Explain the role of different segments of nephron in urine formation and osmoregulation with the help of a neat labelled diagram!

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Please find below the solution to the asked query.

A Nephron has two parts:

  • Glomerulus
  • Renal tubule


Tuft of capillaries formed by the afferent arteriole

Renal Tubule : Has many parts
(Bowman’s capsule      Proximal Convoluted Tubule (PCT)   Hairpin-shaped Loop of Henle      Distal Convoluted Tubule (DCT)   Collecting duct   Medullary pyramids → Renal pelvis.)

Glomerulus + Bowman’s Capsule = Malpighian body (Renal Corpuscle)

Urine Formation

Involves 3 basic steps:

  • Glomerular filtration

  • Re-absorption

  • Secretion

Glomerular filtration

  • Kidney filters 1100−1200 mL blood/min

  • Filtration of blood occurs as it passes through three layers.

    • Endothelium of glomerular blood vessels

    • Epithelium of Bowman’s capsule

    • Basement membrane between these two layers

  • Epithelial cells of Bowman’s capsule are called podocytes. Arrangement of these podocytes leaves extremely minute spaces called filtration slits or slit pores.

  • Ultrafiltration occurs through these slits pores, i.e., all plasma components (except proteins) get filtered into the lumen of the Bowman’s capsule.

  • Glomerular Filtration Rate (GFR): 125 mL/min or 180 L/day

  • The glomerular filtration rate is regulated by the juxta glomerular apparatus which releases the hormone renin.


  • GFR = 180 L/day; Urine released = 1.5 L/day. Thus, 99% of filtrate is re-absorbed by the renal tubules.

  • Re-absorption occurs through the epithelial cells of the various segments of the nephrons.

  • Active Re-absorption: Glucose, Na +, amino acids

  • Passive Re-absorption: Nitrogenous waste, water


  • Tubular cells secrete substances such as H +, K   and ammonia into the filtrate.

  • Importance: Maintenance of ionic and acid-base balance of body fluids

Function of the Tubules

  • Proximal Convoluted Tubule

    • Specialised for re-absorption as it is lined by a simple cuboidal brush border epithelium which increases the surface area for absorption

    • Re-absorbs all essential nutrients, electrolytes and water

    • Secretes H+, NH4+, K+ ions and    to maintain pH

  • Henle’s Loop

    • Minimum re-absorption occurs here

    • Helps in maintaining high osmolarity of the medullary fluid

    • Descending loop of Henle: Permeable to water and impermeable to electrolytes; Concentrates the filtrate

    • Ascending loop of Henle: Impermeable to water and permeable to electrolytes; Dilutes the filtrate

  • DCT

    • Conditional re-absorption of Na+, water, HCO 3

    • Selectively secretes H+, K+, NH3

    • Maintains pH and Na−K balance in blood

  • Collecting Duct

    • Concentrates the urine by absorbing large amounts of water

    • Allows passage of urea into the medullary interstitial fluid to maintain osmolarity

    • Secretes Hand K  ions; hence, maintains pH and ionic balance

Hope this information will clear your doubts about the topic.
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