Transcript Section 4

LIU Chuan Yong
刘传勇
Institute of Physiology
Medical School of SDU
Tel 88381175 (lab)
88382098 (office)
Email: [email protected]
Website: www.physiology.sdu.edu.cn
Section 4
Regulation of the Circulation
Introduction
 The aim: to regulate the blood flow of
organs to fit their metabolic requirement in
different condition.
 The regulation of blood flow are of three
major types:
 Neural
 Humoral
 Local
I. Neural Regulation of the
Circulation
1. Innervation of the Circulatory
System
 Cardiac innervation
 Innervation of blood vessels
 Sympathetic vasoconstrictor fiber
 Sympathetic vasodilator fiber
 Parasympathetic nerve fiber to
peripheral vessels
Cardiac innervation
 Sympathetic nerve – noradrenergic fiber
 Parasympathetic nerve- cholinergic fiber
 Noradrenergic sympathetic nerve
 increase the cardiac rate (positive chronotropic
effect)
 Increase the force of cardiac contraction (positive
inotropic effect).
 Cholinergic vagal cardiac fibers decrease the
heart rate.
Cardiac innervation (contin.)
 At rest
 moderate amount of tonic
discharge in the cardiac
sympathetic nerves
 a good deal of tonic vagal discharge
(vagal tone)
 When the vagi are cut in experiment
animals, the heart rate rises
Innervation of blood vessels
 Sympathetic
vasoconstrictor fiber
 Distribution: Almost all
segments of the
circulation.
 The innervation is
powerful in the kidneys,
gut, spleen and skin,
 is less potent in both
skeletal and cardiac muscle
and in the brain.
Innervation of blood vessels
Sympathetic vasoconstrictor fiber
(contin.)
Almost all vessels, such as arteries, arterioles,
venules and veins are innervated,
except the capillaries, precapillary sphincters and
most of the metarterioles.
Tone: Usually the sympathetic vasoconstrictor
fibers keep tonic.
Innervation of blood vessels
 2) Sympathetic vasodilator fiber
 The sympathetic nerves to skeletal muscles
carry sympathetic vasodilator fibers as well as
constrictor fibers.
 release acetylcholine at their endings and
cause vasodilation.
 Importance: increase the blood flow in
skeletal muscle during exercise and stress.
Innervation of blood vessels
 3) Parasympathetic nerve fiber to peripheral
vessels
 Parasympathetic nerve fibers innervate vessels
of the blood vessels in





Meninges (脑膜, 髓膜)
the salivary glands
the liver
the viscera in pelvis
the external genitals
 Importance: Regulate the blood flow of these
organs in some special situations.
2 Cardiovascular Center
 The control center of cardiovascular
activities is the nucleus groups at different
levels






spinal cord
brain stem
hypothalamus
limbic system
cerebral cortex
cerebellum
Cardiovascular Center
 if the brain is sectioned at the level of
the lower pons
 the blood pressure falls
 If the section at the level of the obex
 the fall in blood pressure is more
profound
Cardiovascular centers of the brainstem
 Medulla
oblongata is
essential to
Cardiovascula
r centers.
Cardiovascular centers of the
brainstem
 vasoconstrictor-area
 vasodilator area
 cardioinhibitory area
 relay station of afferent nerve
1．Rostral ventrolateral
medulla,
rVLM
(Vasoconstrictor area)：
2. Caudal ventrolateral
medulla, cVLM
（Vasodilator area）
3． NTS (nucleu of solitary
tract relay station of
afferent nerve)
4． Cardioinhibitory area
1). vasoconstrictor-area (rVLM)
(neurotransmitter: NE neurons)
(l) the cardiac sympathetic center
(2) the sympathetic vasoconstrictor center
2).vasodilator area (cVLM) (NE
neurons)
to inhibit action of rVLM area → vasodilation
3).cardioinhibitory area
(dorsal vagal nucleus and nucleus ambigulus) the cardial
vagus center
4).relay station of afferent nerve
NTS (nucleu of solitary tract) to accept and integrate
afferent impulses and then affect other centers
3. Reflex Regulation of the
Circulation
 Baroreceptor reflexes
 Reflex involving arterial
chemoreceptors
 CNS ischemic response
(1) Baroreceptor reflexes
1) Physiological anatomy of the baroreceptors.
Carotid sinus
 At the bifurcation of
the common carotid
arteries
 the root of internal
carotid artery shows a
little bulge
 has stretch receptors
in the adventitia
 are sensitive to arterial
pressure fluctuations
Carotid sinus.
(contin.)
 Afferent nerves travel
in the carotid sinus
nerve
 a branch of the
glossopharyngeal nerve.
(IXth cranial nerve)
Aortic arch.
baroreceptors
in the adventitia of the arch of aorta
Function
 similar to the carotid sinus receptors.
afferent nerve fibers travel in the aortic nerve,
a branch of the vagus nerve. (Xth cranial nerve)
2) buffer nerves
 Buffer nerves
 The carotid sinus nerves
and vagal fibers from the
aortic arch
 At normal blood pressure
levels, the fibers discharge
at a low rate.
 When the pressure rises,
the discharge rate increases
 when the pressure falls, the
rate declines
Sinus Nerve response to Blood Pressure
 At 0 – 60 mmHg, no
sensitive (aortic
baroreceptors, 030mmHg).
 Between 60 to 80
mmHg: respond
progressively more
and more strongly.
 At 100 mmHg: The
response is the
greatest
 Above 180 mmHg: no
further increase in
response .
3) Relationship between the isolated carotid
sinus pressure and the blood pressure
 Raising the carotid sinus pressure leads to a
fall in arterial blood pressure.
 Lowering the carotid sinus pressure leads to a rise
in arterial blood pressure
CSP, carotid sinus pressure; FABP, femoral artery blood
pressure
 Set point: The point where the carotic sinus
(isolated) pressure and blood pressure are the same.
4) Concept and mechanism of
baroreceptor reflex
Any drop in systemic arterial pressure
decreases the discharge in the buffer nerves,
there is a compensatory rise in blood pressure
and cardiac output.
On the contrary the opposite
Arterial
Baroreceptor
Pressure
Vasoconstrictor Center
Cardio-acceleratory Area
Carotid Sinus
Sinus Nerve
Aortic Arch
Vagus Nerve
Peripheral Vascular Dilation
Heart Rate
Contractility
Cardio-inhibitory Area +
Peripheral Resistance ( R)
Cardiac Output (Q)
Arterial pressure decrease back
towards normal
(5) Importance of the baroreceptor
reflex
 Tonic regulation of blood pressure
 keep the arterial pressure relatively constant
 Pressure buffer system – reduce the blood
pressure fluctuation during the daily events,
such as changing of the posture, respiration,
excitement, and so forth.
(6) Baroreceptor Resetting
 Baroreceptor will adapt to the long term change
of blood pressure.
 if the blood pressure is elevated for a long period of
time, several days or years, the set point will transfer
to the elevated mean blood pressure.
 baroreceptor reflex is not a long term control
system.
 unimportant for long-term regulation of arterial
pressure
(2) Reflex involving arterial chemoreceptors
 Chemoreceptors: situated in the carotid body
and aortic body
Reflex involving arterial chemoreceptors
(contin.)
• have a very rich blood supply,
• ideal for sampling chemical changes in the blood.
• sensitive to the decreased Po2, increased PCO2 and
increased hydrogen ion concentration in the plasma.
• Afferent:
• carotid body afferent fiber - carotid sinus nerve --glossopharyngeal nerve.
• Aortic body afferent fiber - aortic nerve – vagus nerve
Reflex involving arterial chemoreceptors
(contin.)
Response: Stimulation of chemoreceptors
leads to a reflex increase in vasomotor tone,
causes generalized vasoconstriction and
hence a rise in blood pressure.
Importance: is important in regulation of
blood pressure when it fall below the range
in which baroreceptors act (70 mmHg).
(3) CNS ischemic response
 Chemoreceptor reflex:
 useful in regulation of blood pressure when it
falls to a level between 40 and 70 mmHg.
 But if the blood pressure below 40 mmHg,
the last ray of hope for survival is the
central nervous system (CNS) ischemia
response.
 the “last ditch stand” pressure control
mechanism.
CNS ischemic response
(contin.)
evoked by ischemia (poor blood flow) of the
central nervous system.
Reduction in blood flow to the VMC leads to
 reduced Po2
 elevated Pco2
stimulate the VMC directly, leading to
vasoconstriction and consequently rise in blood
pressure.
II Chemical and hormonal control
of cardiovascular function
Introduction
Various hormones, chemicals
Start at a low pace,
Have long-lasting influences
Classification
Vasoconstrictors
Vasodilators
Vasoconstrictors and Vasodilators
 Vasoconstrictors
 Epinephrine and Norepinephrine
 Angiotensin II
 Vasopressin
 Vasodilators
 EDRF (NO)
Epinephrine and Norepinephrine
 The adrenal medulla secrete both
epinephrine (80%) and norepinephrine
(20%)
 carried by blood flow to everywhere in the
body.
 In the blood, only a little norepinephrine
comes form the endings of the adrenergic
fibers.
Adrenergic receptors
Epinephrine
Norepinephrine
α1 receptor on vessels
Vasoconstriction
β1 receptor on heart
Positive effect
β2 receptor on vessels
(skeletal muscle and liver)
Vasodilation
Effect
 On heart in vitro (contractility and
automaticity).
 both increase the force and rate of
contraction of the isolated heart.
 mediated by β1 receptors.
Effect
 On peripheral resistance
 Norepinephrine produces
vasoconstriction in most if
not all organs via α1
receptors
 epinephrine dilates the blood
vessels in skeletal muscle
and the liver via β2
receptors
 overbalances the
vasoconstriction produced by
epinephrine elsewhere
 the total peripheral resistance
drops
Nor: On heart in vivo
 Ps and Pd increase –
barorecepor reflex –
bradycardia –
override direct
cardioacceleratory
effect
 the heart rate and
cardiac out falls.
 Epi: On heart in
vivo
 causes a widening of
the pulse pressure
 baroreceptor
stimulation is
insufficient to
obscure the direct
effect of the hormone
on the heart,
 cardiac rate and
output increase.
Angiotensin II
 very potent vasoconstrictor
 formed in the plasma through a chain reaction.
 triggered by a substance, renin, released form kidneys.
 Renin is released from kidneys in response to renal
ischemia, which may be due to a fall in blood pressure.
Effect of Angiotensin II
 powerful constrictor
 release aldosterone from the
adrenal cortex
 acts on the brain to create the
sensation of thirst.
 inhibit the baroreceotor reflex
and
 increase the release of
norepinephrine from the
sympathetic postganglionic
fiber.
Vasopressin
 antidiuretic hormone (ADH),
 formed in the hypothalamus (mainly)
 secreted through the posterior pituitary gland.
more powerful than angiotensin as a
vasoconstrictor.
 during hemorrhage – increased
vasopressin - raise the arterial pressure as
much as 40 to 60 mmHg.
Vasopressin
 Vasoconstriction has not a physiological
function
 does not increase blood pressure when small
doses are injected in vivo
 In healthy person, the plasma concentration is
too low to induce vasoconstrion
 Acts on the brain to cause a decrease in
cardiac output.
 in the area of postrema
 Acts on the kidney – physiological (ADH)
Endothelium – Derived Relaxing Factor
 Metabolism
Effect of NO
 Relax the vascular smooth muscle directly
 Mediate vascular dilator effect of some hormones
and transmitters (Ach, bradykinin, VIP, substance P)
 Inhibit the tonic excitation of some neurons in the
vasomotor centre.
 Inhibit the norepinephrine release from the
sympathetic postganglionic fiber.
 One or more of these effects are
physiological.
III Autoregulation of Local Blood
Pressure
 Role of Vasodilator Substances.
 CO2, Lactic acid, Adnosine, Adnosine phosphate
compounds, Histamine, K+ and H+
 Myogenic Activity
 Heterometric autoregulation