Regulation of blood vessel
diameter
Prof. Edgaras Stankeviius
Institute of Physiology and Pharmacology
Regulation of the circulation
I. Local (myogenic, metabolic, endothelium-
derived factors)
II. Systemic:
Nervous
Humoral
Rapid
Intermediate
Slow
Neuroeffector organization in a large blood vessel
Verity, Proc.Symp.Physiol.Pharmacol5.Vasc.Neuroeffector Systems, 2-12, 1971
Adrenergic innervation
of a rat mesenteric small artery
Nilsson et al., Acta Physiol. Scand. 126: 121-133, 1986
Nervous regulation of Arterial Pressure
Chemorecepcinis refleksas Kuingo refleksas
(skausmas)
(prieirdi
B receptoriai)
D. Catecholamines
If the hypertension/hypotension is still present after
approximately one day, the baroreceptors will reset to the
new blood pressure levels.
1. Baroreceptors
A sudden increase in
blood pressure
stretches the
baroreceptors and
the increased firing
results in the
vasomotor center
inhibiting
sympathetic drive
and increasing vagal
tone on the SA node
of the heart.
Rapid regulation
Baroreceptor reflex
Arterial Blood Pressure
Firing from
Baroreceptors
Firing from
Sympathetic
system
Time
Chemoreceptors (location: sinus caroticus and aorta)
Chemoreceptors (location: sinus caroticus and aorta)
The signals from chemoreceptors excite the vasomotor center
after the arterial pressure falls below 80 mmHg, only.
- rapid control mechanism at the lower pressures.
Ischemic CNS reaction
Mechanism: BP 60 mmHg increases pCO2
leading to the sympathetic activation and
vasoconstriction.
Catecholamines (kidney)
Adrenalin
(vasodialation in
skeletal muscle
arteries;
vasoconstriction in
intestinal and skin
arteries)
Noradrenalin
(vasoconstriction)
Intermediate control mechanisms of ABP
Arterial stress-relaxation (due to increased
volume)
Changes in filtration-absorbtion from
capillaries to venules (capillary fluid shift
mechanism)
Renin-angiotensin system
Arterial stress-relaxation mechanism (due to increased
volume)
capillary fluid shift mechanism
Renin angiotensin aldosteron system
Renin (kidneyblood)
Angiotensinogen Angiotensin I
(Liverblood) (blood)
ACE (endothelium)
Angiotensin II
Vasoconstriction Aldosteron NA ADH
(peripheral and glomerular) (Na ir H2O reabsorbtion)
Intermediate pressure regulation
Slow control mechanisms of ABP
Renal-body Fluid system
Atrial receptors
Aldosterone
Antidiuretic hormone vasopressin
Atrial natriuretic peptide
Renal-Body Fluid Sysytem
When the body contains to much extracellular
fluid, the blood volume and the pressure rise
At high pressure the kidney excretes the
excess volume into urine and relieves the
pressure
At low pressure the kidney excretion is
decreased
Renal Urinary Output Curve shows
pressure diuresis
The equilibrium point describes the level to which the
arterial pressure will be regulated
Arterial pressure
always returns to
equilibrium point
in the infinitive
feedback gain
principle
Importance of salt in the renal-body
fluid regulation
Increase in salt elevates arterial pressure more
than a water intake
Water can be eliminated
Salt accumulates in the body
Stimulates the thirst center in the brain
Increases osmotic pressure stimulating release
of vasopressin (ADH)
2. Atrial receptors (A and B type fibers)
Function:
A fibers increases sympathetic activation
(Heart rate monitoring during atrial
contraction)
B fibers decreases sympathetic activation,
activates parasympathetic system (rising atrial
volume monitoring)
Iong-term regulation
Atrial receptors (A and B type fibers)
A fibers increases sympathetic
activation (Heart rate monitoring during
atrial contraction)
B fibers decreases sympathetic
activation, activates parasympathetic
system (rising atrial volume monitoring)
3. Aldosterone (mineralocorticoid family) plays a central role in the regulation of blood
pressure mainly by acting on the distal tubules and collecting ducts of the nephron,
increasing reabsorption of ions and water in the kidney, to cause the conservation of
sodium, secretion of potassium, increase in water retention, and increase in blood
pressure and blood volume
4. Antidiuretic Hormone (Vasopressin) (posterior pituitary)
Activation - atrial
receptors B fibers,
angiotensin II.
Mechanism
increases water
reabsorption in
kidney leading to
increase in circulating
blood volume
5. Atrial natriuretic peptide (ANP)
Activation increase
in atrial pressure
Down regulates renin,
vasopressin and
aldosterone release.
Increases diuresis.
Causes vasodilatation
Short-term pressure regulation
a) baroreceptors
b) chemoreceptors
c) ischemic CNS reaction (Cushing reflex)
d) Catecholamines
Long-term pressure regulation
a) Renin angiotensin aldosteron system (RAAS)
b) Atrial receptors
c) Atrial natriuretic peptide (ANP)
c) Antidiuretic Hormone (Vasopressin)
Vessel layers
Tunica intima
Endothelium lines the lumen of all vesels
Vessels larger then 1 mm have basement
membrane
Tunica media
Smooth muscle and sheets of elastin
Function: vasoconstriction and vasodilation
Tunica externa (adventitia)
Collagen fibers (reinforcement)
Lager vessels contain vasa vasorum
The arterial
pressure can be
increased by (A)
shifting the renal
output curve or
(B) by increasing
the intake level of
salt and water
Increased extracellular fluid volume
increases arterial pressure
