The main function of the circulatory system is to give local blood flow to the tissue. There arespecial need of the tissue which is: delivery of oxygen to the tissue delivery of nutrients to the tissue removal of carbon dioxide from tissue maintaining of normal concentration of ions transform of hormones and other substance to tissue

1. Nervous Control of Blood Vessels
Regulation of Arterial Pressure
Prep: Amen Ullah
Lecturer Surgical
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2. Students must know about…!!!
• Cardiac Output
• „Stroke Volume
• „Minute Volume
• Ejection Fraction (Ef)
• „Cardiac Index
• „Heart Rate
• „Peripheral Resistance
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3. FACTORS MAINTAINING CARDIAC
OUTPUT
Cardiac output is maintained (determined) by
four factors:
1. Venous return
2. Force of contraction
3. Heart rate
4. Peripheral resistance.
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4. Local control of blood flow
The main function of the circulatory system is to give local blood
flow to the tissue. There are
special need of the tissue which is:
 delivery of oxygen to the tissue
 delivery of nutrients to the tissue
 removal of carbon dioxide from tissue
 maintaining of normal concentration of ions
 transform of hormones and other substance to tissue
Also body temperature and to the kidney also gives excretion of
waste.
If an organ has high metabolism it has high blood flow
Eg. Thyroid, adrenal gland, liver, kidney.
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5. Humoral regulation of blood vessels
• Humoral control of the circulation means control
by substances secreted or absorbed into the
body fluids—such as hormones and ions.
• Some of these substances are formed by special glands
and transported in the blood throughout the entire body.
• Others are formed in local tissue areas and cause only local
circulatory effects.
• Among the most important of the humoral factors that
affect circulatory function are the following.
A) Vasoconstrictor agents
B) Vasodilator agents
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6. Vasoconstrictor agents
• A) Nor-epinephrine and epinephrine
B) Vasopressin
C) Angiotensin II
D) Endothelin
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7. Vasodilator agents
A) Bradykinin
B) Serotonin
C) Porstaglandins
D) Histamin
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8. Vascular control by ions & other
chemical factors
1) An increase in calcium ion concentration causes Vasoconstriction.
Effect of calcium to stimulate smooth contraction.
2) An increase in potassium ion concentration causes vasodilation.
The ability of potassium ions to inhibit smooth muscle
contraction.
3) An increase in magnesium ion concentration causes powerful
vasodilatation because magnesium ions inhibit smooth muscle
contraction.
4) An increase in hydrogen ion concentration (decrease in pH) causes
dilation of the arterioles.
5) Anions that have significant effects on blood vessels are acetate
and citrate, both of which cause mild degrees of vasodilatation.
6) An increase in carbon dioxide concentration causes moderate
vasodilatation in most tissues, but marked vasodilatation in the
brain.
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9. Local Control of Blood Vessels
 Local control of blood flow is achieved by periodic contraction
and relaxation of the precapillary sphincters.
 The precapillary sphincters are controlled by the metabolic
needs of the tissue.
 Blood flow also increase when by products of metabolism
build up in tissue spaces.
 An increase in carbon dioxide or a decrease in pH causes the
precapillary sphincter to relax.
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10. Blood pressure control mechanisms
There are two basic mechanisms for regulating
blood pressure.
Short-term Mechanisms.
regulate blood vessel diameter, heart
rate and contractility
long-term mechanisms.
Regulate blood volume
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11. Short-term Mechanisms
 Short term control of Blood pressure is mediated by
the:
I. Nervous system ( Baroreceptor mechanism)
II. Chemicals (Chemoreceptor mechanism)
 Control blood pressure by changing peripheral
resistance. ( in sec or minutes)
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12. I. Nervous System
Control BP by changing blood distribution in the
body and by changing blood vessel diameter.
Sympathetic & Parasympathetic activity will
affects veins, arteries & heart to control HR and
force of contraction
The vasomotor center
cluster of sympathetic neurons found in the
medulla.
It sends efferent motor fibers that innervate
smooth muscle of blood vessels.
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13. Baroreceptors
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14. Increased Parasympathetic Activity
• Effect of increased parasympathetic and
decreased sympathetic activity on heart and
blood pressure:
• Increased activity of vagus (parasympathetic)
nerve
• Decreased activity of sympathetic cardiac
Nerves
• Reduction of heart rate
• Lower cardiac output
• Lower blood pressure
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15. Decreased Sympathetic Activity
• Effect of decreased sympathetic activity on
arteries and blood pressure:
• Decreased activity of vasomotor fibers
(sympathetic
nerve fibers)
• Relaxation of vascular smooth muscle
• Increased arterial diameter
• Lower blood pressure
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16. • Effect of increased sympathetic activity
on adrenal glands and blood pressure:
• Increased sympathetic impulses to adrenal
glands.
• Release of epinephrine and norepinephrine to
bloodstream.
• Hormones increase heart rate, contractility and
vasoconstriction. Effect is slower-acting and more
prolonged than nervous system control.
• Increased blood pressure.
Sympathetic Activity on Adrenal Gland
and Blood Pressure
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18. CHEMORECEPTOR REFLEXES
Are sensitive to changes in blood oxygen, carbon
dioxide and pH.
Are located in the carotid bodies and the aortic
bodies.
Increase peripheral resistance in response to low
oxygen levels, high carbon dioxide levels, and
reduced blood pH
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19. ll. Chemoreceptor reflex control of
blood pressure
1. Chemoreceptor's in the carotid and aortic bodies monitor
blood O2, CO2 and pH.
2. Chemoreceptor’s in the medulla oblongata monitor blood
C02 and pH.
3. Decreased blood 02, increased CO2 and decreased pH
decrease parasympathetic stimulation of the heart, which
increases the heart rate.
4. Decreased blood O2, increased CO2, and decreased pH
increase sympathetic stimulation of the heart, which
increases the heart rate and stroke volume.
5. Decreased blood O2, increased CO2, and decreased pH
increase sympathetic stimulation of blood vessels, which
increase vasoconstriction .
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20. Chemoreceptor
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21. HORMONAL MECHANISM
( long term mechanism)
 Epinephrine released from the adrenal medulla as a result of sympathetic
stimulation increases heart rate, stroke volume, and vasoconstrictor.
 Renin is released by the kidneys in response to low blood pressure. Renin
promotes the reproduction of angiotensin II, which causes
vasoconstriction and an increase in aldosterone secretion . Aldosterone
reduces urine output.
 Angiostensin II can also cause vasoconstriction.
 ADH released from the posterior pituitary causes vasoconstriction and
reduces urine output.
 Atrial natriuretic hormone is released from the heart when atrial blood
pressure increases. It stimulates an increase in urine production, causing a
decrease in blood volume and blood pressure.
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22. Renin Angiotensin Aldosterone
mechanism
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