oogenesis, the female tract and endocrine control (1) Flashcards
define oogenesis
formation and development of an ovum (mature oocyte)
what constitutes a follicle
oocytes and surrounding support cells
- they’re located near the surface of the ovaries in the cortex
at what age does a female have the greatest number of oocytes
4 months in utero a fetal female will have around 7 million oocytes formed
- start to die to about 1 million at birth and then continue to gradually decline till the age of ~50
describe mitosis
proliferation of stem cells - produce large numbers of germ cells (oogonia) in the developing ovary
2n (23 chromosomes - 2 pairs)
oogonium cell divides and creates two identical copies of these chromosomes
describe meiosis
reductive division
primary oocytes rest at meiosis 1 in the ovary until they are recruited (if that happens) into the follicular wave
describe meiosis on the oocyte
oocyte undergoes meiosis and produces one daughter cell to become the main ooctye and one daughter cell to become the first polar body (nucleus)
when and how are follicles activated
following puberty waves of ovarian follicles become activated
they can be recognised by changes in the morphology and number of granulosa cells that surround the oocyte
timeframe for a follicle and ovulation
it takes about 85 days from the time of activation of a follicle to when it starts to form an antrum (containing follicular fluid) and be capable of ovulation
describe the dominance of the follicular phase
one follicle will dominate over the others in terms of growth, as only one dominant follicle goes on to be ovulated
describe the timeframe of follicular growth
- primordial follicles
(12-50 years arrested state)
- primary follicles
(2-3 months active growth e.g. 85 days)
- secondary follicles
(2 weeks rapid growth)
- tertiary follicles
what defines a primordial follicle
oocyte has a very thin zona pellucida and a single layer of granulosa cells (flat)
- stromal cells on the outside of granulosa cells
primary follicles
once follicular cells are activated they become a primary follicle and form cuboidal granulosa cells
cells of secondary follicles
granulosa cells
- proliferate forming a multilayered cuboidal structure
- express FSH receptors and produce oestrogen, AMH and inhibin
Theca cells
- express LH receptors
- produce androgens
steriod pathway
progesterone --> androgen --> oestrogen
(can go backwards)
describe the two cell theory of follicular steriodogenesis (how oestrogen is made)
theca cells that sit outside the basement membrane in response to LH make progesterone and androgens
the androgens then move across into the basement membrane into granulosa cells to be aromatised into oestrogens
defining factors of a small tertiary follicle
anturm forms containing follicular fluid
has both a theca interna and a theca externa
zona pellucida
contains 3 proteins
ZP-1 = present in primordial follicles
ZP2 and ZP3 added to activated follicles
important for filtering normal sperm and in blocking polyspermy (selective barrier)
also blocks other species
define atretica
primordial follicles rest until puberty essentially however a lot of them die off via atretica
(most oocytes once activated are not ovulated but become atretic = die)
AMH
antimullerian hormone
suppresses follicular recruitment and development
from primordial to primary
comes from granulosa cells of the bigger follicles (represses development of other follicles)
how is an egg released
Ovulation
pressure build up from fluid inside the ovary and it bursts - oocyte released
controlled process
formation of corpus luteum
granulosa cells become lutenised cells and undergo proliferation referred to as the corpus luteum. They produce prodominately progesteron
hormone control of the ovarian cycle
- corpus luteum regresses, oestrogen and progesterone levels are low, see increased levels of FSH
- FSH stimulation leads to increased follicular growth
- about day 6-7 theres selection of the dominant follicle with increased oestrogen
- oestradiol supress FSH (& LH) in the pituitary
- oestrogen levels rise, by day 12, threshold conc of estradiol is exceeded. Causing a switch from negative to positive feedback
- oestrogen-mediated positive feedback triggers a rise in GnRH leading to increased LH surge
- LH surge induces ovulation
- corpus luteum develops, increased progesterone
- elevated progesterone levels inhibit GnRH, decreased FSH & LH
- Demise of the corpus luteum
describe inhibin
feeds back at the level of the pituitary to inhibit production of FSH
regions of fallopian tubes
infundibulum - region where oocyte is picked up
ampulla - widening
isthmus - main
interstitial portion - passing into uterine body
structure of Fallopian tube
- epithelial lining
- muscular coat
- serosal coat
epithelium
- ciliated
- secretory
- respond to steroids
effect of estrogen in the fallopian tubes
E2 promotes:
- increase in cilia
- increase in secretory activity
- increase in muscular activity
effect of progesterone in fallopian tubes
- decreases muscular activity
- decrease in cilia, but increase in the beat Hz after estrogen priming
- decrease in the volume of secretions
