SOLUTION

Function of the Kidneys

The kidneys perform the primary functions of the urinary system.

Excretion of Waste and Foreign Substances:-The production of urine in the kidneys allows waste products such as ammonia, urea, bilirubin and creatinine to be excreted from the body. Foreign substances such as environmental toxins and drugs can also be eliminated in urine

Vitamin D Hydroxylation and Calcium Maintenance:-The kidneys maintaining calcium levels via the hydroxylation of inactive vitamin D and the production of the active form of vitamin D, 1,25-dihydroxy vitamin (calcitriol), in the proximal tubule.

Erythropoietin and Red Blood Cells:-The kidneys are involved in red blood cell production via; the production of erythropoietin.

Maintenance of Blood Osmolarity: – A constant blood osmolarity of approximately 290 mOsm/L is maintained due to the regulation of solutes conserved or excreted in urine.

Regulation of the ionic Composition of Blood:- The calcium, chloride, phosphate, potassium and sodium ion levels in the blood are all regulated by the kidneys.

Regulation of Blood pH:- The pH of the blood (7.35-7.45) is regulated through the excretion (of hydrogen ions) and conservation (of bicarbonate ions) of ions into the urine.

Regulation of Blood Volume and Pressure:- The elimination of fluids from the body in the form of urine and the conservation of fluids in the body aid in the regulation of both blood volume and blood pressure. m. An increase in renin release leads to an increase in blood pressure, due to an increase in sodium and water reabsorption in the renal tubules.

Regulation of Blood Glucose Levels:- Glutamine is used by the kidneys in the process of gluconeogenesis, in which glucose is synthesized. The glucose thus formed can then be released into the bloodstream to aid in the maintenance of a steady blood glucose level. Glucose counter-regulation can then be achieved. 

Reabsorption and Filtration:-Urine is formed in two stages. First, blood is filtered into the kidney tubules to form a clear fluid (i.e. a filtrate) which contains the Waste substance urea and many useful substances which the body cannot afford to lose. Second, the useful substances are reabsorbed from the filtrate back into the blood leaving only urea and other substances in the kidney tubules which are of no use to the body. The technical words for these two stages are filtration and reabsorption.