CHAPTER 23: Pituitary and Thyroid Hormones Flashcards
Complementary actions of nervous and endocrine system
- work together to maintain internal homeostasis
- integrate body’s response to external environment
characteristics of hormones
- 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
hypothalamus
- what does it do
- connect nervous and endocrine via PITUITARY GLAND
- secrete peptides or glycoproteins hormones that bind to specific rec sites on target tissues
Hypothalamus: Hormones produced/secreted
- RELEASING HORMONES
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)
Hypothalamus: INHIBITING HORMONES
- growth hormone release inhibiting factor (somatostatin)
- prolactin inhibiting factor (PIF)
HPA: Hypothalamic Pituitary Axis
- 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
Hypothalamus: other hormones
- transported to posterior pit gland and released in response to PHYSIO signals
- ADH: antidiuretic hormone/vasopressin
- oxytocin
Drugs affecting the thyroid
iodine/iodide
liothyronine (T3)
levothyroxine (T4)
methimazole
PTU
liotrix
Thyroid and Parathyroid
- 2 hormones
- using iodine in diet to produce T3 and T4
thyroid and parathyroid glands:
-what do they do
- T3 and T4 thyroid hormones
removes iodine from the blood, concentrates it, prepares for attachment to TYROSINE (an AA)
T4: tetraiodothyronine/levothyroxine
T3: triiodothyronine/liothyronine
thyroid and parathyroid hormones purpose
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
Thyroid Hormones Synth and Secretion
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)
T3 vs T4 on synth and secretion
- both can participate in feedback
- T3 signal to anterior pit AND hypo while T4 can only signal to hypo
Thyroid Hormones: MOA
T4 inside cell is deiodinated to T3 (most active form)
enters nucleus and binds to specific rec promoting gene expression
Thyroid Hormones: Pharmacokinetics
- deiodination major route of METABOLISM (passive difussion or uses transporter)
- food, Ca2+, iron salts, Al containing antacids REDUCE T4 absorption
( take on empty stomach )
Hypothyroidism
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
Hypothyroidism: Levothyroxine (T4) Adverse effects
- T4 toxicity: nervousness, palpitations, tachy, heat intolerance
- P450 enzyme inducers speed up metabolism of thyroid hormones–> can dec effectiveness
Hyperthyroidism
- overactive thyroid gland
- graves disease: autoimmune disease of the thyroid
Hyperthyroidism therapy
- dec synth/release of additional hormone
- remove part/or all of thyroid gland
- inhibit synth of hormones
- block release of hormones from follicles
if PT removes part/all of the thyroid gland what do they need to be taking?
levothyroxine
Inhibiting Thyroid Hormone Synthesis: MOA
PTU and methimazole
- 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)
Thyroid Hormone Synthesis Inhibition: Cautions
- PTU and methimazole
PTU: recommended during 1st trimester, too many teratogenic effects with methimazole
PTU assoc. with Hepatotoxicity, rarely agranulocytosis (low neutrophil count)
Blockade of Hormone Release: IODIDE
- 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
IODIDE: adverse effects
- sore mouth/throat
- tongue/larynx swelling
- rashes
- ulceration of mucous membranes
- metallic TASTE
what is thyroid storm?
lots of thyroid hormones being released in the body can lead to CV effects
