CH 6 Puberty Flashcards
What does testosterone do to the brain?
“defeminizes” the brain and eliminates the GnRH surge center in male
What centers do males have? What centers do females have?
Female - surge and tonic center
Male - tonic center only
What is a-fetoprotein produced by? What does it bind to?
Produced by fetal liver
Binds to estradiol-17B and not testosterone
What does a-fetoprotein do in females?
alpha-fetoprotein binds to estradiol-17B, so it can’t cross the blood-brain barrier
What does a-fetoprotein do in males?
alpha-fetoprotein doesn’t bind to testosterone so it can cross the blood-brain barrier
What is aromatization and where does it occur?
Conversion of testosterone to estrogen-18B by aromatase
Occurs in the brain
What is puberty?
Ability to accomplish reproduction successfully
What does pubertal onset require?
Requires development of specific hypothalamic neurons so that there is release of adequate quantities of GnRH at appropriate frequencies
What are the 3 factors puberty is influenced by?
- Acquisition of threshold body size
- Exposure to certain environmental and social cues
- Genetics of animal
What are the 3 different definitions for puberty onset in females?
- Age at first estrus
- Age at first ovulation
- Age at which a female can support pregnancy
What are the 5 different definitions for puberty onset in males?
- Age when behavioral traits are expressed
- Age at first ejaculation
- Age when spermatozoa first appear in ejaculate
- Age when spermatozoa first appear in urine
- Age when ejaculate contains threshold # of spermatozoa
What happens to GnRH pulse frequency after puberty?
^ pulse frequency
^ pulse amplitude
What is age of puberty influenced by?
- breed
- threshold of body size - degree of “fatness”
- external or social factors
What are the external / social factors that influence age of puberty?
- season of birth (sheep)
- photoperiod at time of pubertal onset (sheep)
- presence of opposite sex during peripubertal period (swine and cattle)
- density of housing groups (same sex) (swine)
What causes an increase of GnRH pulses?
acquisition of ability to release high-frequency GnRH pulses from hypothalamic nuclei
Describe preovulatory GnRH surge
GnRH neurons must “fire” frequently and release large quantities of GnRH to indice the LH surge
What does the tonic center do during the preovulatory stage?
Tonic center must also mature in function - regulates tonic frequency of LH surge
What is the main endocrine profile difference between postpubertal males and females?
LH surges in female but there are no LH surges in males
How does degree of “fatness” affect onset of puberty in newborns and growing neonates?
Newborn –> nutrients utilized for maintenance
Growing neonate –> energy consumption increases, body mass increases
This allows use of nutrients for non-essential functions like reproduction
Both age and “fatness” are important to onset of puberty?
How does metabolic status induce puberty?
GnRH neurons are very sensitive to changes in glucose and fatty acids in the blood (females)
What is leptin?
Hormonal peptide produced by fat cells (adipocytes)
Where are leptin receptors located?
liver, kidney, heart, skeletal muscles, pancreas, anterior pituitary, and hypothalamus
What does kisspeptin cause?
Smaller repro tract, never develop puberty when kisspeptin is taken away
How do environmental and social conditions affect the onset of puberty?
In general, sensory neurons of optic and olfactory systems perceive environmental information –> deliver neural inputs to the GnRH neurons of hypothalamus
What is a pheromone?
Chemical in urine recognized by olfactory system
