CHAPTER 6 • NEUROHUMORAL CONTROL OF THE HEART AND CIRCULATION
143
baroreceptors, which leads to reflex
activation of sympathetic influences
acting on the heart and blood vessels
and withdrawal of the vagal activity to
the heart.
*
Peripheral chemoreceptors (e.g.,
carotid bodies) and central
chemoreceptors (e.g., medullary
chemoreceptors) respond to decreased
P02 and pH or increased PC02 of the
blood. Their primary function is to
regulate respiratory activity, although
chemoreceptor activation generally
leads to activation of the sympathetic
nervous system to the vasculature,
which increases arterial pressure.
*
Reflexes triggered by changes in
blood volume, cerebral and myocardial
ischemia, pain, pulmonary activity,
muscle and joint movement, and
temperature alter cardiac and vascular
function.
*
Sympathetic activation of the
adrenal medulla stimulates
the release of catecholamines,
principally epinephrine. This
hormone produces cardiac
stimulation (via ^-adrenoceptors),
and it either decreases (via vascular
P2-adrenoceptors) or increases (via
vascular a,- and a2-adrenoceptors)
systemic vascular resistance,
depending upon the plasma
concentration.
The renin-angiotensin-aldosterone
system plays a major role in regulating
renal excretion of sodium and water.
The overall systemic effect of increased
angiotensin II is increased blood
volume, venous pressure, and arterial
pressure.
Atrial natriuretic peptide (ANP), which
is released by the atria primarily in
response to atrial stretch, functions as
a counterregulatory mechanism for the
renin-angiotensin-aldosterone system.
Therefore, increased ANP reduces
blood volume, venous pressure, and
arterial pressure.
Arginine vasopressin (AVP; antidiuretic
hormone), which is released by the
posterior pituitary when the body
needs to reduce renal loss of water,
enhances blood volume and increases
arterial and venous pressures. At high
plasma concentrations, AVP constricts
resistance vessels.
REVIEW QUESTIONS
For each question, choose the one best
answer:
1.
The cell bodies for the preganglionic
vagal efferents innervating the heart are
found in which region of the brain?
a. Cortex
b. Hypothalamus
c. Medulla
d. Nucleus tractus solitarius
2.
Norepinephrine released by sympathetic
nerves
a.
Binds preferentially to ß2-adrenoceptors
on cardiac myocytes.
h. Constricts blood vessels by binding to
oq-adrenoceptors.
c. Inhibits its own release by binding to
prejunctional P2-adrenoceptors.
d. Decreases renin release in the
kidneys.
3.
Stimulating efferent fibers of the right
vagus nerve
a.
Decreases systemic vascular
resistance.
h. Increases atrial inotropy.
c. Increases heart rate.
d. Releases acetylcholine, which binds to
M2 receptors.
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