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Friday, 3 February 2017

Excretory products and their elimination I

Elimination of metabolic wastes products from the animal body to regulate the composition of body fluids and tissues is called excretion. These wastes products includes ammonia, uric acid, urea, carbon dioxide and ions like Na+, K+, Cl- and phosphates and sulphate.

Ammonia is the most toxic and uric acid is the least toxic. The process of removing ammonia is called ammonotelism and organisms that excrete ammonia are called ammonotelic (bony fishes, aquatic amphibians and insects).

The organism that release urea as nitrogenous wastes are called ureotelic (mammals, terrestrial amphibians). The organism that excretes uric acids are called urecotelic (reptiles, birds and land snails).
Human Excretory System
Human excretory system consists of
i. A pair of kidneys
ii. A pair of ureters
iii. A urinary bladder
iv. A urethra
Kidneys are reddish brown bean shaped structure situated between last thoracic and lumber vertebra. Each with a notch on its inner side called hilum through which ureter, blood vessels and nerves enter.
Inside the hilum has broad funnel shaped space called renal pelvis with projection called calyces.
Inside the kidney are two zone- outer cortex and inner medulla. Medulla is divided into medullary pyramids projecting into calyx.
Cortex extends between medullary pyramids as renal column called Columns of Bertini.

The functional unit of kidney is nephron. Each kidney contains about one million nephrons. Each nephron had two parts- the glomerulus and renal tubules. Glomerulus is the tuft of capillaries formed by afferent arteriole. Blood from glomerulus is carried away by efferent arteriole.

Renal tubules starts with Bowman’s capsule continue with tubular parts divided into Proximal Convoluted tubules, Henle’s loop and Distal Convoluted tubule.

The malpighian tubules, PCT and DCT of nephron are situated in cortical region where as loops of Hanle’s into medulla.

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