Long term regulation of Blood Pressure Nervous mechanisms are not capable of maintaining long term homeostasis Nervous system resets to new state----Receptor adaptation Long term regulation of BP is through: 1. Body fluid control 2. Balance between intake and out put of fluid and salts Regulation of arterial pressure is primarily by conserving or excreting salts and water from circulation via the kidneys to maintain Normal blood volume

Renal body fluid system ↑ECF → ↑blood volume → ↑Blood pressure → ↑Urinary out put of salt and water (Kidneys simply excrete extra volume of Fluid responsible for ↑Blood pressure ) ↓ECF → ↓blood volume → ↓Blood pressure → ↓ urinary out put of salt and water (Retention of salt and water)

Renal body fluid system A few mm Hg rise in arterial pressure → ↑ ↑ Urinary water loss (Pressure diuresis) → ↑ ↑ Urinary Na+ (Pressure Natriuresis)

Pressure Diuresis (Renal output curve) At 50 mm Hg- No urine output At100 mm Hg- Normal urine Vol. 200 mm Hg 7-8 times urine output Renal function curve or Renal urinary out put curve

Effects of addition of Extra fluid Nervous receptors blocked Infusion of 400 ml blood ↑ blood volume ↑ COP ↑ Arterial pressure ↑ Urinary out put Water excreted till the restoration of normal levels

Near infinite feed back Gain principle 150 mm Hg More loss of water and salts than intake Till equilibrium 80 mm Hg Intake of salt and water more than out put

Effect of altered Renal out put curve (ROC) ROC shifted to higher pressure side Salt and water intake normal Equilibrium point shifted to 150 mm Hg Arterial pressure will be maintained at 150 mm Hg

Effect of change in salt and water intake ROC normal Increased level of salt and water intake Equilibrium point shifted to Higher pressure side (160 mm Hg) Arterial pressure will be maintained at 160 mm Hg

Two basic determinants of long term arterial pressure are The level of salt and water intake The degree of shift of the renal function curve along the pressure axis.

Important Excess pure water intake does not maintain elevated pressure It is very quickly excreted in the urine ADH mechanism Excess salt intake is more important for long term elevation of arterial pressure

Renin angiotensin system Besides controlling body fluid volume Kidneys also contribute in BP homeostasis through Renin angiotensin system Fall in pressure cause production of Renin from the kidneys Renin is a protein enzyme produces from JG cells Renin has multiple ways to control BP

Juxtaglomerular apparatus

Effects of Angiotensin II Angiotensin II acts directly on the kidneys to cause salt and water reabsorption Indirectly increases the secretion of aldosterone by adrenal glands.

Importance of vasoconstrictor effect of Angiotensin after hemorrhage BACK

Effects of angiotensin on ROC Angiotensin shifts the ROC to High pressure level Equilibrium point moves to higher pressure level Next

Angiotensin maintains Normal BP Angiotensin maintains normal blood pressure despite variations in salt intake ↑ salt intake →↑ECF volume →↑BP → ↑ blood flow in the kidneys →↓Renin →↓Angiotensin→ ↓renal retention of salt and water → ↓BP ↓ salt intake →↓ECF volume →↓BP → ↓ blood flow in the kidneys →↑Renin →↑Angiotensin→ ↑renal retention of salt and water → ↑BP