5.1: Coitus and Fertilisation

Question 1

How many days does it take for spermatogonia to mature into spermatozoa?

Answer 1

74 days

Question 2

What is an additional role of the epididymis other than transport?

Answer 2

Aids in maturation of the sperm; sperm become motile and gain ability to recognize and fertilize an oocyte

Question 3

What are the three regions of the epididymis?

Answer 3

Caput, cordus and Cauda

Question 4

What are the four phases of coitus in males?

Answer 4

1. Excitement phase (erection)
2. Plateau phase
3. Orgasmic phase (emission and ejaculation)
4. Resolution phase (+/- refractory period)

Question 5

What happens during the phases of the female sexual response?

Answer 5

1. Sexual excitement: blood engorgement and erection of clit, vaginal mucosa, breast and nipples
2. Plateau: glandular activity
3. +/- orgasm **No physiological refractory period

Question 6

Name two stimulants and two efferent pathways that lead to hemodynamic changes in a penile erection

Answer 6

Psychogenic and tactile stimulants can lead to the pelvic nerve (PNS) and the pudendal nerve (somatic) efferent nerve stimulation

Question 7

What signalling molecule is required for an erection? What releases it and why is it so important?

Answer 7

NO released by nerves and endothelial cells decreases intracellular calcium -> smooth muscle relaxation -> erection

Question 8

List four potential causes for erectile dysfunction

Answer 8

1. Psychological: descending inhibition of spinal reflexes
2. Tears in fibrous tissue of corpora cavernosa
3. Vascular (arterial and venous)
4. Drugs

Question 9

List 3 factors that can block NO

Answer 9

Alcohol, anti-hypertensives, diabetes

Question 10

Name three accessory glands that produce secretions to help transport sperm, which contribute the most and least to the sperm’s volume?

Answer 10

1. Seminal vesicle - the most (60%)
2. Prostate
3. Bulbourethral - the least

Question 11

Which accessory glands produce alkaline fluid and what is it’s purpose?

Answer 11

Seminal vesicles and bulbourethral: alkaline fluid neutralizes the acidic secretions from the prostate to protect the male urethra and female repro tract

Question 12

What does the prostate produce?

Answer 12

1. Milky, acidic fluid; contains citric acid and acid phosphatase
2. Proteolytic enzymes: break down clotting proteins to re-liquify semen

Question 13

Which accessory gland produces mucous and why?

Answer 13

Bulbourethral: lubricates the penis end and urethral lining

Question 14

Which muscles and structures must contract in order for an ejaculation to occur?

Answer 14

1. Glands and ducts (smooth muscle)
2. Bladder internal sphincter (to prevent backflow into the bladder)
3. Rythmic striatal muscle; pelvic floor, ischiocavernosus, bulbospongiosus, hip and anal muscles

Question 15

What is a normal volume of sperm per ejaculation?

Answer 15

1.5-4mL

Question 16

What defines oligozoospermia?

Answer 16

Not enough sperm per ejaculation

less than 15 million sperm/mL

Question 17

How does having an estrogen rich vs estrogen AND progesterone rich system impact the likelihood of fertilization?

Answer 17

Estrogen rich: clear, nonviscous mucous around the cervix

Estrogen and progesterone rich: thick sticky mucous plug around the cervix that makes it harder for sperm to swim through

Question 18

What is sperm capacitation? Describe the two main events during the capacitation of sperm and where it takes place

Answer 18

Refers to the physiological changes spermatozoa must undergo to be able to fertilize an oocyte.

Two main maturations:

1. Sperm cell membrane changes to permit an acrosome reaction (losing the sperm’s outer shell); this allows for exposure of certain receptors important for fusion between the sperm and the oocyte’s surface
2. Tail movement changes from beating to a whip-like action

Question 19

Why is it important for fertilization that more than one sperm finds the oocyte?

Answer 19

Extra/remaining sperm disperse the granulosa cumulus cells surrounding the oocyte in layers so one sperm can penetrate through

Question 20

What is the fertile period?

Answer 20

Up to 3 days prior to ovulation

Question 21

Name three features surrounding an oocyte that must be penetrated to allow for the formation of pronuclei

Answer 21

1. Granulosa cell layers
2. Zona pellucida
3. Ovum membrane

Question 22

What triggers the acrosome reaction and which two enzymes are involved?

Answer 22

Triggered by signals released from the cumulus cells (surrounding the oocyte):

1. Hyaluronidase: breaks down the bonds between the cumulus cells (more spaces for sperm to swim through)
2. Acrosin: breaks down the ZP proteins

Question 23

What mechanism is in place to prevent polyspermy?

Answer 23

Once the gamete membranes have fused..
Oocyte releases calcium from the SER -> triggers cortical reaction:

Cortical granules (underneath the egg’s surface) change the structure of the ZP3 protein -> no more sperm can bind

Question 24

What happens in the oocyte during and following the cortical reaction?

Answer 24

The oocyte completes meiosis II and forms the pronuclei, both pronuclei then fuse to form the diploid zygote.

Question 25

What process immediately follows the formation of the diploid zygote?

Answer 25

‘Cleavage’; Cells rapidly divide symmetrically but without cytoplasmic growth

*they are totipotent at this stage

Question 26

What are the daughter cells that are formed from cleavage called? What do they eventually form?

Answer 26

Blastomeres, they eventually form a solid ball called a morula

Question 27

How are monozygotic twins formed?

Answer 27

Splitting of the morula

Question 28

Describe how the zygote travels following fertilization and the processes happening simultaneously to ensure a successful implantation

Answer 28

1. Zygote transports down fallopian tubes -> uterus, it’s floating n chilling for 3 days and nourished by intrauterine fluid
2. Since the corpus luteum hasn’t degenerated there is a rise in progesterone which ‘primes’ the endometrium
3. Embryo reaches blastocyst stage (important it doesn’t develop further pre implantation as it can’t survive on its own)
4. The Trophoblast cells secrete enzymes that degrade themselves and digest the ZP

Question 29

What cellular ‘division’ follows the formation of the blastocyst?

Answer 29

Loss of totipotency:
Outer layer -> trophoblasts
Inner cell mass/embryoblast -> embryo

Question 30

Define an ectopic pregnancy, what are two likely consequences?

Answer 30

Egg implants in a location other than the uterus, will likely result in embryo death and maternal hemorrhage

Question 31

Other than alkaline fluid, what else does the seminal vesicle secrete?

Answer 31

Fructose, prostaglandins and clotting factors

Question 32

What hormone is essential in making sure the ‘hatched’ embryo adheres to the endometrium?

Answer 32

hCG

Question 33

Which days of the uterine cycle does the zygote transform into a blastocyst? How many days after ovulation does implantation tend to commence?

Answer 33

Zygote -> blastocyst: days 14-21

Implantation commences 6 days after ovulation

Question 34

What is the difference between primary and secondary amenorrhea? What are the two commonest causes of secondary amenorrhea and what hormone tests will you use to distinguish them?

Answer 34

Primary: never had periods
Secondary: 3-month cessation of menses (after they’ve begun), commonly caused by pregnancy (Hcg) and weight loss (gonadotrophin levels)