Coition

Question 1

What are the phases in human sexual response?

Answer 1

1. Excitement: Caused by psychogenic/somatogenic stimuli and results in increased sexual arousal.
2. Plateau: Sexual arousal is maintained at steady level with an increase in pelvic haemodynamics.
3. Orgasm: A few seconds of involuntary climax consisting of relief of sexual tension and a wave of intense pleasure.
4. Resolution: Dissipation of arousal with a decrease in pelvic haemodynamics.

Question 2

What are the events that occur in penile erection?

Answer 2

1. Sexual arousal results in stimulation of the pelvic nerve, causing relaxation of smooth muscle mounds and increased arterial input into the corpora cavernosa.
2. There is also reduced venous drainage of the corpora cavernosa (possibly due to smooth muscle flaps that close as corpora swell). This reduces blood flow.
3. After 20-30 seconds, there is a build-up of blood in the spaces between the corpora sinusoids, and increased pressure.
4. Corpora become rigid structures, leading to erectile response.

Question 3

What are the events that occur in penile detumescence?

Answer 3

1. During resolution phase, the smooth muscle mounds contract again and arterial input into the corpora decreases again.
2. Pressure drops and the penis becomes flaccid as blood drains away from corpora cavernosa in the veins.

Question 4

What is the mechanism responsible for penile erection?

Answer 4

1. Increase parasympathetic tone to sacral parasympathetics innervating smooth muscle mounds.
2. Release of prostacyclins and VIP causes increased activity of NOS, and increased NO synthesis.
3. NO stimulates guanylyl cyclase and increases production of cGMP from GTP.
4. cGMP mediates relaxation of smooth muscle by reducing Ca²⁺ influx.
5. cGMP is broken down by PDE.

Question 5

What is the mechanism responsible for penile detumescence?

Answer 5

1. Sympathetic input causes contraction of smooth muscle mounds.
2. Constriction of arterial input into corpora cavernosa.

Question 6

What is the role of muscles in erectile process?

Answer 6

Rigidity of the penis is further increased by contraction of the ischiocavernosus and bulbospongiosus (bulbospongiosus reflex), stiffening the proximal part of the corpora cavernosa.

Question 7

What are the mechanisms of action of viagra?

Answer 7

Viagra promotes erection by inhibiting PDE activity and prolonging the effects of cGMP on smooth muscle mound relaxation.

Question 8

What are causes of erectile dysfunction?

Answer 8

• Neurogenic: Trauma, MS, diabetes
• Arteriogenic: Hypertension, diabetes
• Drugs: Antihypertensives, antidepressants
• Endocrine: Low testosterone

Question 9

What are the events that occur as spermatozoa are moved from seminiferous tubules into the epidydimis?

Answer 9

1. Spermatozoa are released into the seminiferous tubules in a fluid secretion from the Sertoli cells. They are pushed towards the rete testis by bulk flow
2. At this point the sperm are immotile and are unable to fertilise the egg.
3. As the fluid passes through the vasa recta, its ionic composition changes as a result of passive diffusion.
4. As the sperm/fluid mixture passes through the vas efferentia, 90% of the fluid is absorbed, a process mediated by oestrogens found in the fluid secreted by the Leydig cells

Question 10

What process occurs in the epididymis?

Answer 10

Sperm maturation

Question 11

What is the sequence of events that occur during maturation of sperm?

Answer 11

1. Nuclear condensation
2. Acrosomal remodelling
3. Loss of cytoplasmic droplet
4. Increased rigidity in tail due to formation of disulphide bonds
5. Increased cAMP production causes tail to begin functioning
6. Membrane becomes more fluid
7. Surface of sperm coated with glycoprotein (from epididymal secretion) to increase stability

Question 12

What is the key difference between ligation of vas deferens compared to vas efferentia?

Answer 12

• Ligation of the vas efferentia causes loss of fluid absorption, resulting in accumulation of fluid in testes leading to infertility.
• Ligation of the vas deferens (vasectomy) does not cause fluid accumulation due to fluid absorption by the vas efferentia.

Question 13

What process moves semen from epididymis into the vas deferens?

Answer 13

Contraction of smooth muscles in the epididymis

Question 14

What is emission?

Answer 14

Contraction of smooth muscles of the prostate, vas deferens and seminal vesicles propel the semen into the urethra.

Question 15

What mediates emission?

Answer 15

α-adrenergic stimulation from lumbar splanchnics

Question 16

What are the components of seminal fluid?

Answer 16

• Fructose: Nutrition
• Alkaline: Buffers against acidic environment of vagina
• Antioxidants
• Muscle stimulants (prostaglandins): Promotes contraction of cervical muscles and facilitates sperm entry

Question 17

What is the process of ejaculation?

Answer 17

Contraction of striated muscles ischiocavernosus and bulbospongiosus along with contraction of smooth muscles of the urethra, cause propulsion of semen out of the urethra in the process of ejaculation.

Question 18

What mediates ejaculation?

Answer 18

Pudendal nerves

Question 19

What is retrograde ejaculation and how is it prevented?

Answer 19

• Ejaculation into the bladder
• Prevented by contraction of vesicular urethral sphincter

Question 20

What are the functions of Cowper’s glands?

Answer 20

Secrete lubricant to aid process of coition, both before ejaculation and in ejaculate.

Question 21

What are the responses of the female genitalia to sexual arousal?

Answer 21

• Enlargement of the corpora cavernosa, leading to the erection of the clitoris.
• Enlargement of the corpora spongiosa to cause eversion of the labia minora.
• Tenting of the uper vagina.
• Uterine elevation.

Question 22

How is lubrication produced in the female genitalia?

Answer 22

1. Vaginal orifice: Bartholin’s glands
2. Vaginal vestibule: Transudation of fluid from vessels in the walls of the vagina

Question 23

What happens to the semen as it enters the vagina during ejaculation?

Answer 23

1. Coagulation of the semen, due to interaction between enzymes derived from prostatic secretion and fibrinogen-like substrates from seminal fluid. This coagulation helps retain sperm in the vagina.
2. However, after 20-60 minutes, the semen liquefies again through activation of pro-enzymes derived from prostatic secretion.

Question 24

What are the functions of the cervix?

Answer 24

1. Acts as barrier between pathogens and the female genital tract.
2. Selects for most active sperm during coition and removes inactive/abnormal ones.
3. Separates sperm from seminal fluid and mediates capacitation.

Question 25

What are the properties of the cervix and its secretions at different phases of the ovarian cycle?

Answer 25

1. Follicular phase: In follicular phase, when levels of oestrogens are high, the secretion is watery and the cervical os is open, promoting sperm penetration. 2. Luteal phase: In luteal phase, when levels of progesterone are high, the secretion is thick and the cervical os is closed, inhibiting sperm penetration.

Question 26

What are the properties of cervical mucous?

Answer 26

1. Spinnbarkeit: Elasticity of the secretion. Oestrogen = high, progesterone = low. 2. Ferning: Crystallised mucous shows fern pattern. Oestrogen = high, progesterone = low.

Question 27

What is the process of oocyte transport?

Answer 27

1. Ovulated oocytes enter the peritoneal cavity surrounded by cumulus cells and are picked up by the fimbriae. 2. Once in the infundibulum of the fallopian tube, the cumulus cells are gradually lost and the oocytes are wafted down the ampulla towards to uterus by pulsation of cilia (stimulated by oestrogen and pacemaker activity mediated by interstitial cells of Cajal).

Question 28

What is the process of sperm transport?

Answer 28

1. The sperm enter the uterus from the vagina by swimming through the cervical mucous (if it is the right consistency). 2. Once inside the uterus, they swim through using their own propulsion. 3. At the tubal isthmus, the sperm bind to oviductal epithelial cells and become immobile. This stabilises sperm for capacitation. 4. At ovulation, the sperm detach from the epithelium and regain motility. 5. They begin swimming towards the ampulla, probably attracted by chemoattractants released by oocyte and cumulus cells. 6. When a sperm meets the oocyte, fertilisation occurs.