oogenesis, the female tract and endocrine control (1)

Question 1

define oogenesis

Answer 1

formation and development of an ovum (mature oocyte)

Question 2

what constitutes a follicle

Answer 2

oocytes and surrounding support cells

• they’re located near the surface of the ovaries in the cortex

Question 3

at what age does a female have the greatest number of oocytes

Answer 3

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

Question 4

describe mitosis

Answer 4

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

Question 5

describe meiosis

Answer 5

reductive division

primary oocytes rest at meiosis 1 in the ovary until they are recruited (if that happens) into the follicular wave

Question 6

describe meiosis on the oocyte

Answer 6

oocyte undergoes meiosis and produces one daughter cell to become the main ooctye and one daughter cell to become the first polar body (nucleus)

Question 7

when and how are follicles activated

Answer 7

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

Question 8

timeframe for a follicle and ovulation

Answer 8

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

Question 9

describe the dominance of the follicular phase

Answer 9

one follicle will dominate over the others in terms of growth, as only one dominant follicle goes on to be ovulated

Question 10

describe the timeframe of follicular growth

Answer 10

1. primordial follicles

(12-50 years arrested state)

2. primary follicles

(2-3 months active growth e.g. 85 days)

3. secondary follicles

(2 weeks rapid growth)

4. tertiary follicles

Question 11

what defines a primordial follicle

Answer 11

oocyte has a very thin zona pellucida and a single layer of granulosa cells (flat)
- stromal cells on the outside of granulosa cells

Question 12

primary follicles

Answer 12

once follicular cells are activated they become a primary follicle and form cuboidal granulosa cells

Question 13

cells of secondary follicles

Answer 13

granulosa cells

• proliferate forming a multilayered cuboidal structure
• express FSH receptors and produce oestrogen, AMH and inhibin

Theca cells

• express LH receptors
• produce androgens

Question 14

steriod pathway

Answer 14

progesterone 
--> 
androgen
-->
oestrogen

(can go backwards)

Question 15

describe the two cell theory of follicular steriodogenesis (how oestrogen is made)

Answer 15

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

Question 16

defining factors of a small tertiary follicle

Answer 16

anturm forms containing follicular fluid

has both a theca interna and a theca externa

Question 17

zona pellucida

Answer 17

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

Question 18

define atretica

Answer 18

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)

Question 19

AMH

Answer 19

antimullerian hormone

suppresses follicular recruitment and development
from primordial to primary

comes from granulosa cells of the bigger follicles (represses development of other follicles)

Question 20

how is an egg released

Answer 20

Ovulation

pressure build up from fluid inside the ovary and it bursts - oocyte released
controlled process

Question 21

formation of corpus luteum

Answer 21

granulosa cells become lutenised cells and undergo proliferation referred to as the corpus luteum. They produce prodominately progesteron

Question 22

hormone control of the ovarian cycle

Answer 22

1. corpus luteum regresses, oestrogen and progesterone levels are low, see increased levels of FSH
2. FSH stimulation leads to increased follicular growth
3. about day 6-7 theres selection of the dominant follicle with increased oestrogen
4. oestradiol supress FSH (& LH) in the pituitary
5. oestrogen levels rise, by day 12, threshold conc of estradiol is exceeded. Causing a switch from negative to positive feedback
6. oestrogen-mediated positive feedback triggers a rise in GnRH leading to increased LH surge
7. LH surge induces ovulation
8. corpus luteum develops, increased progesterone
9. elevated progesterone levels inhibit GnRH, decreased FSH & LH
10. Demise of the corpus luteum

Question 23

describe inhibin

Answer 23

feeds back at the level of the pituitary to inhibit production of FSH

Question 24

regions of fallopian tubes

Answer 24

infundibulum - region where oocyte is picked up

ampulla - widening

isthmus - main

interstitial portion - passing into uterine body

Question 25

structure of Fallopian tube

Answer 25

• epithelial lining
• muscular coat
• serosal coat

epithelium

• ciliated
• secretory
• respond to steroids

Question 26

effect of estrogen in the fallopian tubes

Answer 26

E2 promotes:

• increase in cilia
• increase in secretory activity
• increase in muscular activity

Question 27

effect of progesterone in fallopian tubes

Answer 27

• decreases muscular activity
• decrease in cilia, but increase in the beat Hz after estrogen priming
• decrease in the volume of secretions