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NE Exam 3 > 38: Thyroid Gland > Flashcards

38: Thyroid Gland Flashcards

1
Q

What cell type secretes thyroid hormones

A

Follicular epithelium

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2
Q

Outermost part of thyroid follicle

A

Basal lamina

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3
Q

Follicular lumen contents

A

Contains colloid, which contains newly synthesized thyroid hormones attached to thyroglobulin, which stores iodine as tyrosine

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4
Q

How much hormone is stored in the thyroid + how much is secreted daily

A

Stored: enough for 2-3 months
Ssecrete: 60 ug daily

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5
Q

Parafollicular / C cell function

A

Secrete calcitonin

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6
Q

Name of T3 and T4

A

T3: triiodothyronine
T4: tetraiodothyronine

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7
Q

Which is the active form, T3 or T4?

A

T3

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8
Q

Which is secreted more, T3 or T4

A

T4 (10x more)

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9
Q

Half life of T3 and T4

A

T3: 1 day
T4: 6 days

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10
Q

How much T3 comes directly from thyroid vs peripheral conversion

A

Thyroid: 1–20%
Conversion: 80-90%

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11
Q

Enzyme that converts T4 to T3 in circulation

A

Deiodinase

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12
Q

Three things that reduce peripheral conversion to T3

A
  1. Fasting
  2. Medical stress
  3. Catabolic disease
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13
Q

Pendrin

A

A Cl/I pump involved in thyroid hormone synthesis, in the apical membrane of follicular cells

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14
Q

Mutation in Pendrin gene / Pendren syndrome

A

Defect in transport of iodine across apical membrane -> hypothyroidism with goiter + sensorineural hearing loss

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15
Q

Wolff-Chaikoff effect

A

High levels of I inhibit organification and synthesis of thyroid hormones

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16
Q

What can deficiency of deiodinase mimic?

A

Dietary deficiency in Iodine

17
Q

What thyroid hormone is favored to be created with a restricted availability of iodine?

A

T3 is favored

18
Q

Three main thyroid hormone binding proteins in the blood + their percentages

A
  1. TBG: thyroxine-binding globulin: 70%
  2. TRR: transthyretin: 10-15%
  3. Albumin: 15-20%
19
Q

Where is TBG synthesized?

A

Liver

20
Q

T3 Resin Uptake Test function

A

Measures circulating levels of TBG to measure levels of bound hormone

21
Q

How T3 resin uptake test works

A
  1. Start with TBG bound to T4 from serum
  2. Add unbound and labeled T3, which will bind unbound TBG sites
  3. Anti-T3 Ab resin adsorbs T3, separating out T3 from T4 - can be measured at this point
22
Q

Level of T4 and T3 in high and low TBG states

A

High TBG: high T4, low T3

Low TBG: low T4, high T3

23
Q

Levels of TBG and T3 in hepatic failure**

A

Low TBG, high T3

24
Q

Hepatic failure effect on thyroid hormone

A

It causes a transient increase in free T3 and T4, followed by an inhibition of synthesis of T3 and T4

25
Q

TBG and T3 in pregnancy

A

High TBG, low T3

26
Q

Conditions that cause high and low TBG

A

High TBG: pregnancy

Low TBG: hepatic failure

27
Q

Pregnancy and thyroid hormones

A

Decrease in free T3 and T4 -> increased synthesis of T3 and T4 - >increased total levels of T3 and T4, but since also high TBG, levels of free H levels are normal -> pt is euthyroid

28
Q

Thyroid hormones cause synthesis of what proteins in most tissues?

A

Na/K ATPase, transport proteins, lysosomal and proteolytic enzymes, structural proteins

29
Q

Three proteins up regulated by thyroid hormones in cardiac muscle

A

Myosin, B1-adrenergics, Ca ATPase

30
Q

Five causes of goiter

A
  1. Grave’s disease
  2. Secondary hyperthyroidism
  3. Lack of iodine
  4. Sporadic hypothyroid
  5. Hashimoto’s
31
Q

two things TSH does to the thyroid

A

Regulates secretion of thyroid hormones + BUT also regulates growth of the gland

32
Q

Secretion of Thyroid hormone vs GH

A

Thyroid: secreted in a steady state
GH: secretion in waves

33
Q

Plasma cholesterol and triglycerides vs thyroid hormone

A

Inversely related

34
Q

Neural changes that cause congenital hypothyroidism

A

Abnormal development of synapses + decreased dendritic branching and myelination -> neural changes irreversible unless replacement therapy starts soon after birth

NE Exam 3 (22 decks)

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