howMed Know Yourself
THE URINARY SYSTEM
THE KIDNEYS, which excrete urineTHE URETERS, which convey urine from the kidneys to the urinary bladderTHE URINARY BLADDER, which stores urine temporarilyTHE URETHRA, which carries urine from the bladder to the exterior of the bodyDEVELOPMENT OF URINARY SYSTEM
Urinary system develops before the genital system.
Both systems develop from intermediate mesoderm
Three overlapping kidney system forms in succession in cranial to caudal sequence.
PHYLOGENETIC STAGES OF OVERLAPPING EXCRETORY ORGANS
•Pronephros, a structure similar to that found in primitive vertebrates (fish).
•Mesonephros, a more advanced system found in amphibia.
•Metanephros which elaborates into the final human form.
PRONEPHROS(EARLY 4th WEEK)
Rudimentary, transitory and non functional
Represented by 7 to 10 solid cell groups in cervical region
Forms vestigial excretory units, nephrotomes
No glomeruli
No connection b/w pronephric duct and excretory tubules
Cranial regress before more caudal ones are formed
End of 4 wks – Disappears
MESONEPHROS/ INTERIM KIDNEYS FUNCTION FOR 4 WKS (upper thoracic to upper Lumber L3 segments )
Formation of glomerulus and S- shaped excretory tubules (Increase in length causes it to bend)
Formation of Bowman’s capsule
Tubules enter into mesonephric/ Wolffian duct, a continuation of the pronephric duct
Function for a short time for about 4 weeks
IN THE MIDDLE OF SECOND MONTH
Formation of urogenital ridge
While caudal tubules are differentiating, cranial tubules & glomeruli show degenerative changes
BY THE END OF SECOND MONTH:
Mesonephric ducts open into cloaca & persist in males as epididymis, vasdeferens, ejaculatory ducts,seminal vesicles
Few caudal tubules persist – Efferent ductules of testes
METANEPHROS/
DEFINITIVE KIDNEY
Appears in 5th wk, lies in pelvic region
Permanent kidney develops from two sources:
Metanephric diverticulum / Ureteric bud
Metanephric blastema (mass of unsegmented mesoderm)
REASONS FOR THE ASCEND OF KIDNEYS
1.Dimunition of body curvature
2.Growth of the body in lumber & sacral regions
Arterial supply changes as it ascends
RECIPROCAL INDUCTION TO FORM PERMANENT KIDNEYS
•The ureteric bud is essential for induction & differentiation in the metanephric mesoderm.
•The metanephric cap is essential for bifurcation of the ureteric bud.
•The collecting ducts are essential for differentiation of the nephrons.
Metanephric diverticulum
is the primodium of:
•Ureters
•Renal pelvis
•Calyces
•Collecting tubules
Metanephric blastema
is the primodium of:
Nephrons
FUNCTION OF THE KIDNEY
•Becomes functional by 12th week
•During fetal life kidneys are NOT responsible for excretion of waste products
WILM’S TUMOR / NEPHROBLASTOMA
•Cancer of kidneys usually unilateral affects children by 5 years of age
•Due to mutation in genes
•Encapsulated & vascularised
RENAL DYSPLASIAS & AGENESIS
may arise if the interaction between the metanephric mesoderm and the ureteric bud fails to occur.
•Cause:
Genes Mutations
•Potters sequence: Anuria, oligohydroamnios & hypoplastic lungs
AUTOSOMAL RECESSIVE POLYCYSTIC KIDNEY DISEASE
Occurs in 1/5,000 births
A progressive disorder in which cysts form from collecting ducts.
The kidneys become very large, and renal failure occurs in infancy or childhood
PHYLOGENETIC STAGES OF OVERLAPPING EXCRETORY ORGANS
•Pronephros, a structure similar to that found in primitive vertebrates (fish).
•Mesonephros, a more advanced system found in amphibia.
•Metanephros which elaborates into the final human form.
PRONEPHROS(EARLY 4th WEEK)
Rudimentary, transitory and non functional Represented by 7 to 10 solid cell groups in cervical region Forms vestigial excretory units, nephrotomes No glomeruli No connection b/w pronephric duct and excretory tubulesCranial regress before more caudal ones are formedEnd of 4 wks – Disappears MESONEPHROS/ INTERIM KIDNEYS FUNCTION FOR 4 WKS (upper thoracic to upper Lumber L3 segments )
Formation of glomerulus and S- shaped excretory tubules (Increase in length causes it to bend) Formation of Bowman’s capsule Tubules enter into mesonephric/ Wolffian duct, a continuation of the pronephric ductFunction for a short time for about 4 weeksIN THE MIDDLE OF SECOND MONTH Formation of urogenital ridgeWhile caudal tubules are differentiating, cranial tubules & glomeruli show degenerative changesBY THE END OF SECOND MONTH:Mesonephric ducts open into cloaca & persist in males as epididymis, vasdeferens, ejaculatory ducts,seminal vesiclesFew caudal tubules persist – Efferent ductules of testesMETANEPHROS/
DEFINITIVE KIDNEY
Appears in 5th wk, lies in pelvic regionPermanent kidney develops from two sources:Metanephric diverticulum / Ureteric bud Metanephric blastema (mass of unsegmented mesoderm)REASONS FOR THE ASCEND OF KIDNEYS
1.Dimunition of body curvature
2.Growth of the body in lumber & sacral regions
Arterial supply changes as it ascends
RECIPROCAL INDUCTION TO FORM PERMANENT KIDNEYS
•The ureteric bud is essential for induction & differentiation in the metanephric mesoderm.
•The metanephric cap is essential for bifurcation of the ureteric bud.
•The collecting ducts are essential for differentiation of the nephrons.
Metanephric diverticulum is the primodium of:
•Ureters
•Renal pelvis
•Calyces
•Collecting tubules
Metanephric blastema is the primodium of:
Nephrons
FUNCTION OF THE KIDNEY
•Becomes functional by 12th week
•During fetal life kidneys are NOT responsible for excretion of waste products
WILM’S TUMOR / NEPHROBLASTOMA
•Cancer of kidneys usually unilateral affects children by 5 years of age
•Due to mutation in genes
•Encapsulated & vascularised
RENAL DYSPLASIAS & AGENESIS
may arise if the interaction between the metanephric mesoderm and the ureteric bud fails to occur.
•Cause:
Genes Mutations
•Potters sequence: Anuria, oligohydroamnios & hypoplastic lungs
AUTOSOMAL RECESSIVE POLYCYSTIC KIDNEY DISEASE
Occurs in 1/5,000 birthsA progressive disorder in which cysts form from collecting ducts. The kidneys become very large, and renal failure occurs in infancy or childhood AUTOSOMAL DOMINANT POLYCYSTIC KIDNEY DISEASE
Cysts form from all segments of the nephron and usually do not cause renal failure until adulthood.More common (1/500 or 1/1,000 births) but less progressive than the autosomal recessive diseaseDUPLICATION OF THE URETER
Results from early splitting of ureteric bud Complete or PartialABNORMAL LOCATION OF THE KIDNEY
Pelvic kidney-— if fails to pass through arterial fork formed by umbilical arteries.Horse shoe kidney-— pushed close during passage; lower lumbar vertebra; ascent prevented by root of Inferior Mesentric ArteryDEVELOPMENT OF URINARY BLADDER
During 4th to 7th week of development, the cloaca divides into urogenital sinus anteriorly & the anal canal posteriorlyUrorectal septum – Formation of perineal bodyThree portions of urogenital sinus: Upper, largest part is Vesical part: Urinary bladder Pelvic part: Prostatic and membranous part of urethra Phallic part : Penile urethra During differentiation of cloaca, the caudal portions of mesonephric ducts are absorbed into the wall of urinary bladder Mucosa of trigone initially mesodermal & later endodermal DEVELOPMENT OF URETHRA
Origin of epithelium — endodermSurrounding C.T. and smooth muscle — splanchnic mesodermAt the end of 3rd month, epithelium of prostatic urethra begins to proliferate and forms a number of outgrowths that penetrate the surrounding mesenchymeIn the male, these buds form the PROSTATE GLAND In the female, the cranial part of urethra gives rise to the URETHRAL AND PARAURETHRAL GLANDS BLADDER DEFECTS
URACHAL FISTULA URACHAL CYST URACHAL SINUSEXSTPROPHY OF BLADDER
Ventral body wall defect, bladder mucosa is exposed Epispadias is a constant feature Caused by lack of mesodermal migration into the region between umbilicus and genital tubercle followed by rupture of thin layer of ectoderm This anomaly is rare, occurring in 2/100000 live births
