LOCAL CONTROL OF BLOOD VESSELS

Sitjar, daisy lhen L.

LOCAL CONTROL

Of blood flow is achieved by periodic contraction and relaxation of the precapillary sphincters.

Blood flow through the capillaries is cyclical because of this contraction and relaxation.

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.

NERVOUS CONTROL OF BLOOD VESSELS

Nervous control of blood vessels is carried out primarily through the sympathetic division of the autonomic nervous system. VASOMOTOR CENTER transmits a low frequency of action potentials to the sympathetic vasoconstrictor fibers. VASOMOTOR TONE an increase in vasomotor tone causes blood vessels to constrict further and blood pressure increase.An decrease in vasomotor tone causes control of blood vessel diameter is an important way blood pressure is regulated.

2 REFLEXES:

Baroreceptor Chemoreceptor

BARORECEPTOR REFLEXES

Keep the blood pressure within its normal range of values

Respond to stretch in arties caused by increased pressure.

THE BARORECEPTOR REFLEX CONTROL OF BLOOD PRESSURE1. Baroreceptors in the carotid sinus and aortic arch monitor blood pressure

2. Action potentials are conducted by the sensory nerves to the cardio regulatory and vasomotor centers in the medulla oblongata .

3. Increased parasympathetic stimulation of the heart decreases the heart rate.

4. Increased sympathetic stimulation of the heart increased the heart rate and stroke volume

5. Increased sympathetic stimulation of blood vessels increases vasoconstrictor.

Baroreceptor reflexes Regulate blood pressure on moment to moment

basis. When a person rises rapidly from a sitting or

lying position to a standing position, blood pressure in the neck and thoracic regions drops dramatically as a result of the pull of gravity on the blood.

This reduction in blood pressure can be so great that blood flow to the brain is reduced enough to cause dizziness or even loss of consciousness.

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.

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 .

Chemoreceptor reflex control of blood pressure

HORMONAL 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.

HORMONAL REGULATION: THE RENIN-ANGIOTENSIN-ALDOSTERONE MECHANISM

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