The Oestrus Cycle

Question 1

What is the duration of the oestrus cycle in sheep?

Answer 1

17 days

Question 2

What is the duration of the oestrus cycle in cattle?

Answer 2

21 days

Question 3

Name a type of glycoprotein involved in the oestrus cycle.

Answer 3

Follicle stimulating hormone (FSH)

Other examples include Luteinising hormone (LH) and Inhibin.

Question 4

What hormone is synthesized by hypothalamus neurons and secreted in pulses?

Answer 4

Gonadotrophin releasing hormone (GnRH)

Question 5

What controls the secretion of GnRH?

Answer 5

Melatonin

Question 6

In seasonally polyoestrus species, what detects light to control melatonin secretion?

Answer 6

Pineal gland

Question 7

What hormone’s pulse frequency controls whether a female is in heat (oestrus) or between heat periods (dioestrus)?

Answer 7

GnRH

Question 8

What is the function of GnRH?

Answer 8

Stimulate gonadotrophin secretion from anterior pituitary

Question 9

What are the subunits of FSH?

Answer 9

Alpha and beta subunits

Question 10

Where is FSH synthesized?

Answer 10

Anterior pituitary

Question 11

What does an increase in FSH drive?

Answer 11

Recruitment and development of follicles towards ovulation

Question 12

What stimulates ovulation?

Answer 12

LH surge

Question 13

What is the main precursor for steroid hormone synthesis?

Answer 13

Cholesterol

Question 14

Where is progesterone synthesized and secreted from?

Answer 14

Luteal cells of corpus luteum

Question 15

What is the dominant hormone in the follicular phase?

Answer 15

Oestradiol (E2)

Question 16

What hormone is secreted by the corpus luteum during the luteal phase?

Answer 16

Progesterone

Question 17

What process does prostaglandin F2alpha signal?

Answer 17

No pregnancy in uterus to stimulate another ovulation

Question 18

What is the role of oxytocin in the corpus luteum?

Answer 18

Inhibits oestrus behaviour

Question 19

What occurs during proestrous?

Answer 19

Rapid follicle growth and dominant E2 secretion

Question 20

During which phase is the female receptive to males and usually ovulates?

Answer 20

Oestrus

Question 21

What happens in metestrous?

Answer 21

CL formation and P4 secretion increases

Question 22

What characterizes dioestrus?

Answer 22

CL fully functional with dominant P4 secretion

Question 23

What are the stages of a follicular wave?

Answer 23

• Recruitment (high FSH, low LH)
• Selection (low FSH, moderate LH)
• Dominance (Low FSH, high LH)
• Atresia (low LH receptor)

Question 24

What hormone acts on the brain to influence behaviours like acceptance of males?

Answer 24

Oestradiol

Question 25

What is the effect of progesterone on GnRH release?

Answer 25

Reduces GnRH pulse frequency

Question 26

What causes luteolysis?

Answer 26

Prostaglandin F2alpha (PGF2alpha)

Question 27

What happens to granulosa and theca cells after follicle rupture?

Answer 27

They transform into luteal cells

Question 28

What is the function of inhibin in the follicular phase?

Answer 28

Suppresses FSH secretion

Question 29

What physiological changes occur at ovulation?

Answer 29

* Increased blood flow to ovary * Follicular fluid volume increases * Breakdown of connective tissue in follicle wall

Question 30

What is measured as PGFM in blood?

Answer 30

Prostaglandin F2alpha

Question 31

What triggers the final oocyte maturation?

Answer 31

LH surge