CHAPTER 23: Pituitary and Thyroid Hormones

Question 1

Complementary actions of nervous and endocrine system

Answer 1

• work together to maintain internal homeostasis
• integrate body’s response to external environment

Question 2

characteristics of hormones

Answer 2

• produced in small amts
• secreted directly into bloodstream
• travel thru blood to specific receptor sites
• inc/dec normal metabolic processes when reacting w receptor sites
• immediately broken down

Question 3

hypothalamus
- what does it do

Answer 3

• connect nervous and endocrine via PITUITARY GLAND
• secrete peptides or glycoproteins hormones that bind to specific rec sites on target tissues

Question 4

Hypothalamus: Hormones produced/secreted
- RELEASING HORMONES

Answer 4

RH (releasing hormones) stim inner pituitary gland to secrete hormones or other glands./tissues

• growth hormone releasing hormone (GHRH)
• thyrotropin (TRH)
• gonadotropin (GnRH)
• corticotropin (CRH)
• prolactin (PRH)

Question 5

Hypothalamus: INHIBITING HORMONES

Answer 5

• growth hormone release inhibiting factor (somatostatin)
• prolactin inhibiting factor (PIF)

Question 6

HPA: Hypothalamic Pituitary Axis

Answer 6

• hypo secretes releasing factors to cause anterior pit to release stimulating hormones
• hormones act w specific endocrine gland to cause release of hormones or stim cell directly

after…..
- this stimulation shuts down producing RH
- leads to dec stim factors and dec hormone release

Question 7

Hypothalamus: other hormones

Answer 7

• transported to posterior pit gland and released in response to PHYSIO signals
• ADH: antidiuretic hormone/vasopressin
• oxytocin

Question 8

Drugs affecting the thyroid

Answer 8

iodine/iodide
liothyronine (T3)
levothyroxine (T4)
methimazole
PTU
liotrix

Question 9

Thyroid and Parathyroid
- 2 hormones

Answer 9

• using iodine in diet to produce T3 and T4

Question 10

thyroid and parathyroid glands:
-what do they do
- T3 and T4 thyroid hormones

Answer 10

removes iodine from the blood, concentrates it, prepares for attachment to TYROSINE (an AA)

T4: tetraiodothyronine/levothyroxine
T3: triiodothyronine/liothyronine

Question 11

thyroid and parathyroid hormones purpose

Answer 11

thyroid:
- regulate rate of metabolism (of carbs, fats, proteins)
- weight gain/loss
- temp regulation (heat/body temp)
- regulate growth/development
- affect O2 consumption, CO, BV
- affect enz system activity

parathyroid: regulate calcium

Question 12

Thyroid Hormones Synth and Secretion

Answer 12

TRH released by hypo–> stim synth and release of TSH by anterior pit gland

SS (somatostatin) released by hypo–> inhibit TSH synth/release

T3 and T4 circulating conc regulate release of hypo hormones (send signals to make more SS less TRH)

Question 13

T3 vs T4 on synth and secretion

Answer 13

• both can participate in feedback
• T3 signal to anterior pit AND hypo while T4 can only signal to hypo

Question 14

Thyroid Hormones: MOA

Answer 14

T4 inside cell is deiodinated to T3 (most active form)

enters nucleus and binds to specific rec promoting gene expression

Question 15

Thyroid Hormones: Pharmacokinetics

Answer 15

• deiodination major route of METABOLISM (passive difussion or uses transporter)
• food, Ca2+, iron salts, Al containing antacids REDUCE T4 absorption
  ( take on empty stomach )

Question 16

Hypothyroidism

Answer 16

underactive thyroid, thyroid gland doesn’t make enough thryoid hormones

• T4 is preferred over T3 for treatment of hypothyroidism bc better tolerate and LONGER half life

Question 17

Hypothyroidism: Levothyroxine (T4) Adverse effects

Answer 17

• T4 toxicity: nervousness, palpitations, tachy, heat intolerance
• P450 enzyme inducers speed up metabolism of thyroid hormones–> can dec effectiveness

Question 18

Hyperthyroidism

Answer 18

• overactive thyroid gland
• graves disease: autoimmune disease of the thyroid

Question 19

Hyperthyroidism therapy

Answer 19

• dec synth/release of additional hormone
• remove part/or all of thyroid gland
• inhibit synth of hormones
• block release of hormones from follicles

Question 20

if PT removes part/all of the thyroid gland what do they need to be taking?

Answer 20

levothyroxine

Question 21

Inhibiting Thyroid Hormone Synthesis: MOA
PTU and methimazole

Answer 21

• Propylthiouracil (PTU) and methimazole inhibit oxidative processes needed for iodination of Tyrosyl groups and condensation of iodotyr to form T3 and T4
• PTU block periph conversion T4 to T3
• Methim preferred–> longer half-life (can do once daily dosing)

Question 22

Thyroid Hormone Synthesis Inhibition: Cautions
- PTU and methimazole

Answer 22

PTU: recommended during 1st trimester, too many teratogenic effects with methimazole

PTU assoc. with Hepatotoxicity, rarely agranulocytosis (low neutrophil count)

Question 23

Blockade of Hormone Release: IODIDE

Answer 23

• inhibit iodination of Tyr, effect last only few days (wolff-chaikoff effect)
• treat thyroid storm prior to surgery, dec the vascularity of thyroid gland
• oral not useful for long term, thyroid will stop responding after few weeks

Question 24

IODIDE: adverse effects

Answer 24

• sore mouth/throat
• tongue/larynx swelling
• rashes
• ulceration of mucous membranes
• metallic TASTE

Question 25

what is thyroid storm?

Answer 25

lots of thyroid hormones being released in the body can lead to CV effects