Reproductive embryology Flashcards
What does the intermediate plate mesoderm form?
The urogenital system
What does the inner cell mass differentiate into?
3 layers- Ectoderm, mesoderm and endoderm
What are the names for the 3 kidneys that develop?
Pronephros – cervical region – vestigial
Mesonephros – thoracolumbar region – briefly functional
Metanephros – pelvic region – functional
When does the genital ridge form?
At about 6 weeks mesonephros forms a long ovoid structure in association with thoracic and upper lumbar vertebrae
Medial part of mesonephric ridge becomes thickened to form a genital/ gonadal ridge.
What do germ cells migrate into genital ridge to make?
Indifferent gonad
What happens in week 6 of embryology to the germ cells?
- Germ cells migrate from yolk sac, via dorsal mesentery, and embed into primitive sex cords (formed from mesenchyme of genital ridges
- This structure is known as the indifferent gonad (why?)
- No migration of germ cells - no gonads
What is the paramesonephric duct?
Epithelium of the mesonephros invaginates to form a tube.
This tube becomes the para-mesonephric duct
Develops lateral to developing gonads and mesonephric duct
Funnel shaped cranial end opens into peritoneal cavity
Caudally, cross ventral to mesonephric ducts
This projects into dorsal wall of urogenital sinus
What do the indifferentated gonad become>
Mesonpehric duct- Wolffian duct
Then paramesonephric duct- Mullerian duct
What happens in the males to form differentiated gonads?
- Gonad forms testis
- Mesonephric duct develops into epididymis, vas deferens, seminal vesicle,
- Paramesonephric duct degenerates
- Urogenital sinus forms bladder, urethra; and prostate
What happens in the females to form differentiated gonads?
- Gonad forms the ovary
- Mesonephric duct degenerates
- Paramesonephric duct forms fallopian tube, uterus, cervix part of vagina
- Urogenital sinus forms bladder and lower part of vagina
How does the indifferent gonad know whether to develop into a testis or an ovary?
How does the testis develop? From week 5 to 7
Wk 5 – primary sex cords, medulla and cortex
Wk 6 primordial germ cells incorporated into primary sex cords
Wk 7 – TDF stimulates primary sex cords à extend into medullaà seminiferous cordsà tubules
How does my seniferous cords branch?
Ends anastomose to make rete testis of medulla
When is the surface epithelium lost?
When thick capsule forms (tunica albuginea of adult testis)
What gives rise to intersitial cells of leydig?
Mesenchyme
What happens to testis developement at week 8?
Leydig cells produce testosterone and other hormones which stimulate masculine differentiation of mesonephric ducts and external genitalia
In males, paramesonephric duct degenerates
Which of these is an image of the testis prepubertal and which is post pubertal
What are the male sex glands?
Seminal vesciles- Outgrowth from caudal end of mesonephric duct
Prostate- Outgrowth(s) from urethra (from urogenital sinus)
Male genitalia is formed under the influence of testosterone
What is involved in development of the gonad?
Indifferent stage
In the presence of TDF- gonad develops into a testis
In its absence gonad develops into an ovary (by default)
What is differences in a female foetus from a male foetus?
No SRY region
No TDF
By default the indifferent gonad develops into an ovary
What is involved in development of the ovary?
Primary sex cords degenerate (leaving the primordial germ cells)
By 10 weeks secondary sex cords develop from surface epithelium
Primordial germ cells become incorporated into them
Primordial germ cells then bud off with single surrounding layer of cortical cord cells to form primordial follicles (from ~16 weeks)
Active mitosis of these early primordial follicles to form additional follicles
By 7th month all follicles have formed
Oocytes enter meiosis and arrested in prophase 1st meiotic division
Some follicular atresia by birth
What is the postnatal ovarian development?
~2 million primordial follicles at birth
Many follicles become atretic before puberty
After puberty, hormonal influences stimulate 12-15 follicles, per 28 day cycle, to develop
Only one follicle (normally) reaches maturity and ovulation
Continues until the menopause
What kind of ovary is each?
Where do the tubular components of the female reproductive system come from?
Absence of testosterone causes degeneration of mesonephros and mesonephric duct
Paramesonephric ducts develop to give rise to female genital tract
What is the origin of female genital tract?
Cranial (open funnel) end of paramesonephric duct becomes associated with ovary
Caudal end of paramesonephric duct (uterovaginal primordium) becomes uterus and superior part of vagina
Inferior part of vagina from urogenital sinus
(Mesonephric duct degenerates)
Where do gonads initally form?
In lumbar region, so positional changes occur as development takes place
How do the testis develop?
- Week 7 – Level of T10 (Diaphragm undescended)
- Week 12 – Level of deep inguinal ring (remains until 7th month)
- Enters scrotum just prior to birth (39 weeks)
How do the ovaries develop?
- Week 7 – Level of T10
- Week 12 – Broad ligament
- Round ligament drawn through inguinal canal to attach to labrum majorum
What is the fibrous cord called?
Gubernaculum
Understnad this diagram
The following aspects are linked to the descent of the gonads:
- Formation of the larger inguinal canal in males
- In the female – the presence of the round ligament and its passage through the inguinal canal
What is cryptochordisism?
Hidden testis
What are the types of cryptorchodism?
Undescended
Ectopic
Retractile testes
Absent testes
What are the complications of undescended testis?
- Infertility
- Malignant transformation (germ cell tumours)
- Testicular torsion
What is shown in blue and if it does not degenerate in women wjhat can it form?
Mesonephric duct is in blue
May not degerate so may forms cysts
These can have an impact on fertility of the women
What anomaly is this?
Complete duplication
What anomaly is this?
Bicornuate uterus
What anomaly is this?
Septate uterus
What anomaly is this?
Arcurate uterus
