Sexual intercourse, which is also referred coitus or copulation, is the reproductive act in which the male reproductive organ enters the female reproductive tract. Upon completion of the reproductive act, sperm cells are passed from the male body into the female, resulting in fertilisation of the female’s ovum and the establishment of pregnancy.

Sexual arousal is necessary in order for sexual intercourse to occur. The sexual response typically occurs in four phases:

• The excitement phase
• The plateau phase
• The orgasmic phase
• The resolution phase.

Phases of the male sexual response

The four stages of the sexual response in males occur as follows:

The excitement phase:

• The first change to occur in a male is the generation of an erection
• Psychogenic stimuli result in stimulation of efferent nerves to the penis through the limbic system from visual sensory cues
• Somatogenic stimuli cause this same stimulation but via sensation such as touching the penis.
• Parasympathetic pelvic neurons are activated, resulting in arteriolar vasodilation in corpora cavernosa which increases penile blood flow
• This initially causes penile filling (latency), followed by penile tumescence (erection).

The plateau phase:

• The plateau phase follows the excitement phase
• There is activation of the sacrospinous reflex, which results in contraction of the ischiocavernosus muscle, venous engorgement and decreased arterial inflow
• The testes become completely engorged and elevated
• The accessory sex glands are stimulated, resulting in secretion of seminal plasma, which makes up around 5% of ejaculate
• This seminal plasma lubricates the distal urethra and neutralises acidic urine in the urethra.

The orgasmic phase:

• The orgasmic phase occurs in two parts; emission and ejaculation
• During the emission part, there is stimulation of the thoracolumbar sympathetic reflex
• This results in contraction of smooth muscle in the ductus deferens, ampulla, seminal vesicle and prostate and contraction of the internal and external urethral sphincters contract
• Semen pools in the urethral bulb at this point
• During the ejaculation part, there is activation of the spinal reflex with cortical control (L1 and L2 sympathetic nervous system)
• This results in contraction of the smooth muscle and ducts and contraction of the internal urethral sphincter
• Filling of the internal urethra stimulates the pudendal nerve, which contracts the ischiocavernosus and bulbospongiosus muscles, resulting in the expulsion of semen.

The resolution phase:

• Activation of the thoracolumbar sympathetic pathway results in the resolution phase of the male sexual response
• This causes contraction of arteriolar smooth muscle in the corpora cavernosa
• Increased venous return results in detumescence flaccidity, which results in the refractory period.

Phases of the female sexual response

The four stages of the sexual response in females occur as follows:

The excitement phase:

• As with males, there is activation of pelvic parasympathetic neurons in response to visual and tactile sensory cues
• This results in vaginal lubrication secondary to vasocongestion
• The clitoris engorges with blood, the uterus elevates into the pelvic cavity, and the inner two-thirds of the vagina lengthens and expands
• There is an accompanying increase in muscle tone, heart rate and blood pressure.

The plateau phase:

• The plateau phase follows the excitement phase
• There is activation of the sacrospinous reflex, which results in a further increase in muscle tone, heart rate and blood pressure
• The labia minora deepen in colour, and the clitoris withdraws beneath the clitoral hood
• Bartholin’s glands secrete mucous, which moistens and lubricates the vestibule in preparation for the entry of the penis
• The uterus becomes fully elevated, and the organismic platform forms in the lower third of the vagina via the swelling of the bulbus vestibuli that narrows the vestibulum.

The orgasmic phase:

• During the orgasmic phase, there is activation of the spinal reflex with cortical control (L1 and L2 sympathetic nervous system)
• Orgasmic platform contracts rhythmically 3-15 times
• The uterus and anal sphincter both contract
• The clitoris remains retracted beneath the clitoral hood
• There is no refractory period, and multiple orgasms are possible.

The resolution phase:

• Activation of the thoracolumbar sympathetic pathway results in the resolution phase of the female sexual response
• The clitoris descends, and engorgement subsides
• The labia return to their unaroused colour and size
• The uterus descends to the unaroused position
• The vagina shortens and narrows back to the unaroused state

Header image used on licence from Shutterstock

Thank you to the joint editorial team of www.mrcgpexamprep.co.uk for this article.