Regulation of the Vasculature

Question 1

Describe general sympathetic innervation to vessels

Answer 1

Most important part of regulating circulation

Almost all vessels except capillaries are innervated in most tissues

Question 2

Describe general parasympathetic innervation to vessels

Answer 2

Regulates specific organs: Salivary glands, Pancreas, Gastric mucosa, external genetalia

Does not play a significant role in the regulation of systemic vascular resistance and arterial BP

Question 3

Describe vascular autonomic receptors

Answer 3

Alpha 1 & 2, Beta 2

NE released from sympathetic nerves preferentially binds to alpha 1 to cause vasoconstriction

Question 4

What is sympathetic vasoconstrictor tone?

Answer 4

The vasoconstrictor center of the brain continuously transmits signals to the sympathetic fibers over the entire body

Maintain a partial state of contraction in blood vessels called vasomotor tone

Question 5

Describe the baroreceptor reflex

Answer 5

Baroreceptors in the carotid sinus respond to increased or decreased stretch

Low BP: Increased sympathetic activity, Decreased PS

High BP: Decreased sympathetic activity, Increeased PS

E.g. Orthostatic hypotension elicits this reflex

Question 6

Describe the cardiopulmonary reflex

Answer 6

Low-pressure receptors located at the venoatrial junctions respond to atrial filling and contraction

Increased volume activates these receptors and causes a decrease in sympathetic activity. Also causes a decrease in ADH release

Decreased volume produces the opposite response

Question 7

Describe the chemoreceptor reflexes

Answer 7

Chemoreceptors found in carotid body and adjacent to the aortic arch increase their firing in response to fall in PO2, or increase in PCO2 or H+

Hypoxemia will cause increased sympathetic activity (and respiratory activity)

Question 8

What is the effect of both Epinephrine and NE on cardiovascular function?

Answer 8

Both can activate cardiac B1 receptors to increase heart rate and myocardial contractility

Can also activate vascular A1 receptor to cause vasoconstriction

Question 9

What are the effects of B2 adrenergic receptors?

Answer 9

Some organs possess these receptors to cause vasodilation

Vascular B2 receptors are more sensitive to epinephrine than A1 receptors

This means a moderately increased level of E can cause vasodilation, whereas higher levels can cause vasoconstriction

Question 10

What is the renin-angiotensin-aldosterone system?

Answer 10

In response to decreased blood volume or sympathetic stimulation, the kidneys activate a hormone system that ultimately causes an increase in arterial pressure

Question 11

What is atrial natriuretic peptide and what is its effect?

Answer 11

Released by atrial myocytes

Involved in long-term regulation of sodium and water balance

Counter-regulatory system for the RAA system

Question 12

Describe the action of vasopressin (ADH)?

Answer 12

Hormone released from the posterior pituitary

Two principle sites of action: kidneys and blood vessels

Increases water reabsorption and causes vasoconstriction

Question 13

How is the relative distribution of blood flow to the organs regulated?

Answer 13

The vascular resistance of the individual organs which is influenced by neurohumoral and local regulatory mechanisms

Question 14

How does metabolism influence blood flow?

Answer 14

Increase in metabolism increases blood flow

Decrease in the oxygen availability to tissues increases blood flow

Question 15

What is the vasodilator theory?

Answer 15

The greater the rate of metabolism, the greater the rate of formation of vasodilator substances in tissue cells

Adenosine, CO2, K, H

Question 16

What is the oxygen lack theory?

Answer 16

Absence of adequate oxygen as a result of increased metabolism causes the blood vessels to relax and dilate

Question 17

What is reactive hyperemia?

Answer 17

Transient increase in organ blood flow that occurs following a brief period of ischemia, usually produced by temporary arterial occlusion

Question 18

What is active hyperemia?

Answer 18

Increase in organ blood flow that is associated with increased metabolic activity of an organ or tissue

Subsides when normal activity is restored

Question 19

What is the role of histamine is local regulation?

Answer 19

Released in response to damage of inflamed

Has a vasodilator effect on the arterioles and the ability to increase capillary permeability

Question 20

What is the role of bradykinin in local regulation?

Answer 20

Formed in blood tissue in response to inflammation

Causes both arterioloar dilation and increased capillary permeability

Also plays a normal role in skin, salivary and gastrointestinal glands

Question 21

What are the roles of endothelial-derived factors?

Answer 21

NO: vasodilators

Endothelial derived hyperpolarizing factor: Vasodilators

Endothelin-1: vasoconstrictors

Arachidonic acid metabolites - Prostacyclin (PGI2): vasodilators

Thromboxanes and leukotrienes: vasoconstrictors

Question 22

What is the myogenic response?

Answer 22

Smooth muscle contraction in response to sudden lumen expansion

Smooth muscle relaxation in response to sudden lumen constriction

Attempt to restore pressure change

Question 23

What is autoregulation?

Answer 23

Intrinsic ability of an organ to maintain a constant blood flow despite changes in perfusion pressure

Autoregulation has limits even in organs that exhibit it to a high degree i.e. pressure can go outside of a range in which autoregulation is effective

May involve both metabolic and myogenic mechanism

Question 24

How does autoregulation vary among organs?

Answer 24

High degere: Coronary circ., Cerebral circ, Renal circ

Moderate: Skeletal muscle circ, GI circ

None: Cutaneous

Question 25

What conditions causes autoregulation to occur and why is it important?

Answer 25

Hypotension - blood flow to the brain and myocardium will not decline appreciably due to their strong capacity for autoregulation

Partial artery occlusion