Male Reproductive System BSN

Male Reproductive System

Functions of the Reproductive System
• • To produce offspring The gonads produce gametes (sperm or ova) and sex hormones
– Primary sex organs (gonads): testes in males, ovaries in females – Sex hormones: androgens (males), and estrogens and progesterone (females)

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All other reproductive organs are accessory
– Ducts, glands, and external genitalia

Meiosis
• Chromosomes
– The diploid number of chromosomes in humans is 46, consisting of 23 pairs of homologous chromosomes – A male has the sex chromosomes XY and a female XX – The haploid number of chromosomes in humans is 23

Anatomy of the Male Reproductive System
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The male reproductive system includes:
Testes Ducts
   Epididymis Ductus deferens Urethra

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Accessory glands
   Seminal vesicles Prostate gland Bulbourethral glands

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Supporting structures
 Scrotum and penis

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Collectively, all of these structures are called the male genitalia

Anatomy of the Male Reproductive System
• Scrotum
– A sac containing the testes – Intrascrotal temperature is kept constant by two sets of muscles:
• • Dartos: smooth muscle that wrinkles scrotal skin Cremaster: bands of skeletal muscle that elevate the testes
– They keep the testes 3°C lower than core body temperature (needed for sperm production)

Anatomy of the Male Reproductive System
 Testes (Histology)
 Each testis is surrounded by two tunics:
 The tunica vaginalis, derived from peritoneum  The tunica albuginea, the fibrous capsule of the testis

 Extensions of the tunica albuginea form incomplete septa
 Septa divide the testis into 300-400 lobules, each containing 1-4 seminiferous tubules
 The uncoiled, combined length of the seminiferous tubules in both testes is nearly half a mile

Anatomy of the Male Reproductive System
 Testes (Histology)
 Seminiferous tubules “sperm factories”:
 Produce the sperm  Converge to form the tubulus rectus

 The straight tubulus rectus conveys sperm to the rete testis  From the rete testis, the sperm :  Surrounding the seminiferous tubules are interstitial cells that produce testosterone
 Leave the testis via efferent ductules  Enter the epididymis

Anatomy of the Male Reproductive System • Testes (Descent)
– During development, the testes pass from the abdominal cavity through the inguinal canal to the scrotum – A tunica vaginalis covers each testis, protecting against friction

Anatomy of the Male Reproductive System
 Spermatogenesis
› › › Sperm cells (spermatozoa) are produced in the seminiferous tubules Cells making up the walls of seminiferous tubules are in various stages of cell division These spermatogenic cells give rise to sperm in a series of events
 Mitosis of spermatogonia, forming spermatocytes  Meiosis forms spermatids from spermatocytes  Spermiogenesis: spermatids form sperm

Anatomy of the Male Reproductive System
• Spermatogenesis
– Spermatogonia: outermost cells in contact with the epithelial basal lamina – Spermatogenesis begins at puberty as each mitotic division of spermatogonia results in type A or type B daughter cells
• • Type A cells remain at the basement membrane and maintain the germ line Type B cells move toward the lumen and become primary spermatocytes

Anatomy of the Male Reproductive System
 Spermatogenesis
› › › › Primary spermatocytes undergo meiosis I, forming two haploid cells called secondary spermatocytes Secondary spermatocytes undergo meiosis II and their daughter cells are called spermatids Spermatids are small round cells seen close to the lumen of the tubule Spermatids develop an acrosome and a flagellum to become sperm cells

Anatomy of the Male Reproductive System • Spermatogenesis
– Sperm have three major regions
• Head: contains DNA and has a helmetlike acrosome containing hydrolytic enzymes that allow the sperm to penetrate and enter the egg Midpiece: contains mitochondria spiraled around the tail filaments Tail: a typical flagellum produced by a centriole

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Anatomy of the Male Reproductive System • Spermatogenesis
– Sustentacular cells
• • Nourish the sperm cells Their tight junctions form a blood-testis barrier
– This prevents sperm antigens from escaping through the basal lamina into the blood – Since sperm are not formed until puberty, they are absent during thymic education

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Produce hormones

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Anatomy of the Male Reproductive System
Ducts: Epididymis
– – Efferent ductules extend from the testes into the head of the epididymis and join the duct of the epididymis The epididymis is a coiled tube system located on the testis that is the site of sperm cell maturation. It consists of a head, body, and tail Nonmotile sperm enter, pass through its tubes and become motile
• Takes 12-16 days
– – – Acrosome matures Ability to fertilize an oocyte develops Flagella become capable of movement

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Upon ejaculation the epididymis contracts, expelling sperm into the ductus deferens

Anatomy of the Male Reproductive System
 Ducts: Ductus Deferens and Ejaculatory Duct
› › Runs from the epididymis through the inguinal canal into the abdominal cavity Its terminus expands to form the ampulla and then joins the duct of the seminal vesicle to form the ejaculatory duct, which connects to the prostatic urethra Propels sperm from the epididymis to the urethra Vasectomy: cutting and ligating the ductus deferens, which is a nearly 100% effective form of birth control

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Anatomy of the Male Reproductive System
• Ducts: Ductus Deferens and Ejaculatory Duct
– The spermatic cord consists of the ductus deferens, blood and lymphatic vessels, and nerves Coverings of the spermatic cord consist of the external spermatic fascia, cremaster muscle, and internal spermatic fascia The spermatic cord passes through the inguinal canal into the abdominal cavity

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Anatomy of the Male Reproductive System Ducts: Urethra
– The prostatic urethra extends from the urinary bladder through the prostate gland to the membranous urethra – The membranous urethra extends through the pelvic floor and becomes the spongy urethra, which continues through the penis

Anatomy of the Male Reproductive System
 Penis
› › A copulatory organ designed to deliver sperm into the female reproductive tract Consists of an attached root and a free shaft that ends in the glans penis
 Prepuce, or foreskin
 Cuff of skin covering the glans penis  Circumcision: surgical removal of the foreskin after birth

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The bulb of the penis and the crura form the root of the penis and the crura attach the penis to the coxal bones

Anatomy of the Male Reproductive System
• Penis
– Consists of erectile tissue
• • The two corpora cavernosa
– Form the dorsum and the sides of the penis

The corpus spongiosum
– Surrounds the urethra and expands to form the glans and bulb of the penis

– Erection: during sexual excitement, the erectile tissue fills with blood causing the penis to enlarge and become rigid

Anatomy of the Male Reproductive System
• Accessory Glands
– Seminal Vesicles
• • • Lie on the posterior wall of the bladder Join the ductus deferens to form the ejaculatory duct Sperm and seminal fluid mix in the ejaculatory duct and enter the prostatic urethra during ejaculation Doughnut-shaped gland that encircles part of the urethra inferior to the bladder Consists of glandular and muscular tissue and empties into the prostatic urethra Pea-sized glands inferior to the prostate Mucous glands that empty into the spongy urethra

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Prostate Gland
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Bulbourethral glands
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Anatomy of the Male Reproductive System
• Semen
– Milky white, sticky mixture of sperm and accessory gland secretions – Provides a transport medium and nutrients (fructose), protects and activates sperm, and facilitates their movement
• The testicular secretions contain sperm cells (4% of total volume) • The seminal vesicle fluid contains fructose, clotting proteins, and prostaglandins (65% of total volume) • The prostate secretions make the seminal fluid more pHneutral. Proteolytic enzymes break down clotting proteins(30% of total volume) • The bulbourethral glands produce mucus, which neutralizes the acidic pH of the urethra (<1% of total volume)

Physiology of Male Reproduction
• Effects of Testosterone
– Produced by interstitial cells – Causes the development of male sex organs in the embryo – Stimulates the descent of the testes – Causes enlargement of the genitalia – Necessary for sperm cell formation

Physiology of Male Reproduction
• Effects of Testosterone – Hair growth stimulation (pubic area, axilla, and beard) and inhibition (male pattern baldness) – Increased skin thickness and melanin and sebum production – Enlargement of the larynx and deepening of the voice – Increased protein synthesis (muscle), bone growth, blood cell synthesis, and blood volume – Metabolic rate increases