please explain the procees of urine formation and working of nephron in detail

A Nephron has two parts:

  • Glomerulus
  • Renal tubule

Glomerulus

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.

Re-absorption

  • 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

Secretion

  • 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, HCO3

    • 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 H+ and K+ ions; hence, maintains pH and ionic balance

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Nephronit consists of aGlomerulus, Bowman's Capsule and renal tubules(which contains Proximal convulated tubule, DIstil Convulated , andloop of Henle)Main Function of Nephron is filtration of Bloodin glomerulus filtration occurs due to osmotic pressure differencebut this filtrate also contains some useful substances like glucose, mineral ionsthese substances are reabsorbed in the loop of Henle

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1.FILTRATION:Urine formation begins with the process of filtration, which goes on continually in the renal corpuscles . As blood courses through the glomeruli, much of its fluid, containing both useful chemicals and dissolved waste materials, soaks out of the blood the blood through the membranes (by osmosis and diffusion) where it is filtered and then flows into the Bowman's capsule. This process is called glomerular filtration. The water, waste products, salt, glucose, and other chemicals that have been filtered out of the blood are known collectively as glomerular filtrate.2.REABSORPTION:Reabsorption, by definition, is the movement of substances out of the renal tubules back into the blood capillaries located around the tubules (called the peritubular copillaries). Substances reabsorbed are water, glucose and other nutrients, and sodium (Na+) and other ions. Reabsorption begins in the proximal convoluted tubules and continues in the loop of Henle, distal convoluted tubules, and collecting tubules3.SECRETION:Secretion is the process by which substances move into the distal and collecting tubules from blood in the capillaries around these tubules .

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