Lecture 27: Reproductive System Overview

What does the hypothalamus release?

Gonadotropin-releasing hormone (GnRH)

What does the anterior pituitary release?

Gonadotropins

FSH for gametogenesis

LH for Gondar hormone synthesis

What hormones do the ovaries release?

Estradiol and progesterone

What hormones do the testes release?

Testosterone and dihydrotestosterone

Inhibin

Produced by both ovaries and testes

Negative feedback of FSH on anterior pituitary

Female reproductive organs

Ovaries

Fallopian tubes

Uterus

Cervix

Vagina

Vulva

Labia

Clitoris

Mons pubis

Breasts

Oogenesis

Starts in utero

Primary oocytes formed and arrested in prophase I of meiosis at birth

Folliculogeneis occurs; primary follicle (granulosa cells) form around the primordial ovum

Several eggs resume meiosis each month during puberty, follicles grow and mature, regulating FSH and LH

Secondary oocyte arresting in meiosis II is released from mature follicle during ovulation and waits to be fertilized

When fertilized, meiosis II completes and a zygote is formed with pronuclei fusion of sperm and egg

How many ovarian follicles in utero?

6-7 million

How many ovarian follicles at puberty?

Only 300-400

They are continuously degrated (atresia)

FSH

Mostly acts on granulosa cells of follicles

Supports follicle growth and maturation

LH

Involved in ovulation

Acts directly on theca and granulosa cells

Surges trigger ovulation

Estradiol and Progesterone

Produced in the ovaries to support follicle maturation

Prepare the uterine lining for implantation

Negative feedback effects on GnRH and LH/FSH except during late follicular phase when positive feedback causes LH surge

Dominant follicle

Largest with most FSH receptors

Releases high amounts of estradiol

Causes positive feedback to increase LH surge → ovulation

What happens if fertilization does not occur?

Estrogen and progesterone production decrease

Menstruation occurs

FSH inhibitor hormones produced by ovaries

Activin and inhibin

Estrogens

Growth and development of sex organs and those associated with reproduction

Progestin

Prepare uterus for implantation

Menopause

Follicle depletion

Estradiol levels drop

LH and FSH rise

Estrogen deficiency symptoms

Male reproductive organs

Penis

Testes

Epididymis

Scrotum

Vas deferents

Seminal vesicle

Prostate

Urethra

Testes

Male gonads

Lie outside of abdominal cavity in scrotum

Sperm production

Sperm production

Spermatogonia → mitosis → meiosis I and II

Germ cell → spermatogonia → spermatocyte → spermatid → mature sperm

Starts at puberty (Testosterone initiates)

Continues throughout life; decreases with age

Spermatogenesis

Occurs in the seminiferous tubules

Sertoli cells inside of tubules respond to FSH and convert spermatid to sperm. They also express androgen receptors that respond to testosterone to enhance spermatogenesis and testes growth

Leydig cells outside of tubules respond to LH to produce testosterone to stimulate germ cell proliferation

Adropause

Testes reduce sensitivity to LH with age

Androgen production drops

LH and FSH levels increase

Sperm production continues but is decreased

Fertilization

Pregnancy

Development

Regulation and pathologies