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PHRM 825 > Thyroid hormones > Flashcards

Thyroid hormones Flashcards

1
Q

Thyroxine (T4) is produced ___ times more than Triiodothyronine (T3)

A

10x

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2
Q

Triiodothyronine (T3) is more ___

A

potent

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3
Q

Physiologic effects of thyroid hormones

Growth and development
* essential for ___ development (absent T3 = cretinism)
* Promote skeletal/muscle growth; ___ at the levels of hyperthyroidism

A
  • brain
  • catabolic
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4
Q

Physiologic effects of thyroid hormones

Metabolic effects
* ___ basal metabolic rate (BMR); Increase ___ consumption.
* Starvation lowers both ___
hormone and thyroid receptor.

A
  • Increase, oxygen
  • T3
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5
Q

Physiologic effects of thyroid hormones

Thermogenesis
* Increase resting ___ production.
* Inability to adjust to environmental temperature

A
  • heat
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6
Q

Physiologic effects of thyroid hormones

Cardiovascular effects
* Increase ___ sensitivity

A

catecholamine

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7
Q

Steps of thyroid hormone synthesis

  1. Dietary iodine → ___ in the stomach
  2. Iodide is actively transported into the cell by ____
  3. In the follicular cell, iodide passes down its electrochemical gradient and into the follicular colloid (partially through the apical transporter, ___). It is oxidized by ___ to ___ at the apical membrane.
  4. Iodide-free ___ is transported to the apical membrane.
  5. Thyroglobulin is ____ at one or two positions, forming the hormone precursors ___, and ___ (iodide organification).
  6. MIT + DIT = tri-iodothyronine (3,5,3ʹ-__) and DIT + DIT = tetra-iodothyronine (T4) = ___. Coupling is dependent on thyroid peroxidase.
  7. Thyroid hormone-containing ____ is retrieved back into the cytosol of the follicular cell as colloid droplets by pinocytosis.
  8. Lysosomal exopeptidases cleave ___
    (or T) from thyroglobulin and the 3
    hormones are ___ into circulation where T4 can be converted to the more active T
    3 by ___.
A
  • I-
  • Na-I symporter (NIS).
  • pendrin, thyroid peroxidase, I
  • thyroglobulin
  • iodinated by thyroid peroxidase, mono-iodotyrosine (MIT), di-iodotyrosine (DIT)
  • T3, thyroxine
  • thyroglobulin
  • T4, released, 5’deiodinase
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8
Q

Iodide organification

Catalyzed by ___

A

thyroid peroxidase

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9
Q

Hypothalamus-pituitary-thyroid axis

Hypothalamus: ___
Anterior pituitary: ___
Thyroid gland: ___

A
  • TRH
  • TSH
  • T4 and T3
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10
Q

Iodine

  • Used for synthesis of ___.
  • high amounts in ___
  • Goiter – an enlargement of the thyroid gland due to a persistent rise in ___
  • ___ – severely stunted physical and mental growth
  • Routinely added to ___
A
  • thyroid hormones
  • seafood
  • TSH
  • Cretinism
  • table salt
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11
Q

Transport

Transported in plasma by
* ___ (TBG) – primary transport protein
* ___ (TTR)
* Albumin
Transport proteins have greater affinity to T4
* Only 0.04% of T4 is ___.
* T4 has a ___ half life than T3; serves as a storage pool (2 – 3 months)
* T3 has a more ___ onset.

A
  • Thyroxine-binding globulin
  • Transthyretin
  • free
  • longer
  • rapid
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12
Q

deiodinase converts T4 to ___

A

T3

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13
Q

Metabolism

  • Deiodination
  • Conjugation to form ___ with the phenolic group
  • Excreted via the ___.
  • Some are hydrolyzed by bacteria; marginal ___ circulation
A
  • glucuronide or sulfate
  • bile
  • enterohepatic
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14
Q

Hypothyroidism Symptoms

  • ___ in metabolic rate – fatigue, mental dullness, lethargy, inattention
  • always cold
  • May occur with thyroid enlargement (nontoxic ____).
  • Dwarfism and mental retardation (____) in infants and children
  • ____ coma – end state of untreated hypothyroidism; water intoxication, shock, and death
A
  • Decrease
  • Goiter
  • cretinism
  • Myxoedema
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15
Q

causes of hypothyroidism

  • ___’s thyroiditis – most common; autoimmune disease that destroys he thyroid gland
  • Destruction or removal of the gland (radiation, X-ray, thyroidectomy)
  • ___ deficiency
  • Congenital (cretinism)
  • Secondary – ___ deficiency
A
  • Hashimoto’s
  • iodine
  • cretinism
  • TSH
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16
Q

Hyperthyroidism Symptoms

  • ____ metabolism – always hot and weight loss
  • Increased ___ and cardiac output
A
  • excess
  • heart rate
17
Q

Hyperthyroidism Causes

  • ___ diseases - Most common; autoimmune; thyroid-stimulating ___;enlargement of the entire thyroid gland (diffuse ___)
  • Subacute thyroiditis - ___ infection of the thyroid gland; transient release of stored thyroid hormones
A
  • Grave’s, IgG, toxic goiter
  • Viral
18
Q

T or F: Toxic uninodular goiter and toxic multinodular goiters are adenomas producing excess T3; occuring mostly in older women

A

True

19
Q

Hypothyroidism: Thyroid hormone replacement therapy

Natural thyroid hormone preparations
* Desiccated thyroid & thyroglobulin (___ or ___)
* ___ T4/T3 blood levels due to inconsistencies in sources

A
  • bovine or porcine
  • variable
20
Q

Hypothyroidism: Thyroid hormone replacement therapy

Levothyroxine (T4)
* Converted to ___ intracellularly.
* ___ onset, long half-life (____); 6-8 weeks to reach steady-state levels.

A
  • T3
  • slow, 7 days
21
Q

Hypothyroidism: Thyroid hormone replacement therapy

Liothyronine (T3)
* ___ onset, ___ duration of action (24 hr) requiring multiple ___ doses
* ___ risk of cardiotoxicity
* ___ to monitor using conventional laboratory tests.

A
  • rapid, short, daily
  • greater
  • difficult
22
Q

Liotrix
* ___ mixture of T4 and T3
* More expensive, but ___ to be more effective than T4 administration alone.

A
  • 4:1
  • not shown
23
Q

Hyperthyroidism: Thioamides

  • Antithyroid agents
  • Methimazole, propylthiouracil
  • Inhibit ___
  • Block iodine ___
  • Block coupling of the ___
  • ___onset (3 – 4 weeks)
  • Require depletion of stored ___
    .
A
  • thyroid peroxidases
  • organification
  • iodotyrosines
  • Slow
  • T4
24
Q

Hyperthyroidism: I 131

  • Radioactive iodine emitting ___ particles and ___ rays
  • t1/2= ___ days
  • Localized destruction of ___

No surgery and lower cost

A
  • β, γ
  • 8 days
  • thyroid follicles
25
Q

Problems of I 131

  • ___ occurs in 80% of patients.
  • Potential increase in certain ___
  • Radiation thyroiditis (in rare cases leading to ____); prevent with pretreatment of ____ drugs
  • Contraindications: Not for pregnant women or nursing mothers.
A
  • hypothyroidism
  • cancers
  • thyroid strom, antithyroid
26
Q

Hyperthyroidism: Iodide

  • Large dose of I- ___ its own uptake, iodine ___ (Wolff–Chaikoff block), release of thyroid hormones, and decreases vascularity of the thyroid
    gland.
  • Beneficial effect is transient and thus not used for ___ management.
  • Lugol’s solution - Aqueous solution of elemental I and KI
  • Used for preparation for ___, Severe ___, Protection from ___ iodine fallout (nuclear accident or military exposure)
  • SE: Hypothyroidism, sensitivity to ___ in some patients (ex. angioedema)
A
  • inhibits, organification
  • long term
  • thyroidectomy, thyrotoxicosis, radioactive
  • iodine
27
Q

hypothyroidsism vs hyperthyroidism

A

PHRM 825 (49 decks)

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