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Q.Explain the structure and function of the human Nephron. How does it contribute to urine formation? OR Explain the organisation of the human skeleton. Distinguish between Axial and Appendicular skeleton with examples.

Jammu Kashmir JkboseJammu and Kashmir Board of School Education (Class 11) 2025Subjective· 5mImportance★★★★★
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The nephron filters blood at the glomerulus, then selectively reabsorbs useful substances and secretes wastes along its tubule, converting ~180 L of filtrate a day into about 1-1.5 L of concentrated urine.

Structure of the Nephron:

Each human kidney contains about a million nephrons, each consisting of:

  1. Malpighian body (renal corpuscle): made of the glomerulus (a tuft of capillaries fed by an afferent arteriole and drained by a narrower efferent arteriole) enclosed within the double-walled Bowman's capsule.
  2. Proximal Convoluted Tubule (PCT): a highly coiled tubule lined with microvilli-bearing cells, lying close to the Bowman's capsule.
  3. Loop of Henle: a U-shaped structure with a descending limb (permeable to water) and an ascending limb (impermeable to water, actively pumps out NaCl), dipping into the renal medulla.
  4. Distal Convoluted Tubule (DCT): a coiled tubule that opens into a collecting duct.
  5. Collecting duct: receives fluid from many nephrons and carries it through the medulla to the renal pelvis, ureter and bladder.

Urine formation — three steps:

  1. Glomerular filtration: blood pressure forces water and small solutes (glucose, amino acids, salts, urea, etc., but not blood cells or large proteins) out of the glomerular capillaries into Bowman's capsule, forming the glomerular filtrate (~180 litres/day in an adult).
  2. Tubular reabsorption: as the filtrate passes through the PCT, loop of Henle, DCT and collecting duct, most of the water (~99%) and useful substances — glucose, amino acids, and most Na+/other ions — are reabsorbed back into the blood by active and passive transport. The PCT alone reabsorbs about 70-80% of the filtrate. …

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