Expulsion - Semen consists of sperm (10%; 50...

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Expulsion The presence of semen in the urethra activates the reflexive muscular contractions that lead to the release of semen. Sympathetic stimulation increases prostatic and seminal vesicle secretions into the urethra and cause the internal urinary sphincter to constrict, preventing the entry of urine into the urethra and semen into the urinary bladder. Neuronal stimulation of the bulbospongiosus muscle causes constriction of the spongy urethra and expulsion of semen. The majority of sperm are in the first millimeter of ejected semen. After orgasm, the vasocongestion, myotonia, and increased heart rate, blood pressure and respiratory rate returns to normal. Unlike women, men experience a refractory period during which they are unable to attain another erection or ejaculation. Semen or Seminal Fluid
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Unformatted text preview: Semen consists of sperm (10%; 50 million/milliliter), prostatic secretions (30%) and seminal vesicle secretions (60%). A typical ejaculation contains about 2 - 5 milliliters of fluid. The secretions of the seminal vesicle include fructose to provide energy for sperm motility and fibrinogen that is activated by secretions of the prostate gland to fibrin , which makes semen stick to the walls of the vagina. Prostatic secretions include fibrinolysin , which degrades fibrin and releases the sperm after about 30 minutes to enable them to swim; prostaglandins (which are also found in seminal vesicle secretions) which are thought to stimulate peristaltic contractions of the uterus; and spermine , which helps neutralize the acidity of the vaginal and uterine cavities....
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