Development of Reproductive Tracts Flashcards
1
Q
What is cloaca
A
- Urinary, GI and reproductive tracts share a common caudal opening
- Hindgut ends in a dilated structure called the cloaca
- Cloaca closed to the outside by the cloacal membrane - no mesoderm
2
Q
What is the urogenital ridge
A
- Region of intermediate mesoderm giving rise to both the embryonic kidney and the gonad
- Gonad derived from intermediate mesoderm plus primordial germ cells (extragonadal)
- Migrate into gonad and direct development of reproductive tract
3
Q
What are primordial germ cells
A
- Special population of cells that act as the ‘seed’ for the next generation
- Allocated shortly after initiated of the current generation
- Arise in the yolk sac and migrate into the retroperitoneum along the dorsal mesentery
4
Q
Briefly explain how the male development pathway occurs
A
- Expression of SRY region on Y chromosomes drives development of male
- Develops testes
- Production of testicular hormones (androgens)
- Develops internal genitalia (male duct system)
- Mesonephric (Wolffian) duct will dominate
5
Q
Briefly explain how the female development pathway occurs
A
- Primordial germ cells do not carry Y chromosome, leading to development of female
- Develops ovary
- Develops internal genitalia (tubes and uterus)
- Paramesonephric (Mullerian) duct will dominate
6
Q
Describe the development of the mesonephric/ paramesonephric ducts in male
A
- Testis produce Mullerian inhibiting hormone
- Suppresses Mullerian (paramesonephric) duct development
- Testis produces androgens
- Supports Wolffian (mesonephric) duct but disappears after its job
7
Q
Describe the development of the mesonephric/ paramesonephric ducts in female
A
- No testis producing Mullerian inhibiting hormone
- No suppression of Mullerian (paramesonephric) duct development
- No testis producing androgens
- Wolffian (mesonephric) duct degenerates
8
Q
Describe the mesonephric ducts
A
- Develop in both male and female embryos
- Develop into embryonic urinary tract (kidneys)
- Drains into urogenital sinus, which later will become urinary bladder
- Surplus to requirement once true kidney develops
- Mesonephric duct maintained by testis derived androgens
- Converted into vas deferens and epididymis
- Migrates with the testis as it descends
- Converted into vas deferens and epididymis
9
Q
Describe the paramesonephric ducts
A
- Develop in both male and female embryos
- Appear as invaginations of the epithelium of the urogenital ridge
- Caudally - make contact with the cloaca (urogenital sinus)
- Cranially - open into the abdominal cavity
10
Q
What composes the external genitalia
A
- Genital tubercle (GT), genital folds and genital swelling
- Urogenital sinus formed as cloacal membrane rupture within the genital fold
11
Q
Outline how the external genitalia in a male develops
A
- In the male, the genital tubercle elongates and genital folds fuse to form the spongy urethra
- Genital tubercle develops into glans penis
- Genital swelling develops into scrotum
- Influence by testis-derived androgen hormones (eg. Dihydrotestosterone)
12
Q
Outline how the external genitalia in a female develops
A
- No fusion of genital folds occurs
- Development of labia majora and labia minora from genital swelling
- Genital tubercle develops into clitoris
13
Q
Describe the descent of the testis
A
- Testis are retroperitoneal so pass behind the peritoneum
- Contraction of gubernaculum guides descent
- Processes vaginalis develops but is cut off from peritoneum once testes have descended
- Forms the tunica vaginalis
14
Q
Describe the descent of the ovary
A
- Gubernaculum attaches ovary inferiorly to labio-scrotal folds
- Ovary descends to the pelvis
- Developed uterus prevents further descent
- Round ligament of the uterus in inguinal canal - remnant of gubernaculum
15
Q
Describe the problem if testosterone-treated female
A
- There is exogenous androgen which supports Wolffian (mesonephric) duct
- However there is no testis, so no Mullerian inhibiting hormone, which causes Mullerian ducts to develop
