Excretory Products and their Elimination

Human excretory system - structure and function

  • Human excretory system contains paired kidneys, paired ureters, uinary bladder and urethra.
  • Kidney is surrounded by an adipose tissue capsule and is bean shaped, dark red in colour and weighs about 150 g is adult male ; 135 g in adult female.
  • The glandular part of the kidney surrounds a large carity called renal sinus and that contains renal pelvis which forms 2-3 calyces.
  • The outer distinct zone in kidney is darker, reddish brown called cortex and inner lighter medulla contains 8-10 conical sections called renal pyramids.
  • The structural and functional unit of kidney is nephron where it is of 2 types (i) Cortical nephron (80-90%) and (ii) Juxtamedullary nephron (10-20%)
  • Ureters (28 cm) are smooth muscled tubes which carry urine from kidneys into urinary bladder.
  • Urethra is 18-20 cm long in human male and 3-4 cm in human female and which opens by urethral orifice (or) urinary aperture that are guarded by urethral sphincters, through which the urine is passed out.
  • Each nephrons consists of 2 parts (i) Malphigian corpuscle (ii) tubule (or) uriniferous tubule.
  • Malphigian corpuscles contains Bowman's capsule and glomerulus.
  • The glomerulus is formed by the branches of afferent arteriole which interconnected to form tuft (or) capillaries capped by Bownman's capsule.
  • Glomerular membrane consists of capillary endothelium, basement membrane, epithelium made of podocytes.
  • The efferent arteriole from glomerulus forms a fine capillary network around renal tubule called as vasa recta.
  • Henle's loop consists of descending tubule which makes a bend in upper medulla for the cortical nephron and deeper in the medulla for juxtamedullary nephron.
  • Distal convoluted tubule (DCT) commences as a short, highly convoluted tubule in the cortex of juxtamedullary region.
  • Collecting tubule (CT) drains a number of ducts of DCT in cortex. It descends to the tip of medulla to form the ducts of Bellins' which empty via calyces into renal pelvis.
  • Juxta-glomerular cells are the dark granules on the smooth muscle cells of the afferent and efferent arteriole. Those granules contain inactive renin which could convert angiotensinogen into angiotensin which increases blood pressure.

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