Sex & Fertilisation Flashcards
How does the motility of sperm change in the epididymis?
At Entry: functionally immature and incapable of movement
At the tail: they are capable of movement and have the potential to fertilise
What is the function of seminal plasma?
- Transport medium
- Nutrition
- Buffering capacity ready for entrance into female repro tract
Which accessory vesicles contribute to seminal plasma and what does each secretion contain?
Seminal Vesicles : alkaline fluid, fructose, prostoglandins and clotting factors
Prostate Gland: milky and slightly acidic, proteolytic enzymes to breakdown clotting proteins
Bulbourethral glands (Cowper’s): alkaline fluid and mucus to lubricate penis
Which site in the female reproductive tract does fertilisation normally occur?
Ampulla of the uterine tube
What are the 4 phases of the Human Sexual Response?
- Excitement
- Plateu Phase
- Orgasm Phase
- Resolution Phase
What are the 2 stimulants of erection?
- Psychogenic
- Tactile (touch)
How do the stimulants of erection lead to penis erection?
- Psychostimulus and Tactile information sent to the brain by the spinal reflex
- Pelvic nerve (PNS) and Pudenal Nerve (somatic) signal to the penis causing haemodynamic changes
What nerve routes make up the pudenal nerve?
S2-S4
Describe the anatomical course of the pudenal nerve
- Branches S2, S3 and S4 form the pudenal nerve
- Leaves the pelvis through the greater sciatic foramen
- Passes under the sacrospinous ligament and re-enters the pelvis through the lesser sciatic foramen
- Passes through the pudenal canal where it gives off branches before continuing to the dorsal nerve or penis or clitoris
What 3 haemodynamic changes are required for erection to occur?
- Sinusoids in corpus cavernosum need to relax
- Arterial dilation in the corpus cavernosum
-
Venous compression by the tunica albuginea
- (stops blood leaving penis)
What is the parasympathetic innervation of erection?
- Pelvic nerve and pelvic plexus
- Cavernous nerve to corpora and vasculature
What is the most important neurotransmitter involved in erection? Explain how it is released?
Nitric Oxide (NO)
- Parasympathetic post glanglionic fibres release ACh which binds to M3 receptors on endothelial cells
- Causes a rise in intracellular [Ca2+] which activates NO formation
- NO diffuses into vascular smooth muscle causing vasodilation, mediated by cGMP
How does viagra treat erectile dysfunction?
Viagra slows the rate that cGMP is degraded, increasing NO
What things can cause erectile dysfunction?
- Drugs (anti-hypertensives mainly)
- Neurological disorders affecting spinal reflex
- Tears in the fibrous tissue of corpus cavernosum
- Vascular problems (arterial and venous)
Emission and Ejaculation is under what control?
Sympathetic Control
What happens during emission in reproduction?
Semen moves to the prostatic urethra by mucular contractions of smooth muscle in the prostate, vas deferens and seminal vesicles
What happens in ejaculation?
Expulsion of semen
Requires contraction of glands and smooth mucle
To prevent retrograde ejaculation the internal sphincter must contract
How does cervical mucus change throughout the menstrual cycle under the influence of different hormones?
Pre-ovulation: Oestreogen is high , mucus is thin & stretchy to allow entry of male gametes
Post ovulation: Oestrogen & Progesterone forms a thick, sticky mucus plug to close of the repro tract from further sperm entry
What happens in capacitation?
- Occurs 6-8 hours after depostion in reproductive tract
- Tail movement changes to whip like movement
- Undergoes acrosome reaction
How long are spermatozoa and oocytes fertile for?
Spermatazoa: 48-72hr
Oocyte: 6-24hr (max)
What is the acrosome reaction?
Essentially the loss of the outer membrane of sperm
Sperm pushes through corona radiata and is able to bind to the ZP3 glycoprotein of the zona pellucida
This triggers digestion of the zona pellucida
What happens to prevent polyspermy?
Once sperm penetrates and fuses to oocyte plasma membrane, the cortical reaction is triggered
A calcium dependent reaction
When does meiosis II complete in the oocyte?
Once oocyte fuses with spermatazoa
Membrane fusion triggers calcium waves which causes meiosis II to occur
What is hatching?
Growing blastocyst hatches out of the zona pelliculada allowing growth and interaction with uterine wall
