cardiovascular physiology qiang xia (夏强), md & phd department of physiology room c518, block...
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Cardiovascular Physiology
Qiang XIA ( 夏强 ), MD & PhDDepartment of Physiology
Room C518, Block C, Research Building, School of MedicineTel: 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
– Reticular substance
of the pons
– Mesencephalon
– Diencephalon
– Hypothalamus
– Cerebral cortex
– Cerebellum
Higher cardiovascular centers
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 60-
180 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.
Baroreceptor neurons deliver MAP information to the medulla oblongata’s cardiovascular control center (CVCC);the CVCC determines autonomic output to the heart.
i.e., MAP is above
homeostatic set point
i.e., reduce cardiac output
Reflex pathway
Typical carotid sinus reflex
Maintaining relatively
constant arterial
pressure, reducing the
variation in arterial
pressure
Physiological Significance
Humoral Regulation
• Vasoconstrictor agents• Vasodilator agents
Renin-angiotensin system
Juxtaglomerular cell
Renin
– 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
Physiological effects of angiotensin II
Epinephrine & Norepinephrine
• Sources
Epinephrine----
adrenal medulla
Norepinephrine----
adrenal medulla
sympathetic nerves
Catecholamines
Norepinephrine
Epinephrine
Effects Epinephrine Norepinephrine
Receptor -adrenoceptor ++ +++
-adrenoceptor ++ +
Heart heart rate + + (in vitro)
- (in vivo)
cardiac output +++ ±
Vessels constriction (skin, visceral) + +++
relaxation (SM, liver) - +++
total peripheral resistance ± +++
Blood pressure systolic +++ +++
diastolic ± ++
MAP + ++
Clinical application positive inotropic pressor agent
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.