Transcript Cardiovascular control mechanism

Cardiovascular control
mechanism
黃基礎
Introduction
• Control of blood volume and
arterial pressure results in
that all of the organs receive
sufficient blood flow.
Central
controller
Sensory nerve
Sympathetic nerve
Parasympathetic n
Sensor
Effector
Changes in BP
Heart and arteriole
Circulatory control system
Sensors
• The animal body employs a variety of
receptors for monitoring the status of
the cardiovascular system.
• There are two main baroreceptors
aortic baroreceptor via vagus nerve
carotid baroreptor via sinus nerve
An increase in blood pressure stretches
the wall of the carotid sinus, causing an
increase in discharge frequency from the
baroreceptors.
Chemoreceptors
Increase
in CO2
+
Chemorecpeotr
vasoconstriction
A rise in arterial pressure
Cardiac receptors
• Atrial receptors
Increase in BP
Increase in
venous pressure
Increase in
atrail filling
Stimulate the
atrial receptors
Reduction in
blood volume
Leasd to diuresis
Inhibition of
ADH release
Cardiac receptors
• Atrial receptors
Increase in BP
Increase in
venous pressure
Increase in
atrail filling
Strtch
the the atrial wall
Reduction in
blood volume
Cause an increase
In urine production
and sodium
excretuib
Cause atial myocytes
to secrete ANP
ANP
_
Renin
release
ADH
release
Reduce
Cardiac
Output
Reduce
BP
Antagonize the
pressor effect of
angiotensin
Central nervous system
• Medullaray CV center
1. Pressor and depressor center
2. Cardioaccerator center
3. Cardioinhibitory center
Central nervous system
• Autonomic nervous system (ANS)
1. Sympathetic preganglionic
fibers arise from cell bodies in
the IML of the spinal cord of the
thoracodorsal regions
• Autonomic nervous system (ANS)
2. The stellate ganglion supplies
postganglionic sympathetic fibers
to the heart
3. All of preganglionic sympathetic
fibers are cholinergic but the
postganglionic sympathetic fibers
are adrenergic or cholinergic
• Parasympathetic nervous system
1. The primary effect of the
parasym. n. s. on CV function
is to slow the heart rate.
2. Impulses conducted by the
vagus nerve affect the S-A node,
A-V node and reduce artial
contractivitility
Neural
pathways for
thr BP control
NTS: nucleus
tractus of the
solitarius
Medullary cardiovascular center
Control of microcirculation
• Capillary blood flow has to be
adjusted to meet the demands of
the tissue.
• Two control mechanisms
1. Neural control
2. Local control
Neural control of capillary blood flow
• Sympathetic stimulation and catcholamine
Stimulation of
alpha receptors
Stimulation of
beta receptors
vasodilatation
vasoconstriction
Vasoconstriction activated by  -adrenergic
receptors would override vasodilatation by  adrenergic receptors
• Neuropeptide Y
1. co-localized with norepinephrine within
sympathetic ganglion and adrenergic nerve
2. nerve endings that surrounded the atrial and
ventricular myocytes and the coronary arteries
contain neuropeptide Y
3. NPY decrease coronary blood flow and the
contraction of cardiac muscle by reducing the
level of IP3
• Parasympathetic stimulation cause to
vasodilation in arterioles
Local control of capillary blood flow
• Endothelium-produced compounds
endothelium can produce NO, endothelin,
and prostacyclin to affect the activity of the
smooth muscle and hence, to regulate the
capillary blood flow
Endothelium-derived
relacing factor
(now known NO)
cGMP
Muscle
relaxation
Local control of capillary blood flow
• Endothelin can produce vasoconstriction
prostacyclin can initiate vasodilation and
act as an anticoagulant. Prostacyclin
functions as an antagonist of the
thromboxane A2 ,which promotes blood
clotting and causes vasoconstriction.
Influammators and other mediators
thromboxane A2 cause vasoconstriction
histamine and kinin produce vasodilatation
• Histamine, bradykinin, and serotonin cause an
increase in capillary permeability
• Metabolic condition associated with activity
decrease in O2, increase in CO2, and H+, a
variety of metabolites (adenosine) , heart, rise
in extracellular K+ , NO, prostacyclin
all of the above substances produce
vasodilation and a local increase in capillary
blood flow.