Download name: okeleke ifeyinwa stephanie matric number: 13

NAME: OKELEKE IFEYINWA STEPHANIE
MATRIC NUMBER: 13/MHSO1/082
DEPARTMENT: MEDICINE AND SURGERY
REPRODUCTIVE PHYSIOLOGY ASSIGNMENT
Question;
Write on the physiology of Erection.
Write on the physiology of Coitus.
PHYSIOLOGY OF ERECTION
HOW ERECTION WORKS
An understanding of the basic physiology of erection (that is, how an erection
works) will allow patients to understand not only the causes of erectile
dysfunction (ED) but will also lay the foundation for the understanding of ED
treatments. The penis is an organ with paired erection chambers (corpora
cavernosa), which are filled with spongy erectile tissue (corporal sinusoids)
composed predominantly of muscle. Erection and loss of erection are related
primarily to blood flow events regulated by the relaxation and contraction,
respectively, of the smooth muscle in the penile arteries and the erectile bodies
themselves. Erection is a hydraulic event, regulated by hormones and nerves,
which allow increased blood flow into and storage of blood within the erectile
bodies leading to an increase in pressure and the development of rigidity
(hardness). Penile erection is triggered by one of two main mechanisms: direct
stimulation of the genitalia or through stimuli coming from the brain (fantasy,
smell, etc.).
Upon stimulation, chemicals are released in the brain that cause signals to pass
down the spinal cord and outward through special nerves (Nervi erigentes) into
the penis. These nerves release another chemical (Nitric Oxide) that causes the
aforementioned smooth muscle to relax and blood rushes into the erectile
bodies, causing erection. Anxiety or fear can prevent the brain signals from
reaching the level required to induce erection. Medical conditions can block the
erection arteries or cause scarring of the spongy erection tissue and prevent
proper blood flow or trapping of blood and, therefore, limit the erection. Thus,
the erection mechanism is much like a tire; a firm tire is dependent upon a hose
that can deliver air in adequate amounts in a speedy fashion and a valve
mechanism that holds the air in place. In the penis the hose is represented by the
erection arteries, which rapidly carry blood into the erectile bodies and the valve
mechanism, while complicated in its structure, ensures that the blood is trapped
inside the erectile bodies until ejaculation occurs or the sexual stimulus has
passed.
PHYSIOLOGY OF COITUS
COITUS refers to the process of sexual intercourse by which sperms are
deposited into the vagina. Physiologically, coitus involves both male and female
act or sexual arousal.
Coitus has a social as well as a sexual function in higher primates, obviously
humans (menstruation is concealed and the female is receptive throughout the
cycle) but archetypally bonobo chimpanzees.
• EPOR model in humans (Masters & Johnson).
1. Excitement. Psychogenic or somatogenic stimuli cause sexual arousal.
2. Plateau. Arousal is intensified; if stimulation is sufficient and prolonged,
orgasm occurs.
3. Orgasm. Brief moment of involuntary climax; intense pleasure; often
myotonia.
4. Resolution. Sexual arousal fades. Pelvic haemodynamics return to
normal. Occurs rapidly (minutes) follow- ing orgasm but may take hours
otherwise.
• This model applies to both sexes. In the male, there is an absolute refractory
period following orgasm in which sex- ual re-arousal and orgasm is impossible; its
duration varies with age (young=quick), and psychological factors in- cluding
novelty of partner/context.
THE MALE.
• Erection results from tactile stimulation the penis and adjacent perineum. The
reflex involves the internal pudendal nerves (afferent) and the parasympathetic
outflow from S2–4 (efferent). Psychogenic stimuli (e.g. visual cues) can also cause
erection so there is descending control.
• Erection is caused by relaxation of the smooth muscle of the dorsal artery and
the arteries to the corpus cavernosum. The arteries dilate, allowing an inflow of
blood. Arterio-venous shunts are closed to prevent drainage and the SM of the
cavernosum relaxes, decreasing resistance to the increase in blood volume there.
Venous ‘bleed’ valves close (and the veins are compressed by the increased
pressure). Low volume, low pressure - high volume, high pressure. The corpus
spongiosum does not increase in turgor as much as the c.c., so compression of the
urethra is avoided.
• Signalling pathways are still not certain. Autonomic NS involves NA and ACh.
Injection of VIP causes erection, but may ultimately end up as a nitric oxide (NO)
signal (enter Viagra).
• The testes are drawn reflexively towards the perineum and the dartos muscle
contracts the scrotum. Testicular volume may increase by 50% due to
vasocongestion.
• Further stimulation leads to emission, in which the contents of the vas deferens,
prostate and seminal vesicles are expelled into the urethra. This is followed by
ejaculation, in which semen is expelled from the posterior urethra (urethral
smooth muscle + bulbocavernosus + ischiocavernosus). Retrograde ejaculation
into the bladder is pre- vented by contraction of the vesical urethral sphincter.
• Other changes of sexual arousal – nipple erection, ↑HR, ↑BP, skin rashes
immediately prior to ejaculation, muscle spasms etc.
THE FEMALE.
• Psychogenic stimulation, stimulation of the vaginal walls and particularly the
clitoris leads to genital changes very similar to the male. Vasocongestion of
genitalia, including clitoral erection. Other effects are also similar, though time
course differs from the male (i.e. longer). Subjective descriptions of orgasms are
very similar in men and women.
• Vaginal lubrication is by transudation of fluid through the vaginal wall.
• The vagina increases in width and length and the uterus elevates, lifting the
cervical os to cause tenting of the vagina.
• At orgasm, vaginal and uterine contractions occur. The cervix may be actively
dipped into the pool of semen by these contractions.
• Behavioral differences in sexual excitability probably reflect differences in
reproductive strategy. Orgasm following coitus occurs in 100% of normal men but
surveys suggest 30–50% of women.
REFERENCES;
● https://www.cornellurology.com
● Textbook of medical physiology
● Reproduction_5_coitus_fertilization_and_implantation.pdf