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 the ability to recognize and fertilize an oocyte

Question 3

What are the three regions of the epididymis? What are three areas where they can differ?

Answer 3

Caput, cordus and Cauda

Can differ in luminal fluid contents, epithelial cell type/size, receptors/transporters

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

What are 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 is released by nerves and endothelial cells and causes decreased intracellular calcium leading to smooth muscle relaxation; allowing an erection to occur

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

What is the mechanism of action in viagra?

Answer 10

Inhibits the PDE-5 enzyme which breaks down cGMP - inevitably promoting a further decrease in intracellular calcium to allow for more vasodilation

Question 11

Name three accessory glands that produce secretions to help transport sperm

Answer 11

1. Prostate
2. Seminal vesicle
3. Bulbourethral

Question 12

Which accessory glands contribute the most and the least to the sperm’s volume?

Answer 12

Seminal vesicles contribute 60% of the volume, Bulbourethral produce a very small volume of secretions

Question 13

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

Answer 13

The seminal vesicles and bulbourethral glands both produce alkaline fluid to help neutralize the acid and protect the male urethra and female reproductive tract

Question 14

Which accessory gland produces milky, slightly acidic fluid and why?

Answer 14

The prostate as it produces citric acid and acid phosphatase

Question 15

Which accessory gland produces proteolytic enzymes and what do they do?

Answer 15

The prostate; these enzymes assist in breaking down clotting proteins to re-liquify semen (in 10-20 minutes)

Question 16

Which accessory gland produces mucous and why?

Answer 16

The Bulbourethral gland to lubricate the end of the penis and the urethral lining

Question 17

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

Answer 17

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 18

What is a normal volume of sperm per ejaculation?

Answer 18

1.5-4mL

Question 19

What defines oligozoospermia?

Answer 19

Not enough sperm per ejaculation; less than 15 million sperm/mL

Question 20

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

Answer 20

An estrogen rich system: clear, nonviscous mucous around the cervix

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

Question 21

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

Answer 21

Sperm capacitation refers to the physiological changes spermatozoa must undergo to be able to fertilize an oocyte. (Although sperm is technically able to fertilize by the time it reaches the female repro tract (i.e in a lab) there are two main maturations that occur in the 6-8 hours that the sperm moves towards the egg within the female repro tract)

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

Question 22

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

Answer 22

The remaining sperm are needed to disperse the granulosa cumulus cells that surround the oocyte in layers (they also have junctions containing mucus-like fluid that helps them stick together) so that one sperm is able to penetrate through

Question 23

What is the fertile period? How long do spermatozoa and oocytes live after being released?

Answer 23

The fertile period is sperm must be deposited up to 3 days prior to ovulation; since spermatozoa can live up to 3 days but oocytes only live 6-24 hours after being released

Question 24

What three features that surround the oocyte must be penetrated to allow for the formation of pronuclei?

Answer 24

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

Question 25

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

Answer 25

The acrosome reaction is triggered by signals released from the cumulus cells (surrounding the oocyte): Two enzymes are released: 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 26

What mechanism is in place to prevent polyspermy?

Answer 26

Once the gamete membranes have fused the oocyte releases a wave of calcium from the SER, this triggers the cortical reaction: underneath the egg's surface you have many cortical granules which are released once one sperm has entered, the granules change the structure of the ZP3 protein making it unavailable for more sperm to bind

Question 27

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

Answer 27

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

Question 28

What process immediately follows the formation of the diploid zygote?

Answer 28

'Cleavage'; when cells rapidly divide but there is no cytoplasmic growth between divisions. They divide symmetrically and are totipotent

Question 29

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

Answer 29

Daughter cells are called blastomeres, they eventually form a solid ball called a morula

Question 30

How are monozygotic twins formed?

Answer 30

The blastomeres eventually form a solid ball of cells (morula), if it splits monozygotic twins are formed

Question 31

Where does the zygote travel following fertilization (and how is it receiving nutrients)? What processes are happening simultaneously to ensure a successful implantation?

Answer 31

The zygote transports down the fallopian tubes to the uterus, it is floating for 3 days and nourished by intrauterine fluid In order for implantation to occur... 1. A rise in progesterone (since the corpus luteum has been around a few days) which 'primes' the endometrium 2. The embryo is developing and reaches the blastocyst stage; (fluid-filled cavity/blastocoele appears) *important it doesn't develop further than this before implantation as it won't be able to survive on its own 3. The Trophoblast cells secrete enzymes that degrade themselves and digest the ZP

Question 32

What cellular division follows the formation of the blastocyst?

Answer 32

Loss of totipotency: The outer layer differentiates into the trophoblasts which surround the embryo and the inner cell mass/embryoblast becomes the embryo

Question 33

Define an ectopic pregnancy, what are two likely consequences?

Answer 33

When the egg implants in a location other than the uterus, (i.e failure of transport of egg) will likely result in embryo death and maternal hemorrhage

Question 34

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

Answer 34

Fructose, prostaglandins and clotting factors

Question 35

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

Answer 35

hCG

Question 36

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

Answer 36

Uterine cycle days 14-21 Implantation commences 6 days after ovulation

Question 37

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 37

Primary: never had periods Secondary: 3-month cessation of menses (after they've begun) The two commonest causes are: 1. pregnancy: Hcg 2. Fall in body weight: gonadotrophin levels