What is the sequence of sexual differentiation? (4 steps)
1. Genetic sex
2. Formation of gonads
3. Formation of ductal system (vas def/epididymus; uterus/vag)
4. Differentiation of external genitalia
In normal male sexual differentiation, what drives an undifferentiated gonad to become a testicle?
How does this testicle cause the regression of the Mullerian ductal system?
Testicular determinants on the Y chromosome (SRY).
Causes testicular development --> seminiferous tubules, sertoli cells --> produce MIF --> causes Mullerian ductal system to regress.
Once testicles start to develop, how do they promote descent into the scrotum?
Testicular development --> Testicular cords, seminiferous tubules, sertoli cells -> Fetal Leydig cells -> Testicular descent -> Scrotal location of testes
Once testicles start to develop, what is the process of promoting the Wolffian system and creation of testosterone?
Testicular development --> Testicular cords, seminiferous tubules, sertoli cells -> Fetal Leydig cells -> Produce testosterone ->Wolffian system developed.
Due to testosterone from the Fetal Leydig cells, DHT and maximum testosterone eventually created -> masculinization
Gonads: at what point in development do they appear?
when do primordial germ cells move to them?
Appear in the 5th week as protuberances over mesonephric ducts
at 4-6 weeks, primordial germ cells move to the protuberances
at 6 weeks' gestation, what state are the gonads in? What cell types are present?
what ductal systems are present?
What is the state of the external genitalia?
Gonads are indifferent (bipotential) at 6 wks. Three cell types present: Germ cells, Mesenchymal cells (become Theca or Leydig), Epithelial cells (become Granulosa or Sertoli)
Both ductal systems are present: Wolffian and Mullerian
External genitalia also indifferent.
Indifferent Mesenchymal cells become what in females? males?
Indifferent Epithelial cells become what in females? males?
Mesenchymal cells --> Theca (F) or Leydig (M)
Epithelial cells --> Granulosa (F) or Sertoli (M)
What is the evidence that SRY is actually the testicular determining factor?
(Sex-determining Region on Y -- on short arm of Y chromo)
Evidence: it is deleted or mutated in XY females
it is present in XX males
What are the 5 components required for normal male differentiation?
(1) testicular determinant genes are expressed
(2) there is bilateral gonadal elaboration of MIS
(3) bilateral gonadal production of testosterone
(4) it is converted at the end organ to dihydrotestosterone
(5) there must exist functional receptors for all of the appropriate proteins including LH, MIS, and androgens.
Without SRY, what will the gonad turn into?
Gonad will turn into an ovary rather than a testis
What is the sequence of normal female gonadal development?
What is required?
Without SRY, the indifferent gonad --> ovarian development and cortical proliferation.
Then Meiosis 1 (oocytes) --> Primordial follicles
Then Ovarian Determinant Genes appear -> Primary Follicles
-> Max number of germ cells (7m), eventually decreases to 2m germ cells by birth.
Only requirements: absence of SRY, ovarian determinant gene action
What composes the internal ductal system in males? females?
Males: epididymus, vas deferens, seminal vesicles
Females: fallopian tubes, uterus, vagina
What causes the differentiation of the internal ductal system to a male phenotype? to a female phenotype?
Male: when MIH (aka AMH, MIS) is produced by Sertoli cells (in testes), the Mullerian system will regress and Wolffian system will develop
Female: when the gonad becomes an ovary, no MIH is produced. Therefore the Mullerian system develops and the Wolffian system regresses.
In order for the Wolffian ductal system to develop, MIF is required. What else is required?
Testosterone is required for the Wolffian ductal system to develop. MIF causes the regression of the Mullerian system; testosterone is still needed to develop the Wolffian.
In order for the Mullerian ductal system to develop, what is required?
Just the absence of MIF so that it does not regress. Doesn't need anything additional in order to develop.
What processes create the vagina, uterus, and tubes from the Mullerian ductal system? What part of the Mullerian ductal system is involved?
-Canalization (makes internal spaces)
Male development: what causes masculinazation of the external genitalia?
What enzyme is required?
Dihydroxytestosterone (DHT) causes the masculinization of external genitalia.
Testosterone --> DHT using enzyme 5-a-reductase.
What are the components of the undifferentiated external genitalia? what does each part become?
Genital tubercle --> penis or clitoris
Urogenital slit --> urethra
Labial/scrotal folds --> scrotum or labia
(this pic was taken from a veterinary site, but how different can it be??)
Repeated question: After germ cell migration, complete normal male sexual differentiation requires what 4 things?
1. Testicular determinant gene action (SRY)
2. Bilateral gonadal elaboration of MIS
3. Gonadal androgen steroidogenesis
4. Competent androgen receptors at the target organ
Does female genital differentiation require the presence of estrogen?
Does not appear to. Estrogen definitely required for puberty, but not for genital differentiation.
What causes the indifferent external genitalia to become feminized?
The absence of DHT.
Incompletely masculinized males (aka male pseudohermaphroditism): what are some possible etiologies?
-deficiency in 5-a-reductase (catalyzes testosterone -> DHT)
-testosterone synthesis defects
Masculinized females (aka female pseudohermaphroditism): what are some possible etiologies?
-Congenital adrenal hyperplasia
-Maternal androgen intake or production
Two disorders of gonadal development?
-True hermaphrodites (have both male and female systems)
List again the 4 steps of sexual differentation: add in the driving force for each step
1. Genetic Sex (XX v. XY)
2. Formation of Gonads (SRY)
3. Formation of Ductal systems (MIH)
4. Differentiation of External Genitalia (DHT)
What does this depict?
White/pink line on right: ovarian streak such as we might see with a 45X karyotype
If a girl is found to have an absent kidney, we should be suspicious for what other possible developmental malformations?
Ductal systems tend to form or mis-form together – this system is guided by the GI/kidney system, so renal anomalies are not surprising. May also have horseshoe kidney, duplication errors, frequent UTIs
Completion of mullerian development --> uterus, vagina, fallopian tubes. With malformation, usually have absence of vagina, no uterus, but almost always have Fallopian tubes.
Would she be able to reproduce? YES, harvest eggs from ovaries, use surrogate.
If the genitalia are ambiguous, and 1 or both gonads have descended into the labioscrotal pouch, what can we conclude about the child's 21-hydroxylase status?
The child does not have 21-hydroxylase deficiency!
What genetic pattern does CAH follow?
(more for boards)
CAH: Auto recessive
Androgen insensitivity: X-linked recessive
5-a-reductase deficiency: Auto recessive