Lecture 8 Flashcards Preview

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Flashcards in Lecture 8 Deck (35):
1

Dopamine normally inhibits PRL.

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

2

Postpartum depression:

Dopamine goes down to facilitate lactation. Makes mother sad.

3

Thyroid gland cell types:

Follicular cells: secrete T3 and T4.
Parafollicular or C cells: release calcitonin, a calcium/phosphate regulator.

4

Average size of thyroid gland:

20-34 g

5

Unique characteristic of thyroid hormones:

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.

6

Storage of thyroid hormones:

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

7

Synthesis of thyroid hormones:

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.

8

TSH's role in thyroid hormone synthesis:

Enhances Na/I symporter activity.

9

Why does iodine need to be oxidized?

Negatively charged iodide can't bind to thyroglobulin.

10

T3 vs T4:

10x more T4 than T3.

11

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

Microtubular action of cytoplasm.

12

Physiological functions of thyroid hormone:

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

13

Thyroid hormone stimulates pretty much everything except:

Decreases serum cholesterol concentration.

14

Effect of thyroid hormone on: bone

Increases osteoblastic and osteoclastic activity for normal growth and development.

15

Effect of thyroid hormone on: liver

Stimulates triglyceride and cholesterol metabolism.

16

Effect of thyroid hormone on: brain

Stimulates axon growth and development.

17

Effect of thyroid hormone on: heart

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

18

Effect of thyroid hormone on: adipose tissue

Stimulates lipolysis.

19

Effect of thyroid hormone on: muscle

Stimulates protein breakdown.

20

Effect of thyroid hormone on: gut

Stimulates carb absorption.

21

T3: target? comparative activity? half-life?

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

22

Making T3 from T4:

5'/3' deiodinase converts T3 into T4.

23

T4: half-life? comparative activity?

Half-life of 6-7 days.
Less active than T3.

24

rT3: activity? structure?

Physiologically inactive.
Two iodines on outer benzyl instead of inner.

25

Structures of T3, T4, and rT3:

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

Making rT3 from T4:

5/3 deiodinase converts T4 to rT3.

27

Two forms of 5'/3' deiodinase:

Type 1: liver, kidneys, thyroid. General circulation.
Type 2: pit, CNS, placenta. Local.

28

Thyroid hormones inside thyroglobulin:

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

29

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

T3: 0.5%
T4: 0.02%

30

Transport of thyroid hormone:

Free or bound to thyroxine-binding globulin.

31

Pregnancy vs thyroxine-binding globulin:

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

32

Liver failure vs thyroxine-binding globulin:

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

33

Hypothyroidism: what is it? treatment?

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

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

34

Disorders related to hypothyroidism:

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

35

Hyperthyroidism: related disorders

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