5 - Female Endocrinology & Puberty Flashcards
What cells release FSH and LH? Inhibin?
FSH and LH released by Gonadotroph cells of anterior pituitary
Inhibin released by granulosa cells of the ovary
LH target
Theca interna & luteal cells of the ovary
Inhibin action
Inhibits FSH secretion
LH action
Ovulation, formation of corpus luteum, progesterone secretion
Hypothalamic center(s) in females
Surge center and tonic center
What does the surge center do? The tonic center?
Surge center releases large amounts of GnRH upon stimulation
Tonic center is a constant “drip” released in small concentrations
How is the hypothalamus inherently female?
Male hypothalamus is defeminized during embryogenesis and the GnRH surge center is eliminated
What interaction plays are important role in not defeminizing the female hypothalamus?
Estradiol with the carrier protein “alpha-fetoprotein”
Explain slides 10 and 11
In male hypothalamic development, testosterone is secreted by the testis which does not bind alpha-fetoprotein and diffuses into the brain through the blood-brain barrier. It becomes estradiol in the brain which defeminizes the hypothalamus.
In the female, estradiol is released by the ovaries and is bound by aFP in the bloodstream which prevents it from crossing the blood brain barrier, and the surge center develops.
Explain the positive and negative feedback loops of GnRH secretion by the hypothalamus?
Estradiol has positive feedback on GnRH production of the surge center
Progesterone has negative/modulatory feedback on GnRH production
What regulates FSH secretion of the ________ ________
Inhibin regulates secretion from anterior pituitary
Slide 13**
Super important
Puberty is…
the process of acquiring reproductive competence
Pubescent process in the female involves…
first ovulation, first estrus, ability to maintain pregnancy
What is the limiting factor to the onset of puberty? How?
Hypothalamus
Onset requires secretion of GnRH at frequency and quantity appropriate to stimulate gonadotropin (FSH and LH) release by anterior pituitary
Surge center of prepubertal female cannot release ovulatory levels of GnRH
Theories on why prepubescent surge center can’t release ovulatory levels of GnRH
- Estradiol levels not high enough to provide adequate stimulation to the surge center
- Hypothalamus not able to respond to Estradiol to produce adequate levels of GnRH (too sensitive to recognize + feedback; estradiol suppresses GnRH release)***
Slides 19,20
Diagrams
Age range of puberty in cattle, sheep, dogs, cats
Cattle = 8 (holstein) to 24 months
Sheep = 4-14 months
Dogs = 6-24 months
Cats = 4-12 months
Factors affecting onset of puberty
- Genetic background
- Plane of nutrition
- Rate of growth
- Exposure to environmental cues
Metabolic triggers of puberty
Blood glucose, blood fatty acids, blood leptin
Growth and maturation result in more…
available energy for non-vital physiological functions such as reproduction
What is leptin? What does it do?
Protein hormone expressed by adipocytes (fat cells)
Provides body with an index of nutritional status (increase fat = increase leptin)
Works by affecting hypothalamic centers (feeding beh, hunger, energy expenditure, repro fxn)
What gene codes for the leptin protein
Ob gene
Knock it out = feeding disorder
Slides 25-27
Diagrams
What happened to ovariectomized lambs who could not oxidize glucose (use it for energy)
Decrease in LH secretion bc not enough glucose for GnRH surge
After GnRH injection, there was an LH surge
How does puberty differ in dairy heifers fed high, moderate and low plane nutrition
Puberty occurs earlier and at a lower body weight with high plane nutrition
What environmental conditions affect puberty
- Photoperiod (seasonal breeders)
- Social contact (male-female, female-female)
How does boar exposure and gilt grouping affect puberty?
Exposure to boar accelerates puberty (with or without physical contact)
Gilts in small groups (2-3) had delayed puberty, large groups (>10) had normal puberty
