A detailed summary of how the mean arterial pressure is regulated via intrinsic and extrinsic reflexes as well as how to measure a blood pressure using an sphygmomanometer.
REGULATION OF ARTERIAL PRESSURE: SHORT & LONG TERM
REGULATION
Regulation of MAP (SHORT TERM):
1. INTRINSIC REFLEXES
Baroreceptor reflex
Chemoreceptor reflex (i.e. Brain Hypoxia – try to increase vasoconstriction
to get blood to brain. )
Cardiopulmonary reflexes – located in heart and pulmonary vessels.
2. EXTRINSIC REFLEXES
Skeletal muscle metaboreceptors – peripheral afferents that respond to
metabolites produced by active muscle (i.e. CO2, pH and lactate).
Facial receptors – detect cold on face – results in an increase in
vasoconstriction – known as ‘diving reflex’.
Pain – moderate pain causes high MAP and tachycardia, whereas sever pain
causes low MAP and bradycardia.
Regulation of MAP (LONG TERM):
Long term regulation of MAP is about regulating volume not HR or vasculature.
KIDNEY
Adjusts renal excretion and absorption of Na+ and H2O.
High sodium levels = high water levels = high blood volume.
Low sodium levels = low water levels = low blood volume.
NATRIURESIS = Na+ excretion.
DIURESIS = Urine production (H2O/Na+).
Low Volume
Triggers renin-aldosterone-angiotensin-system (RAAS).
High renin levels acts on angiotensinogen to form angiotensin I which is then
converted to angiotensin II.
Angiotensin II stimulates aldosterone secretion which increases vasoconstriction and
retention of retention of sodium and water; therefore, increasing preload.
Vasopressin/Anti-diuretic hormone (produced in posterior pituitary) increase water
retention.
High Volume
At a high volume you have natriuresis – Na+ excretion.
Atrial Natriuretic Peptide (ANP) is released from atria and causes vasodilation.
ANP also helps to increase natriuresis and diuresis.
How do you measure a BP using a sphygmomanometer?
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