Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
It is important for any doctor to be able to take a sexual history and to have some idea of how sexual problems are managed. Understanding the physiology of the normal sexual response will allow the doctor to better understand many of the uncomplicated sexual problems.
This chapter is divided in its discussion into issues affecting anatomical males and anatomical females. People with gender incongruence may have sexual problems which may or may not be related to their surgical or hormonal treatment. For simplicity, the issues described in this chapter relate to genital anatomy regardless of a person’s gender identity.
Scientific investigation of the normal sexual response is necessary to our understanding. However, because of conservative attitudes, few scientists have chosen to work in this area until fairly recently. Early researchers were:
Sigmund Freud (1856–1939), an Austrian doctor, was the founder of psychoanalysis and the first to recognise the importance of childhood influences on sexuality. His studies were on patients rather than normal subjects.
Havelock Ellis (1859–1939) studied medicine at St Thomas Hospital, London. His seven-volume Studies in the Psychology of Sex (1897–1928) caused controversy but was the first detached treatment of the subject.
Alfred Kinsey (1894–1956), an American zoologist, became director of Indiana University’s Institute for Sex Research in 1942. To investigate ‘normal’ sexual experience, 18,500 Americans were interviewed. Sexual Behavior in the Human Male was published in 1948 and Sexual Behavior in the Human Female in 1953.
Masters and Johnson: William Masters (1915–2001), a doctor, and Virginia Johnson (1925–2013), a psychologist, working at Washington University, St Louis, carried out the first direct observations on sexual activity under laboratory conditions. Human Sexual Response appeared in 1966, and Human Sexual Inadequacy in 1970.
The field of sexual medicine, or sexology, has developed significantly since the early work of these pioneers and is now a flourishing specialty in itself. There are numerous societies, conferences and journals devoted to the field. Despite this, it is still a niche specialism and not everyone has access to services for sexual problems.
The normal human sexual response can be regarded as having five phases: desire, arousal, orgasm, resolution and the refractory phase ( Fig. 19.1 ). This is the most widely accepted model, first published by Masters and Johnson. There are criticisms of this model and others have developed slightly different models, but this version serves as a useful introduction to the topic.
Sexual desire refers to the general level of interest in sexual pleasure. It is modulated by hormones – hence, the change in sexual interest at puberty. The main hormonal modulator is testosterone. Desire is also dependant on contextual factors, such as mood, environment and levels of sexual attraction.
This phase has three components: central arousal, genital response and peripheral arousal.
This refers to the response to sexual stimuli, which may be visual or tactile or may result from internal imagery or from a relationship. These stimuli act through the cerebral cortex ( Fig. 19.2 ). The areas of the brain involved in sexual arousal are thought to be in the limbic system. There are thought to be excitatory centres with endorphins as the neurotransmitter and inhibitory centres linked to the centres for pain and fear.
The spinal pathways leading to the genitalia are not precisely known but appear to be near the spinothalamic pathways for pain and temperature. Genital responses are due to vasocongestion and neuromuscular changes. Arteriolar dilatation is probably controlled by the parasympathetic sacral outflow at S2, 3 and 4 via the nervi erigentes. Thoracic sympathetic outflow also plays a part. The local neurotransmitters involved include vasoactive intestinal polypeptide, a potent vasodilator found in the penis and vagina.
For male anatomy, engorgement of the corpora cavernosa is due mainly to arteriolar dilatation and probably a reduction in the venous outflow, which results in penile erection ( Fig. 19.3 ). The scrotum tightens due to contraction of the dartos muscle and the testes are elevated due to contraction of the cremaster muscle.
For female anatomy, there is engorgement of the venous plexus surrounding the lower part of the vagina and of the erectile bulbs of the vestibule on either side of the introitus ( Fig. 19.4 ). There is reddening and pouting of the labia minora. The clitoris becomes erect and later is said to retract against the symphysis pubis.
The vagina becomes lubricated by a transudate as the blood supply to the vaginal wall increases. This fluid is not the product of mucous glands. Mucous secretion from the cervix makes relatively little contribution to vaginal lubrication (which is, therefore, usually unaffected by hysterectomy). Secretion from the Bartholin glands, formerly thought to be mainly responsible for lubrication, is only moderate in amount and occurs relatively late during arousal.
Relaxation of the anatomic female’s pelvic floor muscles occurs after vaginal lubrication has started. In the later stages of arousal, the uterus becomes engorged, increases in size and rises in the pelvis. The upper part of the vagina ‘balloons’ and there may be slow, irregular contractions of the lower third of the vagina.
In all sexes, but particularly in those with male anatomy, the genital response interacts with the central response so that arousal becomes self-amplifying, that is, having an erection leads to a desire for sexual pleasure.
Sexual arousal causes:
A rise in systolic and diastolic blood pressure (which may only be transient)
General flushing of the skin
Change in heart rate (either an increase or decrease)
Respiratory changes
Pupillary dilatation
When arousal is heightened, there may be a ‘plateau’ phase during which the couple prolongs the pleasure of intercourse before orgasm.
Orgasm involves genital, muscular and sensory changes, as well as cardiovascular and respiratory responses.
First, there is smooth muscle contraction of the epididymis, vas deferens, seminal vesicle, prostate and ampulla, propelling seminal and prostatic fluid into the urethral bulb. Then, the person becomes aware that orgasm is imminent and ejaculation usually follows within a few seconds. The internal bladder sphincter remains shut but the external sphincter relaxes and semen is propelled along the urethra by rhythmic contractions of the bulbospongiosus and ischiocavernosus muscles.
A few seconds after the onset of the subjective experience of orgasm, there is a spasm of the muscles surrounding the lower third of the vagina (the ‘orgasmic platform’) followed by a series of rhythmic contractions. Uterine contractions may also occur.
There is contraction of rectus abdominis, pelvic thrusting, contraction of the anal sphincter and sometimes carpopedal spasm. Systolic and diastolic blood pressure rises by at least 25 mmHg, and hyperventilation occurs. There is a feeling of intense pleasure and an alteration of consciousness to a variable degree.
The events of arousal are gradually reversed. In those with male anatomy, there is a moderate immediate loss of erection, followed by a slower complete reversal. In those with female anatomy, if no orgasm has occurred, pelvic congestion may take hours to resolve and can be uncomfortable. In all sexes, there is a subjective feeling of relaxation, though its duration may differ between individuals.
There follows an interval during which further stimulation does not produce a response. In males, this varies from minutes in young males to many hours in older males. Some females do not experience a refractory period; only a minority of females (14% according to Kinsey) can have multiple orgasms.
Normal sexual behaviour differs from couple to couple. It also alters with age and with the evolution of a sexual relationship. Couples may present with problems due to difficulties in adjusting to the change from one phase to the next of a relationship.
Adolescents usually have a higher capacity for sexual arousal and a need to explore the bounds of their sexuality. However, coupled with the need to learn about sexual behaviour, adolescents are subject to emotional vulnerability. This can lead to high-risk sexual behaviour. Unsatisfactory sexual experience at this time can result in sexual problems in later life. Young women in their teens are at a higher risk of unwanted pregnancy due to uncertainty about contraceptive needs. In addition, awareness of sexually transmitted infections can be limited at this age.
The early months of a relationship may be characterised by frequent sex, with couples usually learning how to establish good communication and to adjust their sexual behaviour to suit each other’s needs. Should this communication not occur, dysfunctional patterns may develop, potentially resulting in sexual problems and relationship difficulties.
The time it takes for sexual interest to return after childbirth is variable; in some women, it can be a year or more. Problems can result from a difficult birthing experience or postnatal depression but more commonly are due to fatigue and the difficulties of coping with the demands of the new baby.
When the novelty of a sexual relationship has worn off, sexual activity usually becomes less frequent, which may cause anxieties for some couples. Couples may feel they ‘ought’ to be having sex more often, resulting in guilt or anger. Stresses at work for both partners in combination with social commitments can make it difficult for them to find time to relax together. In the years before menopause, women often have menstrual problems. After menopause, there may be a reduction in sexual interest or a problem with vaginal dryness. These can usually be corrected by hormone replacement therapy.
There is a decline in erectile function with age, which can be a manifestation of physical disease ( Fig. 19.5 ). Postmenopausal women may experience low libido and vaginal dryness or atrophy. These factors can impact on the couple’s sexual relationship.
It is important to remember how much people differ from one another and how wide the range of normality may be. Sex can fulfill a multitude of functions, including some of the elements described here.
Reproductive sex is often limited to a short interval in a couple’s relationship once conception has occurred. Couples who have fertility problems may find that this causes difficulty with their sex life or, conversely, may find that after they achieve pregnancy it is difficult to have sex for pleasure only.
Sexual activity is a form of physical exercise, which improves self-esteem and feelings of well-being but is also something to be mindful of in people with physical problems, such as cardiac disease.
Though sex is readily associated with pleasure, there are, in some cultures, taboos that prevent some people from enjoying sex.
Enjoying sex means lowering one’s defences, and sharing this experience strengthens the bond between partners. People who have had to build particularly strong defences – for example, after sexual or emotional abuse in childhood – may have difficulty in relinquishing them.
Become a Clinical Tree membership for Full access and enjoy Unlimited articles
If you are a member. Log in here