Reproductive Unit Physiology

What are gonads?

Organs that produce gametes and sex hormones.

What are the male and female gonads?

Testes and ovaries.

What is a bipotential gonad?

An embryonic gonad that can develop into testes or ovaries.

What does the SRY gene do?

Initiates testis development.

Where is the SRY gene normally found?

On the Y chromosome.

What do Sertoli cells secrete during fetal development?

Anti-Müllerian hormone (AMH).

What does AMH do?

Causes Müllerian ducts to regress.

What do Leydig cells secrete?

Testosterone.

What does testosterone do during fetal development?

Promotes Wolffian duct development.

What do Wolffian ducts develop into?

Epididymis, vas deferens, and seminal vesicles.

What does DHT do during fetal development?

Promotes male external genitalia and prostate development.

What do Müllerian ducts develop into?

Uterine tubes, uterus, and upper vagina.

What happens to Wolffian ducts without testosterone?

They regress.

What happens to Müllerian ducts without AMH?

They persist and develop.

What happens without SRY activation?

Testes do not develop through the typical SRY pathway.

What happens if androgen receptors do not respond to testosterone?

Androgen-dependent male structures fail to develop normally.

What determines the development of reproductive structures?

Chromosomes influence gonadal development; hormones and receptors guide organ differentiation.

What is the male HPG axis?

GnRH → LH/FSH → testes.

What does LH stimulate in males?

Leydig cells to produce testosterone.

What does FSH stimulate in males?

Sertoli cells to support spermatogenesis.

What is spermatogenesis?

Production of sperm in the seminiferous tubules.

What do Sertoli cells do?

Support and nourish developing sperm.

What does androgen-binding protein (ABP) do?

Maintains high testosterone concentrations near developing sperm.

What does inhibin B inhibit?

FSH secretion from the anterior pituitary.

How does testosterone regulate the HPG axis?

Negative feedback decreases GnRH and LH.

What happens if Sertoli cells lose FSH stimulation?

Sperm production may decrease.

What are the ovarian cycle phases?

Follicular → ovulation → luteal.

What happens during the follicular phase?

Follicles grow and the oocyte matures.

What does FSH stimulate in the ovary?

Granulosa cell activity and follicular development.

What does LH stimulate in theca cells?

Androgen production.

What do granulosa cells do with androgens?

Convert them into estrogen.

Which hormone dominates the follicular phase?

Estrogen.

What causes the LH surge?

Sustained high estrogen causes positive feedback.

What does the LH surge trigger?

Ovulation.

What happens during ovulation?

The follicle ruptures and releases a secondary oocyte.

What forms from the ruptured follicle?

Corpus luteum.

What does the corpus luteum primarily secrete?

Progesterone.

Which hormone dominates the luteal phase?

Progesterone.

What happens to LH and FSH during the luteal phase?

They are suppressed by negative feedback.

What happens to the corpus luteum without pregnancy?

Degenerates into the corpus albicans.

What are the uterine cycle phases?

Menstrual → proliferative → secretory.

What causes menstruation?

Falling progesterone and estrogen.

What happens during the proliferative phase?

Estrogen stimulates endometrial growth.

What happens during the secretory phase?

Progesterone promotes glandular secretions for implantation.

Which ovarian phase overlaps with the secretory phase?

Luteal phase.

What happens if the LH surge is blocked?

Ovulation is prevented or disrupted.

Where does fertilization usually occur?

Ampulla of the uterine tube.

What is a blastocyst?

Early embryo with an inner cell mass and outer trophoblast.

What is implantation?

Blastocyst attaches to and embeds in the endometrium.

What does hCG do during early pregnancy?

Maintains the corpus luteum.

Why is progesterone maintained during pregnancy?

It supports the endometrium and prevents menstruation.

How do combined hormonal contraceptives prevent pregnancy?

Suppress ovulation through negative feedback on the HPG axis.

How do condoms prevent pregnancy?

Block sperm from entering the reproductive tract.

How does a vasectomy prevent fertilization?

Blocks sperm transport through the vas deferens.

How do IUDs prevent pregnancy?

Copper impairs sperm;

hormonal IUDs mainly thicken cervical mucus.

What initiates puberty?

Increased pulsatile GnRH secretion activates the HPG axis.

What causes male secondary sex characteristics?

Increased testosterone and DHT.

What causes female secondary sex characteristics?

Increased ovarian estrogen.

What happens if the HPG axis is suppressed before puberty?

Reduced sex hormones may delay sexual maturation.

What is menopause?

Permanent end of menstrual cycles due to ovarian follicle depletion.

What happens to estrogen and FSH during menopause?

Estrogen decreases; FSH increases.

Why does FSH increase during menopause?

Reduced estrogen and inhibin weaken negative feedback.

What is andropause?

Gradual age-related decline in testosterone, unlike abrupt menopause.

What does GnRH stimulate?

LH and FSH release from the anterior pituitary.

What is long-loop negative feedback in the HPG axis?

Gonadal hormones inhibit hypothalamic and pituitary activity.

What happens to LH if testosterone decreases?

LH generally increases due to reduced negative feedback.

What happens if LH receptors are blocked in Leydig cells?

Testosterone production decreases.

What happens if estrogen cannot produce positive feedback?

The normal LH surge does not occur.

What happens to basal body temperature after ovulation?

It rises slightly due to progesterone.

How does progesterone affect cervical mucus?

Makes it thicker and less penetrable to sperm.

How do progestin-only contraceptives prevent pregnancy?

Thicken cervical mucus; some also suppress ovulation.

How does tubal sterilization prevent pregnancy?

Blocks sperm and egg from meeting.

What happens to testosterone after a vasectomy?

It remains essentially unchanged.

What happens to sperm after a vasectomy?

Sperm are still produced but are reabsorbed.

What happens if ovarian follicles stop responding to FSH?

Estrogen production falls and follicular maturation is impaired.

Progesterone

Maintains pregnancy and helps keep the uterus relaxed.

Prostaglandins

Help soften the cervix and promote contractions.

Oxytocin

Stimulates uterine contractions.

Pitocin

Synthetic oxytocin used to induce labor.

Alpha-1

Blood vessel constriction. Found on vascular smooth muscle; activation causes vasoconstriction, which increases vascular resistance and helps raise blood pressure.

Beta-1

Heart stimulation. Found in the heart; activation increases heart rate and contractility, helping the heart pump more blood.

What do LH and FSH stimulate in ovarian follicles?

LH → theca cells → androgens. FSH → granulosa cells → aromatase.

What does aromatase do?

Converts androgens into estrogens. Blocking it decreases estradiol production.