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Physiology of Human Sexual Response

Dr.Mohammed Sharique Ahmed QuadriAssistant professor physiology

Al Maarefa College

بسم الله الرحمن الرحيم

Components of Male Sexual Act

• Coitus or copulation

• Male sex act involves two components

– Erection: Hardening (increase in length and width)of normally flaccid penis, as result of increase blood flow in “erectile tissue” of penis.

– Ejaculation : forceful expulsion of semen into the urethra and out of the penis

Sexual Response Cycle in males • Sexual response is divided into four phases – Excitement phase(Arousal).• Initiated by either physical or psychological stimuli• Heightened sexual awareness.• Vasocongestion(engorgement of sexual organs)-

includes erection

– Plateau phase:• Includes intensification of earlier responses • Characterized by steadily increasing heart rate,

blood pressure, respiratory rate, and Myotonia (increase muscle tone).

Sexual Response Cycle in males

– Orgasmic phase• Includes ejaculation, Rhythmic throbbing of

pelvic muscles• All generalized body responses reaches to peak– Heavy breathing – Heart rate upto 180 beats / min–Marked generalized skeletal muscle contraction– Heightened emotions

• These responses that are collectively experienced as intense physical pleasure( feeling of release) an experience known as orgasm.

Sexual Response Cycle in males

–Resolution phaseReturn of genitalia and body systems to prearousal state• Erection subside(decrease blood flow to penis)• Deep relaxation ( may feel fatigue)• Muscle tone returns to normal • Cardiovascular and respiratory activity returns

to prearousal state.Following orgasm men enters refractory period of variable duration before sexual erection can produce another excitation.

Sexual Response Cycle in Females • Female sexual cycle is similar to male cycle• Also experience same four phases of the sexual cycle– Excitement:• Initiated by either physical or psychological stimuli• Parasympathetically induced vasodilation of

arterioles in vagina & external genitelia( specially clitoris), that results in– Swelling of labia and erection of clitoris (bulbs engorge with

blood)– Secretion of fluid in vagina (act as a lubricant)

• Erection of nipples & enlargement of breast as a result of vasocongetion.• Flushing ( increased blood flow through skin)

Erectile tissue in females

Sexual Response Cycle in Females

– Plateau:• Changes initiated during excitement phase intensify• Systemic responses similar to those in male occur

– Increase heart rate– Increase respiratory rate – Increase muscle tension

• Vasocongetion of lower third of vagina reduces its inner capacity• Uterus raises upwards-enlarging upper two third of

vagina(creates space for ejaculate deposition).

Sexual Response Cycle in Females – Orgasm:• Sympathetic stimulation triggers rhythmic contraction

of pelvic muscle • More intense contraction of lower two third of vagina • Systemic responses similar to that of male orgasm• Experience in females is similar to that in males

except– No female counterpart to ejaculation– Do not become refractory following an orgasm

( multiple orgasm possible)– Resolution • Pelvic vasocongestion and systemic

manifestations gradually subside• Time of great physical relaxation

Erection of Penis • Accompanied by engorgement of erectile tissue with

blood• Erectile tissue(cords of sponglikevascular spaces) :– Corpora cavernosa: two paired on dorsal side– Corpus spongiosum: one on ventral side

• During sexual arousal, these arterioles reflex dilate- erectile tissue fills with blood- penis to enlarge both in length and width and to become more rigid.

• Veins that drain the erectile tissue are mechanically compressed –reducing venous outflow and thereby contributing even further to vasocongestion.

Erectile tissue in Males

Erection reflex

Role of Nitric Oxide in Penile Erection

Vasodilatation and vascular engorgement

Phosphodiesterase 5

sildenafil

Parasympathetic stimulation

NO release from vascular endothelium

Acivates Guanylate cyclase

Relaxation of arteriolar smooth muscles

Activates cGMPbreaks down

Ejaculation

• Also a spinal reflex• Stimulated by sympathetic nervous system • Occurs in two phases:– Emission– Expulsion

Ejaculation – Emission: • Movement of semen into the urethra.• Sympathetic impulses cause sequential

contraction of smooth muscles in the prostate, reproductive ducts, and seminal vesicles. • This contractile activity delivers semen into the

urethra. • During this time, the sphincter at the neck of

the bladder is tightly closed to prevent semen from entering the bladder and urine from

Ejaculation • Expulsion :– Forcible expulsion of semen from the urethra out

of the penis– Filling of urethra with semen activates rhythmic

contraction of muscle at the base of penis- forcibly expelling semen out of urethra.

Erectile Dysfunction(impotence) • Repeated inability to get or keep an erection firm enough for

sexual intercourse• Causes : • Damage to nerve arteries or smooth muscles

– as a result of disease e.g. Diabetes, kidney disease, chronic alcoholism, multiple sclerosis

– Damage resulting from surgerye.ge prostate and bladder surgeries • Medicines:

– Many antihypertensive, antidepressants, cimetidine• Psychological factors:

– Stress, anxiety, , depression, fear of sexual failureTreatment :

Sildenafil citrategene therapy is now being tested

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References

• Human physiology by Lauralee Sherwood, seventh edition

• Text book physiology by Guyton &Hall,11th edition

• Text book of physiology by Linda .s contanzo,third edition