Embryology of Urinary System by Dr. Majid Kakakhel
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Embryology of Urinary System by Resident Urology, Dr. Majid Kakakhel Institute of kidney diseases peshawar
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Embryology of Urinary System by Dr. Majid Kakakhel
- 1. EMBRYOLOGY OF URINARY SYSTEM Nephric System & Its Anomalies Vesicourethra & Its Anomalies By: Dr.MajidJan Kakakhel PGR-Team C InstituteofKidneyDiseases, Peshawar. majidjankakakhel@gmail.com
- 2. NEPHRIC SYSTEM • The nephric system develops progressively as 3 distinct entities: 1. Pro-nephros 2. Meso-nephros 3. Meta-nephros
- 3. Pronephros • Earliest nephric stage in Humans. • Extends from 4th to 14th somites. • Conists of 6-10 pairs of tubules, opens into ducts. • Disappears completely by 4th week of embryonic life. • Rudimentary & non-functional
- 4. Mesonephros • Principal excretory organ during early embryonic life (4-8weeks) • Mesonephric tubules develop from intermediate mesoderm caudal to pronephros shortly before pronephric degeneration.
- 5. Mesonephros • These tubules rapidly lengthens and form S shape loop, medial end forms a cup shape outgrowth ( Bowmans capsule) to which tuft of capillaries is pushed making glomerulus • Laterally, other end connects mesonephric duct.
- 6. Metanephros The Definitive Kidney • The Final phase of development of nephric system, originates from 2 sources: 1. Ureteric Bud 2. Metanephric Mesenchyme (Blastema)
- 7. Metanephros • The ureteric bud grows cephalad and collects mesoderm from the intermediate mesoderm around its tip. • The ureteric bud penetrates the metanephric mesoderm (blastema)
- 8. Metanephros • Here, the bud grows and repeatedly divides. • The first 3 to 5 generation of branches fuse to form the renal Pelvis, • the next divisions become the major calyces, • while further divisions forms the minor calyces and colleting tubules.
- 9. Excretory System • Each newly formed collecting tubule is covered at its distal end by a metanephric tissue cap.
- 10. • Cells of the tissue cap form small vesicles, the renal vesicles
- 11. • Renal vesicles give rise to small S-shaped tubules.
- 12. • One end of the S-shaped tubule becomes cup shape Bowman’s Capsule , to which capillaries grow, and differentiates into glomeruli. • These tubules, together with their glomeruli, forms nephrons or excretory units. • The other end fuses with the collecting tubules and forms an open connection, establishing passageway from Bowman’s capsule to the collecting unit.
- 13. • Continuous lengthening of the excretory tubule results in formation of the proximal convoluted tubule ( PCT), loop of Henle, and distal convoluted tubule ( DCT).
- 14. Congenital Anomalies of Kidney • Ectopic Kidney • Malrotated kidney • Horse-shoe kidney • Bifid ureter • Duplicated ureter • Supernumerary Kidneys • Solitary Kidney
- 15. Ectopic Kidney: • Failure of metanephros to ascend leads to an ectopic kidney. • An ectopic kidney may be on the proper side but low (simple ectopy) or on the opposite side (crossed ectopy) with or without fusion.
- 16. Horse-shoe Kidney: • Fusion of the paired metanephric masses. • Lower poles fused in midline in front of L4 • Ascent is impeded by inferior mesenteric artery
- 17. Renal Agenesis/ Solitary Kidney: • When ureteric but fails to contact Metanephric mesenchyme or when ureteric bud fails to develop.
- 18. Duplicated Ureter: • When An accessory ureteric bud develops from mesonephric duct, meeting the same metanephric mass, forms duplicated ureter. • Rarely, each bud has a separate metanephric mass, resulting in supernumerary kidneys.
- 19. URINARY BLADDER & URETHRA • During the 4th to 7th weeks of development the cloaca divides into: 1.Urogenital Sinus (Anteriorly) 2.Anal canal (Posteriorly)
- 20. Urogenital Sinus Is divided into three parts; A cranial; vesical part; forms most of the bladder and continuous with the allantois. A middle; pelvic part; forms main part of male urethra and entire female urethra. A caudal; phallic part grows towards genital tubercle.
- 21. Urinary Bladder It develops mainly from the vesical part of the urogenital sinus. The trigone is derived from the absorbed caudal ends of the mesonephric ducts. The epithelium is endodermal in origin. The other layers are derived from the splanchinic mesoderm
- 22. • At first, Urinary bladder extends upto umbilicus, where it is connected to the allantois that extends into the umbilical cord • At 15th weeks, the allantois is obiterated, becomes thick fibrous cord Urachus • Urachus extends from apex of the bladder to the umbilicus • In adults it is represented by median umbilical ligament
- 23. URETHRA: The genital tubercle (mesenchymal elevation) develops at the cranial end of the cloacal membrane. Two urethral folds, develop on either side of the urogenital membrane. Laterally two labioscrotal folds develop on either side of the urethral folds. Two urethral folds in male fuse with each other to close the penile urethra. Two urethral folds in female remain separate to form labia minora. Labioscrotal folds)
- 24. The genital tubercle elongates forming the phallus, which is the precursor of the penis. Most of the male urethra : prostatic, membranous and spongy parts is derived from endoderm of the pelvic part of urogenital sinus. The distal part of male urethra in glans penis starts as ectodermal solid cord that grows towards the root of penis to meet the spongy urethra , later it canalizes.
- 25. Anomalies: Urachal anomalies Extrophy of the bladder (Ectopiae vesica); exposure of the posterior wall of the bladder due to a defect in the anterior abdominal wall and anterior wall of the bladder.
- 26. Urachal anomalies A, Urachal cyst, persistence or remnant of epithelial lining of urachus. B, Urachal sinus, discharge serous fluid from the umbilicus. C, Urachal fistula, the entire urachus remains patent and allows urine to escape from the umbilicus.
- 27. Urethral Anomalies 1-Hypospadius : is the most common anomaly, with incomplete fusion of the urethral folds, and abnormal openings of the urethra occur along the ventral (inferior) aspect of the penis. 2-Epispadius : is a rare abnormality, in which the urethral meatus is found on the dorsum of penis, it is most often associated with extrophy of the bladder.
Editor's Notes
- Mesonephros degenerates by 2nd months except few caudal tubules and ducts which makes male genital system
- POSITION OF THE KIDNEY • The kidney, initially in the pelvic region, • later shifts to a more cranial position in the abdomen. • This ascent of the kidney is caused by diminution of body curvature and by growth of the body in the lumbar and sacral regions. • In the pelvis the metanephros receives its arterial supply from common iliac arteries. • During its ascent to the abdominal level, it is vascularized by arteries that originate from the aorta at continuously higher levels. • The lower vessels usually degenerate, but some may remain FUNCTION OF THE KIDNEY • The definitive kidney formed from the metanephros becomes functional near the 12th week. • Urine is passed into the amniotic cavity and mixes with the amniotic fluid. • The fluid is swallowed by the fetus and recycled through the kidneys. • During fetal life, the kidneys are not responsible for excretion of waste products, • The placenta serves this function.
- Mesodermal uro-rectal septum
- In infants and children the bladder is an abdominal organ , it begins to enter the greater pelvis at about 6 years and becomes a pelvic organ until after puberty.