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Anhui Medical University Development of the Urogenital System Lyu Zhengmei Department of Histology and Embryology Anhui Medical University Anhui Medical University ORIGINS----mesoderm ---paraxial mesoderm: somite ---intermediate mesoderm urinary and genital system ---lateral mesoderm paraxial neural intermediate mesoderm groove mesoderm endoderm notochord lateral mesoderm Anhui Medical University Part I Introduction The 【】※ origins of origins of urogenital urogenital system system?? Anhui Medical University differentiation of intermediate mesoderm •intermediate mesoderm Nephrotome nephrogenic cord urogenital ridge mesonephric ridge，gonadal ridge Anhui Medical University 1.Formation of nephrotome Nephrotome: The cephalic portion of intermediate mesoderm becomes segmented, which forms pronephric system and degenerates early. 4 weeks Anhui Medical University intermediate 2.Nephrogenic cord mesoderm Its caudal part gradually isolated from somites, forming two longitudinal elevation along the posterior wall of abdominal cavity Nephrogenic cord urogenital ridge Anhui Medical University 3. Urogenital ridge Mesonephric ridge: The outside part of the urogenital ridge giving rise to the urinary system Gonadal ridge: the innerside part giving rise to the genital system Anhui Medical University Part II Development of Urinary system Three sets of kidney occur in embryo developmnet ( 1)pronephros (2) mesonephros (3) metanephros Development of Bladder and urethra Cloaca Urogenital sinus Congenital anomalies of the urinary system Anhui Medical University Three sets of kidney systems 1 Pronephros •development begins early in fourth week •nonfunctional as a kidney •pronephros attached to pronephric ducts, these ducts are utilized by next set of kidney •pronephric tubule Pronephros degenerate in the end of fourth week Anhui Medical University 2. Mesonephros: •Mesonephros begins development in mesonephric ridge late in the fourth week •lie caudal to pronephros •large and elongated, functional interim, during early embryonic life Anhui Medical University •mesonephros consists of glomeruli and mesonephric tubules which open laterally into mesonephric duct, a continuation of the pronephric duct •mesonephric duct opens into cloaca Mesonephric •Most of the mesonephros tubule Mesonephric degenerates duct •But tubules and ducts have derivatives in adult male reproductive structures Anhui Medical University 3. Metanephros •permanent kidneys •begin development early fifth week •develop from the ureteric bud and the metanephrogenic tissue •Function begins at 11th-12th week •urine produced and released into amniotic fluid Anhui Medical University (1)ureteric bud The ureteric bud is formed from an outgrowth of the mesonephric duct near the cloaca Developing into the ureter, renal pelvis, major and minor calyces and collecting tubules Anhui Medical University Human E35-37, epithelia bud at end of mesonephric duct -----ureteric bud Metanephrogenic ureteric bud induced by blastema metanephric mesenchyme to ureteric differentiate into collecting tubules, bud calyces, renal pelvis, ureter minor calyces ureteric bud associated with Major calyces metanephric mesenchyme nephron Anhui Medical University (2)Metanephrogenic tissue The metanephrogenic tissue formed from the caudal portion of the intermediate mass of mesonephric ridge , and surrounds the end of the ureteric bud. Anhui Medical University Development of nephrons Metanephric vesicles formed in metanephrogenic tissue, which elongate to form S-shaped tubules Capillaries grow into and form glomeruli . Renal capsule and renal tubule Connect with arched collecting tubules Anhui Medical University 4 Ascent of Kidneys The kidney, initially in the pelvic region, with their hila pointed anteriorly eventually come to lie in a retroperitoneal position at the level of lumbar 1(L1) by the ninth week Function of the permanent kidney begins at month 3rd. Anhui Medical University Causes of ascent of kidney: As the pelvis and abdomen grow, the kidneys slowly move upward. By the seventh week, the hilum points medially and the kidneys are located in the abdomen. caused by diminution of body curvature and by growth of the body in the lumbar and sacral regions Anhui Medical University 4. Development of Bladder and urethra Cloaca: Just superior to the cloaca membrane, the primitive gut forms an expansion The urogenital sinus is formed by the division of the cloaca by the uro-rectal septum cloaca Anhui Medical University The urogenital sinus is formed by the division of the cloaca by the uro-rectal septum Mesonephric duct Coronal plane view Ureteric bud urogenital sinus Uro-rectal septum Sagittal plane view hindgut Anhui Medical University urogenital sinus ( 1) the cranial portion, continuous with the allantois and forms the bladder proper. (2) the pelvic part of the sinus forms the prostatic urethra and part of the vagina in females. (3)the caudal portion, forms the penile urethra in males and the vestibule in females. Uro-rectal septum rectum Anhui Medical University allantois the cranial female portion the pelvic urethra and vagina part Uro-rectal septum vestibule the caudal portion Anhui Medical University the cranial portion allantois male urethra (prostatic and membranous) the pelvic part penile urethra the caudal portion Anhui Medical University Part III Congenital anomalies of the urinary system 1. polycystic kidney A failure in the connection between the nephron and the collecting system Kidney contains many cysts, and failure in renal function Anhui Medical University 2. ectopic kidney ( pelvic kidney) Ascent, arterial fork, fail to do so. Remaining in the pelvis. Anhui Medical University 3、horseshoe 4、double ureter The horseshoe kidney is a form of ectopic kidney in which the poles of the two kidneys fuse in the pelvic cavity prior to ascending. This leads to a large U-shaped kidney which is unable to ascend to the level of loin(L1) because it is blocked by the inferior mesenteric artery Anhui Medical University 5、urachal fistula 6、extrophy of bladder Lack of mesodermal migration into the region between the umbilicus and genital The lumen of the allantois persists tubercle Anhui Medical University Three sets of kidney occur Summary in embryo developmnet (1)pronephros (2) mesonephros (3) metanephros Two origins of metanephros: ureteric bud and metanephric tissue Development of Bladder and urethra Cloaca Urogenital sinus Anhui Medical University PartⅣ Development of reproductive system 1. Development of gonads (1) sexual indifferentiation of gonad (2) development of testis (3) development of ovary (4) descent of testis and ovary 2. Development and sexual differentiation of genital ducts (1) indifferent stage (2) differentiation of genital ducts in female (3) differentiation of genital ducts in male 3.Congenital anomalies of the genital system Anhui Medical University 1.Development of gonads (1) Gonadal ridge----- sexual indifferentiation of gonad Although the sex of an infant is determind at fertilization, it is not until the seventh week that the gonads can be differentiated Anhui Medical University gonadal ridge •Gonadal ridge In the fifth week ,The urogenital ridge is divided into mesonephric ridge and gonadal ridge. • Primary sex cords By the sixth week, the epithelium of mesonephric gonadal ridge has developed primary ridge sex cord. the fifth week Anhui Medical University • Primordial germ cell (PGC)： .originate from the endoderm Gonadial around the yolk sac. ridge .migrate along the dorsal mesentery of the gut, appear in the genital ridges in the sixth week. Mesoneph- ric ridge influence development of gonad Primordial germ cell in the fourth week of life in the sixth week of life Dissection of an embryo Anhui Medical University Summary----- The gonad are derived from three sources: • The coelomic epithelium The underlying mesenchyme • The primordial germ cells Anhui Medical University (2) Development of testis One of the critical events in sexual differentiation occurs in the sixth week. SRY gene: Embryos which contain the Y chromosome have a specific gene known as SRY(sex determining region of the Y). This gene code a testes determining factor (TDF) which determines the formation of testes. TDF is expressed in the primordial germ cells . Anhui Medical University TDF induces the testicular cord to condense and extend into the medulla of the indifferent gonad: branch and anastomose the seminiferous cords are separated by mesenchyme During further development, a layer of fibrous connective tissue which separates the sex cords (seminiferous cords) from the surface epithelium, tunica albuginea This mesenchyme will go on to produce Leydig cells Anhui Medical University Leydig cells produce testosterone which maintains the presence of these mesonephric ducts and the tubules of the mesonephros The seminiferous cords are made up of a large number of Sertoli cells which secretes anti-Müllerian hormone The seminiferous cords remain solid until puberty , at which time a lumen develops and they become the seminiferous tubule Anhui Medical University Summary in the sixth week primordial germ cells migrate into gonad ridge- --------indifferent stage of gonad Induced by TDF, primary sex cords differentiate into Seminiferous cord in the seventh week only two type cells: Sertoli cells and spermatogonium, Seminiferous tubules did not start to grow until puberty Sertoli cells which secretes anti-Müllerian hormone Leydig cells produce androgen in the eighth week proliferating of mesenchymal cells under mesothelium form
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