2. Regulation of BP• Short term (seconds to minutes)
• Baroreceptor
• Chemoreceptor
• CNS ischemic response
• Intermediate term (minutes to hours)
• Capillary fluid shift
• Stress relaxation
• Long term (days to years)
• Renal body fluid mechanism
• Renin – angiotensin system
3. Short term Regulation
• Baroreceptors – aortic arch (10th), carotid sinus (9th)
• 60 – 200 mmHg range of MBP
• stretch-sensitive mechanoreceptors
• Hypertension - the baroreceptor reflex mechanism
is reset at a higher level to maintain BP at elevated
level
4.
5.
6.
7. Short term Regulation
• Chemoreceptors – aortic body(10th), carotid body(9th)
• 40 – 100 mmHg range of MBP
• They respond to the chemicals mainly
• a) Hypoxia ( ↓ pO2)
• b) Hypercapnia ( ↑ pCO2)
• c) Acidosis ( ↑ H+)
8.
9.
10. Short term Regulation
• CNS ischemic response
• 15 – 50 mmHg range of MBP
when blood flow to VMC becomes decreased severely enough to
cause cerebral ischemia
↓
The VMC respond directly to the ischemia and become strongly
excited
↓
sympathetic vasoconstriction
• whenever blood flow to the brain decreases dangerously close
to the lethal level - the “last ditch stand”
11. Cushing’s Reflex
Increased intracranial pressure
↓
Cerebral hypoxia and Hypercapnia
↓
Direct effect on VMC
↓
SNS action increases
↓
Vasoconstriction
↓
Increased BP
↓
Reflex bradycardia via baroreceptors
12. Intermediate term
• Capillary fluid shift
• When capillary pressure falls too low → fluid is
absorbed through the capillary membranes from the
tissues into the circulation → building up the blood
volume and increasing the pressure
• when the capillary pressure rises too high → fluid is
lost out of the circulation into the tissues → reducing
the blood volume as well as the pressure
13. Intermediate term
• Stress relaxation & reverse Stress relaxation
When the pressure in the blood vessels becomes
too high
↓
They become stretched and keep on stretching
more and more for minutes or hours;
↓
the pressure in the vessels falls toward normal
14.
15.
16. Long term
regulation• Renal body fluid mechanism
When the body contains too much ECF
↓
the blood volume and arterial pressure rise
↓
direct effect to cause the kidneys to excrete the excess
ECF (pressure naturesis, pressure diuresis)
↓
returning the pressure back toward normal
