Download CV-4-2014

Cardiovascular
Physiology
Qiang XIA (夏强), MD & PhD
Department of Physiology
Room C518, Block C, Research Building, School of Medicine
Tel: 88208252
Email: [email protected]
Regulation of Cardiovascular Activities
Lecture Outline
•Nervous Regulation
•Humoral Regulation
•Autoregulation
Nervous Regulation
Innervation of cardiovascular system
Nervous regulation of the circulation
Cardiac mechanisms of norepinephrine
Mechanisms of norepinephrine
—increase Na+ & Ca2+ permeability
• If , phase 4 spontaneous depolarization,
autorhythmicity 
• Ca2+ influx , phase 0 amplitude & velocity ,
conductivity 
• Ca2+ influx , Ca2+ release , [Ca2+ ]i , contractility 
Asymmetrical
innervation of
sympathetic nerve
Cardiac mechanisms of acetylcholine
Mechanisms of acetylcholine
—increase K+ & decrease Ca2+ permeability
• K+ outward , |MRP| , phase 4 spontaneous
depolarization , autorhythmicity 
• Inhibition of Ca2+ channel, phase 0 amplitude &
velocity , conductivity 
• Ca2+ influx , [Ca2+ ]i , contractility 
Cardiac effect of
parasympathetic
stimulation
Interaction of
sympathetic and
parasympathetic
nerves
Predominance of autonomic nerves
Cardiovascular Center
A collection of functionally similar neurons that
help to regulate HR, SV, and blood vessel tone
Vasomotor center
Located bilaterally mainly in the reticular
substance of the medulla and of the lower third
of the pons
– Vasoconstrictor area
– Vasodilator area
– Cardioinhibitor area – dorsal nuclei of the
vagus nerves and ambiguous nucleus
– Sensory area – tractus solitarius
Vasomotor center
Higher cardiovascular centers
– Reticular substance
of the pons
– Mesencephalon
– Diencephalon
– Hypothalamus
– Cerebral cortex
– Cerebellum
Baroreceptor Reflexes
• Arterial baroreceptors
– Carotid sinus receptor
– Aortic arch receptor
• Afferent nerves (Buffer nerves)
• Cardiovascular center: medulla
• Efferent nerves: cardiac sympathetic nerve,
sympathetic constrictor nerve, vagus nerve
• Effector: heart & blood vessels
Baroreceptor neurons
function as sensors in
the homeostatic
maintenance of MAP
by constantly
monitoring pressure
in the aortic arch and
carotid sinuses.
Characteristics of baroreceptors:
Sensitive to stretching of the vessel walls
Proportional firing rate to increased
stretching
Responding to pressures ranging from 60180 mmHg
Receptors within the aortic arch are less
sensitive than the carotid sinus receptors
The action potential frequency in baroreceptor neurons is
represented here as being directly proportional to MAP.
i.e., MAP is
above
homeostatic
set point
i.e., reduce cardiac output
Baroreceptor neurons deliver MAP information to the
medulla oblongata’s cardiovascular control center (CVCC);
the CVCC determines autonomic output to the heart.
Reflex pathway
Typical carotid sinus reflex
Physiological Significance
Maintaining relatively
constant arterial
pressure, reducing the
variation in arterial
pressure
Humoral Regulation
• Vasoconstrictor agents
• Vasodilator agents
Renin-angiotensin system
Juxtaglomerular
cell
Renin
Physiological effects of angiotensin II
– Constricts resistance vessels
– Acts upon the adrenal cortex to release aldosterone
– Stimulates the release of vasopressin
– Facilitates norepinephrine release from sympathetic nerve
endings
– Stimulates thirst centers within the brain
Epinephrine & Norepinephrine
• Sources
Epinephrine---adrenal medulla
Norepinephrine----
adrenal medulla
sympathetic nerves
Catecholamines
Norepinephrine
Epinephrine
Effects
Receptor
Heart
Vessels
Epinephrine
Norepinephrine
a-adrenoceptor
++
+++
b-adrenoceptor
++
+
heart rate
+
cardiac output
+++
+ (in vitro) － (in vivo)
±
constriction (skin, visceral) +
+++
－
+++
relaxation (SM, liver)
total peripheral resistance ±
Blood pressure systolic
+++
+++
+++
diastolic
±
++
MAP
+
++
Clinical application
positive inotropic
agent
pressor agent
A 23-year-old woman presents to your emergency
service with an anaphylactic reaction after being stung
by several bees. She complains of wheezing and
shortness of breath. On examination, the client is in
acute distress. BP is 98/56 mmHg, PR 110/min, RR
28/min, and temperature 98.7°F. She is immediately
treated with supplemental oxygen. In treating this
condition further, what drug is required most urgently?
A Theophylline
B Glucagon
C Cimetidine
D Methylprednisolone
E Epinephrine
Vasopressin (antidiuretic hormone, ADH)
Endothelium-derived vasoactive substances
•Vasodilator factors
PGI2--prostacyclin
EDRF, NO--endothelium-derived relaxing factor, nitric oxide
EDHF--endothelium-dependent hyperpolarizing factor
•Vasoconstrictor factors
Endothelin
Atrial natriuretic peptide (ANP)
•Produces natriuresis and diuresis
•Decreases renin release
•Reduces total peripheral resistance via vasodilatation
•Decreases heart rate, cardiac output
Autoregulation
Definition:
Intrinsic ability of an organ to maintain a constant
blood flow despite changes in perfusion pressure,
independent of any neural or humoral influences
The End.