Male Reproductive System

homologous structures

homologous structures

Share a common origin during development Example: male testes and female ovaries, or male penis and female clitoris

Primary sex organs

(gonads): testes (male) and ovaries (female)

Primary sex organ purpose

Gametes: sperm (male) and ova (females) Gamete formed by cell division called meiosis

2. Sex hormones (steroid hormones): Testosterone (males) and estrogens and progesterone (females)

accessory reproductive organs

ducts, glands, and external genitalia

testes

the male gonads are the site of gamete and hormone production (e.g., androgens) and the intratesticular duct system (straight tubules [tubuli recti] and rete testes)

extratesticular excurrent duct system

This series of tubes has a common embryonic origin and conducts sperm away from the testes to the copulatory organ; it consists of the efferent ductules, ductus epididymis, ductus deferens, and ejaculatory duct.

accessory sex glands

These contribute to semen volume and function; they include the seminal vesicles, prostate gland and bulbourethral glands.

penis

the copulatory organ; its duct, the urethra, serves as the terminal passage for both the urinary and reproductive systems.

intra and extracurricualr duct system

testes and ducts

tunica vaginalis

outer layer derived from the peritoneum

tunica albuginea

inner layer forms fibrous capsule. Septa divide testis into approximately 250 lobules, each containing one to four seminiferous tubules which are the sites of sperm production.

seminiferous tubules

have thick, stratified epithelium surrounding central fluid-containing lumen.

The epithelium contains spheroid spermatogonia (sperm-forming cells) embedded in support cells (Sertoli cells). Myoid cells surround each seminiferous tubule; they are smooth muscle–like cells that may squeeze sperm and testicular fluids out of the testes.

leydig cells

located in soft tissue surrounding seminiferous tubules; produce androgens, such as testosterone and secrete it into interstitial fluid.

sustentocytes

large columnar cells act as supporting cells and play role in sperm formation

Spermatogenic cells

cells that are surrounded by sustentocytes and give rise to sperm

myoid cells

smooth muscle-like cells surrounding seminiferous tubule that contract to squeeze sperm and testicular fluid through tubules

interstitial endocrine cells

produce androgens and some estrogen

sperm production

Males continuously produce sperm throughout our lives. Sperm need exactly the appropriate range of temperatures to develop correctly (32-35ºC). Too hot, and sperm are malformed; too cold, and they die. The male scrotum allows for the regulation of temperature of the sperm-producing apparatus. The testes (gonads) sit in a sac (the scrotum). Inside the skin of the sac are muscles that can expand and contract as the temperature changes (cremaster muscle).

urethra

Conveys both urine and semen

urethral regions

Prostatic urethra: surrounded by prostate

Intermediate part of the urethra (membranous urethra): in urogenital diaphragm

Spongy urethra: runs through penis; opens at external urethral orifice

penis

made up of spongy urethra and three cylindrical bodies of erectile tissue, spongy network of connective tissue and smooth muscle with vascular spaces Corpus spongiosum: surrounds urethra and expands to form glans and bulb of penis Corpora cavernosa: paired dorsal erectile bodies Erection: erectile tissue fills with blood, causing penis to enlarge and become rigid Crura: proximal ends of corpora cavernosa surrounded by ischiocavernosus muscle; anchors penis to pubic arch

male perineum

Diamond-shaped region between pubic symphysis, coccyx, and ischial tuberosities Suspends scrotum Contains root of penis and anus

embryological origin

The descent of the testes.

sex determination

determined by the SRY gene on the y chromosome, also by the production of testosterone

Hypothalamic-Pituitary-Gonadal-Axis in Sperm Production

Hypothalamus releases gonadotropin-releasing hormone (GnRH)

GnRH binds to anterior pituitary gonadotropic cells, causing them to secrete FSH and LH.

FSH stimulates sustentocytes to release androgen-binding protein (ABP) which keeps concentration of testosterone high near spermatogenic cells, promoting spermatogenesis.

LH binds to interstitial endocrine cells, signaling them to secrete testosterone

Testosterone entering the blood stimulates sex organ maturation, development/maintenance of secondary sex characteristics, and libido

Rising testosterone levels feed back on hypothalamus to inhibit

GnRH and on pituitary to inhibit gonadotropin release

Inhibin: released by sustentocytes when sperm count high; inhibits GnRH and FSH release

meiosis

Gamete formation involves meiosis

In meiosis, the number of chromosomes are cut in half (2n to n) (In mitosis, chromosomes remain 2n).

Meiosis introduces genetic diversity, as all daughter cells are genetically different from the original cell

Involves meiosis I and meiosis II

Four cells are produced at the end but they are NOT “genetically” identical

spermatogenesis

production of sperm (spermatozoa) in seminiferous tubules—adult males make ~90 million sperm daily

steps of spermatogenesis

Mitosis of spermatogonia (stem cell) forms two spermatocytes

Meiosis Spermatocytes form secondary spermatocytes, which form spermatids Spermiogenesis Spermatids become sperm

semen

Milky-white mixture of sperm and accessory gland secretions 2–5 ml semen are ejaculated containing 20–150 million sperm/ml

Contains fructose for ATP production, protects and activates sperm, and facilitates sperm movement

Alkaline fluid neutralizes acidity of male urethra and female vagina and enhances motility

erection

enlargement and stiffening of penis (parasympathetic)

ejaculation

Propulsion of semen from male duct system (sympathetic)