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HUMAN EXCRETORY SYSTEM

 😎HUMAN EXCRETORY SYSTEM 😎 



  • In humans, the excretory system consists of a pair of kidneys, one pair of ureters, a urinary bladder and a urethra. 
  • Kidneys are reddish brown, bean shaped structures situated between the levels of last thoracic and third lumbar vertebra close to the dorsal inner wall of the abdominal cavity. 
  • Each kidney of an adult human measures 10-12 cm in length, 5-7 cm in width, 2-3 cm in thickness with an average weight of 120- 170 g. Towards the centre of the inner concave surface of the kidney is a notch called hilum through which ureter, blood vessels and nerves enter. 
  • Inner to the hilum is a broad funnel shaped space called the renal pelvis with projections called calyces. 
  • The outer layer of kidney is a tough capsule. 
  • Inside the kidney, there are two zones, an outer cortex and an inner medulla. 
  • The medulla is divided into a few conical masses (medullary pyramids) projecting into the calyces (sing.: calyx). 
  • The cortex extends in between the A diagrammatic representation of a nephron showing blood vessels, duct and tubule medullary pyramids as renal columns called Columns of Bertini. 
  • Each kidney has nearly one million complex tubular structures called nephrons, which are the functional units. Each nephron has two parts – the glomerulus and the renal tubule. 
  • Glomerulus is a tuft of capillaries formed by the afferent arteriole – a fine branch of renal artery. 
  • Blood from the glomerulus is carried away by an efferent arteriole. 
  • The renal tubule begins with a double walled cup-like structure called Bowman’s capsule, which encloses the glomerulus. 
  • Glomerulus along with Bowman’s capsule, is called the malpighian body or renal corpuscle. 
  • The tubule continues further to form a highly coiled network – proximal convoluted tubule(PCT). 
  • A hairpin shaped Henle’s loop is the next part of the tubule which has a descending and an ascending limb. 
  • The ascending limb continues as another highly coiled tubular region called distal convoluted tubule (DCT). 
  • The DCTs of many nephrons open into a straight tube called collecting duct, many of which converge and open into the renal pelvis through medullary pyramids in the calyces. 
  • The Malpighian corpuscle, PCT and DCT of the nephron are situated in the cortical region of the kidney whereas the loop of Henle dips into the medulla. 
  • In majority of nephrons, the loop of Henle is too short and extends only very little into the medulla. 
  • Such nephrons are called cortical nephrons. 
  • In some of the nephrons, the loop of Henle is very long and runs deep into the medulla. 
  • These nephrons are called juxta medullary nephrons. 
  • The efferent arteriole emerging from the glomerulus forms a fine capillary network around the renal tubule called the peritubular capillaries. 
  • A minute vessel of this network runs parallel to the Henle’s loop forming a ‘U’ shaped vasa recta. 
  • Vasa recta is absent or highly reduced in cortical nephrons

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