1. EXCRETORY AND REPRODUCTIVE
SYSTEM DEVELOPMENT

3. 4. Degenerates by end of 4th week of development.
external
glomerulus
internal
(glomus)
4. Degenerates by end of 4th 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. Evident at about 20 days after fertilization
pairs of rudimentary tubules in segmented mesoderm
3. Non-functional

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

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

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

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

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

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

11. 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.

12. 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.

13. 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 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.
SEE LECTURE PACKET FOR FIGURES

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

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

16. scrotum
Corpus spongiosum

17. Human male reproductive tract
Tubuli
recti

18. labia majora
labia minora
cervix

19. Human Development
gonadal ridge
genital ridge =
~ 4 weeks

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

21. Human Development ~ 5 weeks
Primordial germ cells migrate from the yolk sac endoderm to the genital ridges during the 5th week of human development.
mullarian duct
Human Development
~ 5 weeks
Gonads start to form during the 5th 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.

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

23. Differentiation of the gonads (testis or ovary) will begin during the 7th 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

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

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

26. (epididymis & vas deferens)

27. (~6 - 7 weeks) Male and female reproductive tract - ductwork
Text
Male and female reproductive tract - ductwork
Fate of the mesonephric and Mullarian ducts.
(~6 - 7 weeks)

28. SEE LECTURE PACKET FOR FIGURES
5-6 weeks

29. 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.

30. ovary
Female
Female
~2.5 months

32. SEE LECTURE PACKET FOR FIGURES
Uterovaginal
plate
SEE LECTURE PACKET FOR FIGURES
Uterovaginal plate
Muller’s tubercle
Vaginal plate
Uterovaginal plate, vaginal 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.

33. MALE AND FEMALE EXTERNAL GENETLE DEVELOPMENT
SEE LECTURE PACKET FOR FIGURES

34. MALE AND FEMALE EXTERNAL GENETLE DEVELOPMENT
SEE LECTURE PACKET FOR FIGURES

35. Fusion Failures of the Urethral Folds
Hypospadias - abnormal opening of the end of the urethra on ventral side of penis.
Occurs in about 1 in 125 to 250 new born males
Cause of hypospadias is not always clear, but it can result from insufficient hormone production (i.e. testosterone, dihydrotestosterone) or lack of sufficient receptors for these hormones.

36. s