thyroid function Flashcards
what two cells are in the thyroid gland
follicular and parafollicular
describe the follicular thyroid cells
single layer epithelial cells in a sphere
what hormones are made and secreted by follicular cells
T4
T3
rT3
what is T4
L-thyroxine
what is T3
L-triiodothyronine
what is rT3
reverse T3
where are hormones stored in the follicular cells
lumina follicle
what does the parafollicular cells secrete
calcitonin
what do thyroid hormones regulate
- rate of O2 cosumption
- heat production
- growth
- secual maturity
- protein and carbohydrate metabolism
describe the hormone pattern of the hypothalamic pituitary thyroid axis
hypothalamus released TRH -> stimulates anterior pituitary secretes TSH -> releases T3 and T4
what regulates TSH secretion
- TRH
- somatostatin
- FT3
- FT4
true or false
FT3 and FT4 stimulate the release of somatostatin from hypothalamus
true
amount of secreted T4 that converts to T3
40%
what is the process of T4 converting to T3
monodeionidination
how much T3 (converted from T4) is converted to rT3
45%
true or false
rT3 is biologically inactive
true
what do thyroid hormones bind to in blood ciruclation
- Thyroxin-binding globulin (TBG)
- thyroxine-binding pre-almbumin
- thyroxine-binding albumin
what is the principle thyroid hormone carrier protein
TBG (thyroxine binding globulin)
what forms of T3 and T4 are active
free forms
which thyroid hormone is more potent, T3 or T4
T3
- 4-5 times more potent
name the disorder:
low to none T3 or T4, increased TSH
hypothyroidism
name the disorder:
T3 and T4 increases, low TSH
hyperthyroidism
what is the most useful test for assessing thyroid function
TSH
describe subclinical hypothyroidism
TSH minimally increased, FT4 in normal range
describe subclinical hyperthyroidism
low TSH, normal FT4
what impacts T4 levels the most
alteration in thyroid hormone-binding proteins WITHOUT representing true clinical thyroid dysfunction
how much T3 is made from originally secreted T3
20%
the other 80% is from converted T4
how many atoms of iodine are attached to T3
3 atoms of iodine
describe Ft4
able to enter tissues = active fraction
describe FT3
present in low numbers - not measured as much
-> increased in hyperthyroidism
describe thyroglobulin antibody testing
leakage of thyroglobulin Ab into blood stream is measured for autoimmune hypothyroidism
describe thyroperoxidase antibody test
TPO Ab activate compliment in hypothyroidism
- early indicatory
describe thyrotropin receptor antibody test
bind TSH receptor to stimulat thyroid gland independent of TSH
present in all forms of autoimme thyrotoxicosis
describe grave’s disease
- autoimmune hyperthyroidism
- antibodies bind TSH receptor to stimulate thyroid gland
- TSH independent release of thyroid hormones
describe hashimoto’s thyroiditis
- autoimmune hypothyroidism
- antibodies destroy thyroid glands
- increased amount TPO antibodies
name the disorder
- T4: decrease
- T3: decrease
- FT4: decrease
- TSH incerease
primary hypothyroidism
name the disorder
- T4: decrease
- T3: decrease
- FT4: decrease
- TSH: decrease
secondary hypothyroidism
name the disorder
- T4: increase
- T3: increase
- FT4: increase
- TSH: decrease
primary hyperthyroidism
nuclear medicine evaluation
radioactive iodine
- measures metabolic activty of thyroid gland based on radioactive iodine take up
- iodine is necessary for thyroid hormone formation = measuring amount taken reflects amount made
thyroid ultrasound
nodule detection
fine needle aspiration
evaluation of thyroid nodules (cellular structures) in absence of hyperthyroidism
what is the most common disorder of the thyroid gland
hypothyroidism
describe thyrotoxicosis
peripheral tissues are presented with (and respond to) excess of thyroid hormone
describe symptoms of Grave’s disease
- thyrotoxicosis
- goiter
- big eyes
- orange peel skin
describe toxic adenoma and multinodular goiter
caused by autonomously functioning thyroid tissue (acts w/o TSH)
present hyperthyroidism
describe amiodarone-induced thyroid disease
- high levels of iodine in drug
- causes inhibiton of thyroid hormone production
- can cause hypothyroidism that overcorrects to hyperthyroidism
- drug treats cardiac arrythmias
describe subacute thyroiditis
inflammation of the thyroid gland, leakage of stored thyroid hormone and repair of the gland
