14) Coitus and Fertilisation Flashcards
What is coitus?
Act of sexual intercourse resulting in deposition of sperms in vagina
What is the effect of oestrogen on Leydig cells?
Increase sperm viability
Describe the change to the sperm’s head as it matures:
Nuclear condensation so head gets smaller
Describe the function of the acrosome:
Hydrolytic enzymes for penetration of ovum
Where are mitochondria found in sperm?
Around contractile filament in midpiece
What causes the loss of cytoplasm and organelles from sperm?
Testosterone
Describe the process by which sperm leave the epididymis:
Sexual arousal -> contraction of epididymal wall muscles -> expels sperm into vas
What happens if sperm aren’t expelled by epididymis?
Phagocytosed by epididymal epithelial cells
What are the phases of coitus?
Excitement
Plateau
Orgasmic
Resolution
What are the differences between male and female coital phases?
Men have refractory period after first orgasm where second is unlikely
Females have no refractory period
Describe the nervous changes in the male excitement phase:
Sensory and psychological stimulation -> limbic system
Activation of sacral parasympathetic and inhibition of sympathetic
Describe the process of arteriolar vasodilation in corpora cavernosa:
Ach acts on M3 receptors in endothelium -> rise in Ca2+ -> eNOS -> NO production -> vasodilation
What changes occur to male genitalia in excitement phase?
Erection of penis
Testes elevate and engorge
Scrotal skin thickens and tenses
What reflex is stimulated in the male plateau phase?
Sacrospinous reflex
How is blood kept in the penis during the plateau stage of coitus?
Contraction of ischiocavernosus (impedes venous return) causing venous engorgement
What glands are stimulated in the male plateau phase of coitus? What is their function?
Bulbourethral glands
Lubricate distal urethra and neutralise acidic urine
What two stages can the male orgasmic phase of coitus be split into?
Emission
Ejaculation
What reflex is stimulated in the emission stage of male orgasmic phase?
Thoracolumbar sympathetic reflex
What structures contract in the emission stage?
SM in ductus deferens, seminal vesicles and prostate
Internal and external urethral sphincters
Describe the ejaculation stage in male:
Filling of internal urethra stimulates pudendal nerve -> genital organs, ischiocavernosus and bulbocavernosus contraction -> expulsion of sperm
What occurs in the male resolution phase?
Sympathetics causes contraction of arteriolar SM in corpora cavernosa
Increased venous return causing flaccidity
Refractory period
Describe some of the changes in the female excitement phase:
Vaginal lubrication due to increased blood flow
Clitoris engorge with blood
Uterus elevates
Inner 2/3rds of vagina lengthens and expands
Describe some of the changes in the female plateau phase:
Labia minora deepens in colour
Bartholin’s gland secretion lubricates vestibule
What structures contract in the female orgasm phase?
Lower 1/3rd of vagina rhythmically 3-15 times
Uterus and anal sphincter
Describe some of the changes in the female resolution phase:
Clitoris descends and engorgement subsides
Labia returns to unaroused size and colour
Uterus descend, vagina shortens and narrows
Describe the changes to the breast in the female excitement phase:
Breast size increases, nipples erect
Describe the changes to the breast in the female plateau and orgasm phases:
Areola size increase, sex flush
Describe the changes to the breast in the female resolution phase:
Decrease size and areola decreases in size
What is the G spot?
Area of sensitivity located along anterior wall of vagina
What changes occur to the female sexual response during ageing?
Reduced desire, rapid resolution
Reduced lubrication
Vagina loses elasticity
What are some examples of changes to desire that cause sexual dysfunction?
Hypoactive or aversion (fear of sex)
Hyperactive
Kluver-Bacy syndrome
What is Kluver-Bacy syndrome?
Bilateral medial temporal lobe lesions causing hyperphagia, hypersexuality, hyperorality
What are some examples of changes to arousal that cause male sexual dysfunction?
Psychological
Tears in fibrous tissue of copora cavernosa
Vascular
Drugs (alcohol)
What is an examples of a change to arousal that causes female sexual dysfunction?
Lack of lubrication
Describe the mechanism of Viagra:
Inhibits cGMP breakdown in corpus cavernosum -> increased NO -> vasodilation -> erection
What is normal volume of ejaculate volume?
2-4 ml
What is a normal sperm count?
20-200x10^6 sperm per ml
Describe the route of sperm to fallopian tubes:
Oxytocin stimulates uterine contractions that move sperm into fallopian tubes
What happens to cervix after ovulation and why?
Thick, sticky plug to prevent bacteria entering uterine cavity
What cytoplasmic maturation occurs to oocyte before ovulation?
MItochondria disperse
ER forms cortical granules round periphery
Lipid droplets provide energy
How long can sperm survive?
5 days
How long can oocyte survive?
6-24 hours
What must sperm penetrate to fertilise oocyte?
Corona radiata and zona pellucida
What is capacitation?
Removal of protein coat, exposing acrosomal enzymes
Tail movement changes to whip like action
What protein do sperm bind to on zona pellucida?
Upon binding what happens?
ZP3
Influx of Ca2+ and acrosomal enzymes begin to digest ZP
What are the two regions of oocyte plasma membrane?
Membrane that overlies metaphase chromosomes (no microvilli)
Remainder which has microvilli and is where sperm bind
What is the fast block to polyspermy?
When sperm enters, Na+ channels open to cause wave of depolarisation across cytoplasm and stops further entry
What is the slow block to polyspermy?
Ca2+ released from ER induces local exocytosis of cortical granules and response is amplified to form wave of exocytosis and prevent further entry
What is syngamy?
Union of male and female pronuclei to form diploid zygote
What can cause polyploidy?
Entry of more than one sperm
Failure of extrusion of second polar body
What causes monozygotic twins?
In cleavage, totipotent cells become divided into 2 separate independent cell masses
What causes dizygotic twins?
2 eggs ovulate and 2 eggs fertilised
Why is cleavage important?
Generate a large number of cells form differentiation and gastrulation
Increase nuclear/cytoplasmic ratio
What can cause ectopic pregnancy?
Failure of transport of morula into uterus
Implantation in incorrect position
Where does hatching occur and why?
Occurs opposite inner cells mass to minimise risk of enzymatic damage to embryo
