endocrine system 1

endocrine system is composed of

hypothalamus, pituitary gland, thymus, thyroid gland, parathyroid glands, adrenal glands, pancreas

endocrine: composed of glands that secrete…

hormones directly into the bloodstream

glands are purely hormonal in function

endocrine glands respond to what kind of signals

chemical signals (i.e. blood levels of ions, other hormones)

control of endocrine system is…

slower and longer lasting

neuroendocrine represents intersection of which two systems?

nervous and endocrine

specialized neuroendocrine cells receive ___ input

neural input via neurotransmitters; respond by releasing hormones into the blood

neuroendocrine control is

fast and directly tied to neural activity

neuroendocrine cells are in what tissues

endocrine tissues, scattered in other organs throughout the body

neuroendocrine cells are

translators; take electrical signals from brain and translate them into chemical signals

endocrine secretion

internal; hormones travel through blood

exocrine secretion

external/luminal; secretions go to body surface or into body cavities

exocrine secretion types

enzymes, fluids, mucus, sweat

endocrine functions onset

slower, longer lasting (systemic)

exocrine onset

usually faster and localized

exocrine system supports

local, physical functions (digestion, lubrication, cooling) through ducts and secretions

endocrine system regulates…

internal physiology by controlling metabolism, growth, homeostasis through hormones

amines

made from amino acids; ex is thyroid hormone, catecholamines

thyroid hormones use ___ for thyroid scans

iodine

catecholamine secreting tumors use what?

MIBG

tumors include adrenal medulla, pheochromocytoma

peptides

short amino acid chains; ex is insulin, PTH

steroids

cholesterol (type of lipid); ex include cortisol, aldosterone, se xhormones

example of steroids imaging in NM

adrenal cortex imaging w NP-59

PET tracers targeting steroid synthesis

when body has enough of a hormone (high supply)…

production slows

negative feedback loops

universal regulatory mechanism used throughout endocrine system

hypothalamic pituitary-target axis

anatomical and functional pathway where negative feedback occurs

chain of control for hypothalamic pituitary target axis

hypothalamus- releases hormone

pituitary- releases stimulating hormone

target gland- releases end hormone

feedback- end hormone inhibits hypothalamus/pituitary

hypothalamus releases what to stimulate anterior pituitary

thyrotropin releasing hormone (TRH)

anterior pituitary, after stimulation from TRH, releases what

thyroid stimulating hormone (TSH)

TSH from anterior pituitary causes thryoid gland to produce what

T3, T4 (triiodothyronine and thyroxine) which is released into the bloodstream

High T3, T4 ___ TRH and TSH release

suppresses

more thyroid hormones causes

faster body functions, and vice versa

main function of T3, T4 is

control of metabolism; regulate body’s metabolic rate

iodine is a structural component to

T3 and T4; it’s used in metabolic process in thyroid cells to produce these hormones

why can RAI be used to image/treat thyroid tissue?

T3, T4 are iodine containing hormones; iodide pulled from blood to synthesize these hormones if thyroid is “hungry” for iodide

thyroid uptake seen on I123/I131 NaI scans reflects what?

how well gland is synthesizing hormones

iodine vs iodide: symbol, charge, uptake in thyroid, NM example

iodine: I, neutral, must be in appropriate chem form, I-123/131

iodide: I-, -1, actively transported by NIS, NaI123/131

iodine is the ___, while iodide is the ___

iodine: element

iodide: negatively charged ionic form of that element

Tc99m sodium pertechnetate accumulates where

in thyroid tissue, mimicking iodine uptake- this is called “thyroid trapping”

RAI shows both trapping and hormone synthesis

higher TSH effect on NM imaging

increased expression of NaI symporters on thyroid cells, and vice versa

maximizes uptake in residual thyroid or cancer tissue

how to increase TSH?

thyroid hormone withdrawal

thyrogen

thyroid hormone withdrawal (THW)

pt stops taking thyroid hormones for 2-3 weeks, causes low T4 levels in blood; pituitary releases more TSH

thyrogen

man made; mimics natural TSH, stimulates remaining thyroid cells to take up iodide

stimulates iodide uptake without causing hypothyroidism

post thyroidectomy, patients take T4; what does this do to pituitary?

pituitary senses adequate T4, keeps lower TSH; helps prevent stimulation or regrowth of any thyroid cancer cells

T4 (thyroxine)

main circulating thyroid hormone

converted into T3 in tissues throughout body

longer half life than T3 (7 days)

thyroid has __ lobes

2; right and left connected by thin isthmus

thyroid pyramidal lobe sometimes extends…

upwards; normal variant, important to recognize on scans

thyroid is made of thousands of what

follicles, lined with follicular cells surrounding colloid

parafollicular (C) cells secrete

calcitonin

follicular cells trap ___, synthesize ___, form ____

trap iodide

synthesize thyroglobulin

form T3/T4

colloid is a storage site for

iodinated thyroglobulin

common focus areas in NM for iodide

hyperactive gland, ectopic tissue, nodules, post surgical remnants

the sodium iodide symporter (NIS) is the plamsa membrane glycoprotein that does what?

mediates active iodide transport in thyroid and other tissues, like salivary/mammary glands, stomach, SI

when iodide enters colloid, it is

oxidized and bound to thyroglobulin

thyroglobulin goes on to make thyroid hormones

biodistribution of Na/I symporters: uptake where

thyroid, choroid plexus, salivary glands, stomach, small intestine

biodistribution of Na/I symporters: early images show

strong stomach wall, then it is secreted into stomach

biodistribution of Na/I symporters: later images show

activity migrating into small bowel; intestinal activity is just excretion