Hypothalamic-Pituitary Gonadal (HPG) Axis

In the female HPG axis, what is the effect of granulosa cells no longer expressing aromatase?

Decreased estradiol production

What happens to estradiol levels when aromatase is not expressed?

They decrease (low estradiol levels)

How does the body respond to low estradiol levels in terms of hypothalamic and pituitary hormones?

Increased GnRH and LH

What happens to LH levels during negative feedback when estradiol is low?

LH increases

In the male HPG axis, what happens to testosterone levels in response to high LH and FSH?

Testosterone levels increase

In this system, testosterone is considered which type of variable?

regulated variable

Why do testosterone levels change in response to LH and FSH

LH and FSH stimulate the testes to produce testosterone

How is the HPG axis predominantly regulated during the female menstrual cycle?

Mostly through negative feedback

Which phase of the menstrual cycle requires positive feedback?

Ovulation

What is the relationship between estradiol and FSH/LH during negative feedback?

Increased estradiol to decreases FSH and LH

What is the relationship between estradiol and FSH/LH during positive feedback?

Increased estradiol to increases FSH and LH

Female HPG axis relies on…

Positive Feedback

How many main populations of kisspeptin neurons are found in the hypothalamus?

Two

What neurohormone do kisspeptin neurons secrete?

Kisspeptin

Where are kisspeptin neurons located in the hypothalamus?

Arcuate nucleus (ARC) and Anteroventral periventricular nucleus (AVPV)

What is true about the two populations of kisspeptin neurons?

They respond differently to estradiol

When does the switch from negative to positive feedback occur during the menstrual cycle?

just before ovulation

What type of feedback is dominant before the switch occurs?

positive feedback

What causes the switch from negative to positive feedback?

prolonged exposure to estradiol in high quantities

Approximately how long must estradiol levels remain high to trigger the feedback switch?

>~42 hours

What does prolonged high estradiol increase to help trigger positive feedback?

Neural progesterone

What is AVPV?

nucleus in the hypothalamus that contains KP neurons

What is POA?

nucleus in the hypothalamus

What does “AP” stand for in the HPG axis context?

Anterior Pituitary

What is the ovary’s role in this system?

female gland; produces estradiol (E2)

What are astrocytes?

glial cells in the hypothalamus

What does NP stand for?

Neural progesterone

What does E2 refer to?

Estradiol

What is ERα?

A type of estrogen receptor that binds estradiol

ERα primarily binds which hormone?

Estradiol

Where are the kisspeptin neurons located in this section of the HPG axis?

AVPV

Kisspeptin neurons in the AVPV have receptors for which molecules?

Estradiol (E2) and neural progesterone (NP)

What happens when estradiol (E2) and neural progesterone (NP) bind to AVPV kisspeptin neurons?

They release high amounts of kisspeptin

Kisspeptin released from AVPV neurons primarily acts on what?

GnRH neurons

What is the overall effect of high kisspeptin release in this pathway

Increased GnRH neuron activation