Thyroid Function Flashcards
What are the two types of cells in the thyroid gland?
Follicular and parafollicular
What thyroid hormones do follicular cells make and secrete?
T4 (L-thyroxine)
T3 (L-triiodothyronine)
rT3 (reverse T3 (biologically inactive))
Where are hormones stored in follicular cells?
Lumina of the follicle
What hormones do parafollicular cells secrete?
Calcitonin (involved in calcium regulation)
List the functions that thyroid hormones are involved in
Rate of O2 consumption
Growth
Sexual maturity
Protein and carbohydrate metabolism
TRH
Released by hypothalamus and stimulates anterior pituitary to secrete TSH
TSH
Regulates synthesis and release of the thyroid hormones
What regulates the secretion of TSH?
TRH
somatostatin: inhibitory factor
FT3 and FT4: stimulate hypothalamus to secrete somatostatin. Exert neg feedback to anterior pituitary to inhibit TSH secretion
H-P-T axis
The negative feedback loop of TRH and TSH
Thyroid hormones circulate the blood bound to what?
Thyroxine-binding globulin (TBG)
Thyroxine-binding prealbumin
Thyroxine-binding albumin
T/F:
Biologically inactive = physiologically active
TRUE
What is the function of TBG?
Principle carrier protein
FT3 and FT4 are physiologically ___
Active
T/F:
T3 is 4-5 times more metabolically potent than T4
TRUE
What is the most useful test for assessing thyroid function
TSH
Characteristics of hypothyroidism
TSH is minimally increased
FT4 stays within normal range
Characteristics of subclinical hyperthyroidism
TSH is low
FT4 is normal
T/F:
Up to 90% of thyroid hormone are protein bound
FALSE
MORE than 99.9% of thyroid protein are protein bound
T/F:
alteration in thyroid hormone binding proteins frequently lead to total T4 outside of normal range without representing true clinical thyroid dysfunction
TRUE
Thyroid produces approximately ___% of T3
20%
T3 contains 3 atoms of ___
Iodine
T/F:
FT4 makes up a large fraction of total thyroxine
FALSE
Small fraction because most are bound to thyroid carrier proteins
FT4 is the ___ ___ fraction of T4
Biologically active! It can enter the tissues.
FT3 is elevated in ___
Hyperthyroidism
What can cause the leakage of Tg into the bloodstream
Destruction through autoimmune hypothyroidism
OR
Inflammation of the thyroid
In what condition do we see anti-Tg autoantibodies in 12%-30% of patients?
Grave’s disease
What antibody does this describe:
Active, complement, and play an important role in the pathogenesis of hypothyroidism
CHECK THIS NOTECARD BECAUSE THE SLIDE NEEDS TO BE FACT CHECKED
Thyroperoxidase antibody (TPO)
The production of this stimulating antibody can cause all forms of autoimmune thyrotoxicosis
Thyrotropin Receptor Antibody (TRAb)
Grave’s disease is the most common cause of ___
Hyperthyroidism
Hashimoto’s thyroiditis causes ___
Hypothyroidism
In Grave’s disease, ab are produced that are directed at ___ ____
TSH Receptor (TSHR)
In what condition can we observe the growth of the thyroid gland and goiter?
Grave’s Disease
In what condition to antibodies lead to decreased thyroid hormone production as the thyroid gland is being destroyed
Hashimoto’s thyroiditis
What does low Radioactive iodine uptake (RAIU) suggest?
Gland is metabolically inactive
What does high Radioactive iodine uptake (RAIU) suggest?
Gland is metabolically active and producing significant amounts of thyroid hormone
Why would we use a thyroid ultrasound?
To detect non-palpable nodules using high frequency sound waves
What is a fine needle aspiration (FNA) biopsy?
First step and most accurate tool in the evaluation of thyroid nodules in the absence of hyperthyroidism
How is hypothyroidism defined?
Low FT4
Normal-High TSH
List primary conditions of hypothyroidism
Hashimoto’s
Treatment for toxic goiter
Excessive Iodine Intake
Subacute thyroiditis
What is a secondary condition of hypothyroidism
Hypopituitarism
What is a condition of tertiary hypothyroidism
Hypothalamic dysfunction
What is thyrotoxicosis?
Many findings that result when peripheral tissues are presented with, and respond to, and excess of thyroid hormone
What are potential causes of thyrotoxicosis?
Excessive thyroid hormone ingestion
Leakage of stored thyroid hormone from thyroid follicles
Excessive thyroid gland production of thyroid hormone
What are symptoms of Grave’s disease
Thyrotoxicosis, goiter, opthalamopathy, dermopathy (orange peel skin(
How do you treat thyroid disease associated with Grave’s?
1) Medication
2) Radioactive Iodine
3) Surgery
What causes a toxic adenoma?
Autonomously functioning thyroid tissue (no TSH needed)
What are treatment options for toxic adenoma / multinodular goiter
1) Surgery
2) Radioactive iodine
3) Thyroperoxidase inhibitor medications
T/F:
Radioactive iodine often kills both the hyperactive nodule as well as functioning thyroid tissue
FALSE
Tends to only kill hyperactive nodules, leaving behind functioning thyroid tissue
Amiodarone-Induced Thyroid Disease
A drug used to treat cardiac arrhythmias that that interfere with normal thyroid function
What are characteristics of amiodarone?
A drug that is fat soluble with a long half life of 50 days
Subacute thyroiditis
Conditions associated with inflammation of the thyroid gland, leakage of stored thyroid hormone, followed by repair of the gland
What is the most common form of subacute thyroiditis?
Postpartum thyroiditis (5-9% of women in postpartum)
TSH, T3, and FT4 in nonthyroidal illness and thyroid nodules
LOW TSH
LOW T3
LOW FT4
T/F:
Thyroid nodules are common and are often not thyroid cancer
TRUE
What is nonthyroidal illness or euthyroid sick syndrome?
Abnormalities in thyroid function tests without thyroid dysfunction
(Often in hospitalized or critically ill patients)