Chapter 31: Male Reproductive System Dr. Kim Wilson

SEXUAL REPRODUCTION Functioning of the reproductive system ensures the survival of the genetic characteristics of a species Male reproductive system consists of organs whose functions are to produce, transfer, and introduce mature sperm into the female reproductive tract, where fertilization can occur

MALE REPRODUCTIVE ORGANS Classified as essential organs for production of gametes or accessory organs that support the reproductive process Accessory glands produce secretions that nourish, transport, and mature sperm Essential organs: gonads (testes) Accessory organs: Genital ducts convey sperm outside the body pair of epididymides, paired vasa deferentia pair of ejaculatory ducts urethra pair of seminal vesicles the prostate bulbourethral glands Supporting structures: scrotum, penis, and pair of spermatic cords MALE REPRODUCTIVE ORGANS

Perineum Structure: roughly diamond-shaped area between thighs Location: extends anteriorly from pubic symphysis to coccyx posteriorly Lateral boundary is the ischial tuberosity on either side Divided into the urogenital triangle and the anal triangle

TESTES Structure and location Several lobules composed of seminiferous tubules and interstitial cells (Leydig cells), separated by septa and encased in fibrous capsule called the tunica albuginea (Figure 31-3) Seminiferous tubules in testis open into a plexus called rete testis, which is drained by a series of efferent ductules that emerge from the top of the organ and enter the head of epididymis Located in scrotum, one testis in each of two scrotal compartments

Microscopic Anatomy of the Testes Interstitial (Leydig) cells: endocrine cells between the seminiferous tubules Seminiferous tubules Spermatogenic cells produce sperm Sustentacular cells: also called nurse or Sertoli cells Support and regulate sperm-producing functions of the testis Produce androgen-binding protein that binds to testosterone to make it more soluble and thus increase its concentration, supporting sperm production Tight junctions between sustentacular cells form the blood-testis barrier, which protects developing sperm from the immune system

Functions of the Testes Spermatogenesis: formation of mature male gametes (spermatozoa) by seminiferous tubules Stimulated by follicle-stimulating hormone from the anterior pituitary (and also gonadotropin-releasing hormone from hypothalamus) Secretion of hormones by interstitial cells Testosterone Type of androgen: maleness hormone Functions include promoting primary and secondary male sexual characteristics and anabolism, affecting fluid and electrolyte balance Regulated by luteinizing hormone from anterior pituitary Inhibin: inhibits release of follicle-stimulating hormone by anterior pituitary, allowing the testis some control over spermatogenesis Estrogen: small amounts secreted by interstitial cells, liver, and other organs; role in males uncertain but may influence spermatogenesis and other functions

Testosterone Secretion

Spermatozoa Structure: consists of a head (covered by acrosome), neck, midpiece, and tail; tail is divided into a principal piece and a short end piece

Reproductive Ducts - Epididymis Structure and location Single tightly coiled tube enclosed in fibrous casing Lies along top and side of each testis Anatomical divisions include head, body, and tail Functions Duct for seminal fluid Also secretes part of seminal fluid Sperm become capable of motility while they are passing through the epididymis

Reproductive Ducts – Vas Deferens Vas deferens (ductus deferens) Structure and location Tube, extension of epididymis Extends through inguinal canal, into abdominal cavity, over top and down posterior surface of bladder Enlarged terminal portion called ampulla; joins duct of seminal vesicle Function Excretory duct for seminal fluid Connects epididymis with ejaculatory duct

Reproductive Ducts – Ejaculatory Duct & Urethra Formed by union of vas deferens with duct from seminal vesicle Passes through prostate gland, terminating in urethra Urethra

Accessory Reproductive Glands Seminal vesicles Structure and location: convoluted pouches 5 to 7 cm long on posterior surface of bladder Function: secrete the viscous, nutrient-rich part of seminal fluid (60% of semen volume) Prostate gland Structure and location Doughnut shaped Encircles urethra just below bladder Function: adds slightly acidic, watery, milky-looking secretion to seminal fluid (30% of semen volume)

Accessory Reproductive Glands Bulbourethral glands Structure and location: Small, pea-shaped structures with approximately 2.5-cm long (1 inch) ducts leading into urethra Lie below prostate gland Function: secrete alkaline fluid that is part of semen (5% of semen volume)

Supporting Structures - Scrotum Skin-covered pouch suspended from perineal region into which the testes descend near the time of birth Divided into two compartments: Contains testis, epididymis, and lower part of a spermatic cord Dartos and cremaster muscles elevate the scrotal pouch

Supporting Structures - Penis Structure: composed of three cylindrical masses of erectile tissue, one of which contains urethra Functions: penis contains the urethra, the terminal duct for both urinary and reproductive tracts; during sexual arousal, penis becomes erect, serving as a penetrating copulatory organ during sexual intercourse Spermatic cords (internal) Fibrous cylinders located in inguinal canals Enclose seminal ducts, blood vessels, lymphatics, and nerves

Seminal Fluid Composition: Flow: Consists of secretions from testes, epididymides, seminal vesicles, prostate, and bulbourethral glands Each milliliter contains millions of sperm Flow: Passes from testes through epididymis, vas deferens, ejaculatory duct, and urethra

Male Fertility Relates to many factors: number, size, shape, and motility of sperm Infertility may be caused by antibodies some men make against their own sperm Male fertility begins at puberty and extends into old age

Reproduction Cycle Reproductive functions begin at time of puberty Development of organs begins before birth; immature testes descend into scrotum before or shortly after birth Puberty: high levels of hormones stimulate final stages of development System operates to permit reproduction until advanced old age Late adulthood: gradual decline in hormone production may decrease sexual appetite and fertility