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NAME: AMADI ONYINYECHI VICTORIA MATRIC NO: 13/ MHS06/006 COURSE CODE: PHS210 DEPARTMENT: MLS DATE: 5/06/2015 ASSIGNMENT WRITE ON THE PHYSIOLOGY OF COITUS AND ERECTION ANSWER Coitus also known as sexual intercourse or copulation, is principally the insertion and thrusting of a male’s penis, usually when erect, into a female’s vagina for the purpose of sexual pleasure or reproduction or both. This is additionally known as vaginal sex or vaginal intercourse. Other forms of penetrative sexual intercourse include penetration of the anus by the penis (anal sex), penetration of the mouth and other forms. A variety of views concern what constitutes coitus or other sexual activity, can also impact views on sexual health. Although coitus denotes penile- vaginal penetration and the possibility of creating offspring i.e. the fertilization process known as reproduction. The male sexual act (coitus) is most times divided into three (3) parts: 1. Erection 2. Lubrication 3. Ejaculation Erection This is the physiological process by which a penis becomes erect by being engorged with blood. Psychic as well as direct physical stimuli to the glans penis or other regions of the body like the scrotum, anal epithelium, perineal structures in general, the lips and tongues in kissing and other erotic areas can reinforce erection in the males. The degree of erection is proportional to the degree of stimulation whether this is physical or psychic. Erections are caused by efferent parasympathetic impulses passing from the spinal cord via the nerve erigentes to the arteries of the penis. These parasympathetic nervous impulses cause the arteries of the penis to dilate. While at the same time they cause constriction of the vein. As a result of arterial dilation more blood flows into the penis but little or no blood leaves the penis because of the partial occlusion of the veins. There are also nonadrenergic non-cholinergic fibres in the Nervi erigentes and these contain large amounts of NO synthase, the enzyme that catalyzes the formation of the powerful vasodilator, nitric oxide. Injection of inhibitors NO synthase prevents the erection normally produced by stimulation of the pelvic nerve in experimental animals. Thus, nitric oxide is an important mediator of erection. Thus, blood builds up under high pressure in the erectile tissue of the penis. The erectile bodies in the penis are surrounded by strong fibrous coats, so that the expansion of the erectile tissue is restricted. High pressure within the sinusoids of the erectile bodies causes ballooning of the erectile tissue to such an extent that the penis becomes hard and elongated. Lubrication During sexual stimulation, apart from causing erection, the parasympathetic nerves also stimulate the bulbourethral glands and the glands of Littre to secret mucus. This mucus flows out through the urethra during intercourse to aid lubrication of coitus. The female sexual organs, rather than the male, supply most of the lubrication of coitus. Adequate lubrication is essential to a successful sexual act because intercourse undertaken when there is inadequate lubrication causes pain and may in fact inhibit rather than stimulate sexual sensation. Some foreplay before the attempt at penetration into the female genital organ usually ensures adequate lubrication. Ejaculation Ejaculation is the climax of the male sexual act. Stimulation of the penis during sexual intercourse results in afferent impulses that arise from the touch receptors in the glans penis and are transmitted to the spinal cord via the internal pudendal nerves. Ejaculation per say is a two ways reflex whose centre lies in the upper lumbar segment of the spinal cord (L1 and L2) as well as the sacral segment of the spinal cord (S1 and S2). When sexual stimulation becomes sufficiently intense, the lumbar centre begins to discharge rhythmic sympathetic impulses that leave the cord at L1 and L2 and are transmitted to the genitals via the hypogastric plexus. These impulses initiate emission, which is the first stage of ejaculation. During emission, the smooth muscles of the epididymis, vas deferens, seminal vesicles and prostatic capsule contract so that the sperm and glandular secretions are expelled into the internal urethra. During ejaculation proper, semen is expelled from the urethra by contraction of the bulbocavernous muscle which in turn compresses the bulbus urethrae under the influence of the rhythmic impulses that now arise in the sacral region (S1 and S2) of the spinal cord. This entire period of emission and ejaculation is called the male orgasm. At its termination, the male sexual excitement disappears almost completely within 1 to 2min and erection ceases, a process known as resolution. Although the cerebrum is of major importance in the male sexual act (coitus), it does not appear to be of critical importance in its accomplishment. Hence, humans and decerebrate animals with spinal cord transection above the lumbar region can exhibit erection and ejaculation following direct genital stimulation.