Regulation of Blood Pressure

1. Nervous System Control
• control of arteriole diameter
• directs blood flow to proper organs and tissues that need it
• REFLEX PATHWAY:
• baroreceptors/chemoreceptors/brain --> afferent nerve fibers --> medulla (vasomotor center) --> vasomotor (efferent) nerve fibers --> smooth muscle of arterioles
2. Vasomotor Fibers to Smooth Muscle of Arterioles
• sympathetic fibers that release norepinephrine (NE); cause vasoconstriction of arterioles
3. Vasomotor Center of the Medulla
• sympathetic neuron cell bodies in the medulla
• receive input from baroreceptors, chemoreceptors, and brain
• vasomotor tone - general constricted state of arterioles set by vasomotor center
4. Baroreceptors
• blood pressure receptors large arteries (carotid sinuses, aortic arch, neck/thorax arteries)
• send blood pressure information to vasomotor center of medulla
• increased pressure --> decreased pressure --> inhibits vasomotor center -> stimulates vasomotor center -> vasodilation vasoconstriction
5. Chemoreceptors

• located in aortic arch and carotid arteries

• carotid and aortic bodies
• monitor OXYGEN and pH levels of the blood
• low OXYGEN or ------------> increase blood pressure, return blood to lungs quickly
• low pH
6. Higher Brain Centers Control on BP
• hypothalamus & cortex also effect vasomotor area
7. Chemical Controls of Blood Pressure
• hormones of adrenal medulla - "fight-or-flight" response to fear; release of norepinephrine and epinephrine from adrenal medulla; causes vasoconstriction and increased BP
• atrial natriuretic factor (ANF) - secreted by the atria of the heart, promotes general decline in blood pressure kidney releasing more Na+ and water, reducing fluid volume
• antidiuretic hormone (ADH) - released by the hypothalamus, causes increase in blood pressure by getting the kidneys to conserve water in the body; eg. during hypotensive situations
• endothelium derived factors
• endothelin - strong vasoconstrictor
• endothelium derived relaxing factor - vasodilation
• alcohol - causes vasodilation
8. Renal (Kidney) Regulation
• direct regulation - fluid loss through urine
• a. low pressure/volume --> conserve water
• b. high pressure/volume --> release more water
• renin-angiotensin mechanism
• low blood pressure --> release of renin --> formation of angiotensin II --> vasoconstriction
  
• release of aldosterone --> Na+/water reabsorption (by kidney)

Category: Physiology Notes