Embryology

Question 1

What are the processes of conception, implantation and placental development?

Answer 1

X

Question 2

How does the early embryo develop and how do multiple pregnancies occur?

Answer 2

X

Question 3

How does the urinary system develop and how is this linked to the development of the reproductive system?

Answer 3

3 sets of kidneys develop: pronephros, mesonephros, metanephros. Mesonephros forms long ovoid structure at 6 weeks. Medical part of mesonephric ridge thickens to form genital gonadal ridge. Germ cells migrate to genital ridge forming indifferent gonad.

1. Indifferent gonad becomes testes/ovary
2. Mesonephric duct becomes epididymis, seminal vesicles, vas deferens/disappears)
3. Paramesonephric duct (disappears/fallopian tube, uterus, vagina)
4. Urogenital sinus forms bladder, urethra, prostate/bladder and lower part of vagina

Question 4

What is germ cell migration and how does the indifferent gonad form?

Answer 4

Germ cells migrate from yolk sac via dorsal mesentary and embed into primitive sex cords (formed from mesenchyme of genital ridges)

when germ cells are in the genital ridge this forms the indifferent gonad

Question 5

How do the testes and male reproductive tract develop?

Answer 5

Chromosome Y contains SRY section: codes for protein TDF.

TDF makes indifferent gonad develop into testes (stimulates primary sex cords, they extend into medulla, creates seminiferous cords then tubules. Seminiferous cords brand and their ends anastasmose forming rete testis of medulla. Surface epithelium lost when thick capsule forms (tunica albuginea)

Primordial supporting cells within the sex cords of the indifferent gonad express SRY and this transforms them into Sertoli cells. They secret MIS (degenerates the PM duct) which transforms mesenchymal cells between cords to form Leydig cells.

Leydig cells produce testosterone which leads to development of the male external genitalia from the mesonephric duct

Male gonads descend:
7th week = T10
12th week = deep in Guineas ring
Enters scrotum just prior to birth
Descent formed the larger inguinal canal in males

Question 6

How does the female reproductive tract develop?

Answer 6

No SRY thus no TDF. By default indifferent gonad will develop into ovary.

1. Primary sex cords degenerate.
2. 10 weeks secondary sex cords develop from surface epithelium, and primordial germ cells are incorporated
3. Primordial germ cells bud off with single surround layer or cortical cord cells to form primordial follicles (~16 weeks)
4. Active mitosis of follicles form additional follicles
5. By 7th month all follicles have for,Ed
6. Oocytes enter meiosis and arrested in prophase of 1st meiotic division

Absence of testosterone means mesonephros and mesonephric duct degenerate
Paramesonephric ducts develop to give rise to female genital tract

Descent of gonads
7th - T10
12th - broad ligament
Round ligament drawn through inguinal canal go attach to labrum majorum

Question 7

What are some common abnormalities of the reproductive tract and their basis?

Answer 7

1. Cryptorchidism:
   absence of testes in scrotum. Causes: undescended, ectopic, retraction or absent
2. Remnants of mesonephric duct
3. Duplicate uterus, septate uterus, bicornuate uterus, arcuate uterus