18 Fertility and assisted reproduction Flashcards
where is the site of oogenesis?
germinal epithelial cells in the ovaries
what is the function of the fallopian tubes/oviducts?
transport secondary oocyte from ovaries to uterus via ciliary action and peristalsis
site of fertilisation
what is the function of the uterus?
site of implantation of fertilised ovum
development of foetus and placenta during pregnancy
what are the two layers of the uterus and their functions?
myometrium - smooth muscle fibres - contractions during labour
endometrium:
- stratum basalis
- stratum functionalis - supports growing foetus (shed during menstruation)
what is the function of the cervix?
controls the opening of the uterus during pregnancy, menstruation or intercourse
what is the function of the vagina?
passageway for menstrual flow
receptacle for the penis during intercourse
how does the lining of the vagina change each month? how is this used in medicine?
cyclical change in degree in keratinisation
used in PAP smears
what is the composition of the mucosa in the vagina? how does this relate to its function?
contains glycogen granules, which are decomposed to organic acids
giving low pH
which reduces microbial growth and sperm motility
what is the function of the labiae minora and majora?
produce lubricant mucus secretion
prevent clitoris from abraision
what is oogenesis?
the formation of secondary oocytes
what occurs during the multiplication phase of oogenesis? {when does it occur?}
{before birth in developing biological female}
primordial follicles in germinal epithelium of ovaries undergo mitosis
producing oogonia
these go through a growth phase to produce a diploid primary oocyte
meiosis stopped at prophase I
when and how is the maturation phase of oogenesis stimulated?
at puberty
FSH is secreted from the anterior pituitary gland and stimulates 12-20 primary oocytes to become haploid secondary oocytes
produces a polar body
what happens during ovulation?
LH secreted following positive feedback of oestrogen
a single secondary oocyte is released from Graafian follicle (which becomes corpus luteum)
what is the fate of the corpus luteum?
secretes progesterone (and oestrogen) to maintain a potential pregnancy
eventually dies
what are the features of the secondary oocyte after ovulation?
corona radiata (granulosa cells)
zona pellucida
cytoplasm
centrioles
haploid nucleus
CSM
polar body
what is the function of the testes?
to produce sperm by spermatogenesis in seminiferous tubules
to produce testosterone and other androgens in interstitial tissue (e.g. Leydig cells) under the influence of LH from the anterior pituitary gland
what is the function of the scrotum?
to regulate the temperature of the sperm by elevating or lowering testicular tissue with the cremaster muscles
what is the function of the epididymis?
to mature and store spermatozoa for up to four weeks
to move sperm into the vas deferens using ciliated epithelial cells and smooth muscle
what is the function of the vas deferens?
to store sperm for several months until ejaculation
to move sperm to the urethra via peristalsis during ejaculation
what is the function of the seminal vesicles?
to secrete a viscous alkaline fluid which contains fructose to act as a respiratory substrate for sperm mobility
what is the function of the prostate gland?
to secrete an alkaline fluid that neutralises the acidity of the vagina
what is the function of the Cowper’s (bulbourethral) gland?
to produce an antacid fluid and a mucus secretion which lubricates the penis during intercourse and flushes out the urethra in preparation for the sperm
what is the function of the penis?
to deliver sperm to the neck of the cervix
what are the two types of erectile tissue in the penis?
corpus cavernosa (dorsal)
corpus spongiosa (ventral)
(become erect from vasodilation)
what is the role of testosterone in males?
development of male sex characteristics:
- primary: male genitalia growth in utero
- secondary: causes physiological changes at puberty (e.g. voice drop; hair growth; growth of genitals)
how does oogenesis/spermatogenesis increase genetic variation?
independent orientation at metaphase I and II
independent assortment at anaphase I and II
crossing over at prophase I
mutation
random fertilisation
what occurs during the multiplication phase of spermatogenesis?
mitotic division of a diploid spermatogonium (type B) in the seminiferous tubules
producing two diploid primary spermatocytes
what occurs during meiosis I in spermatogenesis?
primary spermatocyte moves into adluminal compartment of the seminiferous tubules
undergoes meiosis I to produce 2x haploid secondary spermatocytes
what occurs during meiosis II in spermatogenesis?
secondary spermatocytes divide into haploid spermatocytes
what occurs during spermiogenesis?
differentiation of spermatids:
- tail = flagellum and axial filaments in 9+2 microtubule bundles (elongated centriole)
- organelles (e.g. helical mitochondria)
- acrosome
- haploid nucleus (DNA packaged with specific nuclear basic proteins which are replaced by protamines during spermatid elongation which makes them transcriptionally inactive)
what are the advantages of genetically varied offspring??
adapted better to changing environment
advantageous alleles retained in gene pool
high evolutionary potential
how is gametogenesis initiated?
release of gonadotrophin-releasing hormone (GnRH)
GnRH stimulates anterior pituitary gland to secrete LH and FSH, which act separately on the gonads
outline hormonal control of spermiogenesis
GnRH produced in hypothalamus and stimulates anterior p.g. to secrete LH and FSH
LH binds to Leydig cells which are stimulated to produce testosterone
FSH binds to Sertoli cells, making them more receptive to testosterone
testosterone binds to Sertoli cells and initiates spermatogenesis (also prevents apoptosis of type A cells)
what are the two separate cycles that make up the menstrual cycle?
ovarian
uterine
what are the four phases of the menstrual cycle?
proliferative - regeneration of uterine lining
ovulation - secondary oocyte release into oviduct
secretory - uterine lining secretes nutrients to prepare for blastocyst implantation
menstrual - lining of uterus sheds following implantation failing to occur
what are the two most common reasons for cessation of the menstrual cycle?
pregnancy (temporary)
menopause (permanent)
outline hormonal control of the menstrual cycle/oogenesis
anterior p.g. secretes FSH into blood plasma –> ovaries, where it induces proliferation of granulosa cells for follicle development
oestrogen concentration rises as it is secreted from the maturing follicle –> thickening of the endometrium of the uterus
oestrogen inhibits FSH –> GnRH production –> LH secretion –> ovulation
LH stimulates follicle to become corpus luteum
corpus luteum secretes progesterone, which stimulates the development of blood vessels in the endometrium
if implantation does not occur, corpus luteum dies –> oestrogen and progesterone concentrations fall –> menstruation
how are sperm capacitated?
removal of glycoproteins from sperm head
enzymes specific to the glycoprotein break peptide bonds
producing a polypeptide
which makes the plasma membrane more permeable to Ca2+
what are the components of semen?
sperm
mucus
proteins
fructose - respiratory substrate
citrate + calcium ions
water
alkaline prostate fluids
outline the acrosome reaction in fertilisation
acrosome swells and fuses with sperm head membrane
releasing hydrolytic enzymes by exocytosis
which digest the corona radiata and zona pellucida
specific proteins on sperm head bind to plasma membrane of secondary oocyte
plasma membranes of secondary oocyte and sperm head fuse
haploid nucleus of sperm enters the secondary oocyte forming a diploid zygote
outline the cortical reaction in fertilisation
entry of sperm nucleus activates cortical granules (specialised lysosomes) in secondary oocyte, which release hydrolytic enzymes
which digest the sperm-binding proteins on the plasma membrane
and cause the zona pellucida to harden and thicken, before separating from the ovum
this prevents polyspermy (which would lead to an non-viable ovum)
which hormone is used to test for human pregnancy? why is it used?
human chorionic gonadotrophin (hCG)
secreted from the placenta when a blastocyst successfully implants
outline the procedure of a pregnancy test using urine
the test stick is dipped in a urine sample from the woman believed to be pregnant
dipstick has monoclonal antibodies (mABs) with a coloured latex particle attached
mABs remain mobile when urine is introduced
hCG binds to specific, complementary mAB –> hCG-mAB complex
complexes carried up stick in urine
to a line of immobile mAB specific antibodies, which they bind to, developing a dark line
uncombined mABs continue to move to form a second line to show that the test is working
why might a pregnancy kit give a false negative?
tested too early - hCG only produced after implantation
urine too dilute - do it first thing
hCG concentration extremely high - so many molecules that they can’t bind properly
outline some causes of infertility in females
ovulatory disorders - e.g. PCOS; thyroid problems
blockages in oviducts - e.g. endometriosis; infections
surgery scarring - pelvic or cervical scarring
cervical mucus defects
submucosal fibroids
medication/drugs - e.g. chemo; NSAIDs; neuroleptics
pelvic inflammation disease
outline some causes of infertility in males
semen problems - e.g. low/no sperm count; abnormal sperm
damaged testicles - e.g. infection; cancer; congenital defects
ejaculation disorders - retrograde or premature
hypogonadism - abnormally low levels of testosterone
medication/drugs - e.g. anabolic steroids; chemo; NSAIDs
excessive alcohol consumption
outline causes of infertility in all sexes
weight
STIs - e.g. chlamydia –> damage to fallopian tubes/tenderness of scrotum
smoking
occupational/environmental factors
stress
outline in vitro fertilisation (IVF) as a means of treating infertility
gametes surgically removed from the parents
one secondary oocyte and 100,000 sperm are incubated in the same petri dish for ~ 4 hours
if sperm are struggling to fertilise the ovum, intracyctoplasmic sperm injections (ICSI) are used
once fertilised, zygote continues dividing and genetic tests are carried out
if the zygote is viable, it implanted in the uterus using a canula
what is an advantage and disadvantage of IVF?
+ increases probability of becoming pregnant
- incr. risk of multiple births (several zygotes impanted) ∴ incr. risk of still births/maternal mortality
what are GIFT and ZIFT?
GIFT - sperm and secondary oocyte inserted into the oviduct and fertilisation occurs naturally inside the woman’s body
ZIFT - fertilisation occurs in the lab, then the zygote is transferred to the oviduct
what is ovulation induction? how is it used to treat infertility?
used when oocytes do not develop normally
anti-oestrogen administered from day 5 to 10
–> incr. production of GnRH
–> incr. secretion of LH and FSH from the anterior p.g.
ultrasound detects developing follicles (if present)
what is intrauterine insemination? how is it used to treat infertility?
sperm are removed and washed to remove mucus and non-mobile sperm
concentrated in a specialised medium
sperm can then be injected into the uterus via artificial insemination
what are the four most common forms of artificial insemination?
intravaginal
intracervical
intrauterine
intratubal
