13 - Repro - Conception Flashcards
Name the 4 phases of coitus:
1) Excitement
2) Plateau
3) Orgasmic
4) Resolution
Define coitus:
Act of sexual intercourse resulting in the deposition of sperm into the cervix
Which types of neurons are activated/inhibited during the excitement phase of coitus?
Activated = Sacral parasympathetic neurons Inactivated = Thoracolumbar sympathetic neurons
How does the activation of parasympathetic neurons result in erection?
- Ach acts on M3 receptors on endothelial
- Gq receptors = ^Ca2+ = eNOS activation
- ^NO production
- vasodilation of corpora cavernosa
- ^blood flow to penis
- erection
What happens to the scrotal skin during the excitement phase of coitus?
Thickens + tenses
Which spinal reflex is activated during the plateau phase of coitus in males? What does this activate?
Sacrospinous reflex
- Contraction of ischiocavernosus
- Stimulation of bulbourethral glands
What happens to the testes during the plateau phase of coitus?
Become engorged + elevated
Which spinal reflex is activated during the orgasmic phase of coitus? What are the consequences of this in the male?
Thoracolumbar sympathetic reflex
- Contraction of smooth muscle of vas deferens, prostate, seminal vesicles, internal and external urethral sphincters
- Semen pools in urethral bulb (internal urethra)
What stimulates the pudendal nerve resulting in ejaculation?
Filling of the internal urethra (due to thoracolumbar sympathetic reflex)
What prevents a male from immediate repeated orgasms?
Refractory period due to penile flaccidity occuring in the resolution phase of coitus:
- vasoconstriction in corpora cavernosum allows restoration of venous flow
Describe the changes to the female genital tract during the excitement phase of coitus:
- Clitoris engorges
- Vaginal lubrication
- Inner 2/3rds of vagina lengthens and expands
- Uterus elevates
Describe the changes to the female genital tract during the plateau phase of coitus:
- Labia minora deepen in colour
- Clitoris withdraws under hood
- Bartholin’s gland secretions lubricate vestibule
Where is the orgasmic platform of a female?
Outer 1/3rd of vagina
Why does ageing often reduce sexual desire?
- Change in body shape = lower self-esteem
- Decreased lubrication of female tract
- Loss of elasticity of vaginal tissue
- Decreased number of orgasmic contractions
- More rapid resolution
Immediately post-ejaculation, what happens to prevent sperm being lost in the vagina?
Semen coagulates due to clotting factors (fibrinogen + semenogelin)
Which gland is responsible for the production of the clotting factors present in semen? Name the main 2 clotting factors:
Seminal vesicles:
- Fibrinogen
- Semenogelin
What reactions occur during the passage of sperm from the cervix to the fallopian tube?
- Capacitation
- Acrosome reaction
What occurs during capacitation, and how long does it typically take?
- Removal of glycoprotein coat - exposes acrosomal enzymes
- Tail movements change from waves to whip-like motion
Several hours
Which cells make up the corona radiata?
Follicular cells
What triggers the acrosome reaction?
The passage of sperm through the corona radiata
Describe the acrosome reaction:
- Proteins on head of sperm bind to ZP3 proteins on zona pellucida
- Signalling mechanism = ^Ca2+ and ^cAMP in sperm
- Acrosomal enzymes digest through zona pellucida ~ 15 mins
How long does it usually take for sperm to digest through the zona pellucida?
~ 15 minutes
To which proteins on the zona pellucida do sperm bind to?
ZP3 proteins
Name the reaction which prevents polyspermy:
Cortical reaction
Describe the cortical reaction (to prevent polyspermy):
Fast block = Na+ channels open = depolarisation of oocyte membrane
Slow block = Ca2+ released from ER = exocytosis of cortical granules
Approximately how many sperm per ejaculation reach the fertilisation site?
~ 300 sperm
How many sperm are required to disperse the zona pellucida on average?
~ 299
How long do sperm survive in the female genital tract?
~ 5 days
When is the fertile period of the menstrual cycle?
Day 11-16 of menstrual cycle
Define syngamy:
The union of male and female pronuclei to form a diploid zygote
How can polyploidy occur?
- Failure of cortical reaction
- Failure to extrude second polar body
