Chapter 21: Reproductive System

Male Reproductive System Genital Tract In males the testes, held outside the body in the scrotum (optimum temp of about 350C), produce sperm. Sperm mature in coiled tubes atop each testis, called the epididymis (plural, epididymides). At ejaculation, sperm leave the testes through the vas deferens (plural, vasa deferentia), and pass through the ejaculatory ducts to the urethra. Sperm may be temporarily stored in the vas deferens before ejaculation.

Along the way, secretions (seminal fluid) are added from three glands: two seminal vesicles, the donut-shaped prostate gland at the base of the urinary bladder, and paired bulbourethral glands. These glands add fructose (SV) for energy so sperm can swim, and prostaglandins (SV) that cause uterine contractions; the secretions are slightly basic (prostate) Sperm with secretions from these glands is called semen.

The male reproductive system The testes produce sperm. The seminal vesicles, the prostate gland, and the bulbourethral glands provide a fluid medium for the sperm. Circumcision is the removal of the foreskin. Notice that the penis in this diagram is not circumcised, because the foreskin is present. Table 21.1 (page 415) summarizes the organs of the male reproductive system and their functions.

Orgasm in Males The penis, the organ of sexual, intercourse, becomes erect from sexual arousal that stimulates cGMP in smooth muscle cells to allow erectile tissue to fill with blood; arterioles dilate and veins are compressed. Orgasm involves ejaculation and muscular tension followed by muscular contractions and relaxation. Over 400 million sperm may be in each ejaculate. Cyclic guanosine monophosphate is cGMP. During ejaculation, a sphincter closes off the bladder so that no urine enters the urethra. Viagra inhibits an enzyme that breaks down cGMP, ensuring a full erection will take place. Erectile dysfunction (formerly referred to as impotency) occurs when the erectile tissue doesn’t expand enough to compress the veins. Ejaculation occurs when sperm leave the penis in spurts.

Penis anatomy Beneath the skin and connective tissue lies the urethra, surrounded by erectile tissue (on left). This tissue expands to form the glans penis, which in uncircumcised males is partially covered by the foreskin. On the right, the two columns of erectile tissue in the penis are located dorsally.

Male Gonads, the Testes The testes, which produce sperm and male sex hormones, contain Seminiferous tubules (Spermatogenesis) surrounded by Interstitial cells (Testosterone) Testes originate in the abdominal cavity but descend into the scrotum where it is cool enough for sperm development.

Testes Interstitial cells that lie between the seminiferous tubules within testes produce testosterone. The lobules of the testes contain seminiferous tubules. On the right, a light micrograph of the seminiferous tubules shows interstitial cells occurring in clumps among the seminiferous tubules.

Seminiferous Tubules Seminiferous tubules inside the testes produce haploid sperm through spermatogenesis. Sustentacular cells (Sertoli cells) support, nourish, and regulate the cells during spermatogenesis. Sperm have a head, middle piece, and tail.

The head of the sperm is covered by a cap called the acrosome which stores enzymes needed to penetrate the egg. Sperm do not live more than 48 hours in the female genital tract.

Hormonal Regulation in Males In both males and females, gonadotropin-releasing hormone, or GnRH, secreted by the hypothalamus stimulates the anterior pituitary to release two Gonadotropin Hormones from the Anterior Pituitary Gland. - Follicle-Stimulating Hormone (FSH) - Spermatogenesis and Luteinizing hormone (LH) - Testosterone. FSH stimulates the seminiferous tubules to produce sperm and the hormone Inhibin.

LH stimulates interstitial cells to produce testosterone. Testosterone brings about and maintains the male secondary sex characteristics. Testosterone exerts feedback control over the hypothalamus and anterior pituitary resulting in a constant amount of hormones and sperm production over time. Lutenizing Hormone = Testosterone Follicle Stimulating Hormone (FSH) = Spermatogenesis Male secondary sex characteristics include broader shoulders, deeper voice, increased musculature, and hair on the face, chest, and other body regions. Anabolic steroids resemble testosterone in their effects; however, health problems involving the kidneys, circulatory system, and hormonal balance, arise.