A sperm cell typically matures when they enter the lumen of the seminiferous tubules; fluid secreted by sustentacular cells pushes them along towards the ducts of the testes. During sperm maturation, the sperm acquire motility and the ability to fertilize an ovum. The epididymis can store viable sperm for up to several months and helps propel sperm in to the vas deferens during sexual arousal by peristaltic contraction of its smooth muscle. The vas deferens then conveys sperm during sexual arousal from the epididymis toward the urethra using peristaltic contractions, if not ejaculated, the vas deferens can also store sperm for several months. The union of the duct from the seminal vesicle and the ampulla of the vas deferens form ejaculatory ducts, together they form the urethra. The urethra serves as a passageway for both semen and urine and is divided into parts: the prostatic urethra, membranous urethra and the spongy urethra. Before being ejected, sperm that travelled from the vas deferens is mixed with other liquids to form semen. Semen is a mixture of sperm and seminal fluid that contain secretions from accessory sex glands that include the seminiferous tubules, seminal vesicles, the prostate and bulbourethral glands. Seminal vesicles secrete alkaline, viscous fluid that contains fructose, prostaglandins and clotting proteins and helps to neutralize the acidic environment of the male urethra and female reproductive tract that could otherwise inactivate sperm. The fructose found in this fluid is used for ATP production by the sperm and the prostaglandins contribute to sperm motility and viability, which may contribute to stimulation of smooth muscle contractions within the female reproductive tract. The prostate surrounds the prostatic urethra and secretes a milky, slightly acidic fluid containing several substances that include: citric acid, proteolytic enzymes, acid phosphatase and seminalplasmin. Prostatic secretions are used in a variety of ways, specifically for ATP production of sperm, breaking down of clotting proteins from the seminal vesicles and act as an antibiotic that can destroy bacteria and decrease the number Assignment 3 :: Biology 235: Human Anatomy and Physiology 9
of naturally occurring bacteria in semen and in the lower female reproductive tract. The bulbourethral glands are found on either side of the membranous urethra and open into the spongy urethra During sexual arousal, these glands secrete an alkaline fluid in into the urethra to protect the passing sperm by neutralizing acids from urine in the urethra and secrete mucus to lubricate the end of the penis and lining of the urethra, decreasing the number of sperm that could potentially be damaged during ejaculation. Upon sexual stimulation, parasympathetic fibers initiate and maintain an erection. These fibers produce and release nitric oxide (NO), which cause the smooth muscles in the walls of the arterioles supplying erectile tissue to relax allowing the blood vessels to dilate. A large amount of blood enters the erectile tissue and the release of NO causes the smooth muscle within the erectile tissue to relax resulting in widening of the blood sinuses. The combination of increased blood flow and widening of the blood sinuses results in an erection.
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