BIO 202 ch 23

Trace the HPG axis.

GnRH (hypothalamus) → FSH/LH (anterior pituitary) → FSH stimulates Sertoli cells, LH stimulates Leydig cells → testosterone; testosterone provides negative feedback.

Which cells respond to FSH?

Sertoli cells.

Which cells respond to LH?

Leydig cells.

What do Sertoli cells do?

Support spermatogenesis, form blood-testis barrier, produce inhibin.

What do Leydig cells produce?

Testosterone.

Where does spermatogenesis occur?

Seminiferous tubules of the testes.

What is the blood-testis barrier?

Sertoli-cell barrier that protects developing sperm and maintains the proper environment.

What does inhibin do?

Selectively inhibits FSH secretion.

When are primary oocytes produced?

Before birth during fetal development.

What stage are primary oocytes arrested in?

Prophase I.

What stage is the secondary oocyte arrested in?

Metaphase II until fertilization.

Describe the follicular phase.

FSH stimulates follicle growth and estrogen production.

What triggers ovulation?

LH surge caused by sustained high estrogen.

What is the corpus luteum?

Remnant follicle that secretes progesterone and estrogen after ovulation.

What is the luteal phase?

Corpus luteum maintains the endometrium with progesterone and estrogen.

How does estrogen switch to positive feedback?

Sustained high estrogen causes an LH surge.

Describe the menstrual phase.

Endometrium is shed due to low estrogen and progesterone.

Describe the proliferative phase.

Estrogen rebuilds the endometrium.

Describe the secretory phase.

Progesterone thickens and prepares the endometrium for implantation.

What does progesterone do?

Prepares and maintains the uterus for implantation.

What produces hCG?

The developing embryo/chorion (future placenta).

What is the function of hCG?

Maintains the corpus luteum during early pregnancy.

When does the placenta take over estrogen and progesterone production?

Around weeks 10-12 of pregnancy.

Describe the oxytocin positive feedback loop during labor.

Cervical stretch → oxytocin release → stronger contractions → more cervical stretch until birth.

What does prolactin do?

Stimulates milk production.

What does oxytocin do during lactation?

Causes milk ejection (let-down reflex).