EXCRETORY AND REPRODUCTIVE SYSTEM DEVELOPMENT Human embryo 1

EXCRETORY AND REPRODUCTIVE SYSTEM DEVELOPMENT

Human embryo 1. Evident at about 20 days after fertilization 2. 7 -10 pairs of rudimentary tubules in segmented mesoderm 3. Non-functional 4. Degenerates by end of 4 th week of development. 5. In species with functional pronephros, branch of aorta will form a glomerulus either adjacent to nephrostome in peritoneal coelom or adjacent to tubule

Human embryo: 1. Develops during second month 2. 35 -49 pairs of functional mesonephric tubules in unsegmented intermediate mesoderm 3. 3 - 4 tubules adjacent to each somite 4. Extends from 10 th - 26 th somite 5. Induction - Mesonephric (pronephric) duct must be present. If removed, mesonephric tubules will not form. 6. Evocation - masked morphogen

Metanephros Human embryo: 1. Development begins at end of 1 st month with formation of ureteric bud 2. Development continues for next 2 months, but metanephric kidney is not functional until the 3 rd month

End of first month * * Urogenital sinus region View from ventral side of embryo. Allantois not shown

* * Urogenital sinus region View from ventral side of embryo. Allantois not shown

Metanephric diverticulum will form 1. ureter, Medulla of kidney 2. pelvis of kidney Metanephrogenic blastema 3. major and minor calyxes Cortex of kidney metanephric nephrons 4. papillary collecting ducts * * Urogenital sinus region View from ventral side of embryo. Allantois not shown

Papillary collecting ducts Metanephric diverticulum will form 1. ureter 2. pelvis of kidney Medulla of kidney 3. major and minor calyxes 4. papillary collecting ducts

Metanephric diverticulum will form 1. ureter, Medulla of kidney. 2. pelvis of kidney Metanephrogenic blastema . 3. major and minor calyxes Cortex of kidney metanephric nephrons . 4. papillary collecting ducts * * Urogenital sinus region View from ventral side of embryo. Allantois not shown

Metanephrogenic blastema will form: Cortex of kidney - metanephric nephrons

CLOACAL REGION - SEPARATION OF THE DIGESTIVE AND EXCRETORY SYSTEMS Human Development ~4 weeks

CLOACAL REGION - SEPARATION OF THE DIGESTIVE AND EXCRETORY SYSTEMS SEE LECTURE PACKET FOR FIGURES Formation of the urorectal septum involves the establishment and advance of the Rathke and Tourneux folds.

CLOACAL REGION - SEPARATION OF THE DIGESTIVE AND EXCRETORY SYSTEMS SEE LECTURE PACKET FOR FIGURES As the Rathke and Tourneux folds meet and fuse, the establish the urorectal septum and separate the urinary and digestive tracts from each other.

As the Rathke and Tourneux folds meet and fuse, the establish the urorectal septum and separate the urinary and digestive tracts from each other. SEE LECTURE PACKET FOR FIGURES • As the Rathke and Tourneux folds do their job, the metanephric diverticulum’s connection with the mesonephric duct is moved toward the forming bladder. • Eventually the metanephric diverticulum/ureter ends up connected to the bladder. • This movement of the metanephric diverticulum/ureter to a new connecting point is accomplished by differential growth of the surrounding tissues.

Rathke folds fail to form These or similar sorts of defects occur in 1 in every 4000 births in the U. S.

1. Early in mammalian development, the primordial germ cells (PGCs) are found in a cluster in extraembryonic endoderm of the yolk sac. 2. Prior to about 1990, they were considered to be endodermally derived. 3. Subsequent research has identified these cells during the primitive streak stage in presumptive extraembryonic mesoderm of the epiblast. 4. These cells can be identified by endogenous alkaline phosphatase activity that other cells of the early embryo lack. 5. The alkaline phosphatase will react with a substrate that produces a colored reaction product. 6. The PGCs are now considered to be mesodermally derived. 7. They then migrate to the endoderm, and subsequently migrate to the developing gonads.

Human male reproductive tract Tubuli recti

Corpus spongiosum scrotum

cervix labia minora labia majora

Human Development = gonadal ridge genital ridge ~ 4 weeks

subcardinal anatomosis (renal segment of inferior vena cava) genital ridge left mesonephric duct umbilical (allantoic) arteries allantoic stalk left umbilical (allantoic) vein

Primordial germ cells migrate from the yolk sac endoderm to the genital ridges during the 5 th week of human development. mullarian duct Human Development ~ 5 weeks mullarian duct Gonads start to form during the 5 th week, but at this point they are equivalent in males and females - i. e. not yet testis or ovary. Rete blastema forms from germinal epithelium of genital ridge in both males and females. Cells of rete blastema migrate closer to mesonephric ducts.

Human Development In human female embryos, proliferation of the primary sex cords stops by the end of the 6 th week. ~ 6 -7 weeks

Differentiation of the gonads (testis or ovary) will begin during the 7 th week of development (tunica albuginea in males). The tissues of the genital ridge will bulge into the peritoneal cavity and eventually will hang from a mesentary - mesorchium in male and mesovarium in female. ~ 7 weeks

due to secretion of anti-Mullarian hormone by the sertoli cells in seminiferous tubules.

The ductwork of the male reproductive tract continues its development. The germinal epithelium continues to degenerate

(epididymis & vas deferens)

SEE LECTURE PACKET FOR FIGURES 5 -6 weeks

Text. Male and female reproductive tract ductwork Fate of the mesonephric and Mullarian ducts. (~6 - 7 weeks)

SEE LECTURE PACKET FOR FIGURES 5 -6 weeks

SEE LECTURE PACKET FOR FIGURES In the male, the remnants of the Mullarian ducts are the vagina masculina and appendix testis The mesonephric tubules degenerate in female leaving some non-functional remnants called the epoophoron near the ovary. The mesonephric ducts degenerate in females; however, they sometimes leave a small non-functional duct called the canal of Gartner that extends from the epoophoron to the vagina.

Female ovary ~2. 5 months

Uterovaginal plate SEE LECTURE PACKET FOR FIGURES Muller’s tubercle Uterovaginal plate Vaginal plate Uterovaginal plate, Muller’s Tubercle - other names for the sinovaginal bulb. Vestibule - the region surrounding the vaginal opening that is bordered by the labia minora. Bartholin’s glands - paired glands, one on either side of the vaginal opening, with ducts opening into the vestibule. Secrete a mucus that lubricates the vestibular walls. Developmentally homologous to Cowper’s (bulbourethral) glands in the male.

MALE AND FEMALE EXTERNAL GENITAL DEVELOPMENT SEE LECTURE PACKET FOR FIGURES

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