5.1: Coitus and Fertilisation

Question 1

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

How long do they spend in each location of the tesis?

Answer 1

74 days

~ 50 in seminiferous tubules ~ 12-26 in epididymis

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 recognise and fertilise an oocyte

Question 3

What are the 3 regions of the epididymis?

How do these 3 regions differ?

Answer 3

Caput, cordus and Cauda

Differ in luminal fluid contents, epithelial cell type/size and receptors/transporters

Question 4

What are the 4 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 are the 3 phases of coitus in a female and what happens in each?

Answer 5

1) Excitement: blood engorgement and erection of clitorus, vaginal mucosa, breast and nipples
2) Plateau: glandular activity
3) +/- orgasm

**NO physiological refractory period

Question 6

What are 2 stimulants that trigger efferent activation of haemodynamic changes during a penile erection?

Describe this efferent pathway?

Answer 6

Stimulants:

1. psychogenic (sexual visual/auditiory stimuli)
2. tactile (sensory afferents of penis and perineum)

Via spinal reflex these lead to efferent PNS activation of spinal nuclei S2-S4 (pelvic nerve) ➞ leads to the haemodynamic changes resulting in BF redirected to corpora cavernosa

Question 7

What must happen to the central arteries of the corpora cavernosa during an erection?

Incl changes in SM internal Ca2+of these arteries

Answer 7

Decrease in intracellular calcium within SM of corpora cavernosa arteries ➞ vasodilate

This increases blood flow into corpora cavernosa ➞ increased pressure in arteries and consequently compression of veins

Results in engorgement and erection

Question 8

What are the 3 haemodynamic changes causing Tumescence (erection)

Answer 8

1) Inhibition of sympathetic arterial vasoconstrictor nerves
2) Activation of PNS
3) Activation of nonadrenergic, noncholinergic, autonomic nerves to arteries, releasing NO

Question 9

In order for an erection to occur, endothelial cells are stimulated to release ______, which can also be released directly from ______.

It diffuses into vascular smooth muscle and activates ______ which converts GTP to cGMP.

cGMP causes a decrease in ______ leading to ______ of smooth muscle allowing an erection to occur

cGMP is then degraded by the enzyme ______.

Answer 9

NO, nerves, guanylate cyclase, Ca2+, relaxation, PDE5

Note: ACh is released along with NO from nerve endings which binds the M3 receptor on the endothelial cell to cause NO release

Question 10

List 3 factors that can block NO

Answer 10

1) alcohol
2) anti-hypertensives
3) diabetes

Question 11

Give a medication used to treat erectile dysfunction + its MoA?

Answer 11

Viagra ➞ Inhibits PDE5 which inhibits cGMP breakdown

Prolongs the action of cGMP at the corpora cavernosa

Question 12

List four potential causes of erectile dysfunction

Answer 12

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

Question 13

What is emission, what nervous control is it under and what 2 things does this cause?

Answer 13

Emission is the movement of ejaculate into prostatic urethra (leakage)

It is under sympathetic control which mediates:

• vas deferens peristalsis
• accessory gland secretions

Question 14

List 3 accessory glands of the male repro tract

How much does each contribute to semen and the what are the components + functions of each?

Answer 14

1) Seminal vesicle (60%)

• alkaline fluid ➞ neutralises acid in male urethra and female tract
• fructose, prostaglandins, clotting factors (semenogelin) ➞ coagulates semen to form a cervical plug inside vagina (prevents pysical loss)

2) Prostate (25%)

• milky, slightly acidic fluid
• proteolytic enzymes ➞ dissolve clotting proteins and re-liquefying semen
• citric acid and acid phosphatase

3) Bulbourethral (Cowper’s glands - very small contribution)
* alkaline mucous ➞ lubricates end of the penis and urethral lining

Question 15

What nervous control is ejaculation under?

What 3 things does stimulation of this cause?

Answer 15

Sympathetic control which causes:

1. contraction of SM in glands and ducts
2. contraction of bladder internal sphincter to prevent backflow into the bladder
3. rythmic striatal muscle contractions in pelvic floor: ischiocavernosus, bulbospongiosus, hip and anal muscles

Question 16

What is a normal volume of sperm per ejaculation?

What is low sperm count per ejaculation called and what defines this?

Answer 16

1. 5-4mL
   oligozoospermia: less than 15 million sperm/mL

Question 17

Give 4 reasons why speed of sperm travel varies in different regions of the female tract?

Answer 17

1) pH: optimal pH for sperm is 7.0 - 8.5, pH of <6 slows down sperm
2) glandular secretions: hormones during different times of the female cycle cause changes viscosity of the mucous
3) muscular contractions: occur during coitus and are thought to be the main drive for passive sperm transit
4) signals from oocyte/ovulating ovary: fallopian tube releases fluid to signal egg and direct sperm

Question 18

How do the hormones released at different times of the female cycle impact the likelihood of fertilization?

Answer 18

oestrogen rich system ➞ clear, nonviscous mucous around the cervix, easier for sperm to swim through

oestrogen + progesterone rich system ➞ thick sticky mucous plug around the cervix, harder for sperm to swim through

Question 19

What is capacitation, where does it occur and why is it necessary?

Answer 19

Capacitation is the further maturation of sperm during transport through female repro tract (6-8 hours)

It involves:

• removal of glycoprotein coat ➞ promotes changes in the sperm cell membrane
• change in tail movement: waves to whip-like/thrashing movement

These prepare sperm for acrosome reaction (when in contact with oocyte) and helps propel them along tract

Question 20

The acrosomal reaction is triggered when the sperm head binds to the ______ and/or interacts with the ______ cells of the ovum

Upton binding two enzymes are released; ______, which breaks bond between cells and ______ which breaks down ZP proteins.

The acrosomal reaction occurs in ______ sperm to allow digestion of the ______ to develop a pathway for sperm to reach the ZP and allow gamete fusion

Answer 20

ZP3, cumulus, hyaluronidase, acrosin, multiple, corona radiata

Question 21

How does gamate fusion occur?

Answer 21

1) Acrosin (from acrosomal reaction)- breaks down ZP proteins
2) sperm travels through ZP to reach oocyte membrane
3) sperm nucleus (and some other contents) enter egg cytoplasm

Fertilisation has occured!!!

Question 22

What are cumulus cells and the corona radiata of the ovum?

Answer 22

The cumulus cells/ layer are a cluster of granulosa cells that surround the oocyte. The innermost layer of these is the corona radiata which communicates with the oocyte through the zona pellucida.

Question 23

After fusion of gamete how is the oocyte activated and what steps follow?

Answer 23

1) Fusion of gamete membranes triggers Ca2+ release from SER
2) Cortical reaction occurs ➞ to prevent polyspermy

3) Egg completes meiosis II forming a pronuclei with 2 sets of
chromosomes

4) Pronuclei fusion occurs to form a diploid zygote
5) Embryonic mitosis then occurs (cleavage) to form a morula then a blastocyst

During this transformation, it is gradually transported along uterine tube towards uterus

Question 24

Explain the process of clevage

Answer 24

Clevage is a series of metabolic changes and rapid mitotic division that are symmetrical.

There is no cytoplasmic growth between these divisions

The cells, known as blastomeres, eventually form a solid ball (morula), which is totipotent

Question 25

What happens following the morula stage when the conceptus reached the uterus?

Answer 25

It waits for 3 days for a rise in progesterone, which stimulates smooth muscle relaxation

It then continues a period of cell division to reach the blastocyst stage

Question 26

What changes occur during the blastocyst stage?

Answer 26

A fluid filled cavity appears (blastocoele) and there is a loss of totipotency

• outer layer forms and surrounds embryo (trophoblast)
• Inner cell mass forms (becomes embryo)

Question 27

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

Answer 27

Multiple sperm are needed to disperse the granulosa cumulus cells surrounding the oocyte so that one sperm is able to penetrate through

Question 28

What is the ‘fertile period’?

How is this influenced by the lifespan of spermatozoa and oocytes after being released?

Answer 28

The fertile period is time in which sperm must be deposited in order for fertilisation to occur

This is up to 3 days prior to ovulation as spermatozoa can live up to 3 days but oocytes only live 6-24 hours after being released

Question 29

What 3 layers surrounding the oocyte must be penetrated to allow for the formation of pronuclei?

Answer 29

1) Granulosa cell layers (cumulus layer)
2) Zona pellucida
3) Ovum membrane

Question 30

What triggers the cortical reaction and explain how it prevents polyspermy

Answer 30

Triggered by fusion of the gamete membranes that releases a wave of calcium from SER

Underneath the egg’s surface there are many cortical granules. Once ONE sperm enters these are released and change the structure of the ZP3 protein making it impossible for more sperm to bind

Question 31

How are monozygotic twins formed?

Answer 31

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

Question 32

Describe how the zygote travels following fertilisation and how implantation occurs

incl how it is receiving nutrients and other processes occuring at the same time

Answer 32

Zygote travels down the fallopian tubes to uterus, it is floating for 3 days and nourished by intrauterine fluid

At the same time there is a rise in progesterone (from corpus luteum) which is preparing the endometrium for implantation

As it travels it is developing into a blastocyst (does not develop further until implantation occurs)

Once in the uterus, trophoblast cells secrete enzymes to digest the ZP and the “hatched embryo” adheres to endometrium via outer syncytiotrophoblast layer

NOTE: Implantation commences (6 days after ovulation)

Question 33

When do hCG levels become clinically detectable?

Answer 33

Upon implantation

Question 34

What is an ectopic pregnancy

What is a serious risks of this?

Answer 34

Failure of transport of egg causing it to embed in the uterine tube, ovary or abdomen. The embryo dies as locations other than the uterus are not viable

Severe risk of maternal haemorrhage

Question 35

Describe the histoligcal structure of the vagina

Answer 35

1) layered fibromuscular canal (mucosa, smooth muscular layer [SM], adventitia)
2) Glycogen producing non-keratinised stratified squamous epithelium (E)
3) Highly-vascular lamina propria (LP), which is elastic fibre rich but not gland- bearing

Question 36

Describe the histoligcal structure of the endocervix and exocervix

What is the SCJ junction and where is it located and what commonly occurs at this site?

Answer 36

Endocervix: cervical canal with simple columnar epithelium and mucous glands (NO spiral arteries).

Exocervix: Stratified squamous non-keratinised epithelium.

SCJ: Squamocolumnar junction and can be located at any point across the cervix.

The transformation zone adjacent to the SCJ is where majority of neoplasms originate.

Question 37

What are the parts of the uterine tube? (from uterus toward ovaries)

Answer 37

1) Isthmus
2) Ampulla
3) Infundibulum
4) Fimbriae

Question 38

What are the 3 main layers of the uterus (in to out)?

What are the sublayers found within these the innermost layer

Answer 38

1) endometrium (mucosa)
2) myometrium (muscularis)
3) perimetrium (serosa/adventitia)

Endometrium is divided into the stratum functionalis and stratum baslis.

The stratum functionalis (innermost) is furthur divided into the stratum compactum (i) and stratum spongiosum (o)

Question 39

label the following diagram of the Ampulla

Answer 39