Male Reproductive System

• The primary function of the male reproductive system is to produce sperm for fertilization of the female egg.
• Key components include the testes, duct system, accessory glands, and penis.

Testes

• The testes (or testicles) are the primary male reproductive organs.
• They produce sperm and testosterone.
• They are located within the scrotum, a sac of skin that hangs outside the body.
• Location outside the body allows for temperature regulation, which is crucial for sperm production.
• Sperm production occurs within the seminiferous tubules of the testes.
• Interstitial cells (Leydig cells) between the seminiferous tubules produce testosterone.

Duct System

• The duct system transports and stores sperm as they mature.
• The epididymis is a coiled tube attached to the back of each testis.
• Sperm mature and are stored in the epididymis.
• During ejaculation, sperm are propelled from the epididymis into the ductus deferens (vas deferens).
• The ductus deferens is a tube that carries sperm from the epididymis to the ejaculatory duct.
• The ejaculatory duct is formed by the union of the ductus deferens and the duct of the seminal vesicle.
• It passes through the prostate gland and empties into the urethra.
• The urethra is the tube that carries both urine and semen out of the body.

Accessory Glands

• The accessory glands secrete fluids that contribute to the semen.
• Semen is the fluid that carries sperm.
• The seminal vesicles are located on the posterior side of the bladder.
• They secrete a thick, alkaline fluid containing fructose, which provides energy for sperm.
• The prostate gland surrounds the urethra just below the bladder.
• It secretes a milky, slightly acidic fluid that contains citrate (another nutrient for sperm) and enzymes.
• The bulbourethral glands (Cowper's glands) are located below the prostate gland.
• They secrete a clear, mucus-rich fluid that lubricates the urethra and neutralizes any acidic urine.

Penis

• The penis is the male organ for sexual intercourse.
• It contains the urethra and specialized erectile tissue.
• The glans penis is the enlarged tip of the penis.
• The prepuce (foreskin) is a retractable fold of skin covering the glans penis.
• Circumcision is the surgical removal of the prepuce.
• The penis contains three cylindrical bodies of erectile tissue: two corpora cavernosa and one corpus spongiosum.
• During sexual arousal, the erectile tissue fills with blood, causing the penis to become erect.
• Erection is necessary for penetration and delivery of semen into the female reproductive tract.

Hormonal Control

• The hypothalamus, pituitary gland, and testes regulate male reproductive function through hormones.
• Gonadotropin-releasing hormone (GnRH) is released by the hypothalamus.
• GnRH stimulates the anterior pituitary gland to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
• FSH stimulates Sertoli cells in the seminiferous tubules to support sperm development.
• LH stimulates interstitial cells to produce testosterone.
• Testosterone promotes sperm production and the development of male secondary sex characteristics.
• Secondary sex characteristics include increased muscle mass, deepening of the voice, and growth of body hair.
• Testosterone also has negative feedback effects on the hypothalamus and pituitary gland, regulating GnRH, FSH, and LH secretion.
• Inhibin is a hormone produced by Sertoli cells that inhibits FSH secretion.

Spermatogenesis

• Spermatogenesis is the process of sperm production in the seminiferous tubules.
• It begins with spermatogonia, which are diploid stem cells.
• Spermatogonia undergo mitosis to produce more spermatogonia and primary spermatocytes.
• Primary spermatocytes undergo meiosis I to produce two secondary spermatocytes.
• Secondary spermatocytes undergo meiosis II to produce four spermatids.
• Spermatids are haploid cells that undergo spermiogenesis to become mature sperm.
• Spermiogenesis involves the development of a tail (flagellum) and the acrosome (a cap containing enzymes that help the sperm penetrate the egg).
• Mature sperm are composed of a head, midpiece, and tail.
• The head contains the nucleus with the sperm's DNA.
• The midpiece contains mitochondria that provide energy for movement.
• The tail is a flagellum that propels the sperm.
• The entire process of spermatogenesis takes approximately 64-72 days.

Male Secondary Sexual Characteristics

• These are features that appear during puberty and are driven by the increase in testosterone levels:
• Enlargement of the larynx (Adam's apple) and deepening of the voice.
• Increased hair growth on the face, chest, and pubic area.
• Increased muscle mass and bone density.
• Increased sebaceous gland secretion, which can lead to acne.

Male Sexual Response

• The male sexual response involves both physiological and psychological factors.
• Erection is the first stage, resulting from the engorgement of the penile tissues with blood.
• Lubrication is provided by the bulbourethral glands, which secrete mucus to facilitate intercourse.
• Emission is the movement of sperm and seminal fluids into the urethra.
• Ejaculation is the forceful expulsion of semen from the urethra.
• Orgasm is the pleasurable sensation associated with ejaculation, accompanied by muscle contractions.
• Resolution is the period following orgasm when the body returns to its pre-arousal state.
• There is typically a refractory period after ejaculation during which another erection is not possible.

Aging and the Male Reproductive System

• Male fertility typically declines with age.
• Testosterone levels gradually decrease after age 40.
• This decline can lead to a condition called andropause, characterized by decreased libido, fatigue, and muscle loss.
• Prostate enlargement (benign prostatic hyperplasia or BPH) is common in older men, which can cause urinary problems.
• Erectile dysfunction (ED) is also more common with age, often due to vascular or neurological problems.