Lecture 6: Development of Genitalia Flashcards
What weeks is the embryo considered considered “indifferent”?
Weeks 1-6
What week does sexual differentiation begin?
Week 7
What are the male primoridal germ cells; what week do they arise; and what ‘derm is each from?
- Arise from the epiblast during week 2
- Seroli Cells: from Coelomic Epithelium
- Interstitial (Leydig) cells: from Intermediate Mesoderm
What are the female primoridal germ cells; what week do they arise; and what ‘derm is each from?
- Arise from the epiblast during week 2
- Follicle Cells: from Coelomic Epithelium
- Thecal Cells: from Intermediate Mesoderm
Where do they primoridal germ cells end up after gastrulation and body folding? Explain their migration up until the 6th week.
- Arise from epiblast during week 2
- Migrate through the primitive streak and reside in yolk sac and allantois (endoderm)
- Migrate via dorsal mesentery during the 5th week
- Colonize primary sex cords during 6th week
What is the SRY gene; why is it significant?
- Sex determining Region Y human gene
- These are DNA binding proteins called testis-determining factor (TFD)
- Sex-determining region on the Y chromosome
- If SRY is present you will be male, if absent you will be female
If SRY gene is present what is the cascade of events that occurs in development of a male?
- Causes I.M. to form Leydig Cells which then produce Testosterone causing Mesonephric ducts to persist
- Causes C.E. to become somatic support cells and then Seroli Cells which produce AMH (aka MIF/MIS) which causes Paramesonephric duct degeneration
- DHT will be produced causing the development of Male External Genitalia
If SRY gene is absent what is the cascade of events that occurs in development of a female?
- Causes I.M. to from Thecal cells, which do NOT produce testosterone leading to degeneration of Mesonephric ducts.
- Causes C.E. to form support cells and then Follical cells which do NOT produce AMH so the Paramesonephric ducts persist.
- Estrogen production will lead to the development of Female External Genitalia
What is Ovotesticular DSD?
- True Gonadal Intersex
- Have both testicular and ovarian tissue and an ovotestis
- Phenotype may be male or female, but external genitalia ambigous
What is 46, XX DSD; what causes it; what is commonly seen in this condition?
- Caused by exposure of female fetus to excessive androgens
- Ovaries present, but external genitalia masculanized
- Clitoral hypertrophy, partial fusion of labia majora, and persisten urogenital sinus
- Congenital adrenal hyperplasia (CAH) is common = deficiency is 21-Hydroxylase = reduction in cortiol and excess prod. of androgens
What is 46, XY DSD; the 2 common causes and what’s seen?
- Has testis, but phenotype is female
Caused by:
1) Inadequate production of testosterone and/or AMH (i.e. 5α-reductase deficiency)
2) Androgen insensitivity syndrome (dysf. receptors)
- Testicular development rudimentary to normal and may have persisitent paramesonephric ducts
- External genitalia are female or ambigous
What is the genotype in androgen insensitivity syndrome, normal presentation, and what is seen?
- 46,XY genotype and testes are present
- Normal appearing female external genitalia
- Blind end vagina
- Absent or rudimentary uterus and uterine tubes
- At puberty normal breast development and femal characteristics, but no menstruation.
What will occur if SRY is present, but you have not enough AMH or no AMH?
- Mesonephric ducts and Paramesonephric ducts will BOTH persist so you will have male and female internal genitalia.
- You will have male external genitalia
What will occur if SRY is present and you have a 5α-reductase deficiency (unable to convert testosterone to DHT)?
- Develop male internal genitalia and will have female or ambigous external genitalia until puberty
- At puberty there will be a spike in testosterone and that will lead to masculinization of the genitalia
What is the Coelomic epithelium and what does it give rise to?
- Outer somatic mesoderm lining the urogenital (gonadal) ridge)
- Gives rise to primary sex cords
- Sex cords will be the cortex and medulla of gonads
In males the primary sex cords persist and become what 2 structures?
1) Seminiferous cords
2) Sertoli cells (surface epithelium)
Connective tissue from intermediate mesoderm becomes what 2 things in male gonad development?
1) Leydig Cells
2) Tunica Albuginea
The secondary sex cord arise from what; produce what 2 things in female gonad development?
- Arise from Coelomic epithelium
1) Primordial follicles
2) Graulosa cells
What process produces primordial follicles in female gonadal development?
Active mitosis of oogonia occurs during fetal life producing primordial follicles
Persistence of the Paramesonephric (Müllerian) ducts produces what strucutres?
- Uterine tubes
- Uterus
- Superior part of Vagina
Persistence of the Mesonephric (Wolffian) ducts in males produces what?
- Epididymis
- Vas Deferns
- Seminal Vesicles
- Ejaculatory Ducts
What 2 things to the Mesonephric tubules form in males?
1) Efferent ducts
2) Rete Testis
What are remenants of the Paramesonephric ducts that are sometimes seen in males?
- Appendix testis
- Prostatic utricle
Where are the Paramesonephric ducts located and what do they produce cranial and caudally?
- Located in lateral coelomic bay
- Cranial: uterine tubes
- Caudal: uterovaginal primordium
