1.The maintenance of normal volume and composition of extracellular and intracel

Question

1.The maintenance of normal volume and composition of extracellular and intracellular fluids is vital to life. List and briefly describe the kinds of homeostasis involved. 2.Why does maintaining fluid balance in older people require a higher water intake than in a normal, healthy adult under age 40? 3.Why does potassium concentration rise in patients with acidosis? What is this called? What effects does it have? 4.Saline solution is used to reverse hypotonic hydration. Are body cell membranes permeable to saline? Explain your response. 5.Explain the renin-angiotensin mechanism. 6.Explain how ADH compensates for blood that contains too many solutes.

Explanation / Answer

1. Plasma osmolarity : It is one of the main determinants of extracellular fluid volume. In case osmolarity rises, the fluid from intracellular fluid comes out trying to bring back the osmolarity to normal. Thus it helps in homeostasis

Thirst: in case the plasma osmolarity is increased, thirst centers in hypothalamus are stimulated again it leads to increased intake of water which brings back osmolarity to normal

Increased PH : any increase in pH leads to acidosis which is readily compensated by another compartment . For example HYPERKALEMIA in the intracellular fluid leads to acidosis which is corrected by extracellular fluid. This maintains homeostasis.

2. In elderly people water content is low which causes a relative increase in the plasma osmolarity in them . In order to correct it higher amount of water is needed.

3. Acidosis leads to the damage of ATP dependent Na/K pump. This leads to leakage of POTASSIUM causing HYPERKALEMIA. HYPERKALEMIA may lead to severe cardiac arrhythmia s.

4.Yes body cells are permeable.

5. Renin..... forms angiotensinogen...Forms angiotensin I ......Activated into angiotensin II..... angiotensin II causes VASOCONSTRICTION, Na reabsorption, Aldosterone stimulation, thirst stimulation.

6. Increased solutes...... Increase osmolarity..... Sensed by osmoreceptors ( supraoptic and pqraventricular nucleus)..... Stimulate release of ANTI DIURETIC HORMONE ..... This opens aquaporin channels in COLLECTING DUCTS .... Reabsorption of water..... Normalization of osmolarity.

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