Sex differentiation pt 2 Flashcards
What is the hypothalamo-pituitary-gonadal axis?
It is the interaction between the brain (hypothalamus), pituitary gland, and gonads. Gonads stimulate gametogenesis and hormonogenesis. Hormonogenesis also leads to electrolyte homeostasis, fuel and protein metabolism, and adiposity and muscle mass.
How does the hypothalamo-pituitary-gonadal axis affect different stages of life?
It firstly affects sex determination in the fetus, especially in males. Then it affects sexual changes in puberty for both sexes. Sex hormones then have a special role during pregnancy and parturition in the female (augmented by placental hormones). It finally is important in both sexes at menopause and andropause.
What are plasma testosterone levels like throughout life?
There are two medium peaks (around 250ng/dL) at both fetal and neonatal periods, then it stays low during pre-pubertal phase, and has its highest peak around 500ng/dL, and starts decreasing once adulthood kicks in.
How does DHEAS (dehydroepiandrosterone sulfate) change with age?
it increases and peaks around 25 years old, for both male and female. It shows the change in adrenal androgen expression (adrenarche).
What are the changes in plasma concentration for FSH and LH in male and women?
Male: FSH levels increase constantly but more at stage 2, as LH increases slightly throughout all puberty.
Female: FSH increases and stabilizes towards stage 4-5, as LH increases slowly and peaks at mid puberty (stage 3) until end of puberty (stage 5).
What do the different stages of puberty mean for male and female?
There are 5 stages for puberty:
Male - stage 2 is beginning enlargement of testes, stage 3 is penile enlargement, stage 4 is growth of the glans penis and stage 5 is adult genitalia.
Female - stage 2 is breast buds, stage 3 is elevation and enlargement of breasts, stage 4 is the projection of areolas and stage 5 is adult breasts.
Where does the word puberty come from and what it means?
It is from the latin puberta, which means “to grow hair”.
Puberty includes all of the physiological, morphological and behavioural changes that occur in the growing animal as gonads/brain/phenotype change from adolescent to adult.
What marks the beginning of puberty in female and male?
Male: first ejaculation (semarche)
Female: first cycle (menarche)
These events do not signify fertility though.
How is puberty controlled by GnRH?
Neural mechanisms regulate the pulsatilty GnRH from the hypothalamus (Adult = 90 minutes; Puberty = diurnal). The pulsatile release regulates sexual development. LH, FSH and GnRH are present before puberty but are not released until then because tonic centers are extremely sensitive to negative feedback.
What are two ways to induce pulsatile release of GnRH?
- Gonadotropins can stimulate the pulsatile release of gonads in children
- Administering GnRH in a pulsatile fashion can induce menstrual cycle in monkeys
How do the GnRH neurons work before puberty?
In both female and male, GnRH neurons in both tonic center and surge center of the hypothalamus release low amplitude and low-frequency pulses of GnRH.
How do the GnRH neurons work after puberty?
In female, the tonic center controls basal levels of GnRH but they are higher than in the prepubertal female because the pulse frequency increases. the surge center controls the preovulatory surge of GnRH.
In male, there is no development of a surge center.
What is the overall endocrine mechanism of puberty?
At the onset of puberty, levels of GnRH rise (both amplitude and frequency). Increased pulses secreted from the hypothalamus cause by a decreased sensitivity of tonic center in order to negative feedback from gonadal steroids (surge center doesn’t change sensitivity, simply that E2 levels aren’t high enough to stimulate the surge release before puberty).
What happens in response to increased pulses of LH/FSH?
Levels of steroids increase to support spermatogenesis or folliculogenesis.
What is kisspeptin (KISS1) and what does it do?
KISS1 is secreted from neurons whose cell bodies are located in the anteroventral periventricular (AVPV) and arcuate (ARC) nuclei of the hypothalamus. It signals through its receptor (KISSR1) to regulate pulsatile secretion of GnRH from GnRH neurons.
What are GnRH neurons?
They are KISS peptin neurons, and they develop during puberty. These regulate the release of GnRH associated with development. KISS peptin alters pulsatility of GnRH, which in turn regulates the pulsatility of FSH and LH.
Explain the estradiol-kisspeptin- GnRH positive feedback circuit.
Rising levels of estradiol act to increase kisspeptin expression that then amplifies GnRH neuron activity in a positive feedback manner leading to the completion of puberty onset. After puberty onset, kisspeptin levels fluctuate with the cyclical levels of estradiol to drive the generation of the preovulatory GnRH/LH surge.
What is the relationship between age of puberty and body weight in girls?
Age of puberty in girls has been changing but the body weight has not; constant at 47kg is the weight that must be obtained for the activation of the hypothalamic-pituitary-gonadal axis.
How has the timing of puberty changed over time?
It has become earlier over the past century due to better nutrition and health, so achieving a weight of 47kg is faster.
What are the 3 types of GnRH pulsatility?
A. Pulsatile GnRH (amplitude and frequency modulated by steroid feedback). Pulsatile LH/FSH (response to GnRH modified by estrogen feedback).
B. Long-acting GnRH analog will cause desensitization because will want to reproduce pulsatility factor to stimulate the reproductive axis
C. Reduced (or absent) GnRH will require exogenous GnRH, causing little or no gonadotrophin response.
