Archive for the ‘ L1-Nephron ’ Category

L1-Nephron

Basic Info

žIt is the functional unit of the kidney. žEach kidney contains about one million nephron. žAfter age 40 the number of functioning nephrons decreases by about 10%.

It consists of:

1-Renal corpuscles.

2-renal tubules:

  • —Proximal convoluted tubule.
  • —Loop of henle.
  • —Distal convoluted tubule.

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1) Renal corpusles

It is formed of:

1-Bowman’s capsule: is doubled walled spherical  cup shaped like structure

It is the dilated blind end of the renal tubule

2-Glomerulus: It is a tuft of capillary which are surround by the Bowman’s capsule.

3-Glomerular membrane: (formed of three layers)

—The endothelium of glomerular capillaries —A basement membrane —The epithelium of Bowman’s capsule.

Picture2

Renal Blood Supply

Picture3

JuxtaGlomerular Apparatus

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It  consists of 3 cell types:

Macula densa cells

  • Present at the zone between ascending loop of Henle &DCT.
  • It detects the fall of NaCl leading to renin release.

Juxta-glomerular cells

  • —Located at the wall of afferent arterioles —
  • Respond to wall stretch —
  • Forms &secretes renin

Mesangial cells

  • Interstitial cells act as link between the other 2 types of cells

Function of renin

  • Conversion plasma angiotensinogen to angiotensinI (AI)
  • AI→Angiotensinǁ (Aǁ) by ACE
  • Function of Aǁ:
  1. VC → ↑BP
  2. ↑ aldosterone secretion from supra-renal cortex
  3. ++ secretion of ADH
  4. ++ thirst sensation
  5. ++ Na reabsorption from PCT

The Glomeruli Functions

  • Glomerular filtration is the first step in urine formation
  • It is a passive process
  • The glomeruli act as a semi permeable membrane
  • They filter all the constituents of plasma except the colloids(protein &fat)
  • About 700 ml of plasma passes through the kidney per minute only 125 ml are filtered
  • Factors favoring glomerular filtration
  1. The high pressure in the glomerular capillaries (it is the only capillary in the body that lie between two arteries
  2. Large surface area of the glomerular capillary
  3. High permeability of the glomerular membrane due to the presence of pores

2)Renal Tubules

General Functions

1-Reabsorption: It is the transport of substances from the lumen of the tubules to the blood stream.

2-Secretion: It  is the transport of substance into the tubular lumen. The most important secreted substance include creatinine ,uric acid  H ions &foreign substance.

3-Synthesis: NH3 that play a role in acid base balance.

Proximal convoluted tubule

Functions:

  1. It is the only part where reabsorption of glucose, amino acids and phosphate take place by an active process.
  2. Phosphate reabsorption is controlled by parathyroid hormone.
  3. About 70-75% of Na ions are reabsorbed by an active process.
  4. Passive reabsorption of70-75% of water secondary to Na K glucose & amino acids

Loop of Henle

  • žIt is a U shaped consisting of descending &ascending limbs
  • žIt is concerned with the production of diluted or concentrated urine
  • žThe structure of loop of henle allow them to constitute a counter current system
  • žThis system in which the inflow and outflow passes parallel to each other and in opposite direction.

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How concentrated urine is produced?
  • AT the descending loop of henle:
  1. The walls are highly permeable to water & poorlypermeable to solutes
  2. As a result the tubular fluid becomes hypertonic in the medullary inter stetium.
  • AT the ascending loop:
  1. The walls are highly permeable to solutes & less permeable to water
  2. It is the responsible for creating graded hyper osmolarity

Picture6

Distal convoluted tubules

This segment  is responsible for:

1 –Final adjustment of urine volume.

  • Water reabsorption determine  the volume of urine.
  • It is under the control of anti diuretic hormone (ADH).

2- Regulation of PH &electrolytes.

  • Na is reabsorbed in exchange with either H ions or K ions
  • It is under aldosterone hormone.
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