Dr P. Stewart,
Sydney, Australia.

Functions		Acid/base function
Regulation of water & electrolytes		Excretion of waste products
Filtration		Hormones of the kidney
Selective & passive reabsorption

• Regulation of the water and electrolyte content of the body.
• Retention of substances vital to the body such as protein and glucose
• Maintenance of acid/base balance.
• Excretion of waste products, water soluble toxic substances and drugs.
• Endocrine functions. 

The kidney allows a person to eat and drink according to their habits without changing the composition of their fluid compartments.

Renal Blood Supply is normally is about 20% of the cardiac output. Approximately 99% of the blood flow goes to the cortex and 1% to the medulla. The cortex is the outer part of the kidney containing most of the nephrons. The medulla is the inner part of the kidney and contains the specialised nephrons in the juxta-medullary region, immediately next to the medulla. These nephrons have a greater concentrating ability, the mechanism being explained below.

The kidney is unique as it has two capillary beds arranged in series, the glomerular capillaries which are under high pressure for filtering, and the peritubular capillaries which are situated around the tubule and are at low pressure (figure 1). This permits large volumes of fluid to be filtered and reabsorbed.

The Nephron: Each kidney consists of about one million nephrons. The nephron is made up of a glomerulus and its tubule (figure 2).

The tubule is made up of a number of sections, the proximal tubule, the medullary loop (loop of Henle), and the distal tubule which finally empties into the collecting duct. Urine is formed as a result of a three phase process : Simple filtration Selective and passive reabsorption Excretion.

(Continued ...)

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