Nephron

Nephron


NEPHRON

  • Structural & functional unit of Kidney.
  • Appox. 1 -1 .3 million nephrons each kidney.
  • Total length – 45-65 mm.

STRUCTURE OF A NEPHRON:

Combination of,

  • Filtration apparatus – Glomerulus with Bowman’s capsule
  • Long uriniferous tubule
1. Filtration apparatus:
  • Glomerulus within Bowman’s capsule
  • Together referred as Malphigian body
1a) Glomerulus:
  • Composed of capillaries loops from afferent arterioles
  • Afferent arterioles ramify into capillaries tuft forming glomerulus inside Bowman’s capsule.
  • Glomerular capillaries reunite to form efferent arteriole.
1b) Bowmen’s capsule:
  • Contains glomerulus.
  • Layers:
  • Parietal layer.
  • Visceral layer of epithelium.
  • Encircles glomerulus capillaries.
  • Epithelial cells – “Podocytes”.
  • Space enclosed between two layers continuous with uriniferous tubule lumen.
2. Filtration surface/barrier:
  • Formed by Glomerular membrane.
  • Through which fluid is filtered out from blood into uriniferous tubules.
Components:
  • Glomerular capillary endothelium.
  • Basement membrane (basal lamina).
  • Bowman’s visceral epithelium (podocytes).
Specialized cells:
  • Mesangial cells/ Stellate cells –
  • Located between basal lamina (basement membrane) & endothelium.
  • Contractile.
  • Role in glomerular filtration regulation.
3. Uriniferous tubule:
Divisions:
  • Proximal tubule
  • Loop of Henle
  • Distal convoluted tubule
  • Collecting ducts
3a) Proximal tubule:
  • Longest part of nephron. 
  • Subdivided – 
  • Proximal convoluted tubule (PCT) & Proximal straight tubule.
  • PCT – About 15 mm long & located in cortex.
  • Proximal straight tubule – Located in superficial portion of medulla.

3b) Loop of Henle:

  • Formed by abrupt narrowing of PCT.

Divisions:

  • Thin descending limb forming a loop
  • Thin ascending limb
  • Thick ascending limb.
Differences in Henle loop in cortical & juxtamedullary nephrons:

Cortical nephrons:

  • Short loop of nephron
  • Glomeruli in superficial/outer portion of cortex.

Juxtamedullary nephron:

  • Long loops extend down medullary pyramids.
  • Glomeruli deep in corticomedullary junction/juxtamedullary region of cortex.

Extension of limbs:

  • Thin descending segment & thin ascending segment lie in medulla.
  • Thick ascending segment starts in medulla to extend into cortex.

3c) Distal convoluted tubule (DCT):

  • Start & nestle between its afferent & efferent arterioles.
  • About 5 mm long 
  • Lies entirely in cortex.
  • Ultimately coalesce to form collecting duct.

Specialized cells:

Macula densa –

  • Lies in start of distal tubule
  • At contact point with afferent arterioles

3d) Collecting ducts:

  • 20 mm long
  • Pass through renal cortex & medulla emptying into kidney pelvis at medullary pyramids apexes.
  • 2 types epithelial cells
  • Principal cells (P cells) & Intercalated cells (I cells) 

P cells:

  • Involved in Na+ reabsorption 
  • ADH stimulated water absorption.

I cells:

  • Concerned with acid (H+) secretion
  • HCO3– transport

TYPES OF NEPHRONS:

  • Cortical nephron & Juxtamedullary nephron
1. Cortical nephron:
  • 85% of nephrons with glomerulus located superficially in cortex.
  • Short loop of Henle.
  • No / very short ascending thin segment.

2. Juxtamedullary nephron:

  • Remaining 15% with glomerulus deep incortex at cortico-medullary junction.
  • Long loop of Henle reach deep into medulla upto papilla.
  • Distinct ascending thin segment.
  • Function: 
  • In urine concentration by increasing & maintaining high osmolarity within renal medulla.

Draining end:

  • Efferent arteriole of cortical nephrons drain into peritubular arteries
  • Efferent arteriole of juxtamedullary nephrons drains into Vasa recta along with peritubular capillaries.
Exam Question
 

NEPHRON

  • Approximately 1 -1 .3 million nephrons in each kidney.
  • Total length of nephron – 45-65 mm.
  • Glomerulus composed of loops of capillaries which arise from afferent arterioles.
  • PCT – About 15 mm long & located in cortex.
  • Distal convoluted tubule (DCT) – About 5 mm long.
  • Collecting ducts – 20 mm long passing through renal cortex & medulla.
  • Epithelium in collecting ducts – Principal cells (P cells) & Intercalated cells (I cells) 
  • P cells – Involved in Na+ reabsorption & ADH stimulated water absorption.
  • I cells – Concerned with acid (H+) secretion & HCO3– transport.
  • Juxtamedullary nephron – Remaining 15% with glomerulus deep in cortex at cortico-medullary junction.
  • Long loop of Henle reachs deep into medulla up to papilla.
  • Efferent arteriole of juxtamedullary nephrons drains into Vasa recta along with peritubular capillaries.
Don’t Forget to Solve all the previous Year Question asked on Nephron

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