14) Coitus and Fertilisation

Question 1

What is coitus?

Answer 1

Act of sexual intercourse resulting in deposition of sperms in vagina

Question 2

What is the effect of oestrogen on Leydig cells?

Answer 2

Increase sperm viability

Question 3

Describe the change to the sperm’s head as it matures:

Answer 3

Nuclear condensation so head gets smaller

Question 4

Describe the function of the acrosome:

Answer 4

Hydrolytic enzymes for penetration of ovum

Question 5

Where are mitochondria found in sperm?

Answer 5

Around contractile filament in midpiece

Question 6

What causes the loss of cytoplasm and organelles from sperm?

Answer 6

Testosterone

Question 7

Describe the process by which sperm leave the epididymis:

Answer 7

Sexual arousal -> contraction of epididymal wall muscles -> expels sperm into vas

Question 8

What happens if sperm aren’t expelled by epididymis?

Answer 8

Phagocytosed by epididymal epithelial cells

Question 9

What are the phases of coitus?

Answer 9

Excitement
Plateau
Orgasmic
Resolution

Question 10

What are the differences between male and female coital phases?

Answer 10

Men have refractory period after first orgasm where second is unlikely
Females have no refractory period

Question 11

Describe the nervous changes in the male excitement phase:

Answer 11

Sensory and psychological stimulation -> limbic system

Activation of sacral parasympathetic and inhibition of sympathetic

Question 12

Describe the process of arteriolar vasodilation in corpora cavernosa:

Answer 12

Ach acts on M3 receptors in endothelium -> rise in Ca2+ -> eNOS -> NO production -> vasodilation

Question 13

What changes occur to male genitalia in excitement phase?

Answer 13

Erection of penis
Testes elevate and engorge
Scrotal skin thickens and tenses

Question 14

What reflex is stimulated in the male plateau phase?

Answer 14

Sacrospinous reflex

Question 15

How is blood kept in the penis during the plateau stage of coitus?

Answer 15

Contraction of ischiocavernosus (impedes venous return) causing venous engorgement

Question 16

What glands are stimulated in the male plateau phase of coitus? What is their function?

Answer 16

Bulbourethral glands

Lubricate distal urethra and neutralise acidic urine

Question 17

What two stages can the male orgasmic phase of coitus be split into?

Answer 17

Emission

Ejaculation

Question 18

What reflex is stimulated in the emission stage of male orgasmic phase?

Answer 18

Thoracolumbar sympathetic reflex

Question 19

What structures contract in the emission stage?

Answer 19

SM in ductus deferens, seminal vesicles and prostate

Internal and external urethral sphincters

Question 20

Describe the ejaculation stage in male:

Answer 20

Filling of internal urethra stimulates pudendal nerve -> genital organs, ischiocavernosus and bulbocavernosus contraction -> expulsion of sperm

Question 21

What occurs in the male resolution phase?

Answer 21

Sympathetics causes contraction of arteriolar SM in corpora cavernosa
Increased venous return causing flaccidity
Refractory period

Question 22

Describe some of the changes in the female excitement phase:

Answer 22

Vaginal lubrication due to increased blood flow
Clitoris engorge with blood
Uterus elevates
Inner 2/3rds of vagina lengthens and expands

Question 23

Describe some of the changes in the female plateau phase:

Answer 23

Labia minora deepens in colour

Bartholin’s gland secretion lubricates vestibule

Question 24

What structures contract in the female orgasm phase?

Answer 24

Lower 1/3rd of vagina rhythmically 3-15 times

Uterus and anal sphincter

Question 25

Describe some of the changes in the female resolution phase:

Answer 25

Clitoris descends and engorgement subsides Labia returns to unaroused size and colour Uterus descend, vagina shortens and narrows

Question 26

Describe the changes to the breast in the female excitement phase:

Answer 26

Breast size increases, nipples erect

Question 27

Describe the changes to the breast in the female plateau and orgasm phases:

Answer 27

Areola size increase, sex flush

Question 28

Describe the changes to the breast in the female resolution phase:

Answer 28

Decrease size and areola decreases in size

Question 29

What is the G spot?

Answer 29

Area of sensitivity located along anterior wall of vagina

Question 30

What changes occur to the female sexual response during ageing?

Answer 30

Reduced desire, rapid resolution Reduced lubrication Vagina loses elasticity

Question 31

What are some examples of changes to desire that cause sexual dysfunction?

Answer 31

Hypoactive or aversion (fear of sex) Hyperactive Kluver-Bacy syndrome

Question 32

What is Kluver-Bacy syndrome?

Answer 32

Bilateral medial temporal lobe lesions causing hyperphagia, hypersexuality, hyperorality

Question 33

What are some examples of changes to arousal that cause male sexual dysfunction?

Answer 33

Psychological Tears in fibrous tissue of copora cavernosa Vascular Drugs (alcohol)

Question 34

What is an examples of a change to arousal that causes female sexual dysfunction?

Answer 34

Lack of lubrication

Question 35

Describe the mechanism of Viagra:

Answer 35

Inhibits cGMP breakdown in corpus cavernosum -> increased NO -> vasodilation -> erection

Question 36

What is normal volume of ejaculate volume?

Answer 36

2-4 ml

Question 37

What is a normal sperm count?

Answer 37

20-200x10^6 sperm per ml

Question 38

Describe the route of sperm to fallopian tubes:

Answer 38

Oxytocin stimulates uterine contractions that move sperm into fallopian tubes

Question 39

What happens to cervix after ovulation and why?

Answer 39

Thick, sticky plug to prevent bacteria entering uterine cavity

Question 40

What cytoplasmic maturation occurs to oocyte before ovulation?

Answer 40

MItochondria disperse ER forms cortical granules round periphery Lipid droplets provide energy

Question 41

How long can sperm survive?

Answer 41

5 days

Question 42

How long can oocyte survive?

Answer 42

6-24 hours

Question 43

What must sperm penetrate to fertilise oocyte?

Answer 43

Corona radiata and zona pellucida

Question 44

What is capacitation?

Answer 44

Removal of protein coat, exposing acrosomal enzymes | Tail movement changes to whip like action

Question 45

What protein do sperm bind to on zona pellucida? | Upon binding what happens?

Answer 45

ZP3 | Influx of Ca2+ and acrosomal enzymes begin to digest ZP

Question 46

What are the two regions of oocyte plasma membrane?

Answer 46

Membrane that overlies metaphase chromosomes (no microvilli) | Remainder which has microvilli and is where sperm bind

Question 47

What is the fast block to polyspermy?

Answer 47

When sperm enters, Na+ channels open to cause wave of depolarisation across cytoplasm and stops further entry

Question 48

What is the slow block to polyspermy?

Answer 48

Ca2+ released from ER induces local exocytosis of cortical granules and response is amplified to form wave of exocytosis and prevent further entry

Question 49

What is syngamy?

Answer 49

Union of male and female pronuclei to form diploid zygote

Question 50

What can cause polyploidy?

Answer 50

Entry of more than one sperm | Failure of extrusion of second polar body

Question 51

What causes monozygotic twins?

Answer 51

In cleavage, totipotent cells become divided into 2 separate independent cell masses

Question 52

What causes dizygotic twins?

Answer 52

2 eggs ovulate and 2 eggs fertilised

Question 53

Why is cleavage important?

Answer 53

Generate a large number of cells form differentiation and gastrulation Increase nuclear/cytoplasmic ratio

Question 54

What can cause ectopic pregnancy?

Answer 54

Failure of transport of morula into uterus | Implantation in incorrect position

Question 55

Where does hatching occur and why?

Answer 55

Occurs opposite inner cells mass to minimise risk of enzymatic damage to embryo