Palmer-Endo- Exam 2- Prolactin and Thyroid- Part 1

Prolactin Releasing hormone is released from what nucleus in the hypothalamus?

What mechanism does PRH use?

-paraventricular nucleus

-phospholipase C mechanism

What inhibits prolactin?

What mechanism does this use?

-dopamine (Prolactin inhibiting hormone PIH)

-adenylyl cyclase mechanism

What is the target of prolactin and what is the targets physiological action?

mammary glands; development and milk production

which hormone "technically" stimulates lactotrophs, but receives the name "prolactin releasing hormone" when acting on lactotrophs?

TRH

Explain how dopamine uses the adenyl cyclase mechanism to inhibit prolactin.

Dopamine D2 receptors inhibit adenyl cyclase activity, which reduces cAMP levels. The decrease in cAMP levels leads to a blockage of IP3-dependent release of Ca2+ from intracellular stores.

What is prolactin responsible for?

What mechanism does it use?

-milk production (lactogenesis)

-tyrosine kinase mechanism

When are prolactin levels high in a woman (normally)?

Does this cause lactation to begin? TQ

-during pregnancy

-lactation does NOT begin during pregnancy due to high levels of estrogen and progesterone down-regulating prolactin receptus (blocking their action)

When prolactin acts on the mammary glands, what three things are occurring?

1. Proliferation

2. Differentiation

3. Lactogenesis

What feedback loop does prolactin use?

positive-feedback loop

(baby suckles-> nerve message to mom's brain->pituitary stimulation)

What three components are synthesized in milk due to prolactin stimulation?

1. Lactose (carb)

2. Casein (protein)

3. Lipids

(all for nourishing babyyyyyy)

What happens to estrogen and progesterone levels at birth?

What does this allow to happen?

-levels DROP

- allows inhibition of prolactin to end. Prolactin then stimulates mammary glands for lactogenesis and lactation can occur

T/F: prolactin only plays a role in lactogenesis and oxytocin is the main hormone in development of breasts at puberty.

FALSE: prolactin is responsible for development of breasts during puberty.

A deficiency in prolactin can be due to ______________________, which is caused by damage or abnormal pressure on the _______________ ___________.

A prolactin deficiency leads to failure to _________________ after giving birth.

hypopituitarism; pituitary gland; lactate

What is the most common cause of prolactin deficiency? TQ

What causes this? (3) TQ

Sheehan syndrome

- caused by

1) excessive blood loss during/after childbirth

2) Head injury

3) Infections

What are the causes of excessive prolactin release? (2)

1) destruction of arcuate nucleus (leading to less dopamine)

2) over-active paraventricular nucleus (releasing too much PRH)

Excessive prolactin secretion has what affect on gonadotropin releasing hormone (GnRH)?

What symptoms does this cause? TQ!

- increase prolactin= decrease GnRH

-causes galactorrhea and infertility

Excessive prolactin (which may lead to galactorrhea and infertility) can be treated with what?

bromocriptine: a dopamine AGONIST

Which three conditions lead to high TRH (which therefore results in high PRH), resulting in excess prolactin.

1) primary hypothyroidism

2) secondary hyperthyroidism

3) tertiary hyperthyroidism

Increased prolactin, leading to decreased GnRH causes what consequence in females?

- inhibit ovulation by decreased FSH and LH being produced. resulting in infertility in most cases

Increased prolactin, leading to decreased GnRH causes what consequence in males?

-Low levels of FSH and LH leading to inhibition of spermatogenesis and results in infertility

Parafolicular cells are also called ___________ and produce _______________.

C-cells; Calcitonin

Which cells of the thyroid produce thyroid hormones?

Follicular epithelial cells

which cells of the parathyroid produce parathyroid hormone?

Chief cells of the parathyroid gland

TRH stimulates ______________ to release____________.

What mechanism does this use?

-TSH; thyroid hormones

-phospholipase C mechanism

TSH stimulates _____________ to release _______________.

What mechanism does this use?

- Thyroid gland; Thyroxine (T3), triiodothyronine (T4)

-adenylyl cyclase mechanism

Thyroid hormones (T3 and T4) utilize what mechanism and why?

-steroid hormone mechanism, since they are amine that are lipophilic (acting like steroid hormones).

TRH is secreted from which hypothalamic nucleus?

paraventricular

What are the two roles of TSH?

1) growth and support of the thyroid gland (trophic effect)

2) secretion of thyroid hormones (T3, T4)

Low blood levels of T3 and T4 from the thyroid gland would cause what reaction to occur?

- stimulate release of TRH (hence overall increased T3, T4 that will be secreted)

Does T3 or T4 have a bigger influence on the hypothalamus and anterior pituitary?

T3

The thyroid produces 20% of __________ and 80% of ____________.

______________ is 3x more active, but has a shorter half life.

T3; T4; T3

What are the target tissues of T3/T4?

Heart, kidney, liver and muscle

What is the protein rich lumen of a follicle called?

colloid

What are the 6 steps of thyroid hormone synthesis?

1. Active transport of Iodide into the follicular cell vis Sodium Iodide Symporter

2. Thyroglobulin (Tg) is formed in follicular ribosomes and placed into secretory vesicle

3. Exocytosis of Tg into the follicle lumen, where is it stored as a colloid.

4. iodide oxidation (to iodine) and iodination of the Tg (Organification)

5. Coupling/Conjugation (MIT and DIT)

6. Endocytosis of iodinated Tg back into the follicular cell using proteolysis

(ATE ICE)

This enzyme oxidizes iodide to iodine in the fourth step of thyroid hormone synthesis? TQ

thyroperoxidase (TPO)

When Iodine bind to the benzene ring on Tyrosine residues of thyroglobulin (Tg), this forms what 2 compounds?

- Monoiodotyrosine (MIT) (1 iodine on ring)

-Diiodotyrosine (DIT) (2 iodine on ring)

MIT + DIT=

DIT + DIT =

(after proteolysis)

-T3

-T4 (happens 10 times faster)