Reproduction 7 - Conception & contraception Flashcards
What is emission and how does it occur?
Emission is the movement of ejaculate into the prostatic urethra before ejaculation. This occurs due to peristalsis of the vas deferens and secretions from the seminal vesicles.
List the main constituents of semen & their origins
Think about the role each part hasty
1) Testes: 20 – 200 million sperm per ml
2) Seminal Vesicles: Alkaline fluid, Fructose, Prostaglandins, Clotting factors
3) Prostate gland: slightly acidic fluid, Proteolytic enzymes, Citric acid, Phosphotase
4) From the Bulbourethral Glands (Cowper’s glands): Alkaline fluid, Mucous
Outline the key changes involved in erection
o Inhibition of sympathetic arterial vasoconstrictor nerves
o Activation of parasympathetic nervous system
o Activation of non-adrenergic, non-cholinergic nerves to arteries releasing NO.
Normally vasoconstriction/dilation is governed by more/less sympathetic stimulation. Erection is one of the few examples where an increase in parasympathetic stimulation causes vasodilation.
i) What nerves are involved? ii) What do they stimulate?
iii) Explain the molecular events of the cholinergic nerve in i)
i) Pelvic nerve & non-adrenergic, non-cholinergic, NO releasing nerve
ii) Nitric Oxide release
iii)
▪ Release of Ach –> M3 Receptors on epithelial cells
▪ Rise in [Ca2+] –> Activation of Nitric Oxide Synthase (NOS)
–>Formation of Nitric Oxide (NO)
In erection - how does NO cause relaxation of vascular smooth muscle (vasodilation)?
(Hint: it involves calcium)
↑ NO –> Formation of Cyclic GMP –> Ca2+ taken up into intracellular stores
▪ ↓ [Ca2+] –> Less actin-myosin cross-bridges are formed and smooth muscle relaxes
Why is it important that dilation of the Corpus Spongiosum is limited?
It would compress and close off the urethra - preventing ejaculation of sperm
During erection, which arteries straighten, enlarging their lumen and allow blood to flow into the penis?
The central arteries in the Corpa Cavernosa - helicine arteries
Which muscles compress veins egressing from the corpora cavernosa, impeding the return of venous blood?
The Bulbospongiosus and Ischiocavernosus muscles
List four causes of erectile dysfunction
o Psychological
▪ Descending inhibition of spinal reflexes
o Tears in fibrous tissue of corpa cavernosa
o Vascualar
▪ Arterial and venous
▪ Most common cause
o Factors blocking NO
▪ Alcohol
▪ Anti-hypertensives
▪ Diabetes
How does viagra work (at a molecular level)?
Inhibits the breakdown of cGMP, maintaining erection.
What changes in the female facilitate coitus?
o Vaginal lubrication
o Swelling and engorgement of the external genitalia
o Internal enlargement of the vagina
o Cervical Mucus
▪ Oestrogen – Abundant, clear, non-viscous mucous
▪ Progesterone + Oestrogen – Thick, sticky mucous plug
Describe the mechanism of ejaculation
1. Contraction of glands and ducts ▪ Smooth muscle 2. Bladder internal sphincter contracts ▪ Prevents entry of semen into the bladder 3. Rhythmic striatal muscle contractions ▪ Pelvic floor ▪ Ischiocavernosus – Pudendal (S2-S4) ▪ Bulbospongiosus – Pudendal (S2-S4) ▪ Hip and anal muscles
What control is ejaculation under?
o Sympathetic Nervous System Control (L1, L2)
What is the role of clotting factors/fibrinogen in semen?
This is to prevent sperm being physically lost from the vagina
What re-liquefies semen once in the vagina? (Approx 10-20mins later)
Enzymes found in prostatic secretions.
How far do sperm have to travel to reach the uterine tubes and how long does it take?
15 – 20cm - may last a few hours.
How do sperm physically travel to the uterine tubes?
Own propulsive capacity and the fluid currents caused by the action of ciliated cells in the uterine tract.
i) What is the name of the two key maturational processes that sperm undergo?
ii) What are these processes induced by?
i) Capacitation and the Acrosomal Reaction
ii) influx of calcium and a rise in cAMP in spermatozoa.
Outline the process of capacitation of sperm
o Further maturation of sperm in female reproductive tract (6 – 8 hours)
o Sperm cell membrane changes to allow fusion with oocyte cell surface
▪ Removal of glycoprotein coat
o Tail movement changes
▪ Beat –> Whip-like action
o Sperm become responsive to signals from the oocyte
When does the acrosomal reaction occur? What does it involve?
o When capacitated sperm come into contact with the oocyte zona pellucida
o Membranes fuse ß Start of reaction
o Acrosome swells and liberates its contents by exocytosis
o Proteolytic enzymes and further binding facilitate penetration of the zona pellucida by the sperm (takes about 15 minutes)
What mechanism is an ectopic pregnancy a failure of? What risks does it pose?
o Failure of transport of zygote (??rather than egg)
o Embeds in uterine tube, ovary or abdomen
o Embryo dies
o Severe risk of maternal haemorrhage
What is a secondary oocyte? How many chromosomes?
The secondary oocyte, surrounded by follicular cells (cumulus) embedded in a gelatinous matrix, is released from an ovulatory follicle and picked up by the fimbria of the uterine tube and guided into its lumen by the ciliary movements of epithelial cells towards the ampulla, the site of fertilisation, where the oocyte and sperms come together.
Haploid number of chromosomes
Name two methods of natural contraception
o Abstinence
o Coitus interruptus
▪ Sperm in pre-ejaculate
Barrier Methods prevent sperm from reaching the cervix. Name three such methods, how they work and any particular advantages or disadvantages
o Condoms ▪ Readily available ▪ Also protect against STIs o Diaphragm ▪ Lies diagonally across the cervix ▪ Needs correct fitting ▪ Does not completely occlude the passage of sperm ▪ Holds sperm in the acid environment of vagina and reduces survival time o Cap ▪ Fits across the cervix
