904
Sperm are produced in the testes and are suspended in the seminal fluids produced by accessory glands. The resulting semen is ejaculated into the female reproductive tract during copulation. Prior to copulation, sexual stimulation causes the penis to become erect by increasing the blood flow into the erectile tissues. The male reproductive system is under hormonal control by the hypothalamus and anterior pituitary, with negative feedback coming from hormones produced by the testes.
learning outcomes
You should be able to:
Summarize where the different components of semen are produced, and describe their functions.
Describe the anatomical and functional relationships between Leydig cells and Sertoli cells.
Describe the roles of NO and cGMP in the male sexual response.
Summarize the hormonal changes that occur during puberty in males and how they lead to the development of male secondary sexual characteristics.
What makes ejaculated semen thick and gelatinous, and how do sperm escape the gel to move up the female reproductive tract?
Semen contains fibrinogen secreted by the seminal vesicles. The prostate secretes a clotting enzyme that causes the fibrinogen to polymerize and form a clot. The prostate also secretes the enzyme fibrinolysin, which eventually breaks down the clot and liberates the sperm.
What are the roles of Sertoli cells in spermatogenesis?
Sertoli cells nurture and promote the maturation of sperm, beginning with the primary spermatocyte stage. They provide a suitable environment and essential nutrients. Tight junctions between Sertoli cells protect the developing sperm from water-
cGMP is broken down by an enzyme called a phosphodiesterase. How does an inhibitor of that enzyme treat erectile dysfunction?
Sexual stimulation of the male causes nerve endings in the penis to release a neurotransmitter that stimulates endothelial cells in the blood vessels to release NO. NO diffuses into the muscle cells controlling the diameter of the penile arteries, causing them to relax through increased production of cGMP. The resulting increase in blood flow in those arteries compresses the veins carrying blood out of the penis, and it becomes engorged with blood (an erection). A phosphodiesterase breaks down cGMP, so a phosphodiesterase inhibitor prolongs the effects of cGMP production.
What is the significance of the fact that the testes of a prepubertal male are responsive to FSH and LH?
Since prepubertal testes are responsive to LH and FSH, the cause of their inactivity must either be low production and release of LH and FSH by pituitary gonadotropes or low production of GnRH by the hypothalamus.
Whereas the male reproductive system produces sperm continuously throughout reproductive life, the female system produces eggs that can be fertilized by sperm periodically. We now turn to the cyclical processes by which the female reproductive system produces and releases eggs and prepares the female reproductive tract to receive a developing embryo should fertilization occur.