Title: LIU Chuan Yong
1LIU Chuan Yong ??? Institute of
Physiology Medical School of SDU Tel 88381175
(lab) 88382098 (office) Email
liucy_at_sdu.edu.cn Website www.physiology.sdu.edu.c
n
2Section 4
- Regulation of the Circulation
3Introduction
- The aim of the circulatory regulation is 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
4Neural control of blood flow
- affects blood flow in large segments of the
systemic circulation, - shifting blood flow from the non-muscular
vascular bed to the muscles during exercise - changing the blood flow in the skin to control
body temperature.
5Humoral control
- hormones, ions, or other chemicals in blood
- cause either local increase or decrease in tissue
flow - or widespread generalized changes in flow.
6Local control of blood flow
- in each individual tissue,
- the flow being controlled mainly in proportion to
that tissues need for blood perfusion
7I. Neural Regulation of the Circulation
81. Innervation of the Circulatory System
- Cardiac innervation
- Innervation of blood vessels
- Sympathetic vasoconstrictor fiber
- Sympathetic vasodilator fiber
- Parasympathetic nerve fiber to peripheral vessels
9Cardiac innervation
- Sympathetic nerve noradrenergic fiber
Parasympathetic nerve- cholinergic fiber - Noradrenergic sympathetic nerve
- to the heart increase the cardiac rate
(chronotropic effect) - the force of cardiac contraction (inotropic
effect). - Cholinergic vagal cardiac fibers decrease the
heart rate.
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11Cardiac innervation (contin.)
- moderate amount of tonic discharge in the cardiac
sympathetic nerves at rest - a good deal of tonic vagal discharge (vagal tone)
in humans - When the vagi are cut in experiment animals, the
heart rate rises
12Innervation 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.
13Innervation 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.
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17Innervation of blood vessels
- 2) Sympathetic vasodilator fiber
- The sympathetic nerves to skeletal muscles carry
sympathetic vasodilator fibers as well as
constrictor fibers. - In animals, such as the cat, dog, these
sympathetic vasodilator fibers release
acetylcholine at their endings and cause
vasodilation. - Importance increase the blood flow in skeletal
muscle during exercise and stress.
18Innervation of blood vessels
- 3) Parasympathetic nerve fiber to peripheral
vessels - Parasympathetic nerve fibers innervate vessels of
the blood vessels in - Meninges (??, ??)
- the salivary glands,
- the liver
- the viscera in pelvis
- the external genitals.
- Importance Regulate the blood flow of these
organs in some special situations.
192 Cardiovascular Center
- The control center of cardiovascular activities
is the nucleus groups at different levels for
controlling cardiovascular activities, - including
- spinal cord,
- brain stem,
- hypothalamus,
- limbic system,
- cerebral cortex
- cerebellum.
20Cardiovascular Center
- if the brain of an anesthetized animal is
sectioned at the level of the lower pons, the
blood pressure falls. - If the section is made at the level of the obex,
the fall in blood pressure is more profound.
21Cardiovascular centers of the brainstem
- Medulla oblongata is essential to Cardiovascular
centers.
22Cardiovascular centers of the brainstem
- vasoconstrictor-area
- vasodilator area
- cardioinhibitory area
- relay station of afferent nerve
231.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
24- 1). vasoconstrictor-area (rVLM)
(neurotransmitter NE neurons) - (l) the cardiac sympathetic center
- (2) the sympathetic vasoconstrictor center
25- 2).vasodilator area (cVLM) (NE neurons)
- to inhibit action of Cl area ? vasodilation
263).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
273. Reflex Regulation of the Circulation
- Baroreceptor reflexes
- Reflex involving arterial chemoreceptors
- CNS ischemic response
28(1) Baroreceptor reflexes
- 1) Physiological anatomy of the baroreceptors.
29Carotid 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
30Carotid sinus.(contin.)
- Afferent nerves from these stretch receptors
travel in the carotid sinus nerve - which is a branch of the glossopharyngeal nerve.
(IXth cranial nerve)
31Aortic arch.
- baroreceptors are also present in the adventitia
of the arch of aorta - have functional characteristics similar to the
carotid sinus receptors. - their afferent nerve fibers travel in the aortic
nerve, - which is a branch of the vagus nerve. (Xth
cranial nerve)
322) buffer nerves activity
- The carotid sinus nerves and vagal fibers from
the aortic arch are commonly called the buffer
nerves - At normal blood pressure levels, the fibers of
the buffer nerve discharge at a low rate. - When the pressure in the sinus and aortic arch
rises, the discharge rate increases - when the pressure falls, the rate declines.
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34Sinus Nerve response to Blood Pressure
- The carotid sinus baroreceptors are not
stimulated by intrasinus pressure between 0 60
mmHg (aortic baroreceptors, 0-30mmHg). - Between 60 to 80 mmHg, the carotid sinus
baroreceptors respond progressively more and more
strongly. - The response is the greatest at pressure level
near the normal mean arterial pressure (100
mmHg). - At sinus pressure above 180 mmHg, there is no
further increase in response .
353) Relationship between the isolated carotid
sinus pressure and the blood pressure
- Raising the carotid sinus pressure leads to a
fall in arterial blood pressure.
36- Lowering the carotid sinus pressure leads to a
rise in arterial blood pressure
CSP, carotid sinus pressure FABP, femoral artery
blood pressure
37- Set point The point where the carotic sinus
(isolated) pressure and blood pressure are the
same.
384) Concept and mechanism of baroreceptor reflex
- Any drop in systemic arterial pressure decreases
the discharge in the buffer nerves, - and there is a compensatory rise in blood
pressure and cardiac output. - Any rise in blood pressure produce dilation of
the arterioles and decreases cardiac output until
the blood pressure returns to its previous normal
level.
39Carotid Sinus Aortic Arch
Sinus Nerve
Arterial Pressure
Baroreceptor
Vagus Nerve
Vasoconstrictor Center
Peripheral Vascular Dilation
Cardio-acceleratory Area
Heart Rate Contractility
Cardio-inhibitory Area
Peripheral Resistance ( R)
Arterial pressure decrease back towards normal
Cardiac Output (Q)
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43(5) Importance of the baroreceptor reflex
- To keep the arterial pressure relatively constant
- Through short term regulation of blood pressure
in the rang of 70 mmHg to 150 mmHg, maintain the
mean blood pressure at about 100 mmHg - Tonic regulation of blood pressure
- Pressure buffer system reduce the blood
fluctuation during the daily events, such as
changing of the posture, respiration, excitement,
and so forth.
44(6) Baroreceptor Resetting
- Baroreceptor will adapt to the long term change
of blood pressure. - That is, 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. - Obviously, the adaptation of the baroreceptor
prevents the baroreceptor reflex from acting as a
long term control system. - That makes the baroreceptor system unimportant
for long-term regulation of arterial pressure
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46(2) Reflex involving arterial chemoreceptors
- Chemoreceptors situated in the carotid body and
aortic body
47- They have a very rich blood supply,
- which make them ideal for sampling chemical
changes in the blood. - Chemoreceptors are sensitive to the decreased
Po2, increased PCO2 and increased hydrogen ion
concentration in the plasma. - Afferent
- Afferent nerve fibers form the carotid body
travel in the carotid sinus nerve, which is a
branch of glossopharyngeal nerve. - Aortic body is innervated by the aortic nerve,
which is a branch of the vagus
48- Response Stimulation of chemoreceptors leads to
a reflex increase in vasomotor tone, - which causes generalized vasoconstriction and
hence a rise in blood pressure. - Importance Chemoreceptor mechanism is important
in regulation of blood pressure when it fall
below the range in which baroreceptors act (70
mmHg).
49(3) CNS ischemic response
- Chemoreceptor reflex is 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. - So it sometimes called the last ditch stand
pressure control mechanism.
50- As the name indicates, it is evoked by ischemia
(poor blood flow) of the central nervous system. - CNS ischemia reduces blood flow to the vasomotor
centre (VMC). - Reduction in blood flow to the VMC leads to
reduced Po2 and elevated Pco2 in the medulla
region. - Both these factors stimulate the VMC directly,
leading to vasoconstriction and consequently rise
in blood pressure.
51II Chemical and hormonal control of
cardiovascular function
52Introduction
- Various hormones, chemicals
- Start at a low pace,
- Have long-lasting influences on cardiovascular
function. - Hormones and chemicals are classified into two
groups - Vasoconstrictors
- Vasodilators
53Vasoconstrictors and Vasodilators
- Vasoconstrictors
- Epinephrine and Norepinephrine
- Angiotensin II
- Vasopressin
- Vasodilators
- EDRF (NO)
54Epinephrine 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.
55Adrenergic receptors
a1 receptor on vessels ß1 receptor on heart ß2
receptor on vessels (skeletal muscle and liver)
Vasoconstriction Positive effect Vasodilation
Epinephrine Norepinephrine
56Effect
- On heart in vitro (contractility and
automaticity). - both increase the force and rate of contraction
of the isolated heart. - mediated by ß1 receptors.
57Effect
- On peripheral resistance.
- Norepinephrine produces vasoconstriction in most
if not all organs via a1 receptors - epinephrine dilates the blood vessels in skeletal
muscle and the liver via ß2 receptors. - overbalances the vasoconstriction produced by
epinephrine elsewhere, and the total peripheral
resistance drops.
58Effect
- On heart in vivo (heart rate and cardiac output).
- When norepinephrine is infused introvenously
- the systolic and diastolic blood pressure rise.
- The hypertension stimulates the carotid and
aortic baroreceptors, - producing reflex bradycardia that override the
direct cardioacceleratory effect of
norepinephrine. - Consequently, the heart rate and cardiac out
falls.
59Effect
- On heart in vivo
- Epinephrine 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.
60Angiotensin II
- very potent vasoconstrictor
- formed in the plasma through a chain reaction.
- The chain is 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.
61Effect 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.
62Vasopressin
- Also called antidiuretic hormone (ADH),
- formed in the hypothalamus (mainly)
- secreted through the posterior pituitary gland.
- even more powerful than angiotensin as a
vasoconstrictor. - The high concentration of vasopressin during
hemorrhage can raise the arterial pressure as
much as 40 to 60 mmHg.
63Vasopressin
- The amount of endogenous vasopressin in the
circulation of normal individuals does not
normally affect blood pressure. - it does not increase blood pressure when small
doses are injected in vivo - Acts on the brain to cause a decrease in cardiac
output. - (in the area of postrema, one of the
circumventricular organs) - Acts on the kidney
64Endothelium Derived Relaxing Factor
65Effect 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.
66III Autoregulation of Local Blood Pressure
- Role of Vasodilator Substances.
- CO2, Lactic acid, Adnosine, Adnosine phosphate
compounds, Histamine, K and H - Myogenic Activity
- Heterometric autoregulation
67IV Long-Term mechanism for Arterial Pressure
Regulation
- Renal body Fluid Mechanism
68V Summary of the Integrated Multifaceted System
for Arterial Pressure Regulation
69Introduction
- Arterial pressure is regulated but by several
interrelated systems - each of which performs a specific function.
70If the blood pressure drops suddenly
- two problems confronts the pressure control
system - The first is survival,
- to return the arterial pressure immediately to a
high enough level - that the person can live trough the acute
episode.
71If the blood pressure drops suddenly
- The second is to return the blood volume
eventually to its normal level - so that the circulatory system can re-establish
full normality, - including return of the arterial pressure all the
way back to its normal value
72Three kind of mechanisms in regulating the blood
pressure
- react rapidly, within seconds or minutes
- respond over an intermediate time period, minutes
or hours - provide long-term pressure regulation, days,
months, and years.
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741, Rapidly Acting Pressure Control Mechanisms,
Acting Within Seconds or Minutes
- The baroreceptor feedback mechanism.
- The central nervous system ischemic mechanism.
- The chemoreceptor mechanism
75Effect of Rapidly Acting Pressure Control
Mechanisms
- To cause constriction of the veins and provide
transfer of blood into the heart. - To cause increased heart rate and contractility
of the heart and provide greater pumping capacity
by the heart - To cause constriction of the peripheral
arterioles to impede the flow of the blood out of
the arteries. - All these effects occur almost instantly to raise
the arterial pressure back into a survival range.
762. Pressure Control Mechanisms That Act After
Many Minutes
- The renin-angiotensin vasoconstrictor mechanism
- Stress-relaxation of the vasculature
- Shift of fluid through the tissue capillary wall
in and out of the circulation to adjust the blood
volume as needed.
77(1) The renin-angiotensin vasoconstrictor
mechanism
78(2) Stress-relaxation of the vasculature
- When the pressure in the blood vessels becomes
too high, - they become stretched and keep on stretching
more and more for minutes or hours - as a result, the pressure in the vessels falls
toward normal. - This continuing stretch of the vessels, called
stress-relaxation, can serve as an
intermediate-term pressure buffer.
79(3) Shift of fluid through the tissue capillary
wall in and out of the circulation
- any time the capillary pressure falls too low,
- fluid is absorbed by capillary osmosis from the
tissue into the circulation, - thus building up the blood volume and increasing
the pressure in the circulation.
80Pressure Control Mechanisms That Act After Many
Minutes
- become mostly activated within 30 minutes to
several hours. - can last for long periods, days if necessary.
- During this time, the nervous mechanisms usually
fatigue and become less and less effective
813, Long-Term Mechanisms for Arterial Pressure
Regulation
- The renal blood volume pressure control
mechanism. - Aldosterone
- Importance
- It takes a few hours to show significant response
for these mechanisms. - Return the arterial pressure all the way back.
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