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How does the CNS regulate blood flow?

innervation of blood vessels is mainly via sympathetic vasoconstrictor fibers, primarily NOR

- innervation varies among vessels and capillaries are not at all


Which vessels are highly sympathetically innervated?

-skeletal muscle


Which vessels are sparsely sympathetically innervated?

-coronary vessels

most auto-regulated tissues


Describe the relationship between sympathetic activity (x) and vascular resistance (y).

sympathetic activity is never zero (tonic) on a vessel which allows the system to change quickly

this curve is concave down and asymptotically reaches a limit


What humoral factors regulate BF?

-Epi and Nor are released from adrenal medulla via sympathetic stimulation and interact with alpha and beta adrenergic receptors


What do alpha receptors do? beta?

alpha mediate vasoconstriction and beta mediate dilation


What is angiotensin II?

an oligopeptide that constricts both arteries and veins. Its involved in regulation of arterial pressure and plasma volume. It has a direct vasoconstrictor effect on blood vessels and it directs kidneys to decrease urine output


What is vasopressin?

an oligopeptide that regulates plasma volume by directing kidneys to decrease urine output. At high levels, it also constricts arteries and veins, particularly in the GI area


What effect do bradykinin and histamine have?

vasodilation and increase vascular permeability.


What effect do prostaglandins have?

PGI2 and PGE2 are vasodilators and TxA2 is a vasoconstrictor


What is atrial natriuretic peptide?

an oligopeptide that is released from atrial myocytes and that directs the kidneys to increase urine output


What is NO derived from and how does it regulate BF?

arginine; it decreases intracellular calcium levels and induces vasodilation in large vessels upstream of hyperemia tissue


What is rarefaction?

decreasing the number of blood vessels- long term mechanism like angiogenesis


T or F In humans, angiogenesis does not occur at a high level

T, except in neoplastic tumors


What is hyperopic vascular remodeling?

long term mechanism of regulating blood flow by increasing wall thickness and decreasing the vascular lumen


What things regulate coronary blood flow?

-NOR induces vasodilation via beta2-receptors in resistance arteries in the heart
**-metabolic end products and/or altered oxygen (most important)**


How intense is the vasodilation caused by NOR in the heart?

it accounts for up to 25% of the exercise-induced vasodilation (not occurring at rest)


How is blood flow in the left ventricle different from other organs?

greatest blood flow occurs during diastole (essentially a reactive hyperemia) because contraction during systole compresses resistance arteries and increase vascular resistance. Similar but lesser effect in right heart


Why would the left side of the heart be highly susceptible to infarction?

because of perfusion problems- this problem is amplified if ventricular end-diastolic pressure is increased because cardiac perfusion will then be compromised even during diastole


T or F. During exercise, blood flow to skeletal muscle is mostly under local control



At rest, blood flow to skeletal muscle is mostly under control from what?

the sympathetic nervous system will increase constriction if blood flow drops


What controls circulation in the brain?

some sympathetic an para innervation but mostly local control (strong auto- regulation)

active hyperemia common


What are the two circulatory systems of the liver?

1) portal system- provides 1,100 ml/min BF

2) arterial system- provides 350 ml/min go BF


T or F. The spleen plays the role of reservoir of RBCs and plasma volume

T, can be released during exercise or when BP drops


How is GI circulation controlled?

-active hyperemia (local metabolites and hormones released)
-extrinsic control (by the sympathetic nervous system)


How does GI vascular resistance change after feeding (as a function of time)?

eating stimulates sympathetics (increasing resistance) then Gi begins to digest, and you see a big drop in resistance mediated by metabolites, etc. and then after digestion normalcy is reestablished (active hyperemia)


What controls circulation to the skin?

almost entirely controlled by CNS.


How does the skin react to heat?

When temp rises, blood flow increases to the skin to dissipate it

it opens anastomosing venous plexus in subcutaneous tissue leading to increased heat dissipation


How is renal blood flow regulated?

-high degree of auto regulation of both BF and GFR
-heavily invested with sympathetic fibers. Increased sympathetic activity overrides auto regulation and increases renal vascular resistance.