5.1: Coitus and Fertilisation Flashcards
How many days does it take for spermatogonia to mature into spermatozoa?
74 days
What is an additional role of the epididymis other than transport?
Aids in maturation of the sperm; sperm become motile and gain ability to recognize and fertilize an oocyte
What are the three regions of the epididymis?
Caput, cordus and Cauda
What are the four phases of coitus in males?
- Excitement phase (erection)
- Plateau phase
- Orgasmic phase (emission and ejaculation)
- Resolution phase (+/- refractory period)
What happens during the phases of the female sexual response?
- Sexual excitement: blood engorgement and erection of clit, vaginal mucosa, breast and nipples
- Plateau: glandular activity
- +/- orgasm **No physiological refractory period
Name two stimulants and two efferent pathways that lead to hemodynamic changes in a penile erection
Psychogenic and tactile stimulants can lead to the pelvic nerve (PNS) and the pudendal nerve (somatic) efferent nerve stimulation
What signalling molecule is required for an erection? What releases it and why is it so important?
NO released by nerves and endothelial cells decreases intracellular calcium -> smooth muscle relaxation -> erection
List four potential causes for erectile dysfunction
- Psychological: descending inhibition of spinal reflexes
- Tears in fibrous tissue of corpora cavernosa
- Vascular (arterial and venous)
- Drugs
List 3 factors that can block NO
Alcohol, anti-hypertensives, diabetes
Name three accessory glands that produce secretions to help transport sperm, which contribute the most and least to the sperm’s volume?
- Seminal vesicle - the most (60%)
- Prostate
- Bulbourethral - the least
Which accessory glands produce alkaline fluid and what is it’s purpose?
Seminal vesicles and bulbourethral: alkaline fluid neutralizes the acidic secretions from the prostate to protect the male urethra and female repro tract
What does the prostate produce?
- Milky, acidic fluid; contains citric acid and acid phosphatase
- Proteolytic enzymes: break down clotting proteins to re-liquify semen
Which accessory gland produces mucous and why?
Bulbourethral: lubricates the penis end and urethral lining
Which muscles and structures must contract in order for an ejaculation to occur?
- Glands and ducts (smooth muscle)
- Bladder internal sphincter (to prevent backflow into the bladder)
- Rythmic striatal muscle; pelvic floor, ischiocavernosus, bulbospongiosus, hip and anal muscles
What is a normal volume of sperm per ejaculation?
1.5-4mL
What defines oligozoospermia?
Not enough sperm per ejaculation
less than 15 million sperm/mL
How does having an estrogen rich vs estrogen AND progesterone rich system impact the likelihood of fertilization?
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
What is sperm capacitation? Describe the two main events during the capacitation of sperm and where it takes place
Refers to the physiological changes spermatozoa must undergo to be able to fertilize an oocyte.
Two main maturations:
- 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
- Tail movement changes from beating to a whip-like action
Why is it important for fertilization that more than one sperm finds the oocyte?
Extra/remaining sperm disperse the granulosa cumulus cells surrounding the oocyte in layers so one sperm can penetrate through
What is the fertile period?
Up to 3 days prior to ovulation
Name three features surrounding an oocyte that must be penetrated to allow for the formation of pronuclei
- Granulosa cell layers
- Zona pellucida
- Ovum membrane
What triggers the acrosome reaction and which two enzymes are involved?
Triggered by signals released from the cumulus cells (surrounding the oocyte):
- Hyaluronidase: breaks down the bonds between the cumulus cells (more spaces for sperm to swim through)
- Acrosin: breaks down the ZP proteins
What mechanism is in place to prevent polyspermy?
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
What happens in the oocyte during and following the cortical reaction?
The oocyte completes meiosis II and forms the pronuclei, both pronuclei then fuse to form the diploid zygote.
What process immediately follows the formation of the diploid zygote?
‘Cleavage’; Cells rapidly divide symmetrically but without cytoplasmic growth
*they are totipotent at this stage
What are the daughter cells that are formed from cleavage called? What do they eventually form?
Blastomeres, they eventually form a solid ball called a morula
How are monozygotic twins formed?
Splitting of the morula
Describe how the zygote travels following fertilization and the processes happening simultaneously to ensure a successful implantation
- Zygote transports down fallopian tubes -> uterus, it’s floating n chilling for 3 days and nourished by intrauterine fluid
- Since the corpus luteum hasn’t degenerated there is a rise in progesterone which ‘primes’ the endometrium
- Embryo reaches blastocyst stage (important it doesn’t develop further pre implantation as it can’t survive on its own)
- The Trophoblast cells secrete enzymes that degrade themselves and digest the ZP
What cellular ‘division’ follows the formation of the blastocyst?
Loss of totipotency:
Outer layer -> trophoblasts
Inner cell mass/embryoblast -> embryo
Define an ectopic pregnancy, what are two likely consequences?
Egg implants in a location other than the uterus, will likely result in embryo death and maternal hemorrhage
Other than alkaline fluid, what else does the seminal vesicle secrete?
Fructose, prostaglandins and clotting factors
What hormone is essential in making sure the ‘hatched’ embryo adheres to the endometrium?
hCG
Which days of the uterine cycle does the zygote transform into a blastocyst? How many days after ovulation does implantation tend to commence?
Zygote -> blastocyst: days 14-21
Implantation commences 6 days after ovulation
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?
Primary: never had periods
Secondary: 3-month cessation of menses (after they’ve begun), commonly caused by pregnancy (Hcg) and weight loss (gonadotrophin levels)
