependent on?
What is Oc dependent on?
What happens to Hc as it crosses over the venous side?
- directly proportional to systolic pressure
- directly proportional to albumin (drops if you lose albumin - as in proteinuria)
-decreases as systolic pressure drops
