Learn: Human Reproductive System & Endocrinology

Primary sex characteristics

Reproductive organs directly involved in reproduction (e.g., testes, ovaries, uterus, penis, vagina).

Secondary sex characteristics

Physical changes that develop during puberty but aren't directly involved in reproduction (e.g., body hair, deeper voice).

Testosterone

Main male hormone produced by Leydig cells; promotes reproductive development and sperm production.

Estrogen

Main female hormone produced by developing follicles and corpus luteum; promotes female development.

Progesterone

Hormone produced mainly by the corpus luteum; maintains the uterine lining after ovulation.

Testes

Male reproductive organs that produce sperm and testosterone.

Scrotum

Sac holding testes outside the body to keep them cooler for sperm production.

Epididymis

Organ where sperm mature and are stored.

Vas deferens

Tube transporting sperm from the epididymis toward the ejaculatory duct.

Seminal vesicles

Glands adding fructose-rich fluid to semen to provide energy for sperm.

Prostate gland

Gland adding alkaline fluid to semen to help support sperm function.

Bulbourethral glands

Glands producing lubricating, alkaline fluid before ejaculation.

Urethra

Tube that carries urine or semen out of the body.

Penis

Organ that delivers semen into the female reproductive tract.

Semen

Mixture of sperm and fluids from accessory glands.

Ovum

A mature female gamete or egg cell.

Ovarian follicle

An oocyte surrounded by supporting follicle cells developing inside the ovary.

Ovaries

Female organs producing ova, estrogen, and progesterone.

Fallopian tubes

Tubes transporting the ovum toward the uterus; where fertilization usually occurs.

Uterus

Organ where an embryo can implant and develop.

Endometrium

Inner lining of the uterus that thickens for implantation and sheds during menstruation.

Cervix

Lower opening of the uterus connecting it to the vagina.

Vagina

Organ receiving sperm and acting as the birth canal.

Bacterial STIs

Examples include chlamydia, gonorrhea, and syphilis.

Viral STIs

Examples include HPV, genital herpes, and HIV.

Spermatogenesis feedback loop

Hypothalamus releases GnRH, prompting anterior pituitary to release FSH and LH.

Sertoli cells

Cells inside seminiferous tubules that support and nourish developing sperm.

Leydig cells

Interstitial cells found between seminiferous tubules that produce testosterone.

Negative feedback (spermatogenesis)

High testosterone inhibits the hypothalamus and pituitary, reducing GnRH, LH, and FSH.

Andropause

Age-related decline in testosterone production and reproductive function.

Menstrual cycle basic pathway

Hypothalamus releases GnRH, pituitary releases FSH and LH, stimulating ovaries to produce estrogen and progesterone.

LH surge

Sustained high estrogen causes positive feedback, triggering an LH surge and ovulation.

Ovarian cycle stages

Follicular phase, ovulation, and luteal phase.

Uterine cycle stages

Menstrual phase, proliferative phase, and secretory phase.

Follicular phase

Ovarian phase where follicles develop, estrogen rises, and endometrium begins rebuilding.

Ovulation

Release of the ovum from a mature follicle, triggered by an LH surge.

Luteal phase

Ovarian phase where the ruptured follicle becomes the corpus luteum, producing progesterone.

Menstrual phase

Phase where the endometrium breaks down and is shed if pregnancy doesn't occur.

Corpus luteum

Structure formed from ruptured follicle after ovulation; produces progesterone to maintain uterine lining.

GnRH

Produced by hypothalamus; stimulates pituitary to release FSH and LH.

FSH

Anterior pituitary hormone acting on Sertoli cells in males and stimulating follicles in females.

LH

Anterior pituitary hormone stimulating Leydig cells in males and triggering ovulation in females.

Menopause

Permanent end of menstrual cycles caused by depletion of functional ovarian follicles.

Spermatogenesis vs Oogenesis

Spermatogenesis yields 4 functional sperm; oogenesis yields 1 ovum and polar bodies.

Seminiferous tubules

Coiled structures inside the testes where spermatogenesis occurs.

Primary follicle

Contains a primary oocyte surrounded by developing follicular cells.

Mature/Graafian follicle

Large, developed follicle containing an oocyte ready for ovulation.

Atresia

Degeneration of ovarian follicles that do not successfully ovulate.