SM_176b: Thyroid Basic Physiology

Question 1

Describe the anatomy of the thyroid gland

Answer 1

Thyroid gland anatomy

Question 2

Describe the histology of the thyroid gland

Answer 2

Thyroid gland histology

Question 3

____ is most common cause of thyroid disease worldwide

Answer 3

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

Question 4

____ is severely hypothyroid, deaf, cognitive impairment, and no pubertal development

Answer 4

Cretinism is severely hypothyroid, deaf, cognitive impairment, and no pubertal development

Question 5

Describe thyroid hormone function

Answer 5

Thyroid hormone function

• Essential for growth and development of CNS
• Regulates myocardial contraction / relaxation
• Affects GI motility
• Modules energy expenditure
• Modules lipid metabolism

Question 6

Describe hypothalamic-pituitary-thyroid axis

Answer 6

Hypothalamic-pituitary-thyroid axis

1. Hypothalamus via TRH
2. Pituitary via TSH
3. Thyroid via T4 and T3
4. Peripheral cell

Question 7

Describe thyroid cells

Answer 7

Thyroid cells

Question 8

Thyroid hormone largely circulates as ___

Answer 8

Thyroid hormone largely circulates as bound hormone

(thyroid binding globulin)

Question 9

____ has greatest affinity for T4/T3 but serum concentration of ____ is greatest

Answer 9

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)

Question 10

T4 is a ____ that is converted to ____ within various targets

Answer 10

T4 is a prohormone that is converted to T3 within various targets

Question 11

Describe thyroid hormone action

Answer 11

Thyroid hormone action

1. T4 converted to T3 and rT3
2. T3 goes into cell
3. Upregulates transcription

Question 12

___ thyroid hormone receptor does not have T3 binding

Answer 12

TR-alpha-2 thyroid hormone receptor does not have T3 binding

Question 13

-T3 has effect of ____

+T3 has effect of ____

Answer 13

-T3 has effect of gene silencing and histone deacetylation

+T3 has effect of transcriptional activation and histone acetylation

Question 14

Describe biochemical thyroid function tests

Answer 14

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

Question 15

There is an ____ relationship between TSH and T4

Answer 15

There is an inverse relationship between TSH and T4

Question 16

Describe evaluation of hypo/hyperthyroidism

Answer 16

Evaluation of hypo/hyperthyroidism

Question 17

Sensitive TSH assay is ___

Answer 17

Sensitive TSH assay is immunometric

Question 18

____ is used in thyroid cancer surveillance

Answer 18

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

Question 19

Thyroglobulin antibodies may occur in ____ or ____

Answer 19

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

Question 20

____ is the modality of choice for evaluation of thyroid structure, while ____ and ____ can provide functional information

Answer 20

Ultrasound is the modality of choice for evaluation of thyroid structure, while iodine / technetium isotope and PET can provide functional information

Question 21

Ultrasound is used to characterize ____ in the thyroid

Answer 21

Ultrasound is used to characterize structural alterations in the thyroid

• Nodules
• Cysts
• Hashimoto’s thyroiditis
• Graves disease

Question 22

Ultrasound criteria suggestive of malignancy are ____, ____, and ____

Answer 22

Ultrasound criteria suggestive of malignancy are hypoechoic signal, irregular borders, and microcalcifications

• Best technique to search for suspicious lymph nodes in lateral neck

Question 23

Thyroid nodules may be ___, ___, or ___

Answer 23

Thyroid nodules may be cyst, solid, or complex

Question 24

Describe cyst on ultrasound

Answer 24

Cyst on ultrasound

• Echo free center
• Smooth back wall
• Acoustic enhancement

Question 25

Describe solid nodule on ultrasound

Answer 25

Solid nodule on ultrasound

• Many echo reflections
• Back wall indistinct
• No acoustic enhancement

Question 26

Describe complex nodule on ultrasound

Answer 26

Complex nodule on ultrasound

• Cyst and solid features

Question 27

Uptake of tracer can be quantified to estimate ____ and ____

Answer 27

Uptake of tracer can be quantified to estimate metabolic function and radioiodine uptake

• Radionuclides: 123I, 131I, and 99TcO4

Question 28

¹³¹I is used to treat ____ and ____

Answer 28

¹³¹I is used to treat hyperthyroidism and thyroid cancer

Question 29

This is ____

Answer 29

This is Graves disease

Question 30

This is a ____

Answer 30

This is a toxic adenoma

Question 31

Pemberton sign is used to evaluate ____

Answer 31

Pemberton sign is used to evaluate venous obstruction in goiters

• Bilateral arm elevation causes facial plethora (edema)

Question 32

This is ____

Answer 32

This is advanced papillary thyroid cancer

Question 33

¹²⁷I is the ____

Answer 33

¹²⁷I is the most abundant form of iodine

Question 34

_____ is an enlarged thyroid

Answer 34

Goiter is an enlarged thyroid

Question 35

____ are the most prevalent preventable cause of cognitive impairment

Answer 35

Iodine deficiency disorders are the most prevalent preventable cause of cognitive impairment