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Objectives Development Of The Kidney. Describe the development of kidney. Pronephros. Mesonephros. Metanephros. Discuss the congenital anomalies of kidney. UROGENITAL SYSTEM General Overview: Is derived from intermediate mesoderm: As the embryo folds, the intermediate mesoderm loses its connection with the somite and becomes the urogenital ridge. Nephrogenic cord gives rise to the urinary system. Gonadal ridge gives rise to the reproductive system. The Urinary System Three distinct embryonic "kidneys" develop in a cranial to caudal direction: 1.Pronephros. 2. Mesonephros. 3. Metanephros. Pronephros: Forms at the beginning of the fourth week. Represented by 7 to 10 solid cell groups in the cervical region. These groups form vestigial excretory units,nephrotomes. By the end of the fourth week, all indications of the pronephric system have disappeared. Mesonephros: The mesonephros and mesonephric ducts are derived from intermediate mesoderm from upper thoracic to upper lumbar (L3) segments. In the fourth week first excretory tubules of the mesonephros appear. A glomerulus forms at their medial extremity. Around the glomerulus, the tubules form Bowman’s capsule, and together these structures constitute a renal corpuscle. Laterally,the tubule enters the longitudinal collecting duct known as the mesonephric or wolffian duct. While caudal tubules are still differentiating,cranial tubules and glomeruli degenerate. By the end of the second month, the majority have disappeared. In the male, a few of the caudal tubules and the mesonephric duct persist and participate in formation of the genital system. They disappear in the female. Metanephros: The third urinary organ, the metanephros or permanent kidney, appears in the fifth week. Its excretory units develop from metanephric mesoderm in the same manner as in the mesonephric system. The development of the duct system differs from that of the other kidney systems. The caudal porton of the mesonephric duct produces a ureteric bud. The ureteric bud surrounded by a cap of mesenchyme. The ureteric bud will give: Ureter. Renal pelvis. Calyces. Collecting tubules. The cap of the metanephric mesenchyme will give the: Bowman’s capsule. Proximal convoluted tubule. Ascending & descending of Henle’s loop. Distal convoluted tubule. The kidney "migrates" from its original location in the pelvis up into the abdominal cavity. All nephrons are present at birth. Disorder of the number of kidneys Renal agenesis: Renal agenesia can occur uni- or bilaterally, isolated or combined with other abnormalities (1/4 of all renal agenesias are associated with genital abnormalities, Too many kidneys (doubling) This congenital anomaly is extremely rare. Involved is an independent kidney with its own vascular supply, a capsule and its own urinary tract. The cause is a very early division of the ureter bud. Rotationsanomalis This anomaly is relatively frequent. One speaks of a malrotation if the pyeloureteral connection is oriented ventrally (missing rotation), dorsally (rotation of more than 90°) or laterally (inverse rotation). The kidney and urinary tract are here anatomically and histologically normal. Sometimes, though, one observes anomalies in the connections between ureter and renal pelvis, which can lead to a hydronephrosis Disorder of the ascent of the kidneys or ectopic kidneys A kidney is ectopic when, without ptosis, it does not lie in the lumbar fossa. The ectopia is the result of an incomplete or missing ascent. It can occur in the upper or lower region (pelvic kidney) or even crossed. In a crossed ectopia a kidney migrates to the other side. Its ureter crosses the midline and inserts normally into the bladder. The crossed ectopia can occur unilaterally or bilaterally. In the case of a unilateral crossed ectopia a fusion of the two kidneys often occurs. Ectopias are normally asymptomatic. Horseshoe kidney Its incidence is around 1/600. It is assumed that it arises due to a joining of both kidneys from both sides and during the 5th week when both organs still lie very close together in the small pelvis. The two kidneys are most often bound together at the lower pole. Abnormal kidney size. Hypoplasia: It results from an embryonic developmental stop of the kidney, the structure of which is otherwise normal.. The kidney is small, whereby the renal hypoplasia must be distinguished from a secondary atrophic kidney, resulting from an infection (chronic pyelonephritis). Aplasia: In an aplastic kidney, a fibroused kidney anlage with its own derivates of the mesonephric duct (Wolffian duct) is present. It represents the extreme form of a renal dysplasia and differs from agenesia, in which absolutely no kidney primordium exists. Polycystic kidneys: A renal dysplasia must be distinguished from a simple hypoplasia in which the histological structure is normal. Renal dysplasia is characterized by a congenital anomaly of embryonic renal tissue development. The kidneys develop large epithelial cysts that are localized in the renal parenchyma and lead to the loss of the functional tissue, which can end in renal insufficiency. Vascular anomalies of the kidney: There are many arterial and venous variants of the renal blood supply, reflected in the changing blood supply of the migrating kidneys during their development. Congenital ureteral abnormalities Course anomalies of the ureter: Retrocaval / retroiliac ureter: In this abnormality the right ureter traces out an "S" at the L4 level behind the vena cava (retrocaval ureter). Anomalies of the ureteral diameter Primary megaloureter due to an obstruction: The cause of this abnormality is a constriction in the terminal part of the ureter, leading to a dilatation. Abnormal number of ureters Disorders in the number of ureters belong to the most frequent anomalies of the urinary tract, whereby they are often asymptomatic. They arise from a premature branching of the ureter bud. Complete doubling: Here a complete doubling of the ureters with a second renal pelvis is involved. The ureters empty into the bladder.