Fil & Shef in… The Magical World of Reproductive Development

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Presentation transcript:

Fil & Shef in… The Magical World of Reproductive Development A Shefinski Production Directed by Filipino “Fantastic!” – Aleiks, the Holyhead Herald “What’s for lunch?” - Anonymous

The Gonads - Ovary or Testicle? (I) How and when is the genetic sex is determined? By the presence of the Y chromosome At fertilisation What is a germ cell? Diploid cells that give rise to gametes (i.e. sperm/ovum) Arise in the yolk sac at 3 weeks (primordial germ cells) What tissue does the genitourinary system develop from? Genital ridges of the intermediate mesoderm Endoderm Ectoderm Intermediate mesoderm Turner syndrome – XO genotype is female Gastrulation at day 19

Image(s) taken from this video: https://www. youtube. com/watch Image(s) taken from this video: https://www.youtube.com/watch?v=MureNA-RSZM (many things are in much more detail than you need to know)

The Gonads - Ovary or Testicle? (II) The indifferent gonads Surface Epithelium of the genital ridge proliferates and penetrates the mesenchyme to form primitive sex cords at 6 weeks. At the same time (5-6w) germ cells migrate from the yolk sac and invade the genital ridges The male and female gonads Ovary: Germ cells of XX genotype colonise the cortex Testis: Germ cells of XY genotype colonise the medulla Turner syndrome – XO genotype is female Gastrulation at day 19

Ovarian Development XX Germ cells colonise the cortex of the gonad while the surface epithelium proliferates further Primordial follicles develop as mesenchymal cells surround these germ cells Notes: Remaining cords degenerate Cortex develops even in absence of germ cells Remaining cords as well as the medulla, degenerate.

Testicular Development (I) XY Germ cells colonise the medulla of the gonad Y chromosome gene expression influences masculinisation Primitive sex cords continue to proliferate and colonise the medullary region, forming definitive sex cords These will acquire a lumen and become seminiferous tubules at puberty Dense layer between the cords and the and the epithelium = tunica albuginea Secretion of testosterone by week 8 helps influence the differentiation of the genitalia

Testicular Development (II) Secretion of testosterone by 8th week further aids sexual differentiation of the embryo’s genitalia (discussed later) Notes: Mesenchymal cells differentiate into Leydig cells, which secrete testosterone Surface epithelial cells differentiate into Sertoli cells Dense layer between the cords and the and the epithelium = tunica albuginea Secretion of testosterone by week 8 helps influence the differentiation of the genitalia

Now what? Descent of the gonad Development of the internal genitalia Development of the external genitalia

Descent of the Gonad Where do the gonads develop? On the posterior abdominal wall Where do the gonads end up? Ovaries in the pelvis Testes in the scrotum (~28-33 weeks) Processus vaginalis descends into the labioscrotal folds through the inguinal canal, and pushes layers of the abdominal wall with it Gonad follows as it is attached to the abdominal wall by the gubernaculum (a fibrous cord) What descends with the gonad? Neurovasculature Transversalis fascia => internal spermatic fascia Internal oblique muscle fascia => cremasteric fascia External oblique muscle fascia => external spermatic fascia Processus vaginalis is a fold of the parietal peritoneum, and gives rise to two layers (parietal and visceral) of the Tunica vaginalis Testes migrate through the inguinal canal at 28 weeks, and end up in the scrotum at around 33 weeks

Development of the Internal Genitalia Foetus has a primordial bipotential for both male and female internal ducts: ♂ Mesonephric = Wolffian duct ♀ Paramesonephric = Müllerian duct Müllerian duct is dominant in the absence of stimulus, causing the spontaneous regression of the Wolffian duct Y chromosome gene expression is essential for development of the Wolffian duct Müllerian Inhibitory Hormone (MIH) secreted by Sertoli cells Regression of the Müllerian duct

The Wolffian Duct The Wolffian duct gives rise to structures that include: Epididymis Vas deferens Seminal vesicle

The Müllerian Duct The Müllerian duct gives rise to structures that include: Oviducts (fallopian tubes) Uterus Cervix Upper part of the vagina

External Genitalia Function to transfer gametes Begin as bipotential tissue with three main structures Structure Male Female Urethral Folds Shaft of penis Labia minora Genital Swellings Scrotum Labia majora Genital Tubercle Glans of penis Clitoris We said it was transport in the session – mistake. Internal genitalia – storage, maturation and transport. ♂: Enlargement, Elongation & Fusion ♀: Slight Enlargement; no fusion

Quiz Why do the testes descend into the scrotum unlike the ovaries? Maturation of sperm requires a lower temperature than that offered in the pelvis What is the lymph drainage of the ovaries & testes? Travel up to the para-aortic nodes (~L2) What hormone is essential in determining the differentiation of the internal genitalia? MIH (Mullerian Inhibitory Hormone)