5.1: Coitus and Fertilisation Flashcards
How many days does it take for spermatogonia to mature into spermatozoa?
How long do they spend in each location of the tesis?
74 days
~ 50 in seminiferous tubules ~ 12-26 in epididymis
What is an additional role of the epididymis other than transport?
Aids in maturation of the sperm; sperm become motile and gain the ability to recognise and fertilise an oocyte
What are the 3 regions of the epididymis?
How do these 3 regions differ?
Caput, cordus and Cauda
Differ in luminal fluid contents, epithelial cell type/size and receptors/transporters
What are the 4 phases of coitus in males?
1) Excitement phase (erection)
2) Plateau phase
3) Orgasmic phase (emission and ejaculation)
4) Resolution phase (+/- refractory period)
What are the 3 phases of coitus in a female and what happens in each?
1) Excitement: blood engorgement and erection of clitorus, vaginal mucosa, breast and nipples
2) Plateau: glandular activity
3) +/- orgasm
**NO physiological refractory period
What are 2 stimulants that trigger efferent activation of haemodynamic changes during a penile erection?
Describe this efferent pathway?
Stimulants:
- psychogenic (sexual visual/auditiory stimuli)
- 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
What must happen to the central arteries of the corpora cavernosa during an erection?
Incl changes in SM internal Ca2+of these arteries
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
What are the 3 haemodynamic changes causing Tumescence (erection)
1) Inhibition of sympathetic arterial vasoconstrictor nerves
2) Activation of PNS
3) Activation of nonadrenergic, noncholinergic, autonomic nerves to arteries, releasing NO
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 ______.
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
List 3 factors that can block NO
1) alcohol
2) anti-hypertensives
3) diabetes
Give a medication used to treat erectile dysfunction + its MoA?
Viagra ➞ Inhibits PDE5 which inhibits cGMP breakdown
Prolongs the action of cGMP at the corpora cavernosa
List four potential causes of erectile dysfunction
1) Psychological: descending inhibition of spinal reflexes
2) Tears in fibrous tissue of corpora cavernosa
3) Vascular (arterial and venous)
4) Drugs
What is emission, what nervous control is it under and what 2 things does this cause?
Emission is the movement of ejaculate into prostatic urethra (leakage)
It is under sympathetic control which mediates:
- vas deferens peristalsis
- accessory gland secretions
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?
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
What nervous control is ejaculation under?
What 3 things does stimulation of this cause?
Sympathetic control which causes:
- contraction of SM in glands and ducts
- contraction of bladder internal sphincter to prevent backflow into the bladder
- rythmic striatal muscle contractions in pelvic floor: ischiocavernosus, bulbospongiosus, hip and anal muscles
What is a normal volume of sperm per ejaculation?
What is low sperm count per ejaculation called and what defines this?
- 5-4mL
oligozoospermia: less than 15 million sperm/mL
Give 4 reasons why speed of sperm travel varies in different regions of the female tract?
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
How do the hormones released at different times of the female cycle impact the likelihood of fertilization?
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
What is capacitation, where does it occur and why is it necessary?
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
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
ZP3, cumulus, hyaluronidase, acrosin, multiple, corona radiata
How does gamate fusion occur?
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!!!
What are cumulus cells and the corona radiata of the ovum?
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.
After fusion of gamete how is the oocyte activated and what steps follow?
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
Explain the process of clevage
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
What happens following the morula stage when the conceptus reached the uterus?
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
What changes occur during the blastocyst stage?
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)
Why is it important for fertilization that more than one sperm finds the oocyte?
Multiple sperm are needed to disperse the granulosa cumulus cells surrounding the oocyte so that one sperm is able to penetrate through
What is the ‘fertile period’?
How is this influenced by the lifespan of spermatozoa and oocytes after being released?
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
What 3 layers surrounding the oocyte must be penetrated to allow for the formation of pronuclei?
1) Granulosa cell layers (cumulus layer)
2) Zona pellucida
3) Ovum membrane
What triggers the cortical reaction and explain how it prevents polyspermy
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
How are monozygotic twins formed?
The blastomeres eventually form a solid ball of cells, if it splits monozygotic twins are formed
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
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)
When do hCG levels become clinically detectable?
Upon implantation
What is an ectopic pregnancy
What is a serious risks of this?
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
Describe the histoligcal structure of the vagina
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
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?
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.
What are the parts of the uterine tube? (from uterus toward ovaries)
1) Isthmus
2) Ampulla
3) Infundibulum
4) Fimbriae
What are the 3 main layers of the uterus (in to out)?
What are the sublayers found within these the innermost layer
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)
label the following diagram of the Ampulla
