Kidneys

The urinary system

The Unitary system consists of two kidneys, a single bladder, two ureters, which carry urine from the kidneys to the urinary bladder and a single urethra, which carries urine from the bladder to the outside of the body.

The kidneys

The kidneys are two bean- shaped glands about the size of a tightly clenched first. They lie behind the peritoneum on the posterior aspect of the abdominal wall on either side of the vertebral column. The kidneys extend from the level of the last thoracic (T12) to the third lumber (L3) vertebrae and the rib cage (diaphragm) partially protects them. The liver lies superiorly over the right kidney, causing it to be slightly lower than the left one.

Size

Each kidney is about 10cm long, 6.5cm wide and 3cm thick. It weighs about 120g.

The kidney is dark red in color and covered by tough fibrous capsule. Microscopic Structure

The kidney is composed of two zones, the outer portion of cortex and the inner part medulla. The cortex is dark red in color with rich blood supply while the medulla is paler in color. The collecting area for urine which merges with the upper pelvis is divided into major branches or calyces which later subdivided into smaller calyces; they are referred to as minor calyces. Each calyx cups over projections from the medulla known as pyramid.

The Nephrons

The Nephrons are the functioning units of the kidneys. There are about 1 million nephrons in each kidney and about 50-55mm in length. Each nephron starts at a knot of capillaries called glomerulus. It is fed by a branch of the renal artery, the afferent arterioles takes blood to it and efferent arterioles collect the blood back.

Blood Supply: Renal entries early branches of thedescending abdominal aorta

Venous Return: Corresponding vein, lymphatic drainage: Aortic lymph glands, nerve supply: sympathetic and parasympathetic nerves.

Functions of the kidney

1.           Manufacture Urine:

2.           Elimination of wastes from the body e.g. breakdown production of protein-urea, urates uric Acid, creatinine, ammonia and sulphate.

3.           Elimination of toxins.

4.           Secretion of useful substances to the body. Rennin and erythropoietin.

5.           Regulation of the concentration of solute in the blood, regulate concentration of major ions in the body such as sodium No, chlorine CL potassium K⁺ and calcium C²⁺.

6.           Regulation of pH of the extracellular fluid; the kidneys secrete variable amount of H+ to help regulate the extra cellular fluid pH.

7.           Regulation of RBC synthesis. The erythro erythropoietin secreted by the kidneys regulates the synthesis of RBC in the bone marrow.

8.           Vitamin D synthesis: it plays important role in controlling C²⁺ level in blood by regulating the synthesis of vitamin D.

9.           Regulation of blood volume: by producing either a large volume of dilute urine or a small volume of concentrated urine.