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Excretion

Excretion. Process of excretion in the kidney Filtration Selective reabsorption Tubular excretion. Why is excretion necessary ?.

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Excretion

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  1. Excretion Process of excretion in the kidney Filtration Selective reabsorption Tubular excretion

  2. Why is excretion necessary? • As a result of metabolism, harmful waste products such as carbon dioxide and nitrogenous waste are produced. These wastes affect the normal functioning of cells where they are accumulated. Hence excretion, which is the of removal of waste products formed by metabolism, ensures that these waste products do not build up to toxic levels.

  3. The main excretory organs and their functions The lungs • Lungs excrete carbon dioxide and water in form of water vapour.

  4. The Skin • The sweat glands in the skin extract mainly water, some salts and little urea ( which is a nitrogen-containing or nitrogenous waste) from the blood and from sweat. We lose sweat through the surface of the skin, in this way, the skin excretes excess salts and urea.

  5. Human skin in longitudinal section

  6. The urinary system • The urinary system produces urine. Urine, like sweat, consists mainly of water, some salts and a small percentage of nitrogenous waste such as urea.

  7. The structure and functioning of the urinary system • The urinary system consists of two kidneys, two ureters, the urinary bladder and the urethra. These vessels are closely associated with the urinary system: • Renal artery - carries blood laden with nitrogenous waste to the kidneys. • Renal vein – carries blood with very little nitrogenous waste away from the kidneys.

  8. The Urinary system

  9. Kidneys – A pair of bean shaped organs in the abdominal cavity. The right kidney is usually lower than the left kidney. • Ureters – are a pair of ducts which carry urine from the kidneys to the bladder, each ureter begins within each kidney as a widened portion, the pelvis. • Bladder – Muscular sac which temporarily stores urine. It can hold up to 600ml of urine. • The urethra – Is the tube which carries urine from the bladder to the exterior. In a male the urethra runs through the penis and in female it opens separately from the vagina.

  10. Internal structure of the kidney

  11. Kidney • The kidney is covered on the outside by a thin membrane, the renal capsule. Within the renal capsule is the outer cortex and the inner medulla. The medulla is made up of a number of conical (cone shaped) pyramids. The pyramids have a number of tubes called ducts of Bellini.

  12. The nephron

  13. The nephron • The nephron is the functional unit of the kidney and is structured as follows: It consists of two parts, the Malpighian body and renal tubule. The malpighian body has the following structure: • Made up of network of capillaries, glomerulus, inside a bowman’s capsule. The glomerulus is also called the first capillary network • The inner wall of the capsule is made up of specialized cells called podocytes.

  14. The renal tubule Is made up of: • A proximal convoluted tubule • The loop of henlewith decsending limb, ascending limb and hair pin bend. • A distal convoluted tubule which opens into a collecting tubule.

  15. Blood supply of the nephron • The renal artery entering the kidney branches into smaller arteries. These smaller arteries form afferent arterioles, one supplying each nephron. Within the bowman’s capsule, each afferent arteriole divides to form the first capillary network or glomerulus.

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