Physiology of ovarian cycle, menstrual cycle, fertilisation and implantation

Question 1

What is the ovarian cycle?

Answer 1

cycle in which the oocyte matures, releases from ovary and travels through fallopian tube to uterus

Question 2

What is the uterine cycle?

Answer 2

cycle in which uterine lining grows and prepares for an embryo to implant
it is shed as menstruation if fertilisation does not happen in that cycle

Question 3

What prevents puberty from occurring earlier?

Answer 3

GnRH from hypothalamus is inhibited by cerebral cortex until puberty
puberty begins when this inhibition stops (loss of central inhibition on hypothalamus - maturation of HPO axis)

Question 4

How is GnRH secreted from puberty onwards?

Answer 4

pulsatile
2 hourly

Question 5

Name the components of the HPO axis

Answer 5

hypothalamus - GnRH
pituitary - LH/FSH
ovary - oestrogen/progesterone

Question 6

FSH function

Answer 6

recruitment
increase number of granulosa cells
stimulates aromatase activity - conversion of androgens to oestrogens

Question 7

LH function

Answer 7

acts on theca cells
increases uptake of cholesterol and LDL
production of androstenedione and testosterone

Question 8

How many oocytes develop each month?

Answer 8

10-12
only 1 makes it to full maturity

Question 9

Blood supply of ovaries

Answer 9

gonadal (ovarian) arteries
arise directly from aorta

Question 10

Phases of ovarian cycle

Answer 10

follicular phase
ovulation
luteal phase
menstrual

Question 11

Which hormone triggers ovulation?

Answer 11

surge of LH

Question 12

What occurs in the follicular phase?

Answer 12

ovary - cells around oocyte divide and increase releasing oestrogen

hormonal - oestrogens are low, anterior pituitary releases FSH and LH stimulates the follicle to develop

uterus - endometrial lining thickens

Question 13

When does ovulation occur?

Answer 13

36 hours after LH surge

Question 14

Why are OCPs slightly protective of ovarian cancer?

Answer 14

suppresses ovulation
more breaches of ovarian membrane (ovulation) increases chance of dysplasia and then cancer

Question 15

What happens in menstrual phase?

Answer 15

no pregnancy - corpus luteum disintegrates, oestrogen and progesterone fall - increase FSH and LH

Question 16

What happens in luteal phase?

Answer 16

follicular wall seals
corpus luteum formation
progesterone rises, suppressess follicular growth, endometrial maturation

Question 17

Features of normal menstruation

Answer 17

duration <=8 days
frequency 24-38 days
regularity 7-9 days
volume 5-80ml
no inter-menstrual bleeding or post-coital bleeding

Question 18

Pregnancy is the end product of what 3 processes in women?

Answer 18

ovulation
fertilisation
implantation

Question 19

Describe spermatogenesis

Answer 19

occurs in seminiferous tubules
begins at puberty
sertoli cells act as nursing cells
tight junctions between sertoli cells forms blood-testis barrier
leydig cells secrete androgens (testosterone)

Question 20

What is spermiogenesis?

Answer 20

metamorphosis of small, round spermatid cell into spermatozoon

Question 21

When do sperm mature?

Answer 21

while passing through epididymis

Question 22

Duration of sperm motility

Answer 22

60 hours

Question 23

Duration of sperm fertility

Answer 23

48 hours

Question 24

Length of fertilisability of the oocyte

Answer 24

6-24 hours

Question 25

Describe sperm activation

Answer 25

motility: - acquire motility in final maturation in epididymis - become fully mobile after capacitation capacitation: - gives them the capacity to bind to the oocyte - around 6 hours from ejaculation in the human - triggered by signals in the female genital tract while passing through the cervix acrosome reaction: - acrosome contains enzymes - released when met with oocyte - facilitate gamete fusion

Question 26

Describe ovum activation

Answer 26

zona pellucida = glycoprotein sheet around oocyte sperm receptors for zona pellucida found deep in acrosome sperm can fuse with zona pellucida after acrosome reaction after sperm penetration the zona pellucida undergoes changes to act as protective barrier and prevent polyspermy

Question 27

What happens if more than 1 sperm binds to zona pellucida?

Answer 27

69 chromosomes (if 2 sperm) molar pregnancy

Question 28

What is the nuclear reaction in fertilisation?

Answer 28

sperm chromatins are released into the cytoplasm by breakdown of nuclear membrane male and female pronuclei are formed and migrate to the centre of the cells

Question 29

Steps of fertilisation

Answer 29

capacitation acrosome reaction penetration of corona radiata penetration of zona pellucida fusion of plasma membrane cortical reaction zonal reaction resumption of 2nd meiotic division formation of pronuclei metabolic activation of the egg

Question 30

What is a fertilised ovum called?

Answer 30

zygote

Question 31

What is cleavage in fertilisation?

Answer 31

zygote undergoing rapid cell divisions cleavage completed 30 hours after fertilisation process of cleavage forms morula

Question 32

What is a blastocyst?

Answer 32

morula gets converted to blastocyst blastocyst implants into uterus

Question 33

Where does fertilisation occur?

Answer 33

fallopian tube

Question 34

Usual place of implantation

Answer 34

posterior wall of uterine fundus