Session 7 - Conception and Contraception

Question 1

What is the normal volume of ejaculate in semen?

Answer 1

2-4ml

Question 2

How many sperm per ejaculate

Answer 2

40x10^6

Question 3

What percentage of sperm are motile?

Answer 3

> 60%

Question 4

What are the three contributors to semen volume?

Answer 4

Seminal vesicles - 60%
Prostate - 25%
Bulbourethral -?%

Question 5

What is found in secretions of seminal vesicles

Answer 5

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

Question 6

What is found in secretions of prostate?

Answer 6

o Proteolytic enzymes
 Break down clotting factors, re-liquefying sperm in 10 – 20 minutes
o Citric acid
o Phosphotase

Question 7

Bulbourethral glands

Answer 7

o Very small volume
o Alkaline fluid
o Mucous
 Lubrication of the end of the penis and urethral lining

Question 8

Describe the physiological processes involved in emission

Answer 8

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.

Question 9

What are the physiological stimulants of erections

Answer 9

Psychogenic

Tactile (sensory afferents of penis and perineum)

Question 10

What are the efferents of erection?

Answer 10

Somatic and autonomic efferents
Pelvic nerve - PNS
Pudendal nerve - Somatic

Question 11

Outline the haemodynamic changes in erection

Answer 11

Inhibition of sympathetic arterial vasoconstrictor nerves

Activation of parasympathetic nervous system to stimulate vasodilation

Question 12

How does activation of the parasympahetic nervous sytem cause vasodilation of the penis arteries

Answer 12

 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

Question 13

What happens to blood vessels and muscles in penis to maintain erection?

Answer 13

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.

Question 14

Give three main factors causing erectile dysfunction

Answer 14

Psychological
Tears in fibrous tissue of corpa cavernoasa
Vascular
Factors blocking NO

Question 15

Give three factors blocking NO

Answer 15

Alcohol
Anti-hypertensives
Diabetes

Question 16

How does viagra work?

Answer 16

Inhibits the breakdown of cGMP, maintaining erection

Question 17

Describe the physiological changes in the female which facilitate coitus

Answer 17

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

Question 18

Describe the mechanism of ejaculation

Answer 18

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

Question 19

Describe the process involved in sperm transport through the cervix and uterus

Answer 19

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.

Question 20

How far do sperm in cervix have to travel to reach the uterine tube?

Answer 20

15-20cm

Question 21

How is sperm transported in the uterus?

Answer 21

Own propulsive capacity and fluid currents caused by the actions of ciliated cells in the uterine tract

Question 22

What changes happen to sperm in uterus?

Answer 22

Capacitation and acrosomal reaciton

Question 23

How do changes happen to sperm in uterus?

Answer 23

Influx of calcium and rise in cAMP

Question 24

What is capacitation?

Answer 24

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

Question 25

What is acrosomal reaction?

Answer 25

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

Question 26

What is produced from first meiotic division of ovum?

Answer 26

Secondary oocyte + First polar body

Question 27

What is pronuclei?

Answer 27

2 sets of chromosomes combine, and mitosis then occurs

Question 28

Give sequence of ectopic pregnancy

Answer 28

o Failure of transport of egg
o Embeds in uterine tube, ovary or abdomen
o Embryo dies
o Severe risk of maternal haemorrhage

Question 29

Give two types of natural conception

Answer 29

Abstinence
Coitus interruptus
- Sperm in pre-ejaculate

Question 30

What is vasectomyu?

Answer 30

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

Question 31

Give three barrier methods of contraception

Answer 31

Condoms
Diaphragm
Cap

Question 32

What is a diaphragm?

Answer 32

 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

Question 33

Where is a “cap” fitted

Answer 33

Fits across the cervix

Question 34

Give two parts of hormonal contraceptive

Answer 34

Progesterone

Oestrogen

Question 35

Give two reasons progesterone prevents conception

Answer 35

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

Question 36

Why does oestrogen prevent conception?

Answer 36

o Oestrogen negatively feeds back on anterior pituitary
o Loss of positive feedback mid-cycle
o No LH surge

Question 37

Give four types of hormonal contraceptive

Answer 37

o	Combined OCP 
	(Progesterone and Oestrogen)
o	Progesterone Only Pill (POP)
o	Depot Progesterone (3 monthly injections)
o	Progesterone implants

Question 38

Give two types of intrauterine contraceptive device

Answer 38

Inert copper

Impregnated progesterone

Question 39

How does inert copper work?

Answer 39

 Interferes with endometrial enzymes
 Interferes with implantation
 May also interfere with sperm transport into fallopian tube

Question 40

What is a main form of post-coital contraception?

Answer 40

Combined oestrogen/progesterone

Question 41

When is post-coital contraception given?

Answer 41

o Up to 72 hours after intercourse

Question 42

What are the three main effects of post-coital contraception?

Answer 42

o May disrupt ovulation
o Blocks implantation
o May also impair luteal function