THYROID DISORDERS

Question 1

What connects the two lobes of the thyroid?

Answer 1

Isthmus

Question 2

What 3 hormones are secreted by the thyroid gland?

Answer 2

T3, T4, and calcitonin

Question 3

What are 3 components of thyroid gland follicles?

Answer 3

1. Follicular cells (T thyrocytes)
2. Colloid
3. Parafollicular cells (C thyrocytes)

Question 4

What is the site of thyroid hormone synthesis and storage?

Answer 4

Colloid within thyroid follicles

Question 5

What are 2 components that are synthesized to form thyroid hormones?

Answer 5

Iodide ions, thyroglobulin

Question 6

What is the full name of T4?

Answer 6

Thyroxin

Question 6

What is the full name of T4?

Answer 6

Thyroxine

Question 7

What is the full name of T3?

Answer 7

Triiodothyronine

Question 8

What are 2 differences between T3 and T4 in regards to secretion and potency?

Answer 8

1. T4 accounts for 90% of thyroid secretions
2. T3 is much more potent than T4

Question 9

What is the site of calcitonin secretion?

Answer 9

Parafollicular cells

Question 10

What are the 5 steps of the hypothalamic-pituitary-thyroid axis?

Answer 10

1. Hypothalamus secretes TRH (thyrotropin releasing hormone)
2. TRH stimulates anterior pituitary to secrete TSH (thyroid stimulating hormone)
3. TSH causes thyroid to secrete T3 and T4
4. T3 inhibits the anterior pituitary
5. T4 inhibits the hypothalamus

Question 11

What are 3 functions of thyroid hormones?

Answer 11

1. Increases basal metabolic rate
2. Upregulates beta-adrenergic receptors (i.e. increases sensitivity to catecholamines)
3. Maintains growth & development of all tissues

Question 12

What is the main cause for goiter?

Answer 12

Hyperplasia of thyroid due to excess TSH

Question 13

What is the simple definition of hypothyroidism?

Answer 13

Thyroid hormone deficiency

Question 14

What causes the common symptoms of hypothyroidism such as lethargy, bradycardia, and weight gain?

Answer 14

Thyroid hormone deficiency causes:
1. Decreased basal metabolic rate

2. Decreased sensitivity to catecholamines

Question 15

What is the term for generalized non-pitting edema caused by prolonged hypothyroidism?

Answer 15

Myxedema

Question 16

What causes myxedema?

Answer 16

Deposition of glycosaminoglycans in connective tissue, which holds in moisture

Question 17

Patients with myxedema that are exposed to acute stressors have a risk of developing which life threatening condition?

Answer 17

Myxedema coma

Question 18

Why are TSH levels used to diagnose hypothyroidism and not thyroid hormone levels?

Answer 18

Thyroid hormone levels may remain normal for several weeks due to compensatory mechanisms and storage within thyroid follicles

Question 19

What is the term for a severe thyroid hormone deficiency present at birth?

Answer 19

Congenital hypothyroidism (cretinism)

Question 20

What are 4 potential causes for congenital hypothyroidism?

Answer 20

1. Maternal iodine deficiency
2. Thyroid gland does not develop properly or fails to create hormone
3. TSH, T3 or T4 receptor mutations
4. Hypothalamic or pituitary dysfunction

Question 21

Why may a newborn with congenital hypothyroidism initially appear asymptomatic?

Answer 21

T4 can cross the placenta

Question 22

What test is done to determine whether congenital hypothyroidism is present in newborns?

Answer 22

Postnatal heel prick

Question 23

What are 3 mechanisms behind Hashimoto’s thyroiditis?

Answer 23

1. Defect in antigen-specific regulatory T cells
2. B-cells produce autoantibodies against thyroid cells, thyroglobulin, thyroid peroxidase, TSH receptors, or T3/T4
3. Cytotoxic T cells induce thyroid cell apoptosis

Question 24

What enzyme is produced by the thyroid gland to help synthesize thyroid hormones?

Answer 24

Thyroid peroxidase

Question 25

Why may patients with Hashimoto's thyroiditis experience transient hyperthyroidism?

Answer 25

Damaged follicles release thyroid hormone stores

Question 26

Which thyroid condition affects about 75% of hospitalized patients?

Answer 26

Euthyroid sick syndrome

Question 27

Liver enzymes convert T4 into which 2 forms?

Answer 27

T3 (more active) rT3 (inactive)

Question 28

Explain the pathogenesis of euthyroid sick syndrome

Answer 28

In sick patients, inflammatory cytokines inhibit the production of T3 and promote the production of rT3

Question 29

How will the lab value for TSH differ in patients with euthyroid sick syndrome compared to other forms of hypothyroidism?

Answer 29

TSH will be normal rather than elevated

Question 30

What is the simple definition of hyperthyroidism?

Answer 30

Excessive thyroid hormone secretion

Question 31

What causes the common symptoms of hyperthyroidism such as restlessness, palpitations, weight loss, and feeling hot?

Answer 31

Thyroid hormone excess causes: 1. Increased basal metabolic rate 2. Increased sensitivity to catecholamines

Question 32

What kind of test can be done to provide visualization of thyroid function?

Answer 32

Radioactive iodine uptake study

Question 33

What class of drugs can be used to treat hyperthyroidism?

Answer 33

Thionamides: inhibit thyroid hormone synthesis

Question 34

What kind of treatment is used to destroy part of the thyroid?

Answer 34

Radioactive iodine treatment

Question 35

What is the term for hyperthyroidism caused by an autoimmune disorder?

Answer 35

Grave's disease

Question 36

In Grave's disease, what is the name of the activating antibodies created by B-cells, and what do they do?

Answer 36

1. Thyroid-stimulating immunoglobulins (TSIs) 2. a) Act like TSH by binding to TSH receptors on follicular cells b) Have a much more potent effect, are not regulated by negative feedback c) Causes hyperplasia of the thyroid

Question 37

What causes the ocular changes associated with Grave's disease?

Answer 37

Inflammatory cytokines cause proliferation of fibroblasts and deposition of glycosaminoglycans

Question 38

What is the term for thyroid follicular cell hyperplasia due to mutations in TSH receptors?

Answer 38

Toxic multinodular goiter (Plummer's disease)

Question 39

In toxic multinodular goiter, how will the thyroid gland appear on radioactive uptake study?

Answer 39

Heterogenous

Question 40

What is the term for a life-threatening acute release of excessive thyroid hormone?

Answer 40

Thyroid storm

Question 41

What are 2 potential causes for thyroid storm?

Answer 41

1. Underlying hyperthyroidism 2. Acute stressors

Question 42

What is the cause of common symptoms of thyroid storm such as agitation, dysrhythmias, and hyperpyrexia?

Answer 42

Excess thyroid hormone causes: 1. Hypermetabolic state 2. Excess adrenergic state

Question 43

Why may iodine be used in treating thyroid storm?

Answer 43

Iodine: 1. Inhibits thyroid's sensitivity to TSH 2. Prevents release of thyroid hormone

Question 44

Why may glucocorticoids be used in treating thyroid storm?

Answer 44

Prevents peripheral conversion of T4 into T3

Question 45

What is the most common treatment for thyroid cancer?

Answer 45

Thyroidectomy

Question 46

What are 2 types of thyroid cancer that are characterized by differentiated malignancy of follicular epithelial cells?

Answer 46

1. Papillary thyroid cancer 2. Follicular thyroid cancer

Question 47

Name 4 key features of papillary thyroid cancer

Answer 47

1. Most common thyroid Ca 2. Can metastasize via lymph but usually does not spread beyond neck 3. Slow growing 4. No colloid: hormonally inactive

Question 48

Name 4 key features of follicular thyroid cancer

Answer 48

1. Uni-nodular: presents as one big mass 2. Can metastasize via blood to lung & bones 3. Acts like normal thyroid tissue (i.e. uptake of iodine, production of thyroid hormones) 4. Encapsulated

Question 49

Although it is more aggressive, why does the prognosis for follicular thyroid cancer remain positive?

Answer 49

Because the malignant cells behave like normal thyroid tissue (i.e. takes up iodine), they can be targeted by radioactive iodine

Question 50

Which type of thyroid cancer is characterized by undifferentiated malignancy of follicular epithelial cells?

Answer 50

Anaplastic thyroid cancer

Question 51

Name 4 key features of anaplastic thyroid cancer

Answer 51

1. Rarest form of thyroid cancer 2. Presents as rapid painful enlargement of thyroid 3. Aggressive metastasis 4. Poorly differentiated, disorganized cells with irregular nuclei

Question 52

Which type of thyroid cancer is characterized by malignancy of parafollicular cells (C-thyrocytes)?

Answer 52

Medullary thyroid cancer

Question 53

Name 4 key features of medullary thyroid cancer

Answer 53

1. Uni-nodular 2. Increased calcitonin secretion, normal thyroid function tests 3. Metastasizes through lymph and blood 4. Poorly differentiated cells that form clusters/"nests" in between thyroid follicles