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TERM 3 BIOL2292 PATHO 2 > THYROID DISORDERS > Flashcards

THYROID DISORDERS Flashcards

1
Q

What connects the two lobes of the thyroid?

A

Isthmus

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2
Q

What 3 hormones are secreted by the thyroid gland?

A

T3, T4, and calcitonin

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3
Q

What are 3 components of thyroid gland follicles?

A
  1. Follicular cells (T thyrocytes)
  2. Colloid
  3. Parafollicular cells (C thyrocytes)
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4
Q

What is the site of thyroid hormone synthesis and storage?

A

Colloid within thyroid follicles

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5
Q

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

A

Iodide ions, thyroglobulin

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6
Q

What is the full name of T4?

A

Thyroxin

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6
Q

What is the full name of T4?

A

Thyroxine

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7
Q

What is the full name of T3?

A

Triiodothyronine

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8
Q

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

A
  1. T4 accounts for 90% of thyroid secretions
  2. T3 is much more potent than T4
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9
Q

What is the site of calcitonin secretion?

A

Parafollicular cells

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10
Q

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

A
  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
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11
Q

What are 3 functions of thyroid hormones?

A
  1. Increases basal metabolic rate
  2. Upregulates beta-adrenergic receptors (i.e. increases sensitivity to catecholamines)
  3. Maintains growth & development of all tissues
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12
Q

What is the main cause for goiter?

A

Hyperplasia of thyroid due to excess TSH

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13
Q

What is the simple definition of hypothyroidism?

A

Thyroid hormone deficiency

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14
Q

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

A

Thyroid hormone deficiency causes:
1. Decreased basal metabolic rate

  1. Decreased sensitivity to catecholamines
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15
Q

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

A

Myxedema

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16
Q

What causes myxedema?

A

Deposition of glycosaminoglycans in connective tissue, which holds in moisture

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17
Q

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

A

Myxedema coma

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18
Q

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

A

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

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19
Q

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

A

Congenital hypothyroidism (cretinism)

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20
Q

What are 4 potential causes for congenital hypothyroidism?

A
  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
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21
Q

Why may a newborn with congenital hypothyroidism initially appear asymptomatic?

A

T4 can cross the placenta

22
Q

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

A

Postnatal heel prick

23
Q

What are 3 mechanisms behind Hashimoto’s thyroiditis?

A
  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
24
Q

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

A

Thyroid peroxidase

25
Q

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

A

Damaged follicles release thyroid hormone stores

26
Q

Which thyroid condition affects about 75% of hospitalized patients?

A

Euthyroid sick syndrome

27
Q

Liver enzymes convert T4 into which 2 forms?

A

T3 (more active)
rT3 (inactive)

28
Q

Explain the pathogenesis of euthyroid sick syndrome

A

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

29
Q

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

A

TSH will be normal rather than elevated

30
Q

What is the simple definition of hyperthyroidism?

A

Excessive thyroid hormone secretion

31
Q

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

A

Thyroid hormone excess causes:
1. Increased basal metabolic rate

  1. Increased sensitivity to catecholamines
32
Q

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

A

Radioactive iodine uptake study

33
Q

What class of drugs can be used to treat hyperthyroidism?

A

Thionamides: inhibit thyroid hormone synthesis

34
Q

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

A

Radioactive iodine treatment

35
Q

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

A

Grave’s disease

36
Q

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

A
  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

37
Q

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

A

Inflammatory cytokines cause proliferation of fibroblasts and deposition of glycosaminoglycans

38
Q

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

A

Toxic multinodular goiter (Plummer’s disease)

39
Q

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

A

Heterogenous

40
Q

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

A

Thyroid storm

41
Q

What are 2 potential causes for thyroid storm?

A
  1. Underlying hyperthyroidism
  2. Acute stressors
42
Q

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

A

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

43
Q

Why may iodine be used in treating thyroid storm?

A

Iodine:
1. Inhibits thyroid’s sensitivity to TSH

  1. Prevents release of thyroid hormone
44
Q

Why may glucocorticoids be used in treating thyroid storm?

A

Prevents peripheral conversion of T4 into T3

45
Q

What is the most common treatment for thyroid cancer?

A

Thyroidectomy

46
Q

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

A
  1. Papillary thyroid cancer
  2. Follicular thyroid cancer
47
Q

Name 4 key features of papillary thyroid cancer

A
  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
48
Q

Name 4 key features of follicular thyroid cancer

A
  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
49
Q

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

A

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

50
Q

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

A

Anaplastic thyroid cancer

51
Q

Name 4 key features of anaplastic thyroid cancer

A
  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
52
Q

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

A

Medullary thyroid cancer

53
Q

Name 4 key features of medullary thyroid cancer

A
  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

TERM 3 BIOL2292 PATHO 2 (19 decks)

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