07 - (The Hypothalamo-Pituitary-Ovarian Axis)

Question 1

(The Hypothalamo-Pituitary-Ovarian Axis)

(Hypothalamus)

1. Produces Hormones that do what?

(they may either…)

(promote secretion of the anterior pituitary hormone-releasing hormones/factors)

2. what is main example?

(inhibit secretion of the anterior pituitary hormone-inhibiting hormones/factors)

Answer 1

1. control secretion of anterior pituitary hormones
2. gonadotropin releasing hormone (GnRH)

Question 2

(The Hypothalamo-Pituitary-Ovarian Axis)

(Hypothalamus)

1. produces other peptide hormones in cell bodies of another type of its neurones - these are what?
2. Following synthesis these two hormones travel down the long axons of these cells, as they travesrse the infundibular stalk, to finally be released from what?
3. Thus while these are frequently referred to as posterior pituitary hormones based on their site of release… they are actually produced where?

Answer 2

1. oxytocin and vasopressin
2. the posterior pituitary gland
3. the hypothalamus

Question 3

(The Hypothalamo-Pituitary-Ovarian Axis)

(Hypothalamus)

1. Hypothalamic releasing and inhibiting hormones are peptides, and are produced in very small quantities and precisely timed bursts.
2. By secreting in bursts the signal can do what?
3. If diluted in general circulation they would be largely ineffective… why?
4. This loss of fidelity is circumvented by what?

Answer 3

2. be coded for different effects: Amplitude and Freq can be altered independently ( (8A8F, 8A9F, 9A8F, 9A9F))
3. conc would be diluted; fidelity of burst signal would be lost
4. a pathway of blood vessels from the site of hormone release at the base of the hypothalamus (the median eminence) to the anterior pituitary gland (the hypothalamo-hypophyseal portal system) (hypophysis is another name for pituitary)

(This system is unique in having a capillary plexus at both ends, one at the median eminence of the hypothalamus to pick up the hormones, and the second at the anterior pituitary to aid their transport into the relevant target cells. These hormones thus only travel a very short distance in a small volume blood system.)

Question 4

(Gonadotropin Releasing Hormone) (GnRH)

1. Named because it does what?
2. Peptide synthesized in neurons and transported in the nerve axons to the median eminence of the hypothalamus where it is released into what?
3. For its function it is vital that GnRH secretion is what?
4. If you give constant infusions of GnRH you do what?

Answer 4

1. stimulates synthesis and secretion of the gonadotropins (FSH and LH) from anterior pituitary gland
2. the hypothalamo-hypophyseal portal system
3. pulsatile
4. down-regulate the system and secretion of LH and FSH (to a lesser degree) cease

Question 5

(Feedback Control of GnRH secretion)

1. The biggest feedback influences are what?
2. Progesterone does what?
3. Does estrogen exert negative or positive feedback?

Answer 5

1. estrogen and progesterone (the ovarian steroids)
2. acts at the hypothalamus and exerts an inhibitory control of GnRH secretion
3. can do either

Question 6

(estrogen can exert negative or positive feedback)

1. During progesterone dominated luteal phase…. estrogen does what?
2. In the early follicular phase estrogen acts alone to do what?

this action may be exerted where or where?

3. In the late follicular phase, the higher estrogen level does what?

does so by doing what?

also acts on the anterior pituitary to do what?

The sudden increase in GnRH combined with higher pitutiary sensitiviy = ?

Answer 6

1. acts synergistically with progesterone to decrease secretion of GnRH (long term inhibitory effect)

(in animals withot progesterone, low to moderate levels of estrogen inhibit GnRH also)

2. prevent (inhibit) a premature LH surge (the signal that gives rise to ovulation)

hypothalamus (prevent GnRH release)

pitutiary (prevent LH release) (the pituitary “clamp”)

3. switches from being inhibitory to being stimulatory to cause LH surge

causes increased GnRH release (the GnRH surge) (may be a huge continuous release or due to summation of increase of amplitude of each GnRH pulse)

increase sensitivy of gonadotropes to this GnRH

surge release of LH

Question 7

(Anterior Pituitary Gland)

1. synthesizes and secretes what?

Answer 7

1. the glycoprotein hormones FSH and LH (the gonadotropins)

(the action of both these hormones is necessary for normal function of the ovaries)

Question 8

(Control of Gonadotropin Secretion)

(GnRH)

1. the main factor controlling release of what?
2. What is dependent on GnRH in the long term?
3. Secretory episodes of LH can only follow what?
4. FSH release, while stimulated by GnRH, is what?
5. Higher frequency GnRH pulses tend to favor what?

low frequency pulses favor what?

Answer 8

1. gonadotropins
2. maintenance of LH and FSH synthesis and secretion
3. a GnRH pulse (ie LH release is dependent on GnRH)

(consequently secretion of LH is pulsatile with little release between pulses)

4. less closely under its control, significant release can occur (at least in the short term without a GnRH pulse
5. LH release

FSH release

Question 9

(control of gonadotropin secretion)

(estrogen)

1. Most of the actions of estrogen feedback on LH and FSH secretion are mediated via what?
2. It can also do what?

Answer 9

1. its actions on GnRH secretion
2. act directly on the pitutiary

in either an inhibitory (most of the cycle)

or stimulatory (to generate LH surge)

Question 10

(control of gonadotropin secretion)

(progesterone)

1. produced mainly by what?

and as such, is present when?

2. Progesterone appears to act solely on what?

and thus only reduces what?

Answer 10

1. the corpus luteum

the luteal phase of the cycle (or diestrus)

2. the hypothalamus (no direct pituitary action)

gonadotropin (especially LH) secretion by its action on GnRH

Question 11

(control of gonadotropin secretion)

(Inhibin)

1. is a product of what?
2. acts where to do what?

Answer 11

1. granulosa cells of ovarian follicles
2. at pituitary to decrease FSH secretion