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1. Renin-angiotensin system

The renin-angiotensin system plays an important role in regulating blood volume, arterial

pressure, and cardiac and vascular function. While the pathways for the renin-angiotensin system

have been found in a number of tissues, the most important site for renin release is the kidney.Sympathetic stimulation, renal artery hypotension, and decreased sodium delivery to the distal

tubules stimulate the release of renin by the kidney. Renin is an enzyme that acts upon a

circulating substrate (angiotensinogen) to release a 10-amino acid peptide, angiotension .

Vascular endothelium, particularly in the lungs, has an enzyme, angiotensin converting enzyme

(ACE), that cleaves off two amino acids to form the octapeptide, angiotensin II (AII).

2. Baroreceptor reflex

The baroreceptor reflex is the body's rapid response system for dealing with changes in blood

pressure. This reflex is initiated by stretch receptors, called either baroreceptors or

pressoreceptors, which are located in the walls of several of the large systemic arteries. If a rise in

arterial pressure stretches the baroreceptors and causes them to transmit signals into the central

nervous system. Feedback signals are then sent back through the autonomic nervous system to

the circulation to reduce arterial pressure downward toward the normal level.

Question:

1. Outline the neural mechanisms that control arterial blood pressure and heart rate,

including the receptors, afferent and efferent pathways, central integrating

pathway, and effector mechanisms involved.(in very brief description)

(1) Autonomic nervous system;

(2) Vasomotor center;

(3) Higher nervous centers;

(4) Cardiovascular reflexes:

a. Baroreceptor reflex;

b. Chemoreceptor reflex;

c. Cardiopulmonary reflex;

d. CNS ischemic response.

2. Name the principal hormones that affect arterial blood pressure, and know the

physiologic role of each.

(1) Angiotensin II:

a. Constricts resistance vessels

b. Acts upon the adrenal cortex to release aldosterone

c. Stimulates the release of vasopressin

d. Facilitates norepinephrine release from sympathetic nerve endings

e. Stimulates thirst centers within the brain

(2) Epinephrine and norepinephrine:Effects Epinephrine Norepinephrine

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Vessels

constriction (skin, visceral) + +++

relaxation (SM, liver) +++

total peripheral resistance +++

Blood pressuresystolic +++ +++

diastolic ++

MAP + ++

(3) Vasopressin:

a. Vasoconstriction, increase of arterial pressure;

b. Antidiuretic effect.

(4) Atrial natriuretic peptide:

a. Produces natriuresis and diuresis

b. Decreases renin release

c. Reduces total peripheral resistance via vasodilatation

d. Decreases heart rate, cardiac output