The Oestrous Cycle (Reproductive System)

Question 1

What does it mean by polyostrous animals?

Answer 1

1. Animals become fertile more than once per year, e.g cattle, pigs and mice

Question 2

What does it mean by seasonal polyoestrous animals?

Answer 2

1. Animals have more than one oestrous cycle, but only certain periods of the year, e.g horses, sheep, goats and deer

Question 3

What does it mean by monooestrous animals?

Answer 3

1. Animals that have one oestrous cycle every year, e.g dogs, wolves, foxes and bears

Question 4

What happens within the Dioestrous cycle?

Answer 4

1. Diaestrous is the stage between oestrous cycles
2. Low oestrogen levels, peak progesterone levels

Question 5

What happens within the pro-oestrous cycle?

Answer 5

1. Pro-oestrous is when the follicle within the ovary enlarges
2. Progesterone decreases, meaning oestrogen increases
3. GnRH is secreted to start the increase of LH and FSH

Question 6

What happens within the oestrous cycle?

Answer 6

1. When the animal is in heat- sexually receptive
2. Oestrogen increases, as well as FH and LH leading to ovulation (egg releases)

Question 7

What happens within the metoestrous cycle?

Answer 7

1. The corpus luteum (sac structure after egg release) starts to decay
2. Progesterone levels increases and inhibits oestrogen release

Question 8

Where does the luteal phrase occur?

Answer 8

1. Dioestrous
2. Metoestrous

Question 9

Where does follicular phrase occur?

Answer 9

1. Pro-oestrous
2. Oestrous

Question 10

What are the stages of the oestrous cycle in order?

Answer 10

1. Pro-oestrous- the beginning of heat, body prepares for mating
2. Oestrous- ‘Heat’ female is fertile and receptive to male
3. Metoestrous- ovum fertilised and gestation begins or, uterine lining shed
4. Dioestrous- between cycles if more than once

Question 11

What happens within the Dioestrous stage?

Answer 11

1. Low oestrogen levels, peak levels of progesterone

Question 12

What happens within the pro-oestrous stage?

Answer 12

1. Follicle enlarges progesterone levels decrease and oestrogen increase
2. GnRH released from hypothalamus

Question 13

What happens within the oestrous stage?

Answer 13

1. Period of ‘Heat’ oestrogen levels continue to rise l, FSH increases peak levels of LH stimulates ovulation

Question 14

What happens within the metoestrous cycle?

Answer 14

1. Corpus luteum regresses progesterone levels increase which inhibits the Release of oestrogen

Question 15

What does monooestrous mean?

Answer 15

1. One oestrous cycle per year

Question 16

What does polyoestrous mean?

Answer 16

1. Fertile more than once a year

Question 17

What does seasonally polyoestrous mean?

Answer 17

1. More than one cycle, during certain periods of the year

Question 18

Describe how levels of hormones change through all the stages of the oestrous cycle?

Answer 18

1. Dioestrous is between oestrous cycles and levels of progesterone are at peak
2. Pro-oestrous GnRH is secreted which stimulates the release of FH
3. FSH causes follicles to develop, which secrete oestrogen and stimulate reproductive behaviour
4. During oestrous, the reproductive tract is under the control of oestrogen (heat)
5. Mature follicles reduce FSH secretion and stop producing oestrogen, which triggers LH release and mating behaviour
6. LH stimulates ovulation, and ovum is released from the follicle, leaving behind the corpus luteum
7. Metoestrous the corpus luteum regresses/decays after ovum has been released, this increases progesterone levels and inhibits oestrogen production
8. If pregnant, the placenta produces progesterone to maintain pregnancy. If not, corpus luteum regresses, progesterone levels drop and the female enters dioestous or anoestrous depending on the reproductive strategy