Thyroid hormones

Question 1

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

Answer 1

10x

Question 2

Triiodothyronine (T3) is more ___

Answer 2

potent

Question 3

Physiologic effects of thyroid hormones

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

Answer 3

• brain
• catabolic

Question 4

Physiologic effects of thyroid hormones

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

Answer 4

• Increase, oxygen
• T3

Question 5

Physiologic effects of thyroid hormones

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

Answer 5

• heat

Question 6

Physiologic effects of thyroid hormones

Cardiovascular effects
* Increase ___ sensitivity

Answer 6

catecholamine

Question 7

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 ___.

Answer 7

• 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

Question 8

Iodide organification

Catalyzed by ___

Answer 8

thyroid peroxidase

Question 9

Hypothalamus-pituitary-thyroid axis

Hypothalamus: ___
Anterior pituitary: ___
Thyroid gland: ___

Answer 9

• TRH
• TSH
• T4 and T3

Question 10

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 ___

Answer 10

• thyroid hormones
• seafood
• TSH
• Cretinism
• table salt

Question 11

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.

Answer 11

• Thyroxine-binding globulin
• Transthyretin
• free
• longer
• rapid

Question 12

deiodinase converts T4 to ___

Answer 12

T3

Question 13

Metabolism

• Deiodination
• Conjugation to form ___ with the phenolic group
• Excreted via the ___.
• Some are hydrolyzed by bacteria; marginal ___ circulation

Answer 13

• glucuronide or sulfate
• bile
• enterohepatic

Question 14

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

Answer 14

• Decrease
• Goiter
• cretinism
• Myxoedema

Question 15

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

Answer 15

• Hashimoto’s
• iodine
• cretinism
• TSH

Question 16

Hyperthyroidism Symptoms

• ____ metabolism – always hot and weight loss
• Increased ___ and cardiac output

Answer 16

• excess
• heart rate

Question 17

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

Answer 17

• Grave’s, IgG, toxic goiter
• Viral

Question 18

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

Answer 18

True

Question 19

Hypothyroidism: Thyroid hormone replacement therapy

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

Answer 19

• bovine or porcine
• variable

Question 20

Hypothyroidism: Thyroid hormone replacement therapy

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

Answer 20

• T3
• slow, 7 days

Question 21

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.

Answer 21

• rapid, short, daily
• greater
• difficult

Question 22

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

Answer 22

• 4:1
• not shown

Question 23

Hyperthyroidism: Thioamides

• Antithyroid agents
• Methimazole, propylthiouracil
• Inhibit ___
• Block iodine ___
• Block coupling of the ___
• ___onset (3 – 4 weeks)
• Require depletion of stored ___
  .

Answer 23

• thyroid peroxidases
• organification
• iodotyrosines
• Slow
• T4

Question 24

Hyperthyroidism: I 131

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

No surgery and lower cost

Answer 24

• β, γ
• 8 days
• thyroid follicles

Question 25

# 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.

Answer 25

* hypothyroidism * cancers * thyroid strom, antithyroid

Question 26

# 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)

Answer 26

* inhibits, organification * long term * thyroidectomy, thyrotoxicosis, radioactive * iodine

Question 27

# hypothyroidsism vs hyperthyroidism

Answer 27