6. The Onset of Puberty

Question 1

the hypothalamus is inherently _____

Answer 1

female

Question 2

What causes defeminization of the hypothalamus during embryogenesis?

Answer 2

testosterone crossing blood-brain barrier and being converted to estradiol, thus minimizing the GnRH surge center

Question 3

What does defeminization of the hypothalamus eliminate in males?

Answer 3

GnRH surge center

Question 4

What binds to estradiol in females to prevent estradiol from crossing the blood-brain barrier?

Answer 4

alpha fetoprotein

Question 5

How is postpubertal LH secretion different in males versus females?

Answer 5

• males maintain steady pulsatile rhythm (every 2-6 hours) of GnRH –> LH –> testosterone
• females experience LH and estradiol surge every 20 days

Question 6

The surge of which two hormones is key to ovarian cyclicity in females?

Answer 6

LH and estradiol

Question 7

In heifers and ewes, the first estrus is generally not accompanied by what?

Answer 7

behavior estrus

Question 8

What characteristics in the male mark the onset of puberty?

Answer 8

mounting behaviors and erection

Question 9

What environmental factors promote the onset of puberty in females

Answer 9

• Presence or absence of males
• Season they are born
• Density of groups within the same sex
• Nutrition/ body condition

Question 10

What is the mean age of puberty in bovine male and females?

Answer 10

11 months

Question 11

What is the mean age of puberty in ovine male and females?

Answer 11

7 months

Question 12

What is the mean age of puberty in porcine male and females?

Answer 12

male - 7 months
female - 6 months

Question 13

What is the mean age of puberty in equine male and females?

Answer 13

male - 14 months
female - 18 months

Question 14

What is the limiting factor for the onset of puberty?

Answer 14

ability of the hypothalamus to secrete GnRH

Question 15

Why can’t the prepubertal female stimulate the surge center?

Answer 15

Lacks enough gonadal estradiol

Question 16

After puberty the _____ center controls ____ levels of GnRH and the ____ center controls the ________ surge of GnRH in females.

Answer 16

tonic
basal
surge
pre-ovulatory

Question 17

What happens to GnRH neurons in the male as puberty approaches?

Answer 17

become less sensitive to negative feedback

Question 18

What two factors influence the onset of puberty?

Answer 18

growth rate and body condition

Question 19

What effect does growth rate have on the onset of puberty in females?

Answer 19

Certain degree of “fatness” required for onset of puberty

Question 20

What effect does the presence of males have on the onset of puberty in females?

Answer 20

Decreases age at onset of puberty