Male Reproduction System

Anatomy and Physiology II

BIO 232

Overview of Male Reproductive System

Scrotum

• Sac of skin and superficial fascia outside the abdominopelvic cavity

• Contains the paired oval testes or testicles - midline septum divides the scrotum into two halves

• Superficial location provides a temperature environment 3 degrees below body temp - ideal for sperm development

• Cremaster muscles extend from the internal obliques and can elevate the testes

• Dartos muscles - smooth muscle in the fascia of the scrotum - wrinkles scrotal skin

Scrotum & Testes

The Testes

• Approximately 4 cm long and 2.5 cm in diameter

• Covered in two tunics

• Tunica vaginalis - from peritoneum

• Tunica albuginea - deeper tunic - fibrous capsule

• Septa from this layer divides testes into 250 -300 wedge shaped compartments or lobules

• Each lobule contains 1 to 4 tightly coiled seminiferous tubules - where sperm are made

The Testes

• Rete testis - tubular network into which the seminiferous tubules empty

• The epididymis receives sperm from the rete testis

• Interstitial cells are found in the soft connective tissue surrounding the seminiferous tubules

• These produce androgens (especially testosterone)

• Long testicular arteries supply the testes and testicular veins drain the testes (vine like network)

The Penis

• Consists of an attached root and a free shaft or body

• Ends in an expanded tip called the glans penis

• Skin covering the penis is loose and ends in a cuff of skin called the prepuce or foreskin

• Frequently removed shortly after birth - cicumcision

The Penis

• Erectile tissue - three cylindrical bodies (corpora)

• Spongy tissue that fills with blood during sexual excitement - causing the penis to become enlarged and rigid

• Corpus spongiosum - surrounds the urethra

• Expands distal to form the glands and proximally to from the bulb of the penis

• Paired dorsal erectile bodies - corpora cavernosa - make up most of the penis

• Proximally they form the crus of the pnis that anchors the penis in palce

Male Duct System

• 1. Sperm produced in seminiferous tubules

• 2. Stored in epididymis

• 3. Transported via the ductus deferens or vas deferens - expanded end called ampulla of the ductus deferens

• 4. Next it joins the duct of the seminal vesicle to form an ejaculatory duct

• 5. Each of these ducts passes into the prostate gland and empties into the urthera

• 5. Urethra - terminal portion of the duct system - conveys semen and urine out (at different times)

Accessory Glands

• Seminal vesicles - paired - posterior wall of the bladder - size of a little finger

• Their secretions account for about 60% of the volume of semen

• Yellowish viscous alkaline fluid containing fructose , ascorbic acid, a coagulating enzyme (vesiculase) and prostaglandins

• Prostate Gland - donut shaped - size of a walnut - encircles the urethra as it leaves the bladder

• Secretions - 1/3 of semen volume - milky, slightly acid - contains citrate & enzymes prostate specific antigen (helps activate sperm)

Accessory Glands

• Bulbourethral glands (Cowper’s) - pea-sized - inferior to prostate - produce a thick, clear mucous prior to ejaculation - drains into the spongy urethra and neutralizes traces of acidic urine in the urethra

Semen

• Milky white - somewhat sticky mixture of sperm and accessory gland secretions

• Provides the transport medium, nutrients and chemicals to protect and activate sperm for sperm

• Relatively alkaline ( pH 7.2 to 7.6)

• Antibiotic - seminalplasmin

• Clotting factors - coagulates quickly after ejaculation - then liquefies via fibrinolysin

• Total amount ejaculated - 2-5 ml

• 50 - 150 million sperm per ml

Male Sexual Response - Erection

• Enlargement & stiffening of the penis due to engorgement of the erectile tissues with blood

• When not sexually aroused - arterioles supplying the erectile tissue are constricted and the penis is flacid

• During sexual excitement - parasympathetic reflex is triggered - releases nitric oxide (NO)

• NO relaxes vascular smooth muscle causing arteioles to dilate - erectile tissues now can fill with blood

• Expansion of the corpora cavernosa compresses their venous drainage

Male Sexual Response - Ejaculation

• Propulsion of semen from the male duct system

• Under sympathetic control

• When impulses provoking erection reach a certain critical level - spinal reflex is initiated

• Massive discharge of nerve impulses occurs over sympathetic nerves serving the genital organs

Male Sexual Response - Ejaculation

• Sympathetic activation results in

• Reproductive ducts and glands contract & empty into the urethra

• Bladder sphincter constricts

• Bulbospongiosus muscles of the penis undergoe a rapid series of contractions

• Sperm is ejected at a rate of 200 inches/sec

• Contractions accompanied by intense pleasure

• Also generalized muscle contraction, rapid heart rate and elevated blood pressure

• Entire event - climax or orgasm

• Quickly followed by generalized relaxation & vasoconstriction of the arteioles of the penis - it then becomes flaccid

Spermatogenesis

• Spermatogonia - divide mitotically

• New spermatogonia move to interior & increase in size

• Become primary spermatocytes

• Undergo meiosis

• Primary Spermatocyte ® 2 secondary spermatocytes

• Secondary spermatocytes ® 4 spermatids

• Spermatids ® differentiate into spermatozoa (sperm)

Spermatogenesis

Spermiogenesis

Hormonal Regulation of Male Reproductive

System

• Hypothalamus - produces gonadotropin-releasing hormone (GnRH)

• GnRH controls ant. pituitary gonadotropins

• Folicle stimulating hormone (FSH)

• Luteinizing hormone (LH)

• FSH stim. spermatogenesis indirectly by stim sustentacular cells to release andogen-binding protein (ABP)

• ABP prompts spermatogenic cells to bind and concentrate testosterone which in turn stim spermatogenesis

Hormonal Regulation of Male Reproductive System

• LH binds to interstitial cells & stim them to secrete testosterone & some estrogen

• Also called interstitial cell-stimulating hormone

• Both hypothalamus and ant. pituitary are subject to feedback inhibition

• Testosterone - inhibits hypothalamus & ant, pituitary

• Inhibin - protein hormone produced by sustentacular (Sertoli) cells - inhibits upstream hormone release - maintains sperm production

Brain-Testicular Axis