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DEVELOPMENT OF the Kidneys and Ureters Dr Rania Gabr Objectives • 1- Describe the stages of development of the kidneys and ureters • 2-Discuss the congenital anomalies of the kidneys and ureters Stages of Development of the kidney: • Human kidney is developed from the intermediate mesoderm and passes through 3 stages : 1- Pronephros 2- Mesonephros 3- Metanephros PRONEPHROS • Appears at 4th week. In the cervical region, the cranial part of the intermediate mesoderm is segmented into 7 cell clusters called “nephrotomes”. • Those become cavitated to form 7 “pronephric tubules”. • Each tubule has 2 ends: 1- The lateral end: joins to form pronephric duct. 2- The medial end: joins the coelomic cavity. • The lower end of the pronephric ducts join the cloaca. • Fate of the Pronephros: 1-“Pronephric tubules: and proximal (cranial) part of its duct degenerate 2-The caudal part of the duct persists as the “Mesonephric duct”. MESONEPHROS • It appears at the 6th week as 2 bulges on posterior abdominal wall forming ovoid mesonephric ridges. • It develops in the middle part of the (Intermediate mesoderm) that lies in the thoracic and upper lumbar region. • It is divided into segments which become canalised to form the “mesonephric tubules”. • The Medial ends form the ( internal glomeruli ) while , • the lateral ends join the mesonephric duct which opens in the primitive urogenital sinus. Fate of the Mesonephros • 1- Tubules: - In Males: form the “vasa efferentia”. – Females: form epoophoron and paroophoron. 2- Duct: - Males: 1-Epididymis, 2-vas deferens, 3-seminal vesicle, 4-ejaculatory duct, 5-ureter trigone of urinary bladder and 6- the upper part of the posterior wall of the urethra. In Females: 1-Duct of epoophoron (Gartener`s duct), 2-ureter and 3- trigone of urinary bladder. At the 8th week most of mesonephric tubules degenerate. KIDNEY AND URETER • The human kidney develops from 2 main parts: 1- The ureteric bud, and 2- The Metanephros The ureteric bud • The ureteric bud arises as an outgrowth of the mesonephric duct close to the entrance of the duct at the cloaca • The ureteric bud is responsible for the development of the collecting system Ureter: • The ureteric bud elongates dorso-cranially to be in contact with the metanephros which will form the metanephric cap. • The upper end of the ureter divides to form 2 – 3 major calyces, which further divide into many minor calyces which divide into collecting tubules. • Each collecting tubule will be covered with a piece of the metanephric cap which form renal vesicles which form the rest of the nephron except the collecting tubules which is developed from dividing ureteric bud. • Collecting tubules communicate with the rest of the nephron.(canalization) KIDNEY Metanephros: • It is the caudal part of the intermediate mesoderm in the pelvic cavity. • It forms the metanephric cap (blastema) which divides into small masses following divisions of the ureteric bud. • Each mass is called renal vesicles. • Each vesicle will form: 1234- Bowman’s capsule, proximal convoluted tubule, loop of Henle and distal convoluted tubule. Changes of the external features of the developing kidney: • 1- Ascent of the kidney: It ascends from pelvic cavity to its adult site in the lumbar region on the posterior abdominal wall. This is done by the dorso-cranial elongation of the ureter pushing the kidney. • 2- Change of the blood supply: During its ascent, the arterial supply of the kidney shifts to the nearest main artery . 1- First it is supplied by the Median sacral artery, then 2- Internal iliac, 3- Common Iliac, and finally 4- Abdominal aorta • 3- Loss of fetal lobulation: • The surface of the kidney becomes smooth • 4- Change of the direction of the hilum: from anterior to medial. CONGENITAL ANOMALIES A- KIDNEY • 1- Renal agenesis: Unilateral or bilateral. 2- Congenital polycystic kidney: due to failure of communication between the collecting tubules and rest of the nephron. 3- Pelvic kidney: due to failure of ascent. • 4- Horse shoe kidney: due to fusion between lower ends of both kidneys. Ascent is arrested at level of L3 vertebra. • 5- Rosette kidney: Due to fusion of the upper and lower poles • 6- Persistence of fetal lobulation: The surface of the kidney shows lobulations. • 7- Ectopic kidney: abnormal site of the kidney. • 8- Abnormal rotation Of the kidney: Rarely, the kidney shows lateral rotation instead of medial Rotation or faces anteriorly • 9- Aberrant renal artery: An additional artery that supply the kidney. Might enter from the upper or lower poles. It is usually a non degenerated Artery during ascent. CONGENITAL ANOMALIES B- Ureter • 1- Bifid ureter: Splitting of the upper part of the ureter. • 2- Double ureter and Ectopic ureter: Two separate ureters due to formation of 2 ureteric buds. • One will open normally in the bladder, The other (Ectopic ureter): Male: Opens in the urethra Female: Opens either in : a- the vestibule of the vagina, or b- in the urethra