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PHPY 303 > Lecture 8 > Flashcards

Lecture 8 Flashcards

1
Q

Dopamine normally inhibits PRL.

A

G-alpha protein inhibits cAMP.

G-beta protein activates K+ in channels and inhibits Ca2+ channels.

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2
Q

Postpartum depression:

A

Dopamine goes down to facilitate lactation. Makes mother sad.

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3
Q

Thyroid gland cell types:

A

Follicular cells: secrete T3 and T4.

Parafollicular or C cells: release calcitonin, a calcium/phosphate regulator.

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4
Q

Average size of thyroid gland:

A

20-34 g

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5
Q

Unique characteristic of thyroid hormones:

A

They are peptides, but their receptors are in the nucleus rather than on the cell membrane. They have a similar mechanism of action as steroids.

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6
Q

Storage of thyroid hormones:

A

Follicular epithelial cells are filled with glycoprotein mixture called colloid. The colloid holds 3 months of thyroid hormone.

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7
Q

Synthesis of thyroid hormones:

A

Thyroglobulin synthesis: from RER of follicular cells.
Iodine trapping: Na/I symporter on basolateral membrane.
Oxidation of iodine: thyroid peroxidase in lumen oxidizes I- to I2.
Iodination of thyrosine: thyroid peroxidase in lumen makes mono- and di-iodothyrosine.
Coupling reaction: thyroid peroxidase catalyzes formation of T3 and T4 from mono/dis.
Endocytosis of thyroglobulin: TSH stimulates follicular cells to endocytose T3/T4.
Proteolysis: lysosomal proteases in the vesicle hydrolyse peptide bonds and release T3/T4.
Deiodination: thyroid deiodinase recycles iodine from unused mono/dis.

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8
Q

TSH’s role in thyroid hormone synthesis:

A

Enhances Na/I symporter activity.

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9
Q

Why does iodine need to be oxidized?

A

Negatively charged iodide can’t bind to thyroglobulin.

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10
Q

T3 vs T4:

A

10x more T4 than T3.

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11
Q

How do T3/T4 endocytic vesicles travel to the basolateral membrane?

A

Microtubular action of cytoplasm.

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12
Q

Physiological functions of thyroid hormone:

A 
Growth and development
Increase basal metabolic rate
Increase O2 consumption
Increase Na/K ATPase activity 
Stimulate thermogenesis
Stimulate macromolecule metabolism
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13
Q

Thyroid hormone stimulates pretty much everything except:

A

Decreases serum cholesterol concentration.

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14
Q

Effect of thyroid hormone on: bone

A

Increases osteoblastic and osteoclastic activity for normal growth and development.

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15
Q

Effect of thyroid hormone on: liver

A

Stimulates triglyceride and cholesterol metabolism.

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16
Q

Effect of thyroid hormone on: brain

A

Stimulates axon growth and development.

17
Q

Effect of thyroid hormone on: heart

A

Increase adrenergic receptors, increase response to catecholamines, reduce smooth muscle resistance.

18
Q

Effect of thyroid hormone on: adipose tissue

A

Stimulates lipolysis.

19
Q

Effect of thyroid hormone on: muscle

A

Stimulates protein breakdown.

20
Q

Effect of thyroid hormone on: gut

A

Stimulates carb absorption.

21
Q

T3: target? comparative activity? half-life?

A

Negative feedback on ant pit and hypothalamus.
More physiologically active than T4.
Half-life of 1 day.

22
Q

Making T3 from T4:

A

5’/3’ deiodinase converts T3 into T4.

23
Q

T4: half-life? comparative activity?

A

Half-life of 6-7 days.

Less active than T3.

24
Q

rT3: activity? structure?

A

Physiologically inactive.

Two iodines on outer benzyl instead of inner.

25
Q

Structures of T3, T4, and rT3:

A

T3 has two I on the inner ring and one I on the outer ring.
T4 has two I on both rings.
rT3 has two I on the outer ring and one I on the inner ring.

26
Q

Making rT3 from T4:

A

5/3 deiodinase converts T4 to rT3.

27
Q

Two forms of 5’/3’ deiodinase:

A

Type 1: liver, kidneys, thyroid. General circulation.

Type 2: pit, CNS, placenta. Local.

28
Q

Thyroid hormones inside thyroglobulin:

A

Part of the backbone. Need two cleavages to be free.

29
Q

How much T3 is free? How much T4 is free?

A

T3: 0.5%
T4: 0.02%

30
Q

Transport of thyroid hormone:

A

Free or bound to thyroxine-binding globulin.

31
Q

Pregnancy vs thyroxine-binding globulin:

A

Estrogen stimulates synthesis of TBG, which reduces level of free thyroid hormone, which stimulates synthesis of more.

32
Q

Liver failure vs thyroxine-binding globulin:

A

Reduced TBH synthesis leads to increased levels of free thyroid hormone, which inhibits synthesis of more.

33
Q

Hypothyroidism: what is it? treatment?

A

Primary: problems with thyroid gland. Secondary: problems with pit or hyp.

Treat primary with thyroid hormones.
Treat secondary by manipulating regulators.

34
Q

Disorders related to hypothyroidism:

A

Cretinism
Myxedema: cutaneous/dermal edema caused by too much deposition of connective tissues
Iodine-deficient goiter

35
Q

Hyperthyroidism: related disorders

A

Graves: autoimmune condition. B lymphocytes synthesize abnormal immunoglobulin that binds and activates TSH receptor. Iodine trapping increases. Goiter.

PHPY 303 (8 decks)

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