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Kidney embryology
- 1. EMBRYOLOGY OF KIDNEY BYDr.AJAY RATHOON I
- 3. The Urogenital System Theurogenital system develops from the intermediate mesenchyme (mesoderm) – Urogenital Ridge. The part of the urogenital ridge giving rise to the urinary system is the nephrogenic cord and the part giving rise to the genital system is the gonadal ridge
- 4. Development of Kidneysand Ureters · Three sets of successive kidneys develop in human embryos. The first set — pronephrons— is rudimentary and nonfunctional The second set — mesonephrons — is well developed and functions briefly during the early fetal period. The third set — metanephrons forms the permanent kidneys.
- 6. Pronephron These bilateral structuresappear early in the fourth week. They are represented by a few cell clusters and tubular structures in the neck region The pronephric ducts run caudally and open into the Cloaca . The pronephron soon degenerate; however, most parts of the pronephric ducts persist and are used by the next set of kidneys.
- 7. Mesonephron These large, elongatedexcretory organs appear late in the fourth week, caudal to the pronephron. The mesonephron are well developed and function as interim kidneys for approximately 4 weeks, until the permanent kidneys develop and function. The mesonephric kidneys consist of glomeruli (10 –50 per kidney) and tubules. The mesonephric tubules open into bilateral mesonephric ducts which open into the cloaca . The mesonephron degenerate toward the end of the first trimester.
- 8. Metanephron Metanephron - permanentkidneys —begin to dev approximately 4 weeks later. The permanent kidneys develop from two sources: (1) The ureteric bud ( metanephric diverticulum) (2) The metanephrogenic blastema (metanephric mass of mesenchyme)
- 9. · The uretericbud is a diverticulum (outgrowth) from the mesonephric duct near its entrance into the cloaca. · The metanephrogenic blastema is derived from the caudal part of the nephrogenic cord. · As the ureteric bud elongates, it penetrates the metanephrogenic blastema —a metanephric mass of mesenchyme
- 10. Development of Kidneysand Ureters · The stalk of the ureteric bud becomes the ureter. · The cranial part of the bud undergoes repetitive branching, forming branches which differentiate into the collecting tubules of the metanephrons. · The first four generations of tubules enlarge and become confluent to form the major calices, and the second four generations coalesce to form the minor calices. · The end of each arched collecting tubule induces clusters of mesenchymal cells in the metanephrogenic blastema to form small metanephric vesicles.
- 12. A uriniferous tubule consistsof two embryologically different parts: A nephron derived from the metanephrogenic blastema A collecting tubule derived from the ureteric bud
- 13. · Between the10th and 18th weeks, the number of glomeruli increases gradually and then increases rapidly until the 32nd week. · The increase in kidney size after birth results mainly from the elongation of the proximal convoluted tubules as well as an increase of interstitial tissue. · Nephron formation is complete at birth except in premature infants. Although glomerular filtration begins at approximately the ninth fetal week, functional maturation of the kidneys and increasing rates of filtration occur after birth .
- 14. Positional Changes ofKidneys Initially the primordial permanent kidneys lie close to each other in the pelvis. As the abdomen and pelvis grow, the kidneys gradually relocate to the abdomen and move farther apart. They attain their adult position by the ninth week (contact with the suprarenal glands). This “ascent” results mainly from the growth of the embryo’s body caudal to the kidneys Initially the hilum of each kidney, where blood vessels, the ureter, and nerves enter and leave, face ventrally; however, as the kidneys relocate (“ascend”), they rotate medially almost 90 degrees. By the ninth week, the hila are directed anteromedially. Eventually the kidneys become retroperitoneal (external to the peritoneum) on the posterior abdominal wall.
- 16. Changes in BloodSupply of Kidneys During the changes in the kidneys position, they receive their blood supply from vessels that are close to them: Initially, the renal arteries are branches of the common iliac arteries. Later, the kidneys receive their blood supply from the distal end of the aorta. When they are located at a higher level, they receive new branches from the aorta. Normally the caudal branches of the renal vessels undergo involution and disappear. The kidneys receive their most cranial arterial branches from the abdominal aorta; these branches become the permanent renal arteries.
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- 19. Renal Agenesis · RenalAgenesis (absence): Can be unilateral or bilateral · Renal agenesis results when the ureteric buds do not develop or the primordia (stalks of buds) of the ureters degenerate. · Failure of the ureteric buds to penetrate the metanephrogenic blastema results in failure of kidney development
- 20. Unilateral Renal Agenesis ·Unilateral renal agenesis (absence) occurs approximately once in every 1000 neonates. · Males are affected more often than females and the left kidney is usually the one that is absent. · Unilateral renal agenesis often causes no symptoms and is usually not discovered during infancy because the other kidney usually undergoes compensatory hypertrophy and performs the function of the missing kidney. · Unilateral renal agenesis should be suspected in infants with a single umbilical artery
- 21. Bilateral renal agenesis ·Bilateral renal agenesis is associated with oligohydramnios (small amount of amniotic fluid) because little or no urine is excreted into the amniotic cavity. · This condition occurs approximately once in 3000 births, and is incompatible with postnatal life. · Infants with bilateral renal agenesis usually die shortly after birth.
- 22. Malrotated Kidney · Ifa kidney fails to rotate, the hilum faces anteriorly ; that is, the fetal kidney retains its embryonic position · Abnormal rotation of the kidneys is often associated with ectopic kidneys.
- 23. Ectopic Kidneys · Oneor both kidneys may be in an abnormal position. · Most ectopic kidneys are located in the pelvis, but some lie in the inferior part of the abdomen. · Pelvic kidneys and other forms of ectopia result from failure of the kidneys to ascend.
- 25. Horseshoe Kidney · In0.2% of the population, the poles of the kidneys are fused ; usually it is the inferior poles that fuse. · The large U - shaped kidney usually lies in the pubic region. · Normal ascent of the fused kidneys is prevented because they are held down by the root of the inferior mesenteric artery. · A horseshoe kidney usually produces no symptoms because its collecting system develops normally and the ureters enter the bladder. · Approximately 7% of persons with Turner syndrome have horseshoe kidneys.
- 26. Duplications of UrinaryTract · Duplications of the abdominal part of the ureter and the renal pelvis are common. · These defects result from abnormal division of the ureteric bud.
- 27. · A supernumerarykidney with its own ureter, which is rare, probably results from the formation of two ureteric buds.
- 28. Ectopic Ureter · Anectopic ureter does not enter the urinary bladder. · In males, the ureter usually opens into the neck of the bladder or the prostatic part of the urethra. They may also enter the ductus deferens, prostatic utricle, or seminal gland. · In females, the ureter opens into the neck of the bladder, or the urethra, vagina, or vestibule of vagina. · Incontinence is the common complaint resulting from an ectopic ureter because the urine flowing from the orifice does not enter the bladder; instead it continually dribbles from the urethra in males and the urethra and/or vagina in females .
- 29. Cystic Kidney Diseases ·In autosomal recessive polycystic kidney disease both kidneys contain many small which result in renal insufficiency. · Death of the infant usually occurs shortly after birth. · Multicystic dysplastic kidney disease results from dysmorphology during development of the renal system. · In this kidney disease, fewer cysts are seen than in autosomal recessive polycystic kidney disease and they range in size from a few millimeters to many centimeters in the same kidney. · The cystic structures are wide dilations of parts of the otherwise continuous nephrons, particularly the nephron loops (of Henle ).
- 30. Development of UrinaryBladder · The urogenital sinus is divided into three parts (imaginary): A vesical part that forms most of the urinary bladder and is continuous with the allantois. A pelvic part that becomes the urethra in the neck of the bladder, the prostatic part of the urethra in males, and the entire urethra in females A phallic part that grows toward the genital tubercle ( primordium of the penis or clitoris
- 31. Development of UrinaryBladder · The bladder develops mainly from the vesical part of the urogenital sinus but its trigone (triangular area at the base of the bladder between the openings of the ureters) is derived from the caudal ends of the mesonephric ducts. · The entire epithelium of the bladder is derived from the endoderm of the vesical part of the urogenital sinus. · The other layers of its wall develop from adjacent splanchnic mesenchyme .
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