Neet PG Medicine Notes 1 – Renal System 1 – Development of the Kidney

Develops from two system

  • Intermediate mesoderm
  • Cloaca – endodermal derivative

Structure arising from the cloaca

  • Primitive urogenital sinus
  • Rectum

From the primitive urogenital sinus, we get the urethrovesical canal

So the three structures arising from the cloaca is

  • Urethro means urethra
  • Vesico means bladder
  • Rectum

The kidney is a mesodermal derivative – Intermediate mesoderm

Types of mesoderm

  • Paraxial mesoderm – it gives rise to somite that is myotomes
  • Lateral plate mesoderm – it gives rise to pleura peritoneum etc

Lateral plate mesoderm has two parts

  • Somatopleuric part
  • Splanchnopleuric part

Intermediate mesoderm gives rise to four important structures

  1. Nephrogenic cord or urogenital ridge – gives rise to kidney
  2. Mesonephric duct or the Wolffian duct
  3. Paramesonephric duct or Mullerian duct in females
  4. Gonads

Nephrogenic cord

  • Close to mesonephric duct
  • Three parts to the nephrogenic cord
  1. Pronephros develops by day 22 it regresses by end of the 4th week
  2. Mesonephros develops by the beginning of the 5th week and regresses by 4 months more significant in amphibians
  3. Metanephros is the other name of adult kidney

Metanephros has two parts

The yellow structure inside the red ring is interacting to form the metanephros

  • The first structure is the mesenchyme of the metanephric blastema – gives rise to the excretory part of the kidney
  • The epithelium of the ureteric bud – gives rise to the collecting part of the kidney

The epithelium of the ureteric bud from the mesonephric duct

Metanephros develops from an interaction between the two structures

This interaction is called epithelial-mesenchymal interaction – this is a PGI question

The adult kidney is called metanephros

epithelial-mesenchymal interaction occurs between 5th – 7th week

first fully formed nephron  – 8th week

ascend and rotation  – 9th week

  • fetal kidney – S1-S2
  • adult kidney T12-S3 this is the ascent

Urine formation – 10th week

EMI epithelial-mesenchymal interaction – the gene needed for this interaction is WT1 gene on chromosome 11 this gene is expressed by mesenchyme of metanephric blastema – the other gene is PAX2 gene

WT1 gene mutation two syndromes you can get is

  • WAGR syndrome

    W Wilms tumor
    A aniridia
    G genitourinary anomalies
    R mental retardation
  • Denys Drash syndrome

    Wilms tumor
    Organomegaly – liver spleen kidney
    Male pseudohermaphroditism
    Early renal failure
    Diffuse mesangial sclerosis

Two syndromes of WT1 mutation

  • WAGR syndrome
  • Denys Drash syndrome

WT2 mutation causes

Beckwith-Wiedemann syndrome

  • Microcephaly
  • Hemihypertrophy of testis
  • Wilms tumor
  • An umbilical hernia
  • macroglossia

PAX 2 gene mutation can produce

  • Renal hypoplasia
  • Optic nerve coloboma
  • Rarely unilateral renal agenesis

RET/GDNF mutation van cause

  • Bilateral renal agenesis – associated with Potter’ syndrome

Potter’s syndrome

  • Bilateral renal agenesis
  • Lung hypoplasia
  • Disc-shaped adrenal
  • Absent renal artery
  • Mostly fatal

Unilateral renal agenesis

  • 1:1000
  • More common in females
  • Hypertension
  • Not very dangerous

Bilateral renal agenesis RET

  • Potters syndrome
  • Not compatible with life

Final points

  • INTERMEDIATE MESODERM AND CLOACA – urogenital system
  • Nephrogenic cord or urogenital ridge extends from cervical to the sacral region in the embryo
  • 3 successive stages aligned close to the Wolffian duct
  • Pronephros regresses by 5 weeks
  • Mesonephros is the excretory organ until metanephros regresses by 4th months
  • Metanephros is the adult kidney
  • Epithelial-mesenchymal transition
  • Collecting system develops from the ureteric bud
  • WTI – required for EMI – mutation causes WAGR/DENNYS DRASH
  • RET/GDNF
  • PAX2 – required for EMI
  • Fetal metaphros is at S1-S2 9th week
  • WNT4 and WNT6 needed for tubular growth
  • After birth, new nephrons cant be developed and lost nephrons cant replaces
  • Nephrogenesis is complete by 32-36 weeks
  • After birth only there is an increase in concentration capacity
  • Normal capacity to concentrate urine reached by 18 months
  • People with a poor number of nephrons at birth are more vulnerable to kidney disease
  • A child with low birth weight have more chance of kidney disease
  • Mother blood pressure is related to her age and high-pressure more chance of low birth weight baby

ALWAYS REMEMBER

  • Day 22 – pronephros
  • Formation of ureteric bud – 5th week
  • EMT 5th – 7th week
  • The first nephron formed 8th week
  • Fetal kidney ascent at 9th week
  • Filtration begins 10th week
  • Nephrogenesis complete by 32-36 week
  • Fetal kidney reaches adult concentration by the 18th month

 

 

 

 

 

 

 

 

 

 

 

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