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OSSF II Endocrinology > Thyroid Hormone > Flashcards

Thyroid Hormone Flashcards

1
Q

Thyroid hormone is produced from which amino acid?

A

Tyrosine

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2
Q

How is Iodide shuttled across the follicular cells?

A

Basal: Na/I- Symporter
Apical: Cl/I- transporter

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3
Q

The chemical reactions of TPO are faciliated by

A

Hydrogen Peroxide

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4
Q

What is Methimazole prescribed for and what does it do?

A

Methimazole is prescribed for hyperthyroidism

Inhibits TPO

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5
Q

Why does T4 have a shorter half life in dogs compared to humans?

A

Dogs store more T4 on albumin instead of TBG; Albumin has a lower affinity for T4 than TBG

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6
Q

Which has a shorter half life: T3 or T4?

A

T3 (6 hrs; T4 is 12-24 hours)

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7
Q

Which factors control thyroid hormone levels?

A

Estrogen -> increases TBG

Cortisol/NSAIDs - compete for binding w/ TBG; decreases amount in blood b/c unbound T4 diffuses across membranes

Iodide -> SUPPRESSES hormone synthesis

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8
Q

What form of thyroid hormone exerts negative feedback?

A

FREE T4

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9
Q

Where is D2 found?

A
  • Brain
  • Myocardium
  • Skeletal muscle
  • Brown fat
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10
Q

In which contexts does D3 increase?

A
  • Starvation
  • Sickness
  • Hibernation
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11
Q

Thyroid hormone increases Oxygen consumption in all tissues EXCEPT

A
  • Brain (but used for development/excitation of CNS)
  • Spleen
  • Gonads
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12
Q

Effects of Thyroid Hormones

A
  1. Bone growth (synergy w/ GH and IGF-1)
  2. Erythropoiesis / lowers Hb O2 affinity (by stimulating DPG synthesis)
  3. Increases B-adrenergic receptor
    a. CO
    b. Vasodilation
    c. Net effect = increase perfusion
    d. Leads to dilute urine and thirst
  4. Initiates anlagen (growth) phase of hair
  5. Stimulates carb metabolism (but NO net change in BG)
  6. Stimulates fat metabolism (but net LOSS of plasma cholesterol/TGs)
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13
Q

What are two causes of goiter and their symptoms?

A
  1. Iodine deficiency/toxicity: HypOthyroidism

2. Benign functional tumor: HypERthyroidism

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14
Q

Why does the thyroid swell in hypothyroidism?

A

No negative feedback on TSH; follicular cells proliferate

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15
Q

Two consequences of hypothyroidism in foals

A
  1. Low metabolism
  2. Developmental lesions
    a. Affect hair and bone
    b. Normal thyroid at birth, low during critical development period
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16
Q

How does hyperthyroidism affect ALT?

A

Elevates ALT

17
Q

How does hyperthyroidism affect calcium?

A
  • No NET change in calcium (“normocalcemia”)
  • Calcium initially elevated by bone resorption, but this decreases PTH and increases CT, leading to hypercalciuria
  • However, PHOSPHATE (also released from bone resorption) WILL be elevated in hyperthyroidism

OSSF II Endocrinology (11 decks)

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