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DS Unit 4 > Thyroid > Flashcards

Thyroid Flashcards

1
Q

What are the secretory units of the thyroid gland?

A

Follicles

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2
Q

Define colloid

A

amorphous material composed of thyroglobulin and iodinated thyroalbumin

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3
Q

What are the cell types within the thyroid?

A
  1. Follicles
  2. Colloid
  3. Parafollicular (C cells)
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4
Q

What are some examples of thyroid conditions?

A
  1. Goiter
  2. thyroiditis
  3. hypothyroidism
  4. hyperthyroidism
  5. grave’s disease
  6. thyroid cancer
  7. thyroid nodule
  8. thyroid storm
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5
Q

What is the biologically active thyroid hormone?

A

T3

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6
Q

How are T3 and T4 transported in the circulation?

A
  1. Thyroxin binding globulin (TBG)
  2. Thyroxin binding pre-albumin (TBPA)
  3. Albumin
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7
Q

What % of T3 is free?

A

0.2 - 0.4%

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8
Q

What % of T4 is free?

A

0.03%

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9
Q

what is the functional state of the hormone?

A

Free hormones

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10
Q

What is the function of free T4 and free T3?

A
  1. Regulate normal growth and development by maintaining body temperature and stimulating calorigenesis
  2. Affects carbohydrate, lipid and vitamin metabolism.
  3. Fetal and neonatal development also require thyroid hormones
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11
Q

How does low T4/T3 affect TRH and TSH levels?

A

low T4/T3 causes increased TRH and TSH

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12
Q

How do high T4/T3 affect pituitary response to TRH?

A

Inhibits it. Negative feedback loop

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13
Q

What are the indications for TT4?

A
  1. To confirm abnormal (high or low) TSH results.
  2. Diagnose hyperthyroidism
  3. Diagnose primary and secondary hypothyroidism
  4. Monitoring of TSH-suppression therapy
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14
Q

What is the principle thyroid hormone?

A

TT4

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15
Q

What happens when TT4 <2 ug/dL?

A

myxedema coma is possible

Critical value

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16
Q

What happens when TT4 >20 ug/dL?

A

thyroid storm (untreated hyperthyroidism) is possible.

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17
Q

What affects T4 levels?

A

carrier protein levels

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18
Q

What thyroid levels are screened for in newborns in NYS?

A
  1. Initially tests for t4

2. low T4 (lowest 10th percentile) are screened for TSH

19
Q

What conditions are asst. with increased TT4?

A
  1. Patient has undergone iodinated contrast x-ray studies (if a RIA method is used)
  2. Patient taking certain drugs:
    A. patients with increased TBG due to:
    -Estrogens
    -Oral contraceptives
    B. Heroin, amphetamines
    C. Methadone
20
Q

What conditions are asst. with decreased TT4?

A 
1. Patients taking certain drugs:
A. Anabolic steroids
B. Propylthiouracil
C. Barbiturates
D. Furosemide
E. NSAIs (non-steroidal anti-inflammatory)
F. Androgens
21
Q

What is the major biologically active thyroid hormone?

A

Total T3

22
Q

What is the function of TT3?

A

Mainly responsible for the development of the effects of the thyroid hormone on the various target organs.

23
Q

What are the indications for TT3?

A
  1. Diagnosis of hyperthyroidism
  2. Less useful for diagnosis of hypothyroidism
  3. Monitor thyroid replacement and suppressive therapy
24
Q

What are the normal adult T3 levels?

A

70-205 mg/dL

25
Q

What conditions are asst. with increased T3 levels?

A
  1. Pregnancy because serum proteins are increased.
    A. Drugs:
    -Estrogen, methadone
    -Oral contraceptives
26
Q

What conditions are asst. with decreased T3 levels?

A
  1. Anabolic steroids
  2. Androgens
  3. Phenytoin
  4. Propranolol (Inderal)
  5. Salicylate (high doses)
27
Q

When is measuring FT4 more useful than TT4?

A
  1. If changes in thyroid hormone binding proteins occur
    A. Estrogen-containing preparations
    B. During pregnancy
    C. In the presence of a nephritic syndrome
28
Q

What do high levels of FT4 indicate?

A

Hyperthyroidism

29
Q

What do low levels of FT4 indicate?

A

Hypothyroidism

30
Q

What are the adult ri FT4 levels?

A

0.9 - 1.7 ng/dL

31
Q

Treu/false: FT4 should be assessed with every TT4 measurement

A

True

32
Q

What conditions are asst. with increased FT4 levels?

A 
1. Drugs
A. Heparin
B. Aspirin
C. Propranolol
2. Exogenously administered T4
33
Q

What conditions are asst. with decreased FT4 levels?

A

Furosemide
Phenytoin
Methadone

34
Q

What is the clinical usefulness of free thyroxine index?

A
  1. Evaluate thyroid function
  2. It corrects for changes in thyroid hormone binding serum proteins that can affect total T4 levels.
  3. Used to diagnose hyper and hypothyroidism
35
Q

What is the clinical usefulness of FT3?

A
  1. Diagnosing T3 toxicosis (excess amount of T3 is secreted) – a synonym for hyperthyroidism.
  2. Determining the response to therapy
  3. Differentiating early progression of subclinical hyperthyroidism to overt thyrotoxicosis when FT4 is normal and TSH is suppressed. FT3 is usually increased first!
36
Q

What are the adult RI for FT3?

A

200 – 400 pg/dL (2.0 - 4.0 pg/mL)

37
Q

What is the initial thyroid test for thyroid diagnostics?

A

TSH

38
Q

Why is TSH used in newborns?

A

used to detect primary hypothyroidism in newborns with low screening TT4 levels

39
Q

How is TSH correlated to FT3 or FT4?

A

Very slight changes in FT3 or FT4 levels produce a much greater opposite changes in the TSH levels.

40
Q

What do increased serum TSH levels correlate to?

A
  1. primary hypothyroidism

2. thyroiditis

41
Q

What conditions are asst. with decreased TSH serum levels?

A 
1. Secondary hypothyroidism
A. Pituitary or hypothalamus dysfunction
2. 1° hyperthyroidism
3. Exogenous thyroid hormone therapy
4. Treated Grave’s disease 
5. Euthyroid sick syndrome
42
Q

What are the adult RI TSH levels?

A

0.270 - 4.20 uU/mL

43
Q

What are the newborn RI TSH levels?

A

0.400 - 15.0 uU/mL

44
Q

What additional thyroid tests are available?

A
  1. Thyroglobulin
  2. Thyroglobulin antibody
  3. Thyroxin binding globulin (TBG)
  4. Thyroperoxidase (TPO) antibodies

DS Unit 4 (9 decks)

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