The kidneys and their functions

The kidneys are found on each side of the backbone, situated between the thick muscles of the back and abdomen and are shaped like a bean.

It measures about 4 ½ inches ( 11.4 cm) in length and about 2 ½ inches (6.3 cm) in width and is about 1 inch (1.5 cm) thick.

The kidneys perform several essential functions:

• They filter the metabolic wastes from the blood plasma and excretes it from the body.

• They participate in the maintenance of the constant extracellular environment, required for proper cell functioning.

• They excrete waste products of metabolism - such as urea, creatinine and uric acid.

• They excrete water and electrolytes to match water intake and endogenous production.

• They are able to regulate the excretion of water and solutes by changing the tubular re-absorption or excretion.

• They secrete hormones that participate in systemic and renal hemodynamic regulation (renin, prostaglandins, bradykinin), red blood cell production (erythropoietin), as well as calcium, phosphorus and bone metabolism (vitamin D).

• They also perform other functions such as catabolism of peptide hormones and synthesis of glucose (glyconeogenesis) when fasting.

Each kidney contains about 1,000,000 to 1,300,000 nephrons, which is the basic functioning component of the kidney, and are specialized in such a way that it can move material back and forth between blood plasma and urine in order to conserve essential materials while still eliminating wastes.

Each nephron consists of a glomerulus (it is a tuft of capillaries between two arterioles) and a series of tubes.

The glomeruli are found in the outer part of the kidney (the cortex) and the tubes are present both in the cortex as well as the inner part - the medulla.

Urine is formed when the nephrons filter the blood plasma and the filtrate (or wastes) is converted into urine. This action clears the blood plasma of wastes and non-essential materials.

The blood plasma is filtered across the specialized glomerular membrane (in the glomerulus) into the nephron tubes.

By active and passive membrane transport the nephron tubule reabsorb essential materials from the filtrate and return it to the circulating blood.

The nephron tubule cells can also actively secrete certain materials from the blood to the filtrate to increase the efficiency of clearing the blood plasma.

The kidneys can control the volume and electrolyte composition of urine by either diluting or concentrating the urine formed.

Should the blood plasma become too diluted the kidneys can reabsorb more solutes and less water - leading to more diluted urine, but when the plasma becomes too concentrated, the kidneys will absorb more water and less solutes, which will produce more concentrated urine.

The kidneys also play a function in regulating the pH of the body, which is done by secreting ions and reabsorbing bicarbonate ions.

Other pages of interest

• The regulatory function of the kidneys
• Bilirubin in urine
• Blood in urine
• Glucose in urine
• Ketones in urine
• Leukocytes in urine
• Nitrite in urine
• ph of urine
• Protein in urine
• Specific gravity of urine
• Urobilinogen in urine
• Parameters of urine test strips (dip sticks)

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  • Kidneys and their functions

  • Kidney function regulating body fluids

  • Bilirubin in urine

  • Blood in urine

  • Glucose in urine

  • Ketones in urine

  • Leukocytes in urine

  • Nitrite in urine

  • ph of urine

  • Protein in urine

  • Specific gravity of urine

  • Urobilinogen in urine

  • Parameters of urine test strips (dip sticks)

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