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CC2 (lab)- Endocrinology > Thyroid Gland > Flashcards

Thyroid Gland Flashcards

1
Q

Shape of Thyroid gland

A

butterfly-shaped

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2
Q

This separates the lobes of Thyroid gland

A

Isthmus

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2
Q

How much does thyroid gland weighs?

A

15-25g

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3
Q

Thyroid gland starts to produce hormones at?

A

11 week gestation

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4
Q

The thyroid gland straddles the?

A

Trachea

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5
Q

Cells of the thyroid gland

A
  • Follicular epithelium = T3, T4
  • Parafollicular cells = Calcitonin
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5
Q

LARGEST ENDOCRINE GLAND

A

Thyroid gland

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6
Q

What is the function of thyroid gland?

A

Produce thyroid hormones and iodine storage

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7
Q

Normal Thyroid iodide to plasma iodide ratio

A

25-40:1

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8
Q

Needed for Hormone synthesis

A

Iodine

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9
Q

Intake of Iodine that can cause hormone secretion deficiency

A

<50ug/day

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10
Q

Intake of Iodine for normal function

A

1mg/week (150ug/day)

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11
Q

Absorbs iodine (ring shape)

A

Follicles

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12
Q

Organized thyroid cells

A

Follicles

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13
Q

Reservoir of materials for hormone production

A

Colloid

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14
Q

Colloid is rich in glycoprotein….?

A

thyroglobulin

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15
Q

Colloid is surrounded by?

A

Follicle

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16
Q

A viscous substance

A

Colloid

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17
Q

Group of thyroglobulin

A

tyrosyl group

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18
Q

Thyroglobulin is rich in?

A

tyrosine

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19
Q

Major component of colloid

A

thyroglobulin

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20
Q

Thyroglobulin is synthesized by?

A

follicles

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21
Q

Reflect thyroid mass, injury & TSH receptor stimulation

A

Thyroglobulin

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22
Q

Presence of Thyroglobulin in the blood indicates?

A

Tumor (malignant/benign)

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23
Q

Thyroglobulin is increased in what conditions?

A

Grave’s disease, thyroiditis, and nodular goiter

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23
Q

Biosynthesis is controlled by?

A

Thyroid-stimulating hormone (TSH)

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24
Q

Steps in biosynthesis

A
  1. Iodide trapping/uptake (by Na-iodide symporter)
  2. Oxidation
  3. Iodination of tyrosyl residues by TPO (at thyroglobulin)
  4. Coupling/Condensation reaction
  5. Thyroglobulin is then moved to the colloid for storage
  6. Exocytosis of colloid droplets
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24
Q

In Iodide trapping/uptake (by Na-iodide symporter), the iodide diffuses into the?

A

lumen

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25
Q

Ratio of Lumen iodide to follicular iodide

A

5:1

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26
Q

In oxidation, the iodide is converted to elemental iodide by?

A

thyroid peroxidase enzyme

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26
Q

At basal membrane of follicular cells

A

Iodide trapping/uptake (by Na-iodide symporter)

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27
Q

Where does the iodination of tyrosyl residues by Thyroid peroxidase (TPO) occur?

A

at thyroglobulin

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28
Q

Iodothyronine formed at the optical barrier, follicular cells result in?

A

Monoiodothyronine & Diiodothyronine

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29
Q

T4

A

DIT + DIT by TPO

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29
Q

T3

A

MIT + DIT

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30
Q

In the fifth step in biosynthesis, where is thyroglobulin moved?

A

To the colloid for storage

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30
Q

T4 binding proteins

A

99.95% T4=Plasma protein
0.05%=Free

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31
Q

How many percentages of T4 in:
- TBG
- TBPA
- TBA

A
  • TBG: 75% of T4
  • TBPA: 15-20% of T4
  • TBA: 9% of T4
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32
Q

Thyroxine-binding globulin (TBG) is measured by?

A

immunoassay

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33
Q

These affect TBG, T4 binding

A

Salicylates, phenytoin, penicillin, heparin

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34
Q

How many percentages of T3 in:
- TBG
- TBPA
- TBA

A
  • TBG: 99.5%
  • TBPA: very low
  • TBA: none!!!
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35
Q

Theese increase biologic activity of T3 & T4

A
  • decreased/low affinity of T3 to binding protein
  • increased or high free T3 in plasma
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36
Q

Physiologic Actions of Thyroid gland

A
  1. Basal Metabolic Rate
  2. Tissue growth – (with GH & Somatomedin)
  3. CNS development
  4. Autonomic Nervous System (ANS)
  5. CV & Respiratory Systems
  6. GIT
  7. Skin
  8. Lactogenesis
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37
Q

A physiological action of the thyroid for Heat generation

A

Basal Metabolic Rate

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38
Q

A physiological action of the thyroid that is dependent on TH in the prenatal period

A

CNS development

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38
Q

A physiological action of the thyroid for normal bone growth, formation & maturation

A

Tissue growth with GH and somatomedin

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39
Q

A physiological action of the thyroid that controls oxygen consumption and ensures oxygen delivery to tissue

A

Cardiovascular (CV) and Respiratory system

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40
Q

A physiological action of the thyroid for increase motility, secretion, absorption

A

GIT

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41
Q

Main serum carrier of T3 and T4

A

Thyroxine-binding Globulin (TBG)

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42
Q

A physiological action of the thyroid for increase heat production, sweating

A

Skin

43
Q

This is for deiodination

A

Iodothyronine 5’- deiodinase

44
Q

For T3 circulation (most abundant)

A

Type 1 Iodothyronine 5’- deiodinase

45
Q

found in the brain, maintains T3 levels in CNS

A

Type 2 Iodothyronine 5’- deiodinase

46
Q

Where is the Type 1 Iodothyronine 5’- deiodinase found?

A

Liver and kidney

47
Q

Ratio of T4:T3 in blood

A

20:1

47
Q

This is from direct TG secretion (6-7 days)

A

T4 (major)

48
Q

Most of the Plasma T3-derived

A
  • Extrathyrodial deiodination
  • Liver/Kidney
  • Peripheral tissue
48
Q

T4 accounts for 80% of plasma T3

A

Extrathyrodial deiodination

49
Q

This deiodinate T4

A

Liver/Kidney

50
Q

T4 -> T3/rT3

A

Peripheral tissue

51
Q

Inactive (high in newborns)

A

(reverse)rT3

51
Q

This is more active

A

T3

52
Q

TH (thyroid?) is metabolized by?

A

deiodination, deamination, and conjugation by glucoronic acid

52
Q

Not useful in diagnosing hypothyroidism because levels
are not reduced until they become severe

A

T3

52
Q

3rd major circulating thyroid hormone

A

rT3

52
Q

rT3 is caused by the removal of?

A

Removal of 1 iodine from inner ring of T4

52
Q

Half-life of T4 (T4 metabolism)

A

4 hrs half-life

52
Q

rT3 is elevated in patients with?

A

Euthyroid sick syndrome

53
Q

Used to assess borderline or conflicting laboratory results

A

rT3

54
Q

In the Hypothalamic-pituitary-thyroid axis, if low TH it results in?

A

Increase TRH & TSH

54
Q

In the Hypothalamic-pituitary-thyroid axis, if increased T3, T4 it results in?

A

decrease TRH & TSH

54
Q

High serum iodide results in?

A

transport inhibited, high DIT, T4

55
Q

MAJOR fraction of Organic iodine

A

Tetraiodothyronine (T4)

56
Q

physiologically active form of T3 & T4

A

FT3 & FT4

56
Q

Low serum iodide results in?

A

more absorbed, high MIT, T3

57
Q

Indicator of thyroid secretory rate

A

Serum T4

57
Q

Principal secretory product

A

Tetraiodothyronine (T4)

58
Q

Increase T4 results in?

A

no TSH!!!

59
Q

This is done after the hormone is separated from the protein

A

Immunoassay

60
Q

With most hormonal activity

A

Triiodothyronine (T3)

60
Q

How many percent of T3 from tissue deiodination of T4
(outer ring)

A

75-80%

61
Q

Triiodothyronine (T3) is used for diagnosing?

A

T3 thyrotoxicosis

61
Q

Indicator of recovery or recurrence of Hyperthyroidism (low in cord blood)

A

Triiodothyronine (T3) – “3, 5, 3’ TriIodothyronine”

62
Q

1st seen in hyperthyroidism

A

Increase T3

63
Q

Triiodothyronine (T3) is measured by?

A

competitive immunoassay

64
Q

Increase T3 and T4, decrease TAG levels

A

HYPERTHYROIDISM

65
Q

Signs and symptoms of HYPERTHYROIDISM

A
  • Heat intolerance (increase sweating)
  • Emotionally labile
  • Tachycardia
  • Unexplained weight loss
  • Tremors, restlessness, hyperkinesis, anxiety,
    irritability
  • With diarrhea and increased appetite
65
Q

Decrease T3 and T4, increase TAG level

A

HYPOTHYROIDISM

66
Q

Signs and symptoms of HYPOTHYROIDISM

A
  • Cold intolerance (decrease sweating)
  • Bradycardia, Fatigue
  • Dryness of skin
  • Unexplained weight gain, dyspnea, hair loss
  • Mental dullness, muscle weakness, constipation
  • Yellow discoloration of skin (hypercarotenemia)
  • Decrease Na+, increase CK
67
Q

Severe hypothyroidism leads to?

A

Pleural and Peritoneal effusions, irregular mens, periorbital edema, myopathy, anemia

68
Q

increase T3,T4, FT4, rT3; decrease TSH, normal TBG

A

Primary Hyperthyroidism

69
Q

increase T3, T4, and TSH! (Pituitary problems)

A

Secondary Hyperthyroidism

70
Q

Increase: aTPO, ATG, TBII, TSI

A

Primary Hyperthyroidism

70
Q

“TSH” to compare with primary

A

Secondary Hyperthyroidism

70
Q

With diffuse toxic goiter

A

Grave’s disease

71
Q

With Exophthalmos and Pritibial Myxedema

A

Grave’s disease

71
Q
  • most common, autoimmune
  • Due to circulating antibodies to TSH receptor
A

Grave’s disease

71
Q

Grave’s disease is how many times more common in girls?

A

6x

71
Q

Test for Grave’s disease

A

TSH receptor antibody test

72
Q

Low TBG = Low T4, normal FT4 and TSH

A

Nephrotic syndrome, Decrease Protein production

72
Q

Low TSH, normal FT3 & FT4
- without symptoms

A

Subclinical Hyperthyroidism

72
Q

Thyroid is woody/stony hard mass

A

Riedel’s thyroiditis

73
Q

High Estrogen = high TBG = increase binding capacity = increase total T4 and T3, normal FT4, T3 and TSH (due to negative feedback of anterior pituitary)

A

Pregnancy

73
Q

Decrease T3, T4, FT4, rT3; increase TSH, normal TBG

A

Primary Hypothyroidism

73
Q

with weak Thyroid-stimulating activity

A

Human chorionic gonadotropin (hCG)

73
Q

Increase FT4 and T3, Low TSH

A

HCG after fertility

74
Q
  • Normal or increase: aTPO, ATG, TBII
  • Normal to decrease: Tg
A

Primary Hypothyroidism

75
Q

decrease T4, decrease TSH (Pituitary no TSH!)
- Decrease T3, FT4

A

Secondary Hypothyroidism

76
Q

Decrease T3 and T4 and TSH

A

Tertiary hypothyroidism

77
Q

Normal T3, T4 and FT4; TSH slightly increase
- No signs and symptoms

A

Subclinical hypothyroidism

77
Q
  • painful thyroiditis
  • TPO antibody is absent
  • Increase Thyroglobulin and ESR
A

Subacute granulomatous/Subacute non-suppurative
thyroiditis/ De Quervain’s

77
Q

Also known as “chronic autoimmune thyroiditis”

A

Hashimoto’s disease

78
Q

Common cause of primary hypothyroidism

A

Hashimoto’s disease

79
Q

With Goiter

A

Hashimoto’s disease

79
Q

In Hashimoto’s disease, Thyroid is replaced by _________ sensitized T-cells bind to cell membrane causing cell Lysis and inflammatory reaction

A

nest of lymphoid tissue

79
Q

Test for Hashimoto’s disease

A

TPO antibody = (+) increase TSH
(TPO Ab = tissue destructive disease)

80
Q

“Cretinism”

A

Congenital hypothyroidism

81
Q
  • “puffy face” (moon face)
  • Weight gain, slow speech
  • Thin eyebrows, dry yellow skin
A

Myxedema

81
Q

Peculiar nonpitting swelling of the skin. Skin infiltrated by mucopolysaccharide

A

Myxedema

82
Q
  • Development/functional defect of gland
  • Retarded child
A

Congenital hypothyroidism

83
Q

Due to severe hypothyroidism

A

Myxedema coma

84
Q

These are included in the Newborn Dried Blood Spot Screening (NBS)

A
  • Screening = low T4
  • Confirmatory = high TSH
85
Q

Acutely ill but w/o thyroid disease (low TSH = acute)

A

Euthyroid Sick syndrome (Non-thyroidal illness)

85
Q

Low T3 and T4, Normal to high TSH, high rT3
- Abnormal TBG

A

Euthyroid Sick syndrome (Non-thyroidal illness)

CC2 (lab)- Endocrinology (2 decks)

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