Part of the TeachMe Series
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Original Author(s): Suzannah Fleming
Last updated: 12th February 2024
Revisions: 13

Original Author(s): Suzannah Fleming
Last updated: 12th February 2024
Revisions: 13

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Coitus and conception are the initial stages that occur in humans that allow for the establishment of pregnancy. Sexual intercourse that results in the deposition of sperm in the vagina at the level of the cervix is known as coitus.

For coitus to occur humans need to be sexually aroused. Sexual arousal is then followed by a series of phases. These phases are:

  • Excitement phase
  • Plateau phase
  • Orgasmic phase
  • Resolution phase.

In this article, we shall look at the various phases of coitus and some clinical conditions.

Male Sexual Response

The changes that occur to allow coitus involve genital and systemic alterations in both sexes. The first part of sexual stimulation in a male results in the production of an erection.

An erection may be produced due to psychogenic or somatogenic stimuli. Psychogenic stimuli cause stimulation of efferent nerves to the penis via the limbic system from sensory cues such as images. Somatogenic stimuli cause this same stimulation but through sensations such as touching the penis.

Fig 1 – Diagram to show the engorgement of blood vessels involved in producing and maintaining an erection in males

The plateau phase in males results in an increase in penile erection, an increase in the size of the testicles and a rise in heart rate and blood pressure.

Following on from the plateau phase there is the orgasmic phase. The orgasmic phase has two parts: emission and ejaculation. Emission is where several structures contract to mix the contents of ejaculate. Ejaculation is where semen is then expelled from the prostatic urethra due to muscular contractions.

The final part of the sexual response cycle is the resolution phase and in males, this is split into two stages. The first stage results in the penis reducing from full erection to 50% larger than its unstimulated size and the second, longer phase, results in the penis reducing to its normal unstimulated size.

Stages of Male Sexual Function:

Males Nervous system stimulated Consequence
Excitement phase Sacral parasympathetic neurons Arteriolar vasodilation in corpora cavernosa which increases penile blood flow

Penile filling (latency)

Penile tumescence (erection)

Plateau phase Sacrospinous reflex Contraction of ischiocavernosus

Venous engorgement and decreased arterial inflow

Testes become completely engorged and elevated

Stimulates secretion from accessory glands which will make up 5% of ejaculate

Lubricates distal urethra and neutralises acidic urine in the urethra

Orgasmic phase Emission Thoracolumbar sympathetic reflex Contraction of smooth muscles in ductus deferens, ampulla, seminal vesicle and prostate

Internal and external urethral sphincters contract

Semen pooled in the urethral bulb

Ejaculation Spinal reflex with cortical control (L1, L2 sympathetic) Contraction of glands and ducts

Contraction of urethral sphincter

Filling of the internal urethra stimulates the pudendal nerve, which contracts genital organs, ischiocavernosus and bulbocavernosus – resulting in the expulsion of semen

Resolution phase Thoracolumbar sympathetic pathway Contraction of arteriolar smooth muscle in corpora cavernosa

Increased venous return leads to detumescence flaccidity which results in the refractory period

Table 1 – Summary of the male phases of coitus

Female Sexual Response

The autonomic nervous system that controls the four parts of coitus is the same in males and females, however, the responses of the genital organs are different.

Within females, the excitement phase results in anatomical changes that increase the circumference of the vaginal diameter at the level of the pelvis and lubricate the vagina for penile entry.

Following the excitement phase, the plateau phase results in the labia minora becoming red in appearance as well as the respiratory rate, heart rate and blood pressure increasing.

Within females, the orgasmic phase does not include emission and ejaculation. The orgasm includes contraction of the lower third of the vagina and can extend to the whole vagina and uterus. The final phase of resolution encompasses several changes that result in the return of the structures to normal unstimulated states.

Stages of Female Sexual Function:

Females Nervous system stimulated Consequence
Excitement phase Sacral parasympathetic neurons Vasocongestion

Vaginal lubrication

Clitoris engorges with blood

Uterus elevates

Increase in muscle tone, heart rate and BP

Inner two-thirds of the vagina lengthens and expands

Plateau phase Sacrospinous reflex Further increase in muscle tone, heart rate and BP

Labia minora deepens in colour

Clitoris withdraws under hood

Bartholin gland secretion to lubricate vestibule for entry of penis

Uterus is fully elevated and organismic platform forms in the lower one-third of the vagina

Orgasmic Spinal reflex with cortical control (L1, L2 sympathetic) The orgasmic platform contracts rhythmically 3-15 times

Uterus contracts, anal sphincter contracts

Resolution phase Thoracolumbar sympathetic pathway Clitoris descends and engorgement subsides

Labia return to unaroused colour and size

Uterus descends to unaroused position

Vagina shortens and narrows back to the unaroused state

No refractory period so multiple orgasms are possible

Table 2 – Summary of the female phases of coitus

Male Vs Female Sexual Response

There are several differences in the physiological sexual response of males and females:

  • Emission and ejaculation do not occur in the female
  • Females are capable of several orgasms and the orgasm may last relatively longer than that of a male
  • Females can reach the plateau phase and sustain it then return to an unstimulated state without orgasm

Clinical Relevance – Ageing and the Sexual Response

Several changes occur in females as a result of ageing:

  • Reduced vasocongestion response, causing reduced vaginal lubrication
  • Vaginal and urethral tissue lose elasticity
  • Length and width of the vagina decrease which reduces the expansile ability of the inner vagina during arousal
  • The number of orgasmic contractions is often reduced
  • More rapid resolution

Clinical Relevance – Sexual Dysfunction

Sexual dysfunction can be caused by a change in desire or arousal. The most common type of sexual dysfunction is when there is a problem with desire. Below are several types of sexual dysfunctions caused by an abnormality in desire:

  • Hypoactive – little or no interest in sex
  • Aversion – revulsion or fear of sex
  • Hyperactive
  • Nymphomaniac
  • Kluver Bucci syndrome


In males, a problem with arousal is called impotence. Impotence can be caused by descending inhibition of spinal reflexes due to psychological problems, tears in the fibrous tissue of corpora cavernosa, vascular abnormalities (atherosclerosis and diabetes) and certain drugs. Viagra (sildenafil) can be prescribed for males and works by inhibiting cGMP breakdown and results in an increased nitric oxide action that produces an erection.

Sperm abnormalities may be another reason for sexual dysfunction and this could be a low level of sperm within the ejaculate (oligospermia) or sperm morphological defects.


Vaginismus is a condition that may affect individuals with vaginas. It is described as “involuntary contraction of the vaginal musculature, which usually leads to a failure in penetration”. This can be as a result of a number of psychosocial factors in an individual’s life including stress, previous abuse, or substance misuse.