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Term II: Endocrinology > Thyroid > Flashcards

Thyroid Flashcards

1
Q

What does thyroid hormone do?

A

Controls rates of growth and metabolism

Thermogenesis/maintenance of core body temp

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2
Q

Iodine is used only by thyroid gland. What does the thyroid gland do to iodine?

A

Concentrates it and incorporates it into thyroid hormone T3 and T4

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3
Q

What clinical conditions occur if you have an iodine dietary excess?

A

Wolff-Chaikoff phenomena - reduction in TH levels caused by ingestion of large amount of iodine

Jod-Basedow phenomena - Hyperthyroidism after administration of iodine
Does not occur in people with normal thyroid glands

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4
Q

What is the purpose of a trophic hormone?

A

Nutrition - pituitary hormones exert nutrifying effects on target hormones - proper uptake of energy

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5
Q

What is the purpose of tropic hormones?

A

Directs synthesis and release of hormone of target organs

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6
Q

What are the two cellular signaling mechanisms of TSH action?

A

Gs –> Adenyl cyclase –> cAMP

Phospholipase C –> IP3 –> Ca2+

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7
Q

What is the effect of TSH on thyroid follicular cells?

A

Tropic effect - expression and regulation of every step in T4 synthesis and secretion
Trophic effect - can be seen in goiter

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8
Q

Which thyroid hormone is responsible for negative feedback?

A

T3 - this is the active form of TH

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9
Q

How many iodine atoms does thyroxine have?

A

4 - aka T4

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10
Q

How many iodine atoms does triiodothronine have?

A

3 - aka T3

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11
Q

How does epithelia of follicular cells change from an inactive thyroid state to an active thyroid state?

A

Cuboid –> Columnar

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12
Q

What do parafollicular cells do in the thyroid?

A

Calcium metabolism

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13
Q

What molecule is the colloid of the thyroid follicular cells rich in? What is it synthesized by?

A

Thyroglobulin - ER of follicular cell

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14
Q

Are T1 and T2 secreted?

A

No they are recycled until T3 and T4 are made

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15
Q

What hormone regulates synthesis of TH?

A

TSH

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16
Q

How does TH circulate in blood? What form of TH circulates?

A

99.7% bound to protein - TBG, albumin

T4 circulates

17
Q

What does end organ cell do if it needs T3? What if it doesn’t need T3?

A

Deiodinates circulating T4

Doesn’t need it - turns it into inactive (reverse) T3

18
Q

What are the effects of TH?

A
  1. Brown adipose tissue –> synthesis of UCP-1 leading to thermogenesis
  2. Reproduction –> Follicle dev, spermatogenesis, sex-hormone binding globulin (SHBG)
  3. Bone –> Maturation of chondrocytes, endochondral ossification, linear growth
  4. Muscle –> Creatine phosphate, bone remodeling
  5. Tooth and hair follicle dev
  6. Subcutaneous –> Inhibition of fibronectin synthesis
  7. CNS –> brain growth, in utero (growth of cortices, prolif of axons and dendrites), in infancy (increased T3 receptors), in adults (mental alertness, memory, reflexes, emotions)
  8. CV –> Increased β-adrenergic receptors, so increased heart rate and contractility (tachycardia)
19
Q

How does fetus get TH?

A

Depends on maternal TH traveling across placental barrier to influence fetus

20
Q

What causes cretinism? Symptoms?

A

Mother had no TH, so child has abnormal growth.

Muscular flaccidity, CNS retardation, large tongue, hernia b/c of weak muscles

21
Q

What are some signs of hypothyroidism?

A

Low intelligence, delayed puberty, deep voice, weight gain

22
Q

What are some signs of hyperthyroidism?

A

Rapid speech and reflexes, swelling of goiter

23
Q

What is Grave’s disease? What would levels of TSH look like in someone with Grave’s?

A

Hyperthyroidism - autoimmune disease where Abs mimic TSH and bind to receptors so you make a huge amt of TH

TSH would be near zero b/c of so much neg. feedback

24
Q

What is secondary hypothyroidism?

A

Issues with pituitary - no TSH is secreted even if patient is injected with TRH

Term II: Endocrinology (8 decks)

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