Puberty

Question 1

Puberty

Answer 1

-Acquisition of reproductive competence.
-Puberty occurs over time, is different in males and females
-based on the development of hypothalamic GnRH neurons

Question 2

Know the final step of development that is necessary for puberty to occur (induces puberty)

Answer 2

-In order for puberty to begin, pulse frequency and amplitude of GnRH must be high enough
-in female enough estradiol must be produced and in the male sensitivity to testosterone and E2 (which are inhibitory) must be reduced

Question 3

Know how brain is feminized

Answer 3

-Produces estradiol
-NO defeminization because alpha-fetoprotein binds fetal estradiol and does not allow access across the Blood Brain Barrier.
Surge center and tonic center both form

Question 4

Know how the brain is defeminized

Answer 4

-Testosterone -> Estradiol -> Defeminizes hypothalamus (no surge center)
-Conversion of testosterone to estradiol occurs in the brain
-Tonic Center only forms

Question 5

Know the factors that influence puberty

Answer 5

-Metabolic
-environmental
-social factors
-genetic
-hormonal

Question 6

Metabolic

Answer 6

Puberty can only begin when animals reach a certain percent of their mature body weight as this indicates the animal is placing less and less energy into growing (Beef-30-40%; Dairy-55-65%; Sheep-40-65%)

Question 7

Environmental

Answer 7

Month of birth influences the age seasonal breeders begin puberty (5-6 mo. for Spring lambs and 10-12 mo. for Fall lambs; heifers born in Autumn reach puberty earlier than heifers born in the Spring)

Question 8

Social Factors

Answer 8

-Small groups of only females reach puberty the latest
-followed by large groups of females
-then any group of females with or without physical contact to a male reach puberty at the same time

Question 9

Genetic

Answer 9

Certain breeds are bred to reach puberty early and times vary depending on genetics

Question 10

Hormonal

Answer 10

Dependence on GnRH secretion

Question 11

Know the different events/characteristics that we use to measure attainment of puberty for females and for males

Answer 11

-Age at first estrus
-Age at first ovulation
-Age when the female can support a pregnancy
-Age when mounting and erection begins
-Age at first ejaculation
-Age when spermatozoa first appear in ejaculate
-Age when semen contains a threshold number of spermatozoa

Question 12

Age at first estrus

Answer 12

Easy to determine but may not actually be the time of first ovulation

Question 13

Age at first ovulation

Answer 13

Highly accurate but difficult to determine without ultrasound, palpation, or laparoscopy

Question 14

Age when the female can support a pregnancy

Answer 14

Easy to determine but is unlikely to coincide with first ovulation

Question 15

Age when mounting and erection begins

Answer 15

Easy to determine but may not coincide with the ability to ejaculate or produce spermatozoa

Question 16

Age at first ejaculation

Answer 16

Difficult to determine and may not coincide with the ability to produce enough sperm to cause pregnancy

Question 17

Age when spermatozoa first appear in ejaculate

Answer 17

Accurate but semen must be collected on a weekly basis

Question 18

Age when semen contains a threshold number of spermatozoa

Answer 18

Most practical method to determine age of puberty

Question 19

Know how negative and positive feedback change leading up to puberty for females

Answer 19

Approaching puberty, the female begins a positive feedback mechanism of high ovarian estradiol secretions triggering the hypothalamus to release more frequent pulses of GnRH

Question 20

Know how negative and positive feedback change leading up to puberty for males

Answer 20

-In the prepubertal male, testosterone and estradiol inhibit release of GnRH
-but as puberty approaches GnRH neurons lose sensitivity to these hormones and eventually secrete enough GnRH to cause puberty

Question 21

Know how GnRH pulsatility changes in females

Answer 21

Tonic center secretes frequent pulses of GnRH and the surge center release a single large amount of GnRH

Question 22

Know how GnRH pulsatility changes in males

Answer 22

In the postpubertal male, consistent pulses of steroids and gonadotrophs occur

Question 23

Know what silent ovulation is and why it often happens the first time the female ovulates

Answer 23

-Ovulation that occurs without estrus.
-Often happens during the first ovulation as maximum display of estrus must be preceded by exposure to progesterone

Question 24

Know how feed intake/body size/fatness/metabolism affects puberty

Answer 24

-Sensing neurons determine how much glucose, leptin, and fatty acids are in the blood, they target kisspeptin neurons, which targets GnRH neurons and results in GnRH secretion (a specific amount of GnRH will result in the onset of puberty).
-Management: Greater amounts of fed result in animals attaining mature weight earlier.
-High amounts result in the earliest onset of puberty
-Moderate amounts result in a middle time
-Small amount results in the latest onset.
-Small amounts also cause the animal to be too small for pregnancy.