Puberty Flashcards
Puberty
-Acquisition of reproductive competence.
-Puberty occurs over time, is different in males and females
-based on the development of hypothalamic GnRH neurons
Know the final step of development that is necessary for puberty to occur (induces puberty)
-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
Know how brain is feminized
-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
Know how the brain is defeminized
-Testosterone -> Estradiol -> Defeminizes hypothalamus (no surge center)
-Conversion of testosterone to estradiol occurs in the brain
-Tonic Center only forms
Know the factors that influence puberty
-Metabolic
-environmental
-social factors
-genetic
-hormonal
Metabolic
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%)
Environmental
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)
Social Factors
-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
Genetic
Certain breeds are bred to reach puberty early and times vary depending on genetics
Hormonal
Dependence on GnRH secretion
Know the different events/characteristics that we use to measure attainment of puberty for females and for males
-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
Age at first estrus
Easy to determine but may not actually be the time of first ovulation
Age at first ovulation
Highly accurate but difficult to determine without ultrasound, palpation, or laparoscopy
Age when the female can support a pregnancy
Easy to determine but is unlikely to coincide with first ovulation
Age when mounting and erection begins
Easy to determine but may not coincide with the ability to ejaculate or produce spermatozoa
Age at first ejaculation
Difficult to determine and may not coincide with the ability to produce enough sperm to cause pregnancy
Age when spermatozoa first appear in ejaculate
Accurate but semen must be collected on a weekly basis
Age when semen contains a threshold number of spermatozoa
Most practical method to determine age of puberty
Know how negative and positive feedback change leading up to puberty for females
Approaching puberty, the female begins a positive feedback mechanism of high ovarian estradiol secretions triggering the hypothalamus to release more frequent pulses of GnRH
Know how negative and positive feedback change leading up to puberty for males
-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
Know how GnRH pulsatility changes in females
Tonic center secretes frequent pulses of GnRH and the surge center release a single large amount of GnRH
Know how GnRH pulsatility changes in males
In the postpubertal male, consistent pulses of steroids and gonadotrophs occur
Know what silent ovulation is and why it often happens the first time the female ovulates
-Ovulation that occurs without estrus.
-Often happens during the first ovulation as maximum display of estrus must be preceded by exposure to progesterone
Know how feed intake/body size/fatness/metabolism affects puberty
-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.
