Prenatal Development Flashcards
When is genetic sex determined?
At the time of fertilization
First step in prenatal development
Primordial germ cells from the yolk sac/ allantois migrate into the gonadal ridge in the first trimester
What is the gonadal ridge classified as?
Bipotential (decides on sex based on genetic info)
How is the embryo a male?
Sperm with Y chromosome with SRY gene
What cells are present on the gonadal ridge?
Precursor cells (2)
Primordial germ cells
What do the precursor cells in the male become?
Sertoli cells that secrete desert hedgehog and anti-mullarian hormone
Desert Hedgehog
Tells the second precursor cells to become Leydig cells that produce Testosterone
What do the primordial germ cells in the male become?
Gonacytes that produce sperm throughout the male’s life
Mesonephric Duct (wolffian duct) in males
Gives rise to male internal genitalia
Testosterone is essential for development
Paramesophric duct (Mullarian duct) in males
Degernerates due to AMH
What happens after Leydig cells secrete testosterone?
Development of testis and regression of the mesonephros (temporary version of the kidney)
What does the remnant mesonephros give rise to in males?
Future efferent duct after combining with epithelial cords (future seminiferous tubules)
What does the mesonephric duct generate in males?
Epididymus and vas deferens
Dihydrotesterone
5a-reductase will convert testosterone into dihydrotesterone to develop into external genitalia because it’s 100 times more potent than testosterone
What does the genital tubercle become in males?
Glans penis
What does the urogenital/ genital folds become in males?
Fuse to form the ventral aspect of the penis
What does the labioscrotal/genital swelling do in males?
Become the scrotum
How is the female embryo developed?
Egg is fertilized with sperm with the XX genotype (SRY gene absent)- default pathway
For the female, what does the primordial germ cells give rise to?
The eggs
For the female, what do precursor cells become?
Granulosa (follicle cells) that secrete theca cells that secrete estrogen
Which structures regress in the female?
Mesonephros tubules and epithelial cords
Mesonephric duct as well because no testosterone
What does the Coelomic epithelium become?
Future cortex
What does the Paramesonephric duct become in females?
Develop into internal female genitalia (uterus, cervix, part of the vagina, oviduct) due to the absence of the AMH
For the female what does the Cranial and caudal urogentical sinuses develop into?
Bladder and vestibule respectively
In females, what does the genital tubercle become?
Clitoris
In females what does the urogentical fold do?
Remain separate as the labia minora
In females, what does the labioscrotal swelling become?
The labia majora where the remain fused
Karyotype XY-SRY Mutation
No desert hedgehog, leydig cells, T, DHT–> mesonephric duct generateates and male system doesn’t develop –> external genitalia of the female
No Sertoli cells, AMH –>Mullerian ducts develop producing female genitalia
What happens to animals with the XY-SRY mutation?
Dysfunctional ovary with female internal and external genitalia
Common in horses
Persistent Mullerian Duct Syndrome
Sertoli cells form but don’t secrete AMH (mutation in the AMH gene)
The individual will have internal female and male genitalia and external male genitalia
Complete Androgen Insensitivity Syndrome
Mutation in the androgen receptor so T and DHT can’t activate downstream signaling
What is the outcome of androgen insensitivity syndrome?
Abnormal development of the male duct system
Female external genitalia will develop
Freemartin statistics in cattle
92% of heterosexual twins result in freemartin heifer
86,000 freemartin calves born annually in the US
Twins in cattle
Common blood supply between two fetuses due to fusion of chorio-allantois portion of the placenta
5% twinning rate i Holstein cattle
What happens to the females during freemartin?
Due to shared blood supply with male, female fetus is exposed to AMH and testosterone
Wide variation in external genitalia, maldevelopment or no development of internal genitalia
Transabdominal Phase of Testicular Descent
Enlargement of the distal gubernaculum, making it short and fat (swelling)
Regulated by insulin-like 3 (ligand) protein secreted by leydig cells and pancreas
Inguinal-Scrotal phase of Testicular Descent
Testis moves through inguinal region because gubernaculum shrinks
Shrinks and pull testis deeper into the scrotum
Controlled by T (androgen receptor)
What are the testicular descent abnormalities?
Cryptorchidism
Inguinal Hernia
