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Physiology of Human Sexual Response and contraception

Lecture -6

Dr. Zahoor Dr. Shaikh Mujeeb Ahmed

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SEXUAL ACT

• Union of sperm and ovum requires sexual act between male and female to deliver semen containing sperms, in female vagina ( coitus, copulation ).

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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. It is a local vascular response . It is due to parasympathetic stimulation.

– Ejaculation : forceful expulsion of semen into the urethra and out of the penis. It is sympathetic response .

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SEXUAL ACT

• Physiological responses which occur during sexual act are similar in male and female. There are FOUR stages

1) Excitement phase 2) Plateau phase 3) Orgasmic phase 4) Resolution phase

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Sexual Response Cycle in males • Sexual response is divided into four phases

1. Excitement phase(Arousal).• Initiated by either physical or psychological stimuli• Heightened sexual awareness.• Vasocongestion(engorgement of sexual organs)-

includes erection

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

blood pressure, respiratory rate, and increase muscle tone.

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Sexual Response Cycle in males

3. 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.

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Sexual Response Cycle in males

4. 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.

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Erection of Penis • Accompanied by engorgement of erectile tissue with

blood. It is spinal reflex• Erectile tissue (cords of sponge like vascular spaces) :– Corpora cavernosa: two paired on dorsal side– Corpus spongiosum: one on ventral side

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Erection of Penis (cont…) • During sexual arousal, these arterioles reflexly dilate

and 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.

• Erection can occur in 5-1o seconds

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Erectile tissue in Males

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Erection reflex

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Role of Nitric Oxide in Penile Erection

Vasodilatation and vascular engorgement

Phosphodiesterase 5

Parasympathetic stimulation

NO release from vascular endothelium

Acivates Guanylate cyclase

Relaxation of arteriolar smooth muscles

Activates cGMPbreaks down

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Effect of sildenafil (Viagra)on 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

X

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Ejaculation

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

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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

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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.

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SEMEN

• Average volume – 3 ml (2-6 ml) • Sperm count– 180-400 million (66 million/ ml) • Both quality and quantity of sperm is important • Quality means motility and structure of sperm,

if abnormal motility or distorted tails of sperm there will be less chances of fertilization.

• Applied – Man is considered clinically INFERTILE if his sperm count falls below 20million/ml

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Composition of human semen

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AppliedErectile 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 surgery e.g prostate and bladder surgeries • Medicines:

– Many antihypertensive, antidepressants, cimetidine• Psychological factors:

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

Sildenafil citrate

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ERECTILE DYSFUNCTION

• Erectile dysfunction is wide spread • 50% of men between 40-70 years experience

some impotence. • Impotence increase to 70% by the age of 70

years. • Viagra (sildenafil) acts by inhibiting

phosphodiesterase ( PDE5) therefore cGMP remains active for longer time and penile arteriolar vasodilatation continues.

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Sexual Response Cycle in Females • Female sexual cycle is similar to male cycle• Also experience same four phases of the sexual cycle– 1) 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)

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Erectile tissue in females -Clitoris

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Erectile Tissue in Female

• Clitoris is like male homolog the penis and is composed of erectile tissue ( clitoris is derived from Wolfian duct) as male organ penis, because in female wolfian duct degenerate and forms clitoris.

• Clitoris is much larger than it is visible externally • Function of clitoris-- Increased pleasure

signaling, support vaginal wall.

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Sexual Response Cycle in Females

2. 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).

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Sexual Response Cycle in Females 3. 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– There is no ejaculation in female– Female do not become refractory following an

orgasm ( multiple orgasm possible)4. Resolution • Pelvic vasocongestion and systemic

manifestations gradually subside• Time of great physical relaxation

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Contraception

• Is prevention of pregnancy before the implantation has taken place .

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Methods of Contraception

1. Blockage of sperm transport to ovumI. Natural Methods

1. Rhythmic abstinence 2. Coitus interruptus

II. Barrier methodsIII. Use of spermicidal IV. Sterilization

1. tubal ligation 2. vasectomy

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Methods of Contraception (cont…)

2. Prevention of ovulation Hormonal contraceptive (OCP)

3. Blockage of implantation 1. IUCD2. Emergency contraception/morning after pill

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1. Blockage of sperm transport to ovum

Natural methodsRhythmic abstinenceCoitus interruptus

periodic or rhythmic abstinence i.e. avoidance of sexual intercourse during woman’s fertile period Following methods are used

• Calendar method:– The women predicts when ovulation to occur

based on keeping careful records of previous cycles

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Blockage of sperm transport to ovum

• Basal body temperature method: – Body temperature rises slightly a day after the

ovulation– safe period is considered to begin after the basal

body temperature remains elevated for 3 days

• Coitus interruptus: withdrawal before ejaculation

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Barrier methods

Barrier methods: prevents entry of sperm into vagina or uterus

For males (condom)For females ( diaphragm or cervical cap )Sponge

Spermicidal: SuppositoriesGelFoam tabletsCreams

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Sterilization• Permanent Methods – Female sterilization ( i.e

tubal ligation or Tubectomy)

– Male sterilization (vasectomy):

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2. Prevention of ovulation Hormonal contraceptive

• Oral contraceptives – Combined pills– Progesterone only pill– Once a month pill

• Injectable

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Hormonal contraceptive(continued)

Oral contraceptivesContains synthetic estrogen and progesterone like steroids

(ethinyl estradiol & norgesterel/norethesterone)Tablets are taken once daily for 21 days commencing at 5th

day of menstrual cycle ,it is than stopped for 7 days during which time bleeding occurs

Mechanism of action:They act by inhibiting the release of FSH & LH by anterior

pituitary by negative feedback mechanism, preventing the development of graffian follicle ,ovulation & formation of corpus luteum is prevented

Increases viscosity of cervical mucus ,preventing the sperm penetration

Endometrial maturation is also altered preventing blastocyst implantation

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Hormonal contraceptive(continued)

• Injectable long acting prgestational preparation which can be given once in a three months– Sub dermal implants of progesterone have also

been tried – Dermal patch

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3. Blockage of implantation • Intra Uterine Contraceptive

Device(IUCD):– Are devices which are

introduced & left inside the uterus for longer period of time .

Mechanism of action :They produce local nonspecific

inflammatory reaction in the endometrium & prevent implantation of blastocyst .

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• Side effects :– Bleeding – Abdominal pain / backache – Displacement – Perforation

Intra Uterine Contraceptive Device(IUCD)(continued)

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Average failure rates of common contraceptive techniques

Contraceptive methodAverage failure rate (100 women-year)

Natural method 20-30

Chemical contraceptive 20

Barier method 10-15

OCP 2-2.5

IUCD 4

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