Lecture 11 Control of Blood Flow Flashcards Preview

Human Physiology 1 -- Zach H. > Lecture 11 Control of Blood Flow > Flashcards

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True or False:

The more you increase metabolism, the more you increase oxygen availability.

False, the more you increase metabolism, then you decrease oxygen availability.


What effect does decreased oxygen availability have on blood vessels?

decreased oxygen availability -> blood vessel relaxation -> vasodilation


What is the definition of Vasomotion?

Cyclical opening and closing of pre-capillary sphincters.


What is reactive hyperemia?

Situation in which tissue blood flow is blocked (from seconds to hours or more) and then the blood flow is unblocked, thus yielding a blood flow increase of 4-7x that of normal blood flow.

*pathological condition


What is active hyperemia?

When any tissue becomes active, rate of blood flow increases.


What are the two types of blood flow control?

1) Acute Control

2) Long-term Control


What affect does long-term control (blood flow control) have on angiogenesis? What is the duration of long-term control?

Long-term control increases in sizes/numbers of vessels and occurs over a period of days, weeks, or months.


What are the two theories that regulate acute control of blood flow to tissues?

Vasodilator Theory

Oxygen (nutrient) Lack Theory


When looking at the regulation of blood flow to tissues under-control by the vasodilator theory, what would have to happen to simulate the formation of vasodilators? Vasodilators like adenosine, CO2, Histamine, K, and H+ ions.

Metabolism would have to increase, thus decreasing oxygen availability, which stimulates the formation of vasodilators.


In the oxygen (nutrient) lack theory that refers to blood flow control to tissues, what stimulates blood vessel relaxation, and thus vasodilation to increase blood flow to a specific tissue?

Decrease in Oxygen Concentration.


Fill in the Blank:

The number of _______ _______ open at any given time is roughly proportional to nutritional requirements of tissues.

The assumption is that _____ _____ require oxygen to remain contracted.

pre-capillary sphincters

smooth muscles


At 100% arterial oxygen saturation blood flow is normal. Once arterial oxygen saturation drops to 25%, how many times greater is the blood flow to that hypoxic tissue?

3 times great blood flow to that tissue.


Does autoregulation have any affect on blood pressure, or is it just regulatory of blood flow to tissues?

Autoregulation does not return blood pressure back to normal. It just regulates blood flow to tissues.

*Within minutes, blood flow returns to normal even with elevated pressure.


What are the two theories used to look at blood flow autoregulation?

Metabolic Theory

Myogenic Theory


Explain the underlying mechanism behind the metabolic theory and how autoregulation of blood flow works.

Have an increase in blood flow to a region of tissue. This is sensed as too much oxygen or nutrients to a region of tissue, thus resulting in the wash out of vasodilators. Resulting in vasoconstriction and reduced blood flow to that region of tissue.


Explain the mechanism of myogenic theory and how it's involved in autoregulation of blood flow to a region of tissue.

The vessels in the region of tissue experiencing increased blood flow sensing stretching of the vessels. This in turn stimulates reactive vasculature constriction and the blood flow to that region of tissue is decreased.


Why does the long-term control of blood flow through a muscle remain mostly constant after autoregulation than does acute control of blood flow through a muscle after autoregulation?

Due to increase in number and size of capillaries and arterioles in the long-term control mechanism.


What is the special acute blood flow control mechanism in the kidneys? What does it involve?

Special acute blood flow mechanism is tubuloglomerular feedback

Involves the macula densa/juxtaglomerular apparatus


What is the special acute blood flow control mechanism in the brain?

There is an initial increase in CO2 and/or H+ -->
(note: this increase can be caused by increase in metabolism or a blockage of blood flow to the brain)

This causes cerebral vessel dilation -->

Causes washing out of excess CO2 / H+


What is the special acute blood flow control mechanism in the skin?

This is the system that controls body temperature by regulating blood flow.

Involves sympathetic nerves via CNS

3 ml/min/100 g tissue --> 7-8 L/min for entire body


What is endothelin and what action does it have on damaged cells?

Endothelin is a 21 amino acid long peptide that causes vasoconstriction.


What kind of cell produces nitric oxide (NO)?

Endothelial cells produce NO


Nitric oxide, along with what enzyme, activates cGTP -> cGMP?

soluble guanylate cyclase


In which cell type does cGTP get converted to cGMP?

Vascular Smooth Muscle Cells


What does cGMP activate to cause vasodilation in the endothelial cell?

cGMP activates protein kinases


Why is it so dangerous when there is damage to endothelial cells?

Hypertension can cause damage to endothelial cells, which in turn leads to the release of endothelin. Endothelin causes vasoconstriction and the damage of endothelial cells ceases the release of NO into the smooth muscle cells. Thus, cGTP is not converted to cGMP and vasodilation does not occur.


Which enzyme mediates the conversion of oxygen + L-Arginine to NO + L-Citrulline?

eNOS (nitric oxide synthetase; NO has half-life of 6 seconds)


Does norepinephrine and epinephrine control vasodilation or vasoconstriction?



Which vasoconstriction molecule normally acts to increase the total peripheral resistance?

Angiotensin II


True or False:

Vasopressin is a very powerful vasoconstrictor and has a major function to control fluid volumes via the kidney.


aka = ADH