SUMMARY OF EXCRETORY PRODUCT AND THEIR ELIMINATION- NEET 2020

 SUMMARY OF EXCRETORY PRODUCT AND THEIR ELIMINATION- NEET 2020

Kidney

Mạny nitrogen containing substances, ions, CO2, water, etc. That accumulate in the body have to be elinimated Nature of nitrogenous wastes formed and their excretion vary amòng animals, mainly depending on the (availability of water). Ammonia, urea and uric acid are the major nitrogenous wastes excreted. Protonephridia, nephridia, malpighian tubules, green glands and the kidneys are the common excretory In animals. They not only eliminate nitrogenous wastes but also help in the maintenance of ionic and acst balance of body fluids. In humans, the excretory system consists of one pair of kidneys, a pair of ureters, a urinary bladder urethra. Each kidney has over a million tubular structures called nephrons. Nephron Is the functional unit of  kidney and has two portions - giomerulus and renal tubule. Glomerulus is a tuft of capillaries formed from afferent arterioles, fine branches of renal artery. The renal tubule starts with a double walled Bowman's capsule and is further differentiated Into a proximal convoluted tubule (PCT), Henle's loop (HL) and distal convpies tubule (DCT). The DCTs of many nephrons join to a common collecting duct many of which ultimately open into  the renal pelvis through the medullary pyramids. The Bowman's capsule encloses the glomerulus to Malpighian or renal corpuscle.

Urine formation involves three main processes.
 Like- filtration, reabsorption and secretion. Filtration is a non-selective process performed by the glomerulus using the glomerular capillary blood pressure.  About 1200 blood is filtered by the glomerulus per minute to form 125 ml of filtrate in the Bowman's capsule per mina (GFR). JGA, a specialised portion of the nephrons, plays a significant role in the regulation of GFR. Nearly per cent reabsorption of the filtrate takes place through different parts of the nephrons. PCT is the major site of reabsorption and selective secretion. HL primarlly helps to maintain osmolar gradient (300 mOsmol- 1200 mOsmolL-1) within the kidney Interstitium.

DCT and collecting duct allow extensive reabsorption of water and certain electrolytes, which help in osmoregulation: H+, K+ and NH3 could be secreted Into the filtrate the tubules to maintain the ionic balance and pH of body fluids. A counter current mechanism operates bet the two limbs of the loop of Henle and those of vasa recta (capilary parallel to Henle's loop). The filtrate gets concentrated as it moves down the descending limb but is diluted by the ascending limb. Electrolytes and are retained in the interstitium by this arrangement, DCT and collecting duct concentrate the filtrate about times ie. from 300 mOsmoll.-1 to 1200 mOsmoll-1, an excellent mechanism of conservation of we Urine is stored in the urinary bladder till a voluntary signal from CNS carries out its release throunh urethra. micturition,Skin, lungs and liver also assist in excretion.