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Digestion and Metabolism - Wk 2 > thyroid gland > Flashcards

thyroid gland Flashcards

1
Q

thyroid gland secretes:

A
  • thyroid hormones (T3, T4)
  • calcitonin
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2
Q

what are the key features of the endocrine system

A
  • release hormones into intercellular or perivascular CT spaces
  • cells arranged in clusters or cords
  • associated with dense capillary beds and wide thin-walled vessels called sinusoids
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3
Q

what are follicles

A
  • functional units of thyroid gland
  • spheres of low cuboidal to high columnar cells
  • centers filled with colloid
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4
Q

what are follicular cells

A
  • acidophilic
  • polar cell morphology
  • apical microvilli
  • golgi, ER
  • vaculoes
  • large membrane-bound colloid droplets
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5
Q

what do follicular cells store

A

pro-hormone in follicle lumen

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6
Q

what do follicular cells secrete

A

active thyroid hormone (T3 and T4) into pericapillary space

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7
Q

what do follicular cells concentrate

A

iodine from blood

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8
Q

what is iodine essential for

A

T3/T4 synthesis

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9
Q

what can an iodine deficiency cause

A

goiter

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10
Q

what is thyroglobuoin

A
  • glycoprotein
  • synthesized by ER/golgi complex and secreted via secretory vesicles into follicle lumen
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11
Q

where is thyroperoxidase and what does it do

A
  • on apical surface
  • iodinates thyroglobulin on tyrosines
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12
Q

where is iodinated thyroglobulin taken up

A

follicular lumen

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13
Q

what is thyroglobulin broken down into

A
  • thyroxine (T4) and triiodothyronine (T3)
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14
Q

how much of the circulating T3 is formed in the liver

A

83%

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15
Q

what is thyroxine (T4)

A
  • pro-hormone
  • converted to T3 by target cells and liver
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16
Q

what is thyronamines (TAMs)

A

family of decarboxylated and deiodinated metabolites of T3 and T4

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17
Q

what are the three TH distributor proteins

A
  • thyroxine-binding globulin
  • transthyretin
  • albumin
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18
Q

what do TH distributor proteins form

A

a buffering network for free T4 in blood - helps protect against hypothyroidism or hyperthyroidism

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19
Q

what kind of thyroid hormones enter target cells

A

only free T4 and T3

20
Q

describe the HPT axis

A
  • TRH from hypothalamus stimulates adenohypophysis to release TSH
  • TSH stimulates thryoid follicular cells
21
Q

what are goitrogens

A

substances that interfere with thyroid hormone production

22
Q

what happens if there is too much iodine

A

diminish T3/T4 hormone production

23
Q

what is triiodothyronine (T3)

A
  • accelerates metabolic rate of body
  • increase cell metabolism, growth, differentiation, development
  • increases protein, carbohydrate and fat metabolism
24
Q

what do thyroid hormones influence

A

metabolism and function of all organs

25
Q

how do thyroid hormones function

A

via nuclear receptors

26
Q

what do thyroid hormone receptors do

A

regulate gene expression

27
Q

how are thyroid hormone receptor functions defined

A

mutations that cause resistance to thyroid hormone: RTH
* mutations in TR beta and alpha

28
Q

what does UCP1 do

A

increases the conductance of the inner mitochondrial membrane to make BAT mitochondria generate heat rather than ATP

29
Q

what does stress do to the HPT axis

A

shuts it down - net lower TH production

30
Q

what does cold do to the HPT axis

A

activates expression of thyroid hormone

31
Q

how does T4 regulate cancer

A

via the plasma membrane associated integrin receptors

32
Q

describe hypothyroidism

A
  • lethargy and obestity (most common)
  • derm symptoms
  • alopcecia along trunk or tail head
  • skin thickened
  • dull dry hair
33
Q

what are less common signs of hypothyroidism in dogs

A
  • cardiovascular
  • neuromuscular myopathies and megaesophagus
  • facial nerve paralysis, vestibular disease, lower motor neuron disorders
  • repro disorders in females
  • corneal lipid reposits and GI problems
34
Q

how to treat canine hypothyroidism

A

levothyroxine = synthetic T4

35
Q

what is the most common type of primary hypothyroidism in dogs

A

lymphocytic thyroiditis

36
Q

what is lymphocytic thyroiditis

A
  • circulating thyroid autoantibodies
  • antibodies to follicular cell, colloid, or thyroglobulin antigens
37
Q

what do high doses of glucocorticoids do to thyroid function

A

reduce conversion of thyroxine (T4) to the more active triiodothyronine (T3)

38
Q

hyperthyroidism

A

most common endocrinopathy of cats, typically caused by adenomatous hyperplasia of the thyroid gland

39
Q

what are clinical signs of hyperthyroidism

A
  • hypermetabolism
  • activation of symathetic nervous system
  • long-standing hyperthyroidism leads to hypertrophic cardiomyopathy, and death
  • liver hypermetabolism
40
Q

what is toxic nodular goiter caused by

A

aberrant signal transduction of the thyroid follicular cells

41
Q

what does the TSH receptor activate

hyperthyroidism cats

A

receptor-coupled guanosine triphosphate-binding proteins (G proteins) in thyroid follicular cells

42
Q

does diet play a role in feline hyperthyroidism

A

canned cat food has been implicated as a cause because BADGE, substance used to make liner of easy-open cans and cats susceptible to toxic effects of BADGE

43
Q

what is the treatment of choice for cats with hyperthyroidism

A

radioactive iodine (RAI) therapy

44
Q

what does felimazole (methimazole) do

A

prevents iodine and perozidase form their normal interactions with thyroglobulin to form T4 and T3

45
Q

what is RAI therapy

A
  • thyroid gland absorbs all iodine in blood
  • large dose of RAI is taken, the radiation collects in thyroid cells
  • destroys the thyroid gland and cancer cells
46
Q

what are the advantages and disadvantages to RAI therapy

A

advantages
* gets tid of tumor completely
* targets thyroid tumor cells elsewhere in body

disadvantages
* requires cat to be in tx ward for 2 wks
* kitty litter is handles as radioactive waste

Digestion and Metabolism - Wk 2 (5 decks)

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