The Thyroid Hormone- Metabolism and Control Flashcards
THE THYROID
The thyroid gland is responsible for the production of two hormones: _______ and _______
thyroid hormone and calcitonin.
Calcitonin is secreted by _____________ cells and is involved in calcium homeostasis.
parafollicular C
Thyroid Anatomy
The thyroid gland is positioned in the (upper or lower?) (anterior or posterior?) part of the neck and is shaped like a _____.
It is made up of ____ lobes that rest on each side of the _______, with a band of thyroid tissue—called the ________—running anterior to the trachea and bridging the lobes.
Low anterior
butterfly; two; trachea
isthmus
(Anterior or Posterior?) to the thyroid gland are the parathyroid glands that regulate serum calcium levels and the __________ nerves that innervate the vocal cords.
Posterior
recurrent laryngeal
Thyroid Hormone Synthesis
Thyroid hormone is made primarily of the trace element ____, making _______ metabolism a key determinant in thyroid function.
iodine; iodine
The recommended minimum daily intake of iodine is ____ g, If iodine intake drops below ___ g daily, the thyroid gland is unable to manufacture adequate amounts of thyroid hormone and thyroid hormone deficiency—hypothyroidism—results.
150; 50
Thyroid Hormone Synthesis
Thyroid cells are organized into ________.
These are spheres of thyroid cells surrounding a core of a ____ substance termed ________, whose major component is _________, a glycoprotein manufactured exclusively by thyroid ______ cells.
follicles; viscous; colloid
thyroglobulin
follicular
Thyroglobulin is rich in the amino acid _________. Some of these ______ residues can be ________, producing the building blocks of thyroid hormone.
On the outer side of the follicle, _____ is (passively or actively?) transported into the thyroid cell by the —————— located on the basement membrane.
tyrosine; tyrosyl
iodinated
iodine; actively
Na/I symporter
Thyroid Hormone Synthesis
Inside the follicle, catalyzed by a membrane-bound enzyme called __________, concentrated _____ is oxidized and bound with _______ on thyroglobulin.
This results in production of ________ and ————-
This same enzyme also aids in the coupling of _______ to form_________________ or __________
These are the two active forms of thyroid hormone.
thyroid peroxidase (TPO)
iodide; tyrosyl residues
monoiodothyronine (MIT) and diiodothyronine (DIT).
two tyrosyl residues
triiodothyronine (T3)
thyroxin (T4)
Protein Binding of Thyroid Hormone
When released into the circulation, only _____% of T4 and _____% of T3 are unbound by proteins and available for hormonal activity.
0.04; 0.4
The three major binding proteins, in order of significance, are
____________
—————-
_______________.
thyroxine-binding globulin (TBG)
thyroxine-binding prealbumin (TBPA)
albumin
The quantity of T4 and T3 in the circulation can be significantly affected by the amount of binding protein available for carrying these hormones.
T/F
T
high estrogen levels during pregnancy lead to ___eased thyroxine-binding protein production by the liver.
incr
Protein Binding of Thyroid Hormone
High TBG levels result in higher levels of bound thyroid hormones, leading to (low or high?) levels of total T3 and total T4.
In _________ individuals, levels of the active free thyroid hormone remain in the normal range. In some instances, however, measurement of free T4 and free T3 may be necessary to eliminate any confusion caused by abnormal binding protein levels.
High
euthyroid
Control of Thyroid Function
Understanding of the hypothalamic-pituitary-thyroidal axis is essential for correctly interpreting thyroid function testing.
TRH is synthesized by neurons in the _______ and ———— nuclei of the _______ and stored in the _________ of the hypothalamus.
When secreted, this hormone stimulates cells in the ________ gland to manufacture and release ________(_____), which , in turn, circulates to the thyroid gland and leads to increased production and release of thyroid hormone.
supraoptic and supraventricular
hypothalamus; median eminence
anterior pituitary ; thyrotropin (TSH).
TESTS FOR THYROID EVALUATION
______
___________
_______
________
RADIO IODINE (NUCLEAR MEDICINE TECHNIQUES) THYROID ULTRASOUND
FNAC
TSH
T3
T4
THYROID AUTOANTIBODIES
The most useful test for assessing thyroid function is the _______
TSH
TESTS FOR THYROID EVALUATION- Blood Tests
TSH
Over the years, three generations of assays have been developed.
All the assays are capable of diagnosing primary ____thyroidism with _______ levels of TSH.
Second-generation TSH immunometric assays, with detection limits of 0.1 mU/L, can effectively screen for ____________.
Third-generation TSH chemiluminometric assays, with detection limits of 0.01 mU/L, can more accurately _____________________________
hypo; elevated
hyperthyroidism
distinguish between euthyroidism and hyperthyroidism
TSH assays
The sensitivity of the ______-generation TSH assays has led to the ability to detect what is termed _______ disease—or a (mild or severe?) degree of thyroid dysfunction—due to the large reciprocal change in ____ levels seen for even small changes in ______
third; subclinical
TSH
free T4
TSH assays
In subclinical hypothyroidism, the TSH is __________ while the free T4 _______________
Likewise, in subclinical hyperthyroidism, the TSH is ________ while the free T4 is ______.
minimally increased
stays within the normal range.
suppressed; normal
Serum T4 and T3
Serum total T4 and T3 levels are usually measured by ________,__________, or similar immunometric technique.
Because more than _____% of thyroid hormone is protein bound, alteration in _____________, unrelated to thyroid disease, frequently lead to total T4 and T3 levels outside of the normal range.
Because of this, assays have been developed to measure ———- and ———, the biologically active forms of thyroid hormone, and free T4 kits have replaced total T4 determinations.
radioimmunoassay (RIA), chemiluminometric assay
99.9; thyroid hormone–binding proteins
free T4 and T3
Thyroglobulin
This prohormone in the circulation is proof of ___________________. This fact makes thyroglobulin an ideal tumor marker for thyroid cancer patients.
the presence of thyroid tissue, either benign or malignant.
Patients with well-differentiated thyroid cancer who have been treated successfully with surgery and radioactive iodine ablation should have undetectable thyroglobulin levels.
T/F
T
Thyroglobulin
Thyroglobulin is currently measured by double-antibody RIA, enzyme- linked mmunoassay (ELISA), immune radiometric assay (IRMA), and immune chemiluminescent assay (ICMA) methods.
T/F
T
Thyroglobulin
The accuracy of the thyroglobulin assay is primarily dependent on the ________________ used and the absence of _____________________
Even with modern assays, ______________________ interfere with measurements and lead to unreliable thyroglobulin results.
specificity of the antibody
antithyroglobulin autoantibodies
anti thyroglobulin auto antibodes
Thyroglobulin
For this reason, it is critically important to screen for ___________ whenever thyroglobulin is being measured. If antibodies are present, the value of the thyroglobulin assay is marginal.
Approximately ___% of patients with well-differentiated thyroid cancer will have ____________________________.
This is approximately twice as high as in the general population.
autoantibodies
25
anti thyroglobulin autoantibodies
Thyroglobulin
If a patient with well-differentiated thyroid cancer and anti thyroglobulin autoantibodies has been successfully treated with ________ and ___________________, autoantibodies should disappear over time.
surgery and radioactive iodine ablation
Thyroid Antibodies
In autoimmune thyroid disease,antibodies are directed at thyroid tissue with variable responses.
The most common cause of hyperthyroidism is an autoimmune disorder called ___________. The antibody in this condition is directed at the _____ receptor and stimulates the receptor, leading to growth of the thyroid gland and production of excessive amounts of thyroid hormone.
This condition can be diagnosed with tests that detect antibodies to the TSH receptor.
Graves’ disease
TSH
Thyroid Antibodies
____________________________ (TSAb, TSI) use a bioassay to determine presence of autoimmune hyperthyroidism.
Tests for TSH receptor antibodies (TSHR-Ab) can detect antibodies directed against the _______ whether they act to _________ or _____________
Thyroid stimulating antibodies
TSH receptor ; stimulate or block the TSH receptor.
Both stimulating and blocking antibody assays will be positive in 70%–100% of patients with Graves’ disease.
T/F
T
__________________—commonly known as Hashimoto’s thyroiditis—is at the other end of the autoimmune continuum.
Chronic lymphocytic thyroiditis
Hashimoto’s thyroiditis
In this condition, antibodies lead to decreased thyroid hormone production by the thyroid gland.
The best test for this condition is the ___________, which is present in 10%–15% of the general population and 80%–99% of patients with autoimmune hypothyroidism
thyroid peroxidase (TPO) antibody
Nuclear Medicine Evaluation
_____________ is useful in assessing the metabolic activity of thyroid tissue and assisting in the evaluation and treatment of thyroid cancer.
Radioactive iodine
the most common cause of hypothyroidism in the developed world is???
Hashimoto thyroiditis
When radioactive iodine is given ______, a percentage of the dose is taken up by the thyroid gland.
This percentage is called the _____________.
High uptake suggests that the gland is _____________ and ________________________.
Low uptake suggests that the gland is __________________
orally
radioactive iodine uptake (RAIU)
metabolically active and producing significant amounts of thyroid hormone
metabolically inactive.
Because ______ stimulates iodine uptake by the thyroid gland, it is important to interpret the scan with _________ in conjunction with an assessment of ____ levels.
TSH
radioactive iodine
TSH