5. Sexual function and fertilisation

Question 1

what changes do sperm undergo in the epididymis

Answer 1

Sperm maturation, dependent on epididymis maturation by androgens:

1. concentration
2. completion of sperm modelling, eg acrosomal shaping
3. become motile (although are still transported via muscular epididymal contractions)
4. surface membrane coated with glycoproteins - for protection and oocyte interaction

Question 2

describe the production of semen

Answer 2

i. spermatozoa are secreted from epididymis via vas deferens…
ii. vas deferens unites with seminal vesicle duct to form ejaculatory duct, where spermatozoa are added to seminal fluid
iii. fluid continues down duct into prostate gland where alkaline prostatic fluid is added
iv. semen now in urethra then receives secretions of bulbourethral glands
v. expelled during ejaculation

Question 3

what % of semen is derived from seminal vesicles and what is the function of this

Answer 3

60-70%

1- alkaline fluid: neutralises acid in male urethra and female repro. tract
2- fructose: main energy source for anaerobic glycolysis
3- clotting factors (semenogelin)
4- prostaglandins: female immune response suppression? stimulate muscular activity in female tract?

Question 4

what % of semen is derived from prostate and what is the function of this

Answer 4

25%

1- zinc: stabilise sperm cell chromatin
2- citric acid: calcium ion chelator which initially offsets clotting
3- proteolytic enzymes: for breakdown of clotting proteins, re-liquefying semen in 10-20mins
4- acid phosphatase

Question 5

what % of semen is derived from bulbourethral and what is the function of this

Answer 5

<1%

1- alkaline fluid
2- mucous: lubrication of urethral lining and end of penis, prevents sperm diffusion out of semen

Question 6

name the 4 phases of the male sexual response

Answer 6

1. excitement phase
2. plateau phase
3. orgasmic phase (emission + ejaculation)
4. resolution phase

Question 7

describe the spinal reflex involved in the excitement phase

Answer 7

i. psychogenic and tactile stimulation…
ii. sensory afferents of penis and perineum…
iii. efferent impulses:
- somatic - pudendal n.
- autonomic (PNS) - pelvic n.

Question 8

describe the effects of stimulation in the excitement phase

Answer 8

i. post-ganglionic fibres release ACh… binds to M3 Rs on endothelial cells… increased [Ca2+]i… NOS activation and NO formation… relaxation of vascular SM

ii. haemodynamic changes:
- arterial vasodilation in copora cavernosa… increased penile blood flow
- engorgement of corpora cavernosa occludes emissary venous drainage…

ii. erection

Question 9

what is the main difference between erection and ejaculation

Answer 9

erection = parasympathetic control

ejaculation = sympathetic control

Question 10

what are the 2 parts of the male orgasmic phase

Answer 10

i. emission: sympathetic stimulation… smooth muscle contraction in vas deferens, prostate and seminal vesicles… mov. of semen into prostatic urethra
ii. ejaculation: filling of internal urethra stimulates pudendal n. (S2-4)… contraction of SM of glands, ducts and internal urethral sphincter (prevents retrograde ejaculation)… voluntary rhythmic striated muscle contraction (pelvic floor and perineal muscles - ischiocavernosus and bulbospongiosus)… expulsion of semen

Question 11

how does the character of cervical mucus change over course of menstrual cycle - why

Answer 11

• prior to ovulation (oestrogen alone): thin, stretchy Spinnbarkeit mucus - facilitates sperm entry
• post-ovulation (oestrogen + progesterone): thick, sticky mucus plug - protects conceptus from outside invasion

Question 12

what change occurs in sperm in the female reproductive tract

Answer 12

capacitation:
1- reorganisation of sperm cell membrane - allows fusion with oocyte cell surface

2- tail mov. changes from beat to whip-like action - propels sperm forward

3- removal of protein coat of sperm, exposing acrosome enzyme - capable of undergoing acrosome reaction

Question 13

why can hyperprolactinaemia cause infertility

Answer 13

increased serum prolactin… increased dopamine (prolactin inhibiting hormone) as -ve FB… also inhibits gonadotropins… decreased FSH and LH… decreased oestrogen so no LH surge and no ovulation

Question 14

suggest a treatment option for hyperprolactinaemia amenorrhea

Answer 14

bromocriptine dopamine agonist - inhibits AP production of prolactin

Question 15

which drug might be used to increase fertility in an annovulatory women

Answer 15

clomiphene citrate

weak oestrogenic effect… binds oestrogen Rs and decreases their conc. by inhibiting process of R replenishment… H-P axis blinded to circulating levels of endogenous oestrogen… increases GnRH (no negative feedback) and FSH… follicle maturation and oestrogen release…. drug is stopped causing LH surge and ovulation due to very high Oe level