Reproduction 7 - Conception & contraception

Question 0

What is emission and how does it occur?

Answer 0

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 1

List the main constituents of semen & their origins

Think about the role each part hasty

Answer 1

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

Question 2

Outline the key changes involved in erection

Answer 2

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.

Question 3

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)

Answer 3

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)

Question 4

In erection - how does NO cause relaxation of vascular smooth muscle (vasodilation)?

(Hint: it involves calcium)

Answer 4

↑ NO –> Formation of Cyclic GMP –> Ca2+ taken up into intracellular stores

▪ ↓ [Ca2+] –> Less actin-myosin cross-bridges are formed and smooth muscle relaxes

Question 5

Why is it important that dilation of the Corpus Spongiosum is limited?

Answer 5

It would compress and close off the urethra - preventing ejaculation of sperm

Question 6

During erection, which arteries straighten, enlarging their lumen and allow blood to flow into the penis?

Answer 6

The central arteries in the Corpa Cavernosa - helicine arteries

Question 7

Which muscles compress veins egressing from the corpora cavernosa, impeding the return of venous blood?

Answer 7

The Bulbospongiosus and Ischiocavernosus muscles

Question 8

List four causes of erectile dysfunction

Answer 8

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

Question 9

How does viagra work (at a molecular level)?

Answer 9

Inhibits the breakdown of cGMP, maintaining erection.

Question 10

What changes in the female facilitate coitus?

Answer 10

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 11

Describe the mechanism of ejaculation

Answer 11

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 12

What control is ejaculation under?

Answer 12

o Sympathetic Nervous System Control (L1, L2)

Question 13

What is the role of clotting factors/fibrinogen in semen?

Answer 13

This is to prevent sperm being physically lost from the vagina

Question 14

What re-liquefies semen once in the vagina? (Approx 10-20mins later)

Answer 14

Enzymes found in prostatic secretions.

Question 15

How far do sperm have to travel to reach the uterine tubes and how long does it take?

Answer 15

15 – 20cm - may last a few hours.

Question 16

How do sperm physically travel to the uterine tubes?

Answer 16

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

Question 17

i) What is the name of the two key maturational processes that sperm undergo?
ii) What are these processes induced by?

Answer 17

i) Capacitation and the Acrosomal Reaction

ii) influx of calcium and a rise in cAMP in spermatozoa.

Question 18

Outline the process of capacitation of sperm

Answer 18

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 19

When does the acrosomal reaction occur? What does it involve?

Answer 19

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)

Question 20

What mechanism is an ectopic pregnancy a failure of? What risks does it pose?

Answer 20

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

Question 21

What is a secondary oocyte? How many chromosomes?

Answer 21

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

Question 22

Name two methods of natural contraception

Answer 22

o Abstinence
o Coitus interruptus
▪ Sperm in pre-ejaculate

Question 23

Barrier Methods prevent sperm from reaching the cervix. Name three such methods, how they work and any particular advantages or disadvantages

Answer 23

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

Question 24

How does progesterone work as a contraceptive? (two ways)

Answer 24

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 25

How does oestrogen work as a contraceptive?

Answer 25

o Oestrogen negatively feeds back on anterior pituitary

o Loss of positive feedback mid-cycle

o No LH surge - no ovulation

Question 26

Name some methods of hormonal contraception

Answer 26

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

Question 27

What are intrauterine devices and how do they work?

Answer 27

o An IUD is a small T-shaped plastic and copper device that’s inserted into the uterus uterus

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

o Can also get Progesterone impregnated IUD - works similar to progesterone oral contraceptive

Question 28

What is emergency post-coital contraception and how does it work?

Answer 28

Taken after unprotected sexual intercourse or contraceptive failure, such higher doses may prevent pregnancy from occurring

o Combined Oestrogen / Progesterone High Dose
▪ Or Progesterone only
o Up to 72 hours after intercourse
o May disrupt ovulation
o Blocks implantation
o May also impair luteal function