Embryology Flashcards
Which system forms a template for reproductive system?
The urinary system
When does the genital ridge form?
Week 5-6
What structure thickens to become the genital/gonadal ridge?
Medial part of the mesonephric ridge
What has to happen in order to produce Indifferent Gonads (not differentiated into a definitive testis or ovary yet) and in time Gonads?
Germ cells migrate from the yolk sac, via dorsal mesentery and embed into primitive sex cords (these are formed from proliferation of the epithelium in each Genital ridge)
How does the para-mesonephric duct form?
- Epithelium of the mesonephros invaginates to form a tube.
- This tube becomes the para-mesonephric duct
Where does the cranial end of the paramesonephric duct open into?
The peritoneal cavity
True or false: The paramesonephric duct crosses ventral (anteriorly) to the mesonephric duct
True
Where does the paramesonephric duct project into at it’s caudal end?
It projects into the dorsal wall of the urogenital sinus
What do the paramesonephric ducts devlop into in the female?
The genital tract:
- Fallopian tubes
- Uterus
- Cervix
- The upper one-third of the vagina.
What happens to the paramesonephric duct in males?
It degenerates
What does the mesonephric duct develop into in males?
- Epididymis
- Vas deferens
- Seminal vesicle
In males, what structures does the urogenital sinus develop into? (3)
- Bladder
- Urethra
- Prostate - outgrowth from the urethra
In females, what structures does the urogenital sinus develop into? (2)
- Bladder
- Lower part of vagina
What happens to the mesonephric duct in females?
It degenerates
How does the indifferent gonad (un-differentiated) know whether to develop into a testis?
Sex-determining Region Y (SRY) is a gene found on Y chromosomes that leads to the development of male phenotypes, such as testes.
- The SRY encodes for a protein called TDF (testis determining factor)
- Primordial germ cells (within the sex cords of the indifferent gonad) express the SRY
- TDF makes the indifferent gonad develop into a testis
- The SRY transforms the primordial cells into Sertoli cells which secrete MIS (Mullerian-inhibiting-substance)
- Paramesonephric duct degenerates
- MIS transforms mesenchymal cells between the sex cords to form Leydig cells
- Leydig cells produce testosterone - male external genitalia
Testis development
The male external genitalia are formed under the influence of what hormone?
Testosterone
How does an indifferent gonad develop into an ovary?
- No SRY region
- No TDF (which results in development of testis)
So, by default the indifferent gonad develops into an ovary
Postnatal ovarian development
- There are approx 2 million primordial follicles at birth
- Many follicles become atretic before puberty (Degenereated)
- 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
Absence of testosterone causes what to happen in females?
Degeneration of mesonephros and mesonephric duct
During development how do the ovaries descend?
- The ovaries originate on the posterior abdominal wall (T10) and move down to within the pelvis.
- The movement is arrested by the gubernaculum (formed in development and connects the ovary to the labum majora)
- Later in pregnancy the gubernaculum becomes the round ligament
Descent of the testis
- 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)
- The gubernaculum guides the testes through the inguinal canal into the scrotum.
What is Gartner’s cysts?
- Most common benign cystic lesions of the vagina.
- They represent embryologic remnants of the caudal end of the mesonephric duct (should disintegrate in females)
What is Cryptorchidism?
Parents notice absence of testes in scrotum (cryptorchidism). Reasons for this could be:
- Undescended
- Ectopic
- Retractile testes
- Absent testes
Managed by Orchiopexy: Surgery to move an undescended (cryptorchid) testicle into the scrotum and permanently fix it there. Orchiopexy typically also describes the surgery used to resolve testicular torsion.
What are some complications associated with undescended testis?
- Infertility
- Malignant transformation (germ cell tumours)
- Testicular torsion - when tissues around the testis are not attached well causing the testes to twist around the spermatic chord. This cuts off the blood flow to the testicle.
What is Orchiopexy?
What are some anomalies of the paramesonephric duct that can affect females?
- Complete duplication of the uterus
- Bicornuate uterus
- Septate uterus (septum in the middle of the uterine cavity)
- Arcuate uterus - the uterine anomaly that is least commonly associated with reproductive failure.
