Presentation on theme: "RENAL REGULATION OF BODY FLUID Dr. Eman El Eter. What is the impact of the following on your body fluid volume and osmolarity? What happens when you."— Presentation transcript:
What is the impact of the following on your body fluid volume and osmolarity? What happens when you are exposed to hot weather? What if you have a stomach bug and excessive diarrhea? What if you drink 2 liters of fluids?
ECF Constant concentration of electrolytes & solutes They create the osmolarity of ECF Na+, Cl- most abundant osmostic molecules. Osmolality is determined by the amount of extracellular NaCl and water which depends upon balance between intake and excretion of these substances. Normal plasma Na+ = 140-145 mEq/L Osmolarity = 300 mOsm/L
Control of ECF osmolarity & Na+ concentration 1-Osmoreceptor –ADH mechanism. 2- Thirst mechanism
Osmoreceptor mechanism Changes in plasma osmolarity can lead to a cascade of events to return it back to normal.
What happens if ECF osmolarity increased? ECF osmolarity (+) osmoreceptors in Ant. Hypothalamus & Send signals to Supraoptic nucleus, Then to posterior Pituitary (+) ADH To increase H2O absorption
Where in the brain ADH is formed? Main site for ADH synthesis ADH is stored in posterior pituitary
Osmotic vs non-osmotic stimuli; effect on ADH Rapid response AVP=arginine vasopressin=ADH
Non-osmotic stimuli releasing ADH Arterial baroreceptor reflex Chemoreceptor reflex Whenever BP & blood volume reduced, ADH is released water retention by the kidney to restore BP to normal. Day-to-day regulation of ADH secretion is effected mainly by changes in plasma osmolarity.
Role of thirst in controlling ECF osmolarity & Na+ concentration To stay in balance water intake = water loss Fluid intake is regulated by thirst mechanism Stimuli of thirst mechanism: A. Increase thirst: Increased osmolarity ECF. Decreased ECF volume. Decreased blood pressure. Angiotensin II. Dryness of the mouth. B. Decrease thirst? -Gastric distention decreases thirst.
Role of thirst in controlling ECF osmolarity & Na+ concentration, cont…. The desire to thirst is completely satisfied when: Plasma osmolarity, Blood volume, Or both return to normal
Role of Ang II & aldosterone They do not normally play a major role in controlling ECF osmolarity and Na+ concentration. Their major role is to absorb sodium through distal convoluted tubules, leading to greater extracellular fluid volume and sodium quantity.
Take home message ADH-thirst is the most powerful feedback system in the body for controlling extracellular fluid osmolarity and sodium concentration