Week 2 - Non-Pregnant Oestrus Cycle

Question 1

What is the oestrus cycle?

Answer 1

repetitive patterns of hormones and behaviours which lead to the ovulation of a follicle

Question 2

State 3 ways the Oestrus cycle can be described in terms of

Answer 2

behaviour
hormones
state of ovaries

Question 3

*Describe the Oestrus cycle in terms of Behaviour

Answer 3

pro-oestrus
oestrus
metoestrus
dioestrus

Question 4

Describe the Oestrus cycle in terms of State of Ovaries

Answer 4

luteal phase
follicular phase

Question 5

For Pro-oestrus:
- State what each hormone is doing
- State why for each (1) (1) (1) (2)

Answer 5

progesterone concentrations are decreasing
because the corpus lute is undergoing luteolysis

FSH concentrations are increasing
because there is less progesterone to suppress GnRH

LH concentration are increasing
because there is less progesterone to suppress GnRH

oestradiol concentrations are increasing
because there is more FSH to stimulate the development of follicles
and follicles secrete oestradiol

Question 6

For Pro-oestrus:
- What Behaviour would you expect to see?
- Why?

Answer 6

the female is attracted to the male but will not permit mating

due to increasing oestradiol concentrations

Question 7

For Oestrus:
- Describe the order of events happening in this phase up until ovulation (6)

Answer 7

the developing follicles produce more oestradiol

causing oestradiol concentrations to increase

at high concentrations oestradiol switches to having a positive feedback effect on GnRH instead of a negative feedback effect

causing a surge in GnRH from the surge centre

causing a surge in LH concentration

this surge in LH induces ovulation

Question 8

For Oestrus:
- Describe what happens to hormone concentrations after ovulation and why (3)

Answer 8

oestradiol concentrations decrease as the follicle has ovulated so is no longer producing oestradiol

LH concentration decreases as the GnRH concentrations decrease after the surge

FSH concentrations decrease as the GnRH concentrations decrease after the surge

Question 9

For Oestrus:
- Why do we not see a surge in FSH when we get the LH surge?

Answer 9

because FSH is being suppressed by inhibin secreted by the developing follicle

Question 10

For Oestrus:
- Generally describe the behaviour seen
- What causes this?

Answer 10

the female is attracted to the male and will permit mating

the very high concentration of oestradiol

Question 11

For Metoestrus:
- What has happened to the hormone concentrations?
- Explain why (1) (1) (1) (3)

Answer 11

progesterone concentrations are increasing
because the remains of the ovulated follicle have become the corpus luteum which secretes progesterone

FSH concentrations have decreased to basal levels
because progesterone suppresses GnRH secretion

LH concentrations have decreased to basal levels because progesterone suppresses GnRH secretion

Oestradiol concentrations have decreased to basal levels
because progesterone suppresses GnRH secretion
so there is less FSH to stimulate the development of follicles
and follicles produce oestradiol

Question 12

For Metoestrus:
- What behaviour should we expect?
- Why? (3)

Answer 12

rejection of male

because the fertilisation window has now closed
so there is no reason to waste energy on copulation
driven by increasing progesterone

Question 13

For Dioestrus:
What is happening to Progesterone concentration and why during:
- early dioestrus
- late dioestrus (3)

Answer 13

progesterone concentration is high and constant
because the corpus luteum is producing high concentrations of progesterone

progesterone concentrations start to decrease
because maternal recognition of pregnancy has not occurred
because the oocyte is not fertilised
so the corpus luteum starts to degrade by luteolysis

Question 14

For Dioestrus:
- What hormone released induces luteolysis after failure of maternal recognition of pregnancy?

Answer 14

prostaglandin F2 alpha

Question 15

For Dioestrus:
- What behaviour would you expect to see?
- Why? (3)

Answer 15

rejection of male

because the fertilisation window has now closed
so there is no reason to waste energy on copulation
driven by high progesterone

Question 16

In terms of the state of the ovaries, which Behavioural phases are part of:
- Follicular phase
- Luteal phase

Answer 16

pro-oestrus
oestrus

metoestrus
dioestrus

Question 17

State the names of 2 Steroid Hormones

Answer 17

oestradiol
progesterone

Question 18

State the names of 2 gonadotrophin hormones

Answer 18

LH
FSH