SM_176b: Thyroid Basic Physiology Flashcards
Describe the anatomy of the thyroid gland
Thyroid gland anatomy
Describe the histology of the thyroid gland
Thyroid gland histology
____ is most common cause of thyroid disease worldwide
Iodine deficiency is most common cause of thyroid disease worldwide
- Others: congenital hypothyroidism, autoimmune thyroid disease such as Graves disease (hyperthyroidism) or Hashimoto’s thyroiditis (hypothyroidism), thyroid nodules, thyroid carcinomas
____ is severely hypothyroid, deaf, cognitive impairment, and no pubertal development
Cretinism is severely hypothyroid, deaf, cognitive impairment, and no pubertal development
Describe thyroid hormone function
Thyroid hormone function
- Essential for growth and development of CNS
- Regulates myocardial contraction / relaxation
- Affects GI motility
- Modules energy expenditure
- Modules lipid metabolism
Describe hypothalamic-pituitary-thyroid axis
Hypothalamic-pituitary-thyroid axis
- Hypothalamus via TRH
- Pituitary via TSH
- Thyroid via T4 and T3
- Peripheral cell
Describe thyroid cells
Thyroid cells
Thyroid hormone largely circulates as ___
Thyroid hormone largely circulates as bound hormone
(thyroid binding globulin)
____ has greatest affinity for T4/T3 but serum concentration of ____ is greatest
TBG has greatest affinity for T4/T3 but serum concentration of transthyretin is greatest
- More of T3 than T4 is free hormone
- Affinity for T4/T3 is TBG > transthyretin > albumin
- Serum concentrations: albumin (3.5 g/dL), transthyretin (25 mg/dL), TBG (2 mg/dL)
T4 is a ____ that is converted to ____ within various targets
T4 is a prohormone that is converted to T3 within various targets
Describe thyroid hormone action
Thyroid hormone action
- T4 converted to T3 and rT3
- T3 goes into cell
- Upregulates transcription
___ thyroid hormone receptor does not have T3 binding
TR-alpha-2 thyroid hormone receptor does not have T3 binding
-T3 has effect of ____
+T3 has effect of ____
-T3 has effect of gene silencing and histone deacetylation
+T3 has effect of transcriptional activation and histone acetylation
Describe biochemical thyroid function tests
Biochemical thyroid function tests
- TSH
- Total T4
- Total T3
- Free T4, free T3
- Antibodies
- TSH receptor - Graves disease
- Thyroperoxidase - Hashimoto’s thyroiditis
- Thyroglobulin - when measuring thyroglobulin
- Thyroglobulin: tumor marker for papillary and follicula thyroid cancer
- Calcitonin: tumor marker for medullar thyroid cancer
There is an ____ relationship between TSH and T4
There is an inverse relationship between TSH and T4
Describe evaluation of hypo/hyperthyroidism
Evaluation of hypo/hyperthyroidism
Sensitive TSH assay is ___
Sensitive TSH assay is immunometric
____ is used in thyroid cancer surveillance
Thyroglobulin is used in thyroid cancer surveillance
- Detectable thyroglobulin: residual or recurrent thyroid or thyroid cancer tissue
- More thryoid tissue -> higher thyroglobulin level
- Increase in thyroglobulin may only be detectable under conditions of high TSH: withdrawal from thyroid hormone and rhTSH
Thyroglobulin antibodies may occur in ____ or ____
Thyroglobulin antibodies may occur in thyroid cancer or noaml patients
- Can interfere with thyroglobulin measurement
- Thyroglobulin antibodies are an indicator of resideual or recurrent thyroid cancer tissue
____ is the modality of choice for evaluation of thyroid structure, while ____ and ____ can provide functional information
Ultrasound is the modality of choice for evaluation of thyroid structure, while iodine / technetium isotope and PET can provide functional information
Ultrasound is used to characterize ____ in the thyroid
Ultrasound is used to characterize structural alterations in the thyroid
- Nodules
- Cysts
- Hashimoto’s thyroiditis
- Graves disease
Ultrasound criteria suggestive of malignancy are ____, ____, and ____
Ultrasound criteria suggestive of malignancy are hypoechoic signal, irregular borders, and microcalcifications
- Best technique to search for suspicious lymph nodes in lateral neck
Thyroid nodules may be ___, ___, or ___
Thyroid nodules may be cyst, solid, or complex
Describe cyst on ultrasound
Cyst on ultrasound
- Echo free center
- Smooth back wall
- Acoustic enhancement
Describe solid nodule on ultrasound
Solid nodule on ultrasound
- Many echo reflections
- Back wall indistinct
- No acoustic enhancement
Describe complex nodule on ultrasound
Complex nodule on ultrasound
- Cyst and solid features
Uptake of tracer can be quantified to estimate ____ and ____
Uptake of tracer can be quantified to estimate metabolic function and radioiodine uptake
- Radionuclides: 123I, 131I, and 99TcO4
131I is used to treat ____ and ____
131I is used to treat hyperthyroidism and thyroid cancer
This is ____
This is Graves disease
This is a ____
This is a toxic adenoma
Pemberton sign is used to evaluate ____
Pemberton sign is used to evaluate venous obstruction in goiters
- Bilateral arm elevation causes facial plethora (edema)
This is ____
This is advanced papillary thyroid cancer
127I is the ____
127I is the most abundant form of iodine
_____ is an enlarged thyroid
Goiter is an enlarged thyroid
____ are the most prevalent preventable cause of cognitive impairment
Iodine deficiency disorders are the most prevalent preventable cause of cognitive impairment
