Download physiology_of_coitus_and_erection_1

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.