Coitus Flashcards
How is sperm produced and transported to the vas deferens?
Spermatogonia takes 74 days before becoming mature spermatozoa
(50 days in seminiferous tubules, 12-26 days in epididymis)
1000 spermatozoa produced/s
6.5 million/g/day in 20yr olds, 3.8 million/g/day in over 50yr olds
Sertoli cells in seminiferous tubules produce fluid to push sperm into the vas deferens
Sperm stored in the vas deferens until degradation/ejaculation (fluid from Sertoli cells is reabsorbed)
What are the different phases of coitus?
- Excitement phase
- Plateau phase
- Orgasmic phase
- Resolution phase (+/- refractory period)
What are the features of the female sexual response?
Blood engorgement & erection of clitoris, vaginal mucosa, breasts, & nipples
Increased lubrication by glands in vaginal mucosa
+/- orgasm
No physiological refractory period
Outline the mechanisms involved in penile erection.
Stimulants —————–> Efferents ——-> Haemodynamic changes
Stimulants:
- psychogenic (rapid; ~5s-10s)
- tactile (sensory afferents of penis & perineum)
Efferents:
- somatic & autonomic
- pelvic nerve (PS)
- pudendal nerve (S)
Haemodynamic changes:
- tumescence + skeletal muscle around base of penis (increased pressure maintains rigidity)
What are the nerves and blood vessels involved in tumescence of the penis?
Inhibition of sympathetic arterial vasoconstrictor nerves & activation of parasympathetic nervous system ——-> vasodilatation of central arteries of copora cavernosa (via reduction in [Ca2+]i)
Activation of NANC nerves to arteries —> release of NO —> stimulates action of guanylyl cyclase —> conversion of GTP to cGMP —> protein kinase activated —> Ca2+ enters the SER —> fall in [Ca2+]i
Veins occluded to prevent blood leaving the penis
Fibrous tissue restricts expansion (ensures high pressure is maintained)
note: corpus spongiosum is not affected as much, otherwise sperm could not leave the urethra
How does viagra cause erections?
Viagra (sildentafil) inhibits phosphodiesterase 5 (which breaks down GMP used to make cGMP)
Maintains vasodilatation
Give some examples of the causes of erectile dysfunction.
40% at 40yrs, 70% at 70yrs
- psychological (descending inhibition of spinal reflexes) e.g. anxiety, depression, stress
- tears in fibrous tissue if corpora cavernosa
- vascular
- drugs e.g. anti-depressants, anti-histamines, diabetic drugs, anti-hypertensives (diuretics & beta-blockers), alcohol (inhibits NO —> vasodilatation)
- low testosterone
- MS, Parkinson’s, stroke
- Peroni’s disease (bent penis)
- penile fractures (of fibrous ring around corpus cavernosum)
- micropenis
- hypertension, cardiac disease, Leriche syndrome, diabetes (neuropathy & peripheral vascular disease)
- cystic fibrosis
- sickle cell anaemia —> priapism
What is emission?
Movement of ejaculate into the prostatic urethra —> leakage of some semen BEFORE ejaculation
?fertilisation can occur
- vas deferens peristalsis (symp.)
- accessory gland secretions e.g. bulbourethral (parasymp.)
Outline the mechanisms of ejaculation.
~0.5m/s
200-300 million sperm reached
Spinal (L1/L2) & cerebral reflexes
- contraction of glands & ducts (smooth muscle)
- internal urethral sphincter contracts (stops reflux of semen into bladder; if this does not occur —> “dry orgasm”)
- rhythmic striated muscle contractions (pelvic floor, ischiocavernosus, bulbospongiosus, hip & anal muscles)
What are the components of normal ejaculate?
- 2-4ml
- 20-200 million sperm/ml (total of over 40 million sperm in ejaculate)
- 60%+ sperm swimming vigorously
- less than 30% abnormal morphology (certain amount acceptable due to rapid gametogenesis e.g. 2 tails, twisted bodies, 2 heads, etc.)
- ejaculate solidifies, then liquefies within 1hr (then not viable)
How much does each gland contribute to the contents of semen?
Seminal vesicles (60%):
- alkaline (neutralises acid environment of male urethra & female reproductive tract)
- fructose (substrate for sperm)
- clotting factors (clots semen after release) e.g. semenogelin
Prostate (25%):
- milky & slightly acidic
- proteolytic enzymes (break down clotting proteins —> re-liquefies semen in ~10-20min —> releases sperm —> enables fertilisation)
Bulbourethral (Cowper’s) gland:
- alkaline
- mucous (lubricates end of penis & urethral lining)
How much sperm reaches the site of fertilisation in the uterus? Why is this needed?
~300 reach fertilisation site (0.00006%)
Only 1 sperm required to fertilise ovum, but 299+ required to disperse the surrounding zona pellucida to allow fertilisation
What is capacitation of sperm?
Further maturation of sperm in female reproductive tract (6-8hrs)
Sperm cell membrane changes to allow fusion with oocyte cell surface and tail movement changes from beat to whip-like (3mm/hr —> only 5min to penetrate cervix)
How long do gametes survive? When is the fertile period?
Spermatozoa survive ~48-72hrs in reproductive tract
Oocytes survive ~6-24hrs maximum
Fertile period = sperm deposition up to 3 days prior to ovulation/day of ovulation (i.e. 14 days prior to menstruation)
How does sperm penetrate the oocyte?
- Sperm pushes through granulosa cells (corona radiata + zona pellucida)
- Proteins on sperm head binds to ZP3 proteins of zona pellucida
- Acrosomal enzymes hydrolyse zona pellucida
- Sperm penetrates & fuses with oocyte
- Cortical granules burst to prevent more sperm from entering (prevents polyspermy)
