06

Sexual Development, Menstrual Cycle

Actually understand the female reproductive cycle, 5-alpha reductase deficiency, androgen insensitivity, and more!

What to do next: Integration/Application Questions

Now that you’ve learned, it is CRITICAL that you add these questions (you can copy them word for word) to your Anki cards, and do your Anki cards. Learning things alone is insufficient, so you need to make cards and do those cards to make sure that you maintain that knowledge.

 

To facilitate that process, here is a recap of the integration/application questions, and their answers, that you should turn into cards.

 

Walk through the normal male development using the “4 questions” (genome, gonads, internal genitalia, external genitalia)

What is the genome?

–46 XY

What are the gonads (ovary or testis)?

–Y chromosome → SRY gene → testes

What are the internal genitalia?

–Testes → Leydig cells → testosterone → male internal genitalia

–Testes → Sertoli cells → MIS → degrade paramesonephric ducts

What are the external genitalia?

–Testosterone via 5 α reductase→ DHT “super testosterone” → genital tubercle = penis

 

5 α reductase deficiency patients – using the “4 questions” (genome, gonads, internal genitalia, external genitalia) explain their development 

–What is the genome?

46 XY

–What are the gonads (ovary or testis)?

Y chromosome → SRY gene → testes

–What are the internal genitalia?

Testes → Leydig cells → testosterone → male internal genitalia

Testes → Sertoli cells → MIS → degrade paramesonephric ducts

–What are the external genitalia?

Female/ambiguous initially, then during puberty, male external genitalia, when testosterone overcomes the lack of DHT potent signalling

 

Androgen insensitivity syndrome patients – using the “4 questions” (genome, gonads, internal genitalia, external genitalia) explain their development

Genome

–46 XY

Gonads

–Y chromosome → SRY gene → testes

Internal genitalia

–No testosterone signal → no male internal

–Testes → sertolicells → MIS → no female internal

External genitalia

–Female external genitalia from lack of testosterone signalling; blind-ending vagina w/o cervix

 

A 24 year old woman comes to the physician because she has never had menstruation.  Physical exam demonstrates small breasts, no palpable uterus, and an absence of axillary and pubic hair.  Karotypic analysis demonstrates 46, XY.  Biopsy of her gonadal structures demonstrates seminiferous tubules.

What is the diagnosis?  Why does she lack a uterus?  What would you see on speculum exam?

Androgen insensitivity syndrome

Recall the 4 questions for this:

–46 XY

Gonads

–Y chromosome → SRY gene → testes

Internal genitalia

–No testosterone signal → no male internal

–Testes → sertolicells → MIS → no female internal

External genitalia

–Female external genitalia from lack of testosterone signalling; blind-ending vagina w/o cervix

Follicular phase – during the typical reproductive cycle, what hormone(s) is/are being made, and by what structure?

Follicle making estrogen

 

Luteal phase – during the typical reproductive cycle, what hormone(s) is/are being made, and by what structure?

Corpus luteum making estrogen + progesterone (NOTE: this is why you use progesterone levels as a measure of whether you are pre-/post-ovulation)

 

If there is fertilization of the ovum, what signal allows for continued hormone production?

If conception → implantation → hCG↑ → rescue the corpus luteum

 

If there is NO fertilization of the ovum, what happens to hormone production?  Why, and what does this lead to?

If NO conception → no implantation → no hCG→ corpus luteum regression → corpus albicans → NO hormone production → No hormones to support the endometrium → sloughing of endometrium (menses)

 

hCG levels – when do they start to fall during a typical pregnancy?  Why would this make sense?

hCG levels fall near the end of the 1st trimester

Recall that hCG’s actual role is to rescue the corpus luteum, so it can continue to make hormones for the developing embryo during the 1st trimester.  However, as the placenta develops, it eventually takes over hormone production from the corpus luteum, such that hCG no longer needs to be produced to rescue it.

 

Progestin challenge – explain mechanism by describing when you use it

Test of anovulation (i.e. in case of anovulation, giving progestin should → bleeding

In anovulation: continuous estrogen → endometrial hyperplasia; progesterone given MIMICS post-ovulation hormones → endometrial maturation; withdrawal → bleeding

Test: progesterone exogenously → endometrial maturation; when progesterone levels drop → endometrial sloughing

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