3 - Special Circulation: Organ Flashcards
When the body is at rest, what areas receive most of the blood flow?
GI Tract, Kidneys, Skeletal Muscle, Heart, Brain
What governs blood flow to individual organs?
Neurohumoral and Local Regulatory mechanisms that govern vascular resistance
What coronary arteries supply the left ventricle/left atrium?
What coronary arteries supply the right ventricle/right atrium/inferopsterior region of left ventricle?
Left: Left Coronary Artery (LCA) -> Left Anterior Descending (LAD) + Circumflex (CFX)
Right: Right Coronary Artery (RCA)
When does most of the blood flow to the mycardium occur?
Why?
Diastole
Blood flow to coronary decreases during systole
When the heart is contracting during systole, and compressing the vessels in/on the myocardium wall
Clinical: Why can heart rate reduce coronary perfusion if coronaries are diseased?
Coronaryies receive blood during diastole
High heart rate = shortened diastole
Normally, coronary arteries dilate with increased HR, but in disease states this reserve is limited
What is the primary regulator of coronary blood flow?
What are two important compounds for dilation control?
Changes in tissue metabolism
- Adenosine - Dilate coronaries when myocardium become hypoxic, or when cardiac metabolism increases during cardiac work
- Nitric Oxide - Produces flow dependent dilation
Explain Sympathetic Stimulation of the Coronaries, and Functional Sympatholysis
What is the dominant controlling mechanism in the system?
Sympathetic nerves usually cause vasoconstriction, at the heart they cause this briefly, then vasodilation
Sympathetics activation of heart increase HR/inotropy through B1 adrenoceptors, which lead to increased vasodilator metabolites that inhibit the vasoconstrictor response, and cause vasodilation (Functional Sympatholysis)
***The metabolic control of coronary flow overrides the direct coronary nervous effect within seconds***
What can be a key response to insufficient coronary blood flow?
Collateral Vessels can help get some oxygen to myocardial tissue
What main arteries supply the brain?
How do you calculate Cerebral Perfusion Pressure (CPP)?
2x Internal Carotid (most significant)
2x Veterbral Arteries
CPP = MAP - ICP
What can lead to increases in ICP?
What can this cause?
Intracranial Bleeds, Cerebral Edema, Tumors
Can cause collaped veins, reduced blood flow
What is the most important regulator of cerebral blood flow?
Metabolism of tissue–Arterial PCO2
Increased acidity = increase blood flow
****
UNLESS there is a massive decrease in PO2 then this will trigger increased cerebral flow
What does the brain display to regulate cerebral blood flow? What can shift this?
Excellent Autoregulation!
Chronic hypertension can shift this to the right
Why does the sympathetic nervous system have little impact on the cerebral flow?
Autoregulation mechanisms can override nervous effects
Neuropeptides originating in the brain can have vasodilating (VIP, CGRP, P) or vasoconstricting (NPY) effects
What is the nature of skeletal muscle microvascular in contracting vs non contracting state?
What is the nature of blood flow?
Non-contracting = 25% perfusion of capillaries
Contracting = 100%
During repetive motions (walking) flow decreased during contraction and increases during relaction due to mechanical compression; one contraction stops there is further increase
During sustained contraction, decrease flow during contraction, followed by post-contraction hyperemic response
How is local regulation of skeletal muscle blood flow accomplished?
How is nervous control of muscle blood flow accomplished?
Decreased oxygen greatly enhances flow; causes arteriolar vasodilation–increases in adenosine, K+, lactic acid, CO2, H+ also drive vaso dilation
Sympathetic vasoconstrictor nerves dominate in resting states; upon use, flow-regulating local mechanisms assume control (above)
