2.2 - the menstrual cycle: lecture

Question 1

describe the gamete production in males

Answer 1

continuous

Question 2

describe the gamete production in females

Answer 2

1. tract needs to prepare for implantation
2. needs to build in a ‘waiting phase’
   therefore, gamete production needs to be periodic

Question 3

effects of oestrogen on hypothalamus and AP in terms of feedback? (female)

Answer 3

can be positive or negative depending on the concentration
low - inhibit LH/FSH
high - positive feedback (LH surge)

Question 4

effects of testosterone on hypothalamus and AP in terms of feedback? (males)

Answer 4

negative feedback on hypothalamus and AP

Question 5

what does menstrual cycle refer to? (umbrella term)

Answer 5

both ovaries and endometrium

Question 6

what are the stages of menstrual cycle?

Answer 6

preparation
ovulation
waiting

Question 7

what is the preparation stage of the menstrual cycle?

Answer 7

preparation of gamete = ovarian cycle

preparation of endometrium = uterine cycle

Question 8

what happens in the ovulation stage of the menstrual cycle?

Answer 8

release of the gamete

Question 9

what happens in the waiting stage of the menstrual cycle?

Answer 9

pause, maintaining the endometrium until a signal is received to indicate that fertilisation has happened (from conceptus)

Question 10

what are the control over the menstrual cycle?

Answer 10

1. gonadotrophins acting on ovary (produce steroid hormones - LH, FSH)
2. ovarian steroids:
   acting on tissues of reproductive tract (endometrium)
   act to control cycle (follicular + luteal phase)

Question 11

describe the HPO axis in females

Answer 11

GnRH produced by hypothalamus –> AP –> release gonadotrophins (FSH, LH) –> ovary

Question 12

what is the effect of gonadotrophins acting on ovaries?

Answer 12

1. promoting follicular development

2. production of ovarian hormones: steroid (oestrogen, progesterone), inhibin

Question 13

what is the HPO axis controlled by?

Answer 13

effects of gonadal hormones

negative AND positive

Question 14

what are the stages of the endometrial cycle?

Answer 14

menses
proliferative phase
secretory phase

Question 15

what happens at the start of the menstrual cycle?

Answer 15

no ovarian hormone production
early development of follicles begin
low steroid and inhibin levels - therefore little inhibition at hypothalamus + AP

Question 16

what happens to FSH levels at the start of the menstrual cycle?

Answer 16

free form inhibition (low steroid and inhibin, as follicle development only just beginning, so little inhibition at hypothalamus + AP)
FSH levels rise

Question 17

what does FSH bind to in females?

Answer 17

granulosa cells

Question 18

what are the effects of FSH?

Answer 18

follicular development continues

theca interna appears (outer layer)

Question 19

what happens as follicle continues to develop?

Answer 19

capable of oestrogen secretion

inhibin secretion begins (inhibits FSH - for 1 dominant follicle, as female are born with all follicles)

Question 20

what are the stages of development of an oocyte into an ovum?

Answer 20

primary oocyte (4n DNA) –> primordial follicle –> primary follicle –> secondary follicle –> early tertiary follicle –> graafian follicle –> ovulated ovum

Question 21

difference between primordial follicle and primary follicle?

Answer 21

primary follicle has zona pellucida (protein outer)

cells change from pregranulosa –> granulosa

Question 22

difference between primary follicle and secondary follicle?

Answer 22

theca cells appear in secondary follicle

Question 23

difference between secondary follicle and early tertiary follicle?

Answer 23

theca cells differentiate to theca interna and externa
antrum appears (space between theca and granulosa cells)
BM under theca cells

Question 24

when is first meiotic division completed?

Answer 24

between early tertiary follicle and graafian follicle

Question 25

difference bewteen early tertiary follicle and Graafian follicle?

Answer 25

secondary oocyte (2n DNA) and first polar body (2n DNA) present in Graafian follicle

Question 26

what are the stages undergone by Graafian follicle to turn into ovulated ovum?

Answer 26

beginning of second meiotic division FERTILISATION completion of second meiotic division (POST fertilisation)

Question 27

what are the structures present in an ovulated ovum?

Answer 27

corona radiata | second polar body

Question 28

what is the purpose of the mid-follicular phase?

Answer 28

need 1 dominant follicle | need to prevent recruitment of any further follicles

Question 29

what are the hormonal changes that happen in mid-follicular phase?

Answer 29

1. gonadotrophin levels can rise further (LH) 2. follicular inhibin rising - selective inhibition on FSH by AP (dissociate FSH + LH, cause LH surge)

Question 30

what are the hormonal changes that occur in preparation for ovulation? (think oestradiol)

Answer 30

circulating oestradiol + inhibin rise rapidly (from follicle, positive feedback) oestradiol production no longer dependent on FSH (inhibin) surge in LH

Question 31

what are the changes to progesterone in prepartion for ovulation?

Answer 31

progesterone production begins: granulosa cells become responsive to LH (LH receptors develop on the outside of granulosa cells)

Question 32

what happens to GnRH in preparation for ovulation?

Answer 32

modulation of GnRH pulse generator | pulse gets more rapid

Question 33

how does high oestradiol affect GnRH?

Answer 33

high oestradiol enhances sensitivity of AP gonadotrophs to GnRH (in late follicular phase - just before ovulation)

Question 34

what happens to meiosis in ovulation?

Answer 34

meiosis I completes | meiosis II begins (but pause until fertilisation then complete)

Question 35

when does ovulation occur?

Answer 35

about 3 hours post LH surge

Question 36

what happens in ovulation?

Answer 36

mature oocyte extruded through the capsule of the ovary | release oocyte into fallopian tube

Question 37

what are the oestrogen changes of mid-follicular phase?

Answer 37

follicular oestrogen now at concentration where it exerts POSITIVE feedback at hypothalamus AND AP

Question 38

what happens to the follicle after ovulation?

Answer 38

the follicle is luteinised

Question 39

what does a luteinised follicle post ovulation secrete? what does this result in?

Answer 39

oestrogen and progesterone in large quantities (inhibin continues to be produced - suppresses FSH, prevent another follicle from developing before the corpus luteum is broken down - further gamete development suspended: waiting phase established)

Question 40

what happens to LH post ovulation? why?

Answer 40

LH is suppressed - further gamete development suspended (prevent LH surge): waiting phase established negative feedback due to presence of progesterone (on hypothalamus and AP)

Question 41

what happens in the waiting phase?

Answer 41

endometrium build lining and wait for signal from oocyte (fertilised = conceptus) LH suppressed by progesterone from luteinised follicle inhibin suppresses FSH

Question 42

what are the hormones produced in luteal phase?

Answer 42

corpus luteum produces progesterone and oestrogens from androgens CL produces inhibin (no FSH): promotes production of progesterone (why?)

Question 43

what happens as a result of the hormones produced by CL in luteal phase? why?

Answer 43

CL regresses spontaneously in the absence of a further rise in LH (progesterone suppresses)

Question 44

what happens at the end of the menstrual cycle? leading to?

Answer 44

absence of further rise in LH, corpus luteum regresses dramatic fall in gonadal hormones (FSH + LH) relieving negative feedback (on AP + hypothalamus) cycle starts again (IF fertilisation has NOT occurred)