Download SECTION 3 VASCULAR PHYSIOLOGY Ⅰ. Functional properties of

SECTION 3 VASCULAR
PHYSIOLOGY
Ⅰ. Functional properties of
different blood vessels
1. Artery:
Aorta and large artery
Pressure reservoir vessels
1.Elastic reservoir vessels:
Systole: store of energy
↑
Elastic fiber elasticity
Stretched
Distensibility Distole: release of energy
recoil maintain distolic←→kinetic energy
elastic reservoir pressure
intermittent flow → continuous flow
Middle artery:
carry blood to arterioles
distribution vessels
Small artery and arteriole:
resistance vessels are regulated
by neurohumoral factors
Control of capillary blood flow
2. Capillary vessels: exchange vessels
Exchange of substances between
blood and interstitial fluid.
Precapillary sphincter.
Control of inflow of capillaries
A-V shunt (anastomosis)
Blood flow from arteriole to
venules by passing capillary.
3. Venous Vessels, capacitance
vessels: large vein, vena cava.
Blood reservoir
big compliance, low mean
venous pressure, low
resistance vessels
Venous valve; venule.
Ⅱ.Blood flow, resistance to blood
flow and pressure
Hemodynamics
1.Blood flow: Blood volume passing
a given section in the cardiovascular system per unit time (ml/s).
(1).
P1-P2
F = ————
R
(2). Poiseulle’s law for laminar
flow.
πΔpr4
F = ————
8ηL
Laminar flow
Velocity of different layers
is different
parabolic
no vibration
no sound
Turbulent flow
blood flow is in direct proportion to
square root of pressure difference
Vibration
Sound (murmur)
Wasteful energy
Empirical equation: Reynold’s
number: NR=ρDV/η
ρ(rho): density of fluid.
D: diameter of the tube.
V: velocity of flow.
NR< 2000 laminar flow
NR< 3000 turbulent flow
2. Resistance to blood flow:
P1-P2
8η1
F = ———
R = ———
R
πr4
Resistance comes from external
friction (L, r) ,internal friction (η).
Total peripheral resistance is mainly
determined by arterioles(60～70%).
Resistance and arterial blood
pressure affect blood flow of
organ and redistribution of
blood flow of organs
3.Blood pressure. 1mmHg = 0.133 Kpa.
Two requirements for blood pressure
formation:
(1) Blood filling in cardiovascular
system.
Mean circulatory filing pressure ∽
blood volume
——————— = 7mmHg
vascular volume
affect venous return to heart.
(2) Heart work
Pressure energy + Kinetic energy
Pressure (systole)
diastolic
pressure
forward flow
Ⅲ. Arterial Blood Pressure
1.Normal value
Systolic Pressure:100～120mmHg,13.3～16 kPa
Diastolic Pressure: 8～10 kPa, 60～80mmHg
Pulse Pressure: 4.0～5.3 kPa, 30～40mmHg.
Mean arterial pressure(MAP) = DP + 1/3 (pulse P):
100 mmHg(13.3kPa)
Fall of blood pressure is in direct
proportion to resistance to blood
flow
2. Determinants of arterial blood
pressure
(1) arterial blood volume
(2) arterial compliance
ΔVolume/Δpressure
If we assume that arterial compliance
remains constant, arterial blood
pressure will depend on arterial blood
volume and vascular volume
Blood volume
BP ∽ ————————
vascular volume
If a vascular volume does not change
arterial blood volume → arterial BP
↑
↑
↓
↓
—
—
Arterial blood volume is determined by the
rate of inflow and outflow of arterial system.
Rate of inflow：cardiac output
Rate of outflow: resistance and BP.
AP = F × R = HR×SV×R
Inflow
outflow → arterial blood AP
volume
>
↑
↑
<
↓
↓
=
-
3. Factors affecting arterial
pressure
(1) stoke volume
(2) heart rate
(3) peripheral resistance
(4) aorta large artery
(5)circulatory blood flow
Factors
results
SV HR PR E BV SP DP PP
↑
↑
↑
↓
↑
Ⅴ.Venous pressure and venous return
1. Central venous pressure 4～12 cm H2O
Affect factors：
(1) Heart pump action
(2) Venous return velocity
An index of cardiovascular function
2. Peripheral venous pressure
2. Effect of gravity on
venous pressure
Orthostatic hypotension
3. Venous return and affecting factors
(1) Mean circulatory filling pressure
(2) Cardiac contractility
(3) Sympathetic nerve
(4) Muscle pump
(5) Thoracic pump
Ⅳ.Microcirculation
1. Architecture of microcirculation.
(1) Thoroughfare or preferential
channel.
(2) A-V anastomosis or A-v shunt.
(3) Arteriole →metareriole →
precapillary sphincter →true
capillary→ venule.
4. Hemodynamic of microcirculation
(1) big cross section area
slow velocity of blood flow
(2) capillary pressure depends on
precapillary resistance / postcapillary
resistance: 5:1
(3) alternate opening and closing of
capillaries
2. Exchange of substances between
blood and interstitial fluid
(1) Diffusion: the most important way.
Lipid soluble substances: O2, CO2
non-lipid soluble substances:
Rate of diffusion =(DA/a)(Co-Ci)
D: diffusion coefficient
(2) Pinocytosis.
(3) Filtration and absorption
Outward force > inward force filtration
<
reabsorption
Capillary hydrostatic interstitial
pressure
hydrostatic pressure
Interstitial colloid
plasma colloid
osmotic pressure
osmotic pressure
VI Formation of interstitial fluid
V = Kf [ ( Pc +if ) – (p + Pif ) ]
3. Factors affecting the formation of
interstitial fluid.
(1) Capillary hydrostatic pressure.
(2) Colloid osmotic pressure.
(3) Lymph return.
(4) Capillary permeability.
SECTION 4
REGULATION OF
CARDIOVASCULAR ACTIVITY
Significance:
To maintain normal blood pressure,
blood flow to be relativity constant.
To redistribute blood supply to
different tissue and organs.
To redistribute blood supply to
different tissue and organs.
Ways of regulation:
BP = cardiac out × Resistance
8ηL
R = ———
πr4
Neural control: reflex
Humoral control; humoral factors
Autoregulation: intrinsic regulation
Cardiovascular reflex
(1) Arterial baroreflexes:
Carotid sinus baroreflex
Aortic baroreflex
(2) Cardiopulmonary reflex
(3) Chemoreceptor reflex
A. Neural regulation
1. Innervation of the heart
dual innervation
(1) cardiac sympathetic nerve
(2) cardiac parasympathetic nerve
Cardiac Symp n
Cardiac Vagal n
IML1-5
Amgiguus N, Dorsal
motor N of vagus
Preganglionic f
ACh
Preganglionic f
ACh
Postganglionic N
N receptor
Postganglionic f
NE
 receptor
propranolol
Effects
inotropic
chronotropic
dromotropic
Blocker
Postganglionic f
Ach
M receptor
atropine
(1) Effects of vagal nerve
Vagal nerve ending → ACh. →
binds to M cholinergic receptor
→↑permeability to K+ results
in:
↓automaticity of S-A node:
↓contractility due to :
↑K+ efflux at phase 3 repolarization
→↓AP duration → Ca2+ influx ↓
→ [Ca2+]i↓;
ACh inhibits Ca2+ influx → [Ca2+]i
↓→ ↓contractility.
↓conductivity
The left Vagus n:↓conductivity in
A-V node
The right Vagus n: ↓automaticity
in S-A node.
(2) Effects of cardiac sympathetic
nerve:
Cardiac sympathetic nerve ending
→ noradrenaline → binds to βadrenergic receptor→↑permeability
to Ca2+ leads to:
↑Automaticity
↑Conductivity
↑Contractility
The left Symp n：↑contractility.
The right Symp n：↑HR.
2. Innervation of blood vessels
(1) Vasoconstriction fiber
Pre ganglionic
neurons
IML T1-L2
ganglionic
neurons
adrenergic f
cholinergic f. ACh
N receptor
 receptor vasoconstriction
 receptor vasodilation

NE

Sympathetic
vasoconstrictor
tone
↑
vascular tone
↑
vasoconstriction
↓
↓
vasodilation
tonic activity
bidirectional regulation
In artery vessels:
arterioles > arteries > venous >
capacitance vessels > precapillary
sphincters
Density of symp vasoconstriction
fiber in organs;
Skin > Skeletal > Visceral organs,
Cerebral vessels,
Coronary vessels.
(2) Vasodilation nerve fibebs
1) Sympathetic vasodilation never fibers
Cerebral cortex relay in hypothalamus and
Midbrain → medulla oblongata→ spinal
cord → Sym fiber → ACh → Vasodilation
in skeletal M.
No tonic activity; defense reaction.
2) Parasymp. vasodilation never
fibers.(ACh)
Origin in some nuclei in brain
stem and IML in sacral segments.
Innervation of blood vessels in brain,
liver, GI tract, external genitals:
Local regulation of blood flow.
(3)Non-cholinergic, non-adrenergic
fibers
NO, peptides
B. Cardiovascular center
1.Cardiovascular center in medulla
oblongata
After transection between pon and
medulla oblongata, BP remains normal.
Stimulation of sciatic nerve induces the
increase in BP.
After transection at obex in medulla,
BP drops to 40 mmHg, no response of
BP to stimulation of sciatic nerve.
Medulla can maintain normal BP, and
is called basal center of
cardiovascular activity integration.
(1) Rostral ventrolateral medulla
(RVLM)
(2) Caudal ventrolateral medulla
(CVLM)
(3) Nucleus of solitary tract
(NTS)
(4) Cardiac vagal center
(1) Rostral ventrolateral medulla
(RVLM)
Cardiac sympathetic tone
Sympathetic vasoconstriction tone
Stimulation of RVLM→↑BP,↑HR.
Destruction of RVLM, BP decreases
to 40mmHg.
RVLM is very important center in
maintain normal BP, it has vasomotor
tonity.
(2) Caudal ventrolateral edulla
(CVLM)
Receives signals from NTS
sends axons to RVLM
Inhibition of RVLM
(3) Nucleus of solitary tract (NTS)
receives signals from arterial
baroreceptors and cardiopulmanary
receptors
sends axons to vagal center and
CVLM
(4) Cardiac vagal center
nucleus ambiguus, dorsal
motor nucleus of vagus
receives axons fom NTS
NTS →CVLM →RVLM
N.ambiguous
dorsal motor
N of vagus
Symp. Preganlionic
neurons in IML.
3. Hypothalamus
(1) Hypothalamus is higher
integrated center of autonomic
system, including feeding,
regulation of body temperature,
fluid balance and endocrine
secretion.
(2). Anterior hypothalamus
Stimulation causes the decrease in BP
and HR
Sends axons directly to SPN of IML in
spinal cord.
Receives axons of NTS in medulla.
Plays role in arterial baroreflex.
NTS → AH → IML → Symp. f.
(3) Posterior and lateral hypothalamus
Stimulation of defence area
cause defensive reaction:
Behavior: Rage, attack reaction or fighting
associated with hissing, growling, spitting,
piloerection, pupil dilation, biting
Cardiovascular reactions:
↑BP,↑HR, Vasodilation in skeletal
muscle.
vasoconstriction in skin and splanchnic
organs.
4. Cerebral cortex.
(1) Limbic area regulates the activity of
lower centers.
(2) Motor and premotor area causes
vasoconstriction of skin, splanchnic and
renal vessels, but vasodilation in skeletal
muscles.
(3) Responses of BP to pain, anxiety and
during exercise.
C. cardiovascular reflexes
1. Arterial baroreflexes:
Carotid sinus baroreflex
Aortic baroreflex
(1). Barorecrptor is located in adventitia of
carotid sinus and aortic arch
Characteristics:
a. Response to stretch, not to pressure
itself
b. Activity is directly related to BP level
c. More sensitive to pulsatile pressure
than nonpulsatile pressure.
(2) Afferent nerve: Buffer nerves
Carotid sinus nerve - a branch of
glossopharyngeal nerve connected
with carotid sinus baroreceptor
Aortic nerve-running in vagus n
connected with aortic baroreceptor
Reflex arc
BP
Carotid &aortic
receptors
NTS
vagal center
CVLM
RVLM
cardiac vagus
HR
cardiac symp
SV
MIL
symp vasoconstrictor
CO
PR
BP
(3) Function of baroreflex.
a.Experimental evidence:
(a) Effect of carotid clamping;
(b) Buffer nerve cut or stimulated
(c) Perfusion of isolated carotid
sinus.
Method
Results:
baroreflex function curve.
Features of the curve:
Anti “S” shape
Sinus threshold pressure
Sinus saturation pressure working range
Equilibrium point or operating point ( Set
point ):ISP = arterial pressure.
Negative slope (gain) - Negative feedback
Slope is no uniform.
(4) Functional significances of arterial
baroreflex:
To keep arterial pressure at normal level
To stabilize arterial pressure and prevent
arterial pressure from large fluctuation
Baroreflex resetting.
Operating point and baroreflex
function curve shift upward or
downward.
2. Cardiopulmonary reflex
(1). Atrial volume receptor
Location: in the junction of pulmonary
vein and left atrium, vena cava and
right atrium
Reflex action:
Tachycardia (bainbridge reflex) 1895.
Increase in urine due to↓renal
Sympathetic efferent activity and
↓antidiuretic hormone.
(2).Left ventricular receptor.
a. Mechanoreceptors:
Location: Left ventricle.
Stimulation of ventricle.
Afferent n: vagus n.
Reflex action: similar to arterial
baroreflex, i.e. decrease in BP
and HR.
b. Chemoreceptor in ventricle:
Coronary chemoreflex (Bezold- Jarisch
reflex)
Reflex effects: decrease in BP and HR
Stimulation: Veratridine, nicotine,
bradykinin, prostagladins, myocardial
infarction.
Vagal afferent n.
2. Chemoreceptor reflex
(1) Respiratory depth and frequency
increases;
(2) Vasoconstriction in skeletal M,
splanchnic viscera, kidney.
(3) Blood flow in brain and liver
increases. BP inceases
(4)↑HR, ↑cardiac output due to
a.↑respiration rate and depth
b.↑catecholamine from adrenal
medulla.
If respiration rate and depth keep
constant→ BP↑
a.↓HR, ↓cardiac output
b. vasoconstriction in skeletal M
Splanchnic organs and kidneys
c. Coronary vosodilation
Diving rflex
Significances of chemoreceptor reflex
Uunder normal condition chemoreflex plays
a litte role in control of cardiovascular
activity, but in an emergency (asphyxia,
hypoxia, acidosis, severe hypotension) blood
pressure is maintained by this reflex,
because bilateral buffer nerves are cut,
blood pressure will drop to very low level.
B. Humoral regulation of
cardiovascular system
1. Renin - angiotension system.
angiotensinogen ( α2-globulin)
kidney renin
angiotensinⅠ(decapeptide)
converting enzyme
angiotensinⅡ(octapeptide)
angiotensinase A
AT1 receptor
angiotensin Ⅲ(heptapeptide)
(1).Action
a. The increase in BP
Arterial constriction→↑total peripheral
resistance
Venous constriction →↑venous return
→↑SV.
Stimulation of secretion of aldosterone
→renal tubule reabsorption of Na+,H2O
→↑blood volume.
Facilitation of NE release from adrenergic
fiber endings, modulation of sympathetic
function.
Central effects of angiotensin Ⅱ.
Action site: Circumventricular organs;
Organum vasoculosum of the lamina
terminalis (OVLT), Subfornical organ
(SFO), Area postrema (AP).
Regulation of renin release
a. Renal mechanisms:
renal vascular baroreceptor.
b.Renal sympathetic n
c. Plasm Na+↓,plasm K+↑
Hemorrhage
2.Epinephrine(adrenaline EP)
norepinephrine (noradrenaline NE)
Origin: adrenal medulla.
Secretion: EP 80%, NE 20%.
Effect: similar to that of sympathetic
nerve.
(1)Heart: positive chronotropic and
inotropic effect.
(2)Blood vessels:
α-adrenergic receptor: vasoconstriction.
β-adrenergic receptor: vasodilation.
The action of EP and NE on
cardiovascular system has some
differences which depend on the
distribution and affinity of α- and
β- receptors.
3. Antidiuretic hormone (vasopressin)
Synthesis in supraoptic nucleus
and paraventricular nucleus.
Store in posterior pituitary gland
(neurohypophysis).
Release ADH to blood stream.
Action :
V1 receptor: constriction of blood
vessel increase in blood pressure.
V2 receptor: reabsorption of H2O
from collecting duct.
Dehydration,
hemorrhage:↑AVP
4. Endothelium-derived vasoactive
substances. Prostacyclin (PGI2)
(1) Endothelium-derived relaxing factor:
Nitric oxide (NO)
NO synthase
L-Argine
NO + L-citrulline
NO activates guanylyl cyclase which
increases cGMP formation. cGMP
decreases [Ca2+]i and relaxes vascular
smooth muscle.
Phosphodiesterase hydrolyses cGMP
Factors of activation NOS: ACh,
bradykinin, substance P, mechanical stress
3.Endothelin
21 amino acid residues, strong
vasoconstrictor
iv endothelin causes first decrease in
BP and followed by long-term of the
increase in BP
5. Atrial natriuretic peptide (ANP)
Action:
vasodilation, ↓cardiac output ↓HR
↓extracellular fluid volume:
↑excretion of water and Na+
↓release of renin and aldosterone
Factors of releasing ANP:
↑atrial blood volume.
6. Kallikrein-kinin system
Kallikreins: proteolytic enzymes
kininogens
Plasma Kallikrein
tissue Kallikrein
kinins: bradykinin, lysylbradykinin
angiotensin converting enzyme (ACE)
Vasodilator, capillary permibility
C. Local regulation of blood flow
1. Active hyperemia
2. Blood flow aytoregulation
D. Blood volume and long term
regulation of blood pressure
Renal-body fluid control system
SECTION 4 CORONARY
CIRCULATION
I. Anatomic consideration.
II. Feature of coronary flow.
ΔP
F=
R
ΔP: perfusion pressure (aortic P atrial P), R: resistance
During systole myocardial contraction
compress coronary vessels which result
in the increase in coronary resistance.
During diastole release of compression
leads to the decrease in coronary
resistance. Therefore, coronary flow
depends on: 1.diastolic pressure.
2.duration of diastole.
Cyclic change of
coronary flow
Pressure gradient
Ⅲ.Regulation of coronary blood flow.
Normal value: 60-80ml/100g.min.
Exercise 300-400ml/100g.min
O2 consumption 7-9ml/100g.min.
O2 extraction 65-70%
O2 content in coronary venous blood
is 5ml/100ml. O2 content in skeletal
muscle venous blood is 17-18ml/100ml.
1. Myocardial metabolic level
↑cardiac activity, ↑cardiac
consumption O2 ,↓PO2,
adenosine
CO2, H+, lactic acid, K+,
prostaglandins.
Effects of PO2 on coronary flow
ATP
PO2
ADP
AMP
5’nucleotidase
adenosine → vasodilation
adenosine adenosine
Kinase
diaminase
inosine
2. Neurol control
(1).Sympathetic nerve: NE
α-receptor → vasoconstriction
β-receptor →↑myocardial
contraction→ ↑metabolism,
coronary vasodilation
(2). vagal nerve:
ACh → coronary dilation.
↓metabolism→ coronary
constriction
3.Hormone regulation
NE, EP, thyroxin → coronary
dilation
AngiotensinⅡ, vasopression →
coronary constriction.
(2).Regulation of vasopressin release
a.Osmotic control;
Osmotic receptor in anterioventral third
↑
Ventricle (AV3V)
∣
↓
↑plasma osmotic PVN,SON↑
pressure
↓
ADH↑
↓
Reabsorption of water
From collecting ↑
↓
Blood volume ↑
b. non-osmotic control.
* volume receptor
↓
vagal afferent nerve(+)
↓
ADH↓
* arterial baroreceptors (+)
↓
sinus n and aortic n↑
↓
ADH↓
* Pain, Surgical stress,
emotion stress → ADH↑