Gametogenesis And Reproductive Embroyology Flashcards
Difference between genetic/gonadal and phenotypic sex
Genetic = determined at conception
- XX or XY
Gonadal = established during the 7th week of gestation based on absence or presence fo functional SRY gene
- the SRY gene is on the Y-chromosome and encodes for the Testis-determine factor (TDF). It’s presence in week 7 induces indifferent gonads into testies by inhibiting signaling factors for ovaries
Phenotypic = affected by expression of certain hormones during development
(Testosterone/MIF/DHT)
Hormones that affect sexual differentiation during gestation
Testosterone
- expression occurs in 8th week
- stimulates development of the vas deferens/seminal vesicles and epididymis
MIF
- expression occurs in the 8th week
- inhibits development of the uterus, Fallopian tubes, cervix and upper vagina
DHT
- expression occurs in 9-12th weeks
- stimulates development of the prostate, penis and scrotum
Androgenic hormones vs estrogen in embryology
Androgenic hormones
- testosterone and dihydrotestosterone
- promotes growth and differentiation of the male reproductive tract from the mesonephric duct and external genitalia
- produces anti mullarian hormone which inhibits growth and differentiation of the paramesonephric duct (female reproductive tract)
Estrogen
- produced by ovaries after week 8 which promotes the growth and differentiate of the female reproductive tract and external genitalia
- estrogen inhibits mesonephric duct formation
Gametogenesis 4 phases
1) origin and migration of primordial germ cells to the genital ridge
2) increase in number of germ cells occurs via rapid mitosis once the primordial germ cells reach the gonadal/genital ridge
- turns into millions and this period varies slightly between females and males
- females = induces oogonia proliferation during the 2nd-5th month of pregnancy
- males = induces spermatogonia in the 2nd trimester. Then ceases and resumes once puberty is reached
3) meiosis occurs and produces gametes
3 types of gonadal ridge cell types
1) mesenchymal cells
- makes up the gonadal ridge medulla
- in males = leydig cells
- in females = ovarian support stroma
2) mesothelial cells
- make up the gonadal ridge cortex
- males = seminiferous tubules
- females = ovarian follicles
3) primordial germ cells
- future gamete cells
- males = makes sperm
- females = makes oogonia
Meiosis 1
Similar to mitosis except
- prophase 1 synapses occurs and crossover occurs
Phases
1) prophase 1: chromosomes condense and the nuclear envelope breaks down and cross over occurs
2) metaphase 1: pairs of homologous chromosomes move to the equator of the cell and line up
3) anaphase 1: homologous chromosomes move to opposite poles of the cell
4) telophase 1 and cytokinesis: chromosomes gather at poles and the cytoplasm divides
- ends up with 2 haploid 2N cells
Meiosis 2 is the same meiosis 1 except chromosomes dont replicate and result in 4 haploid 1N cells
How does meiosis differ between females and males
Males = each round produces 4 viable haploid spermatids
Females = each round produces 1 viable haploid oocyte with 3 polar bodies forming (arrested oocyte)
How does oogenesis occur before birth and during puberty
Before birth:
- Meiosis occurs but arrests a primary oocyte in prophase-1
- is surrounded by a perimordial follicle at this time
Puberty and on
- meiosis of a primary oocyte occurs and arrests in metaphase 2 as a secondary oocyte
- generates a polar body each time primary -> secondary
- will move from metaphase 2 if a the fertile oocyte is penetrated by sperm
- gets released from the follicle during ovulation
Spermatogenesis
Begins at puberty (not before)
A spermatogonium (46,XY) is released and divided into secondary spermatocytes (23,X and Y) and eventually 4 spermatids (23,X/X/Y/Y)
46,XY disorders of sex development (DSD)
Include
- androgen insensitivity
- low androgen production
- LH/hCG receptor depletion
- pure or partial gonadal dysgenesis
- ovotesticular
- testis regression
Sex chromosome DSD’s
Include 45,XO (Turner syndrome) 47,XXY (Klinefelter syndrome) 45,XO/46,XY (mixed gonadal dysgenesis) 46, XX/46,XY (ovotesticular DSD)
46,XX DSDs
Include
- androgen excess in females (fetal/maternal or placental)
- gonadal dysgenesis
- ovotesticular development
Androgen insensitivity syndrome
Testicular femininization syndrome
X-linked recessive mutation that produces a 46,XY chromosome (genetically male) who has a resistance to testosterone at the cellular level (kinda like DM type 2 but for testosterone)
- there are mutations in cellular androgen receptors
Will produce female external genitalia with a vagina that has a blind end pouch
- no uterus or uterine tubes will be present
- will produce breasts and female sex characteristics at birth
The testes will underdeveloped and usually reside in the inguinal canal, abdomen or labia majora (they are also cryptochidism testies)
Lab results
- before puberty = high testosterone
- after puberty = high estrogen and LH with high testosterone
- genetic testing confirms
Treatment
- estrogen replacement for complete androgen insensitivity
- if partial and wants to be male (gender identity) then can give high dose androgen therapy
- either way, also need to do a gonadectomy after puberty to prevent malignancy
46,XX DSD
“Female pseudohermaphroditism”
Patient is 46,XX at birth (genetically female)
However they typically present with some sort of disorder (CAH/21-hydroxylase is the most common) that causes a production of androgens in utero
Produces external genitalia that are male but also have a upper vagina, uterus and uterine tubes all of which technically work since the ovaries are also present and fertile
Cryptochidism
Refers to a condition that results in failure of testes to descend into the scrotum
Most common birth defect in neonate males (up to 30% chance)**
If the testicles don’t descend by year 5 = sterility
Also shows high risk for germ cell tumors
