Reproductive Biology and Embryology

Interphase occurs just prior to cell division. Prepubertal male primordial germ cells are reactivated from interphase at puberty and enter rounds of mitosis followed by meiosis 1 and 2 to produce unique haploid sperm.

In the absence of a Y chromosome, the fetus develops ovaries and female phenotypes. Hence, SRY switches on the male sex determination.

In gonadal development, undifferentiated primordial germ cells arise from the endoderm lining the yolk sac.

Mesenchyme arising beneath the germinal epithelium in the testes is the precursor to testicular interstitial cells or Leydig cells. In the ovaries it is the precursor to ovarian stroma or thecal cells.

Once the Mullerian ducts have reached the urogenital sinus and the vaginal plate has formed, the ducts will begin to fuse centrally. This forms the body of the uterus.

A Sertoli cell is a 'nurse' cell of the testes. The MIS glycoprotein is produced by Sertoli cells of the testes during fetal and neo-natal life in males.

The right testicular vein drains into the inferior vena cava at an acute angle.

The internal pudendal arteries serve as the penile blood supply by entering the penis dorsally and running deep into the tissues of the corpora cavernosa. The internal pudendal artery becomes the penile artery.

Both the epididymis and the vas deferens are made up of ducts, which have muscular components. These muscular parts aid in peristalsis, which helps move spermatozoa along the ducts.

Innervation of the penis comes from the pudendal nerve which is made up of the 2^nd, 3^rd and 4^th sacral nerves. The penile nerve (also known as the dorsal nerve of the penis) is the deepest branch of the pudendal nerve.

Primordial germ cells are maintained against the basement membrane of the seminiferous tubules; Sertoli cells do not appear to have a role in this process.

During initial follicular growth, the oocyte grows larger, granulosa cells increase in number and a zona pellucida or protein matrix, forms around the oocyte. The fluid filling the follicler continues to accumulate and the cellular surface of the follicle thins in preparation for ovulation. This process can be seen grossly and has been described as a blister on the ovarian surface.

Mullerian inhibiting substance (MIS) is responsible for causing the müllerian ducts to degenerate, accounting for the sole development of male internal genitalia in a fetus with a functional testis. If it is absent during fetal development, female internal genitalia would develop by default.

Follicle-stimulating hormone (FSH) causes maturation of a cohort of early-stage ovarian follicles; one of these will ultimately become the dominant or Graafian follicle.

After delivery the myometrium contracts to expel the placenta and to minimise blood loss from  the body.