Question

1. Briefly describe the role of electrolytes in the movement of water between the body’s fluid compartments and then, based on this general principle, explain how the hormone aldosterone promotes an increase in blood pressure.

Answer 1

Electrolytes are minerals that have an electric charge and are found in body tissues,blood and other body fluids.The number of positively charged and negatively charged ions should be equal in number.A balance is to be maintained between the body fluids and electrolytes for the survival and proper functioning of cells. Sodium, potassium, calcium, phospate and magnesium are the ions found in body which performs the various functions of maintaining body osmolarity,acid base balance,movement of nutrients etc.

Sodium and potassium are the major cations found in extracellular fluid and is responsible for the maintaining the osmotic pressure gradient between the interior of cells and their environment.These ions create hypertonic or hypotonic environment on which the movement of water depends.When there is higher concentration of ions in the tissues or cells there is hypertonicity and leads to accumulation of water in the same direction to dilute the ions.The net movement of water molecules are towards increased ion concentrations by the process of endosmosis.

Aldosterone is the steroid hormone,mineralocorticoid secreted from the adrenal cortex.It primarily maintains the blood pressure by regulating the levels of sodium and potassium in blood.When the blood pressure falls down less blood reaches kidney which releases Renin by Juxta glomerulus cells.Now a whole cascade is set up of Angiotensinogen,Angiotensin I,AngiotensinII and Aldosterone to balance the blood pressure.Aldosterone increases sodium ion reabsorption into blood by tubular epithelial cells.Water also moves in the same direction.Potassium moves out from the blood into the kidneys and excreted through urine.An increase in aldosterone thus increases blood pressure and vice versa.