Session 7 - Conception and Contraception Flashcards
What is the normal volume of ejaculate in semen?
2-4ml
How many sperm per ejaculate
40x10^6
What percentage of sperm are motile?
> 60%
What are the three contributors to semen volume?
Seminal vesicles - 60%
Prostate - 25%
Bulbourethral -?%
What is found in secretions of seminal vesicles
o Alkaline fluid
Neutralises the acid in the male urethra and female reproductive tract
o Fructose
o Prostaglandins
o Clotting factors
Fibrinogen
Holds sperm in place after ejaculation, before liquefaction
What is found in secretions of prostate?
o Proteolytic enzymes
Break down clotting factors, re-liquefying sperm in 10 – 20 minutes
o Citric acid
o Phosphotase
Bulbourethral glands
o Very small volume
o Alkaline fluid
o Mucous
Lubrication of the end of the penis and urethral lining
Describe the physiological processes involved in emission
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.
What are the physiological stimulants of erections
Psychogenic
Tactile (sensory afferents of penis and perineum)
What are the efferents of erection?
Somatic and autonomic efferents
Pelvic nerve - PNS
Pudendal nerve - Somatic
Outline the haemodynamic changes in erection
Inhibition of sympathetic arterial vasoconstrictor nerves
Activation of parasympathetic nervous system to stimulate vasodilation
How does activation of the parasympahetic nervous sytem cause vasodilation of the penis arteries
Pelvic nerve
Normally vasoconstriction/dilation is governed by more/less sympathetic stimulation. This is one of the few examples where an increase in parasympathetic stimulation causes vasodilation.
Release of Ach M3 Receptors on epithelial cells
Rise in [Ca2+] Activation of Nitric Oxide Synthase (NOS) Formation of Nitric Oxide (NO)
o Activation of non-adrenergic, non-cholinergic nerves to arteries releasing NO.
o NO diffuses into and causes relaxation of vascular smooth muscle (vasodilation)
↑ NO Formation of Cyclic GMP Ca2+ taken up into intracellular stores
↓ [Ca2+] Less actin-myosin cross-bridges are formed and smooth muscle relaxes
What happens to blood vessels and muscles in penis to maintain erection?
The central arteries in the Corpa Cavernosa (helicine arteries) straighten, enlarging their lumen and allowing blood to flow into and dilate the cavernous spaces in the corpora of the penis.
The Corpus Spongiosum also dilates, but not very much as it would compress and close off the urethra.
The Bulbospongiosus and Ischiocavernosus muscles compress veins egressing from the corpora cavernosa, impeding the return of venous blood. This combined with the dilation of the helicine arteries causes the Corpa Cavernosa to become engorged with blood near arterial pressure, causing erectile bodies to become turgid (enlarged and rigid) and erection occurs.
Give three main factors causing erectile dysfunction
Psychological
Tears in fibrous tissue of corpa cavernoasa
Vascular
Factors blocking NO
Give three factors blocking NO
Alcohol
Anti-hypertensives
Diabetes
How does viagra work?
Inhibits the breakdown of cGMP, maintaining erection
Describe the physiological changes in the female which 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
o Spinal reflex o Sympathetic Nervous System Control (L1, L2) 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
Describe the process involved in sperm transport through the cervix and uterus
Immediately after ejaculation, the semen coagulates due to the action of clotting factors. This prevents sperm being physically lost from the vagina.
10-20 minutes later the semen re-liquefies by the action of enzymes found in prostatic secretion.
How far do sperm in cervix have to travel to reach the uterine tube?
15-20cm
How is sperm transported in the uterus?
Own propulsive capacity and fluid currents caused by the actions of ciliated cells in the uterine tract
What changes happen to sperm in uterus?
Capacitation and acrosomal reaciton
How do changes happen to sperm in uterus?
Influx of calcium and rise in cAMP
What is capacitation?
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
What is acrosomal reaction?
o Capacitated sperm comes into contact with the oocyte zona pellucida
o Membranes fuse 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)
o 300 sperm required before break down of ZP
What is produced from first meiotic division of ovum?
Secondary oocyte + First polar body
What is pronuclei?
2 sets of chromosomes combine, and mitosis then occurs
Give sequence of ectopic pregnancy
o Failure of transport of egg
o Embeds in uterine tube, ovary or abdomen
o Embryo dies
o Severe risk of maternal haemorrhage
Give two types of natural conception
Abstinence
Coitus interruptus
- Sperm in pre-ejaculate
What is vasectomyu?
o Prevent sperm from entering ejaculate
o Divide vas deferens bilaterally
o Ensure ejaculate is free of sperm before relying on it for contraception
Check a few months later
Give three barrier methods of contraception
Condoms
Diaphragm
Cap
What is a 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
Where is a “cap” fitted
Fits across the cervix
Give two parts of hormonal contraceptive
Progesterone
Oestrogen
Give two reasons progesterone prevents conception
o Thick, ‘hostile’ cervical mucus plug
Prevents sperm from entering uterus
Main contraceptive action of progesterone
o Negative feedback to hypothalamus / pituitary
Decreases frequency of GnRH pulses
Inhibits follicular development
Why does oestrogen prevent conception?
o Oestrogen negatively feeds back on anterior pituitary
o Loss of positive feedback mid-cycle
o No LH surge
Give four types of hormonal contraceptive
o Combined OCP (Progesterone and Oestrogen) o Progesterone Only Pill (POP) o Depot Progesterone (3 monthly injections) o Progesterone implants
Give two types of intrauterine contraceptive device
Inert copper
Impregnated progesterone
How does inert copper work?
Interferes with endometrial enzymes
Interferes with implantation
May also interfere with sperm transport into fallopian tube
What is a main form of post-coital contraception?
Combined oestrogen/progesterone
When is post-coital contraception given?
o Up to 72 hours after intercourse
What are the three main effects of post-coital contraception?
o May disrupt ovulation
o Blocks implantation
o May also impair luteal function
