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Endocrine Physiology > Thyroid Axis > Flashcards

Thyroid Axis Flashcards

1
Q

Control of t4 secretion

A

T4 decreases the sensitivity of thyrotropes to TRH, decreasing TSH secretion

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2
Q

Thyroid hormone synthesis

A

Thyrocytes uptake iodine and synthesize thyroglobulin, thyroglobulin is exocytosed to the lumen and iodinated

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3
Q

Thyroid hormone release

A

Iodinated thyroglobulin is endocytosed by thyrocytes and then proteolyzed and released

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4
Q

Thyroid peroxidase

A

Iodinates tyrosine residues and then condenses residues to form thyroid hormones

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5
Q

Sodium iodide symporter

A

Transports sodium and iodide on basolateral surface into thyrocyte

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6
Q

Condensation of residues

A

MITs and DITs combining to form T3 or T4

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7
Q

rT3

A

Form of T3 with the wrong iodine removed so it has no biological activity

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8
Q

TSH receptors

A

G protein linked that lead to cAMP and IP3/DAG production to regulate almost all aspects of thyroid hormone synthesis and release

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9
Q

TRH release pattern

A

Pulsatile but also follows circadian rhythms and youth

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10
Q

Wolff-Chaikoff effect

A

Excess of iodide consumption inhibited activity of iodine trapping to prevent hyperthyroidism

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11
Q

Secreted ratio of thyroid hormones

A

4:1

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12
Q

Ratio of thyroid hormone in plasma

A

20:1

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13
Q

Transport of thyroid hormones

A

99% bound to thyroxin-binding globulin but only the free parts are biologically active

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14
Q

T3 receptor

A

In the nucleus, regulate expression of genes

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15
Q

T4 receptor

A

May also bind to cell membrane receptors and activate intracellular events

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16
Q

Effect of activated thyroid receptors

A

Enhanced or suppressed gene expression

17
Q

Isoforms of thyroid receptors

A

Alpha 1 and 2, beta 1 and 2; cat acts as homodimers and heterodimers)

18
Q

T4 half life is ____________, T3 half life is ___________

A

6-7 days, 1 day

19
Q

Where T4 is converted to T3

A

In the liver, kidney, brain, and muscle

20
Q

How thyroid hormones are removed

A

Conjugated in liver, excreted in bile and kidney

21
Q

Physiologic actions of thyroid hormone

A

Involved in synthesis of other hormones, enhance effects of GH, regulate glucose consumption and calorie if hormones, necessary for normal cardiac function

22
Q

CNS regulation by T3

A

Regulates dendritic and axonal growth, myelin formation and synapse formation, r regulate neuronal migration

23
Q

Other effects of thyroid hormone

A

Hematopoiesis, normal gonadal development, T3 increases K/Na pump activity, number and activity of mitochondria, and ATPase activity

24
Q

Gestational hypothyroidism

A

Severely stunted physically and impaired mental development, causing mental retardation, swelling of skin, loss of water and hair, bone thinning, delayed puberty, infertility

25
Q

Hypothyroidism

A

Serum TH is low, causing fatigue, slow heart rate, and dry skin

26
Q

Causes of hypothyroidism

A

Low iodine, anti thyroid factors in diet, mutant receptor, TSH deficiency, mutant transport proteins, impaired synthesis, resistance to thyroid hormone, thyroiditis

27
Q

Causes of hypothyroidism associated with goiters

A

Low iodine, anti thyroid factors, and impaired synthesis

28
Q

Hyperthyroidism symptoms

A

Weight loss, nervousness, sweating, high heart rate and blood pressure, exophthalmia, goiter

29
Q

Causes of hyperthyroidism

A

Pituitary adenoma, thyroid cancer, thyroid it is, Graves’ disease

30
Q

Causes of hyperthyroidism associated with goiters

A

Graves’ disease and thyroid cancer

31
Q

Graves’ disease

A

Thyroid stimulating antibodies activate TSH R, causing excessive thyroid hormone secretion

32
Q

Euthyroid sick syndrome

A

Altered conversion of T4 to T3 due to deiodinases or transport, so they have low circulation T4/3 and high rT3, T4 supplementation doesn’t help

33
Q

ESS treatment

A

Surgery, hormone supplementation, radiation therapy, blockers, stimulants, diet, electrolyte infusions

Endocrine Physiology (7 decks)

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