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endocrine > thyroid gland physiology > Flashcards

thyroid gland physiology Flashcards

1
Q

how many glands does the thyroid gland have

A

2

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2
Q

how are the 2 glands joined together

A

by narrow portion of the gland called the isthmus

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3
Q

where is the gland located

A

over the trachea just below the larynx

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4
Q

what are the major thyroid secretory cells

A

follicular cells

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5
Q

what do the follicular cells form

A

follicle

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6
Q

what are the functional units of thyroid

A

follicles

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7
Q

what is the inner lumen filled part of the follicle called

A

colloid

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8
Q

what does the colloid store

A

thyroid hormone

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9
Q

is the colloid intracellular or extracellular

A

extracellular

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10
Q

what is most of the colloid made of

A

thyroglobulin

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11
Q

what 2 hormones do follicular cells produce

A
  • tetraiodine thyronine (T4) - tri-iodothyronine (T3)
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12
Q

what secretory cells are interspersed between follicles

A

C cells

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13
Q

what do C cells secrete

A

calcitonin

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14
Q

what does calcitonin play a role in

A

calcium metabolism

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15
Q

what are taken up from the blood but the follicular cels

A
  • tyrosine - iodine
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16
Q

what is tyrosine

A

amino acids

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17
Q

how do we acquire iodine

A

dietary intake

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18
Q

what is dietary iodine reduced to

A

iodide

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19
Q

SYNTHESIS AND STORAGE OF THYROID HORMONE

A

SYNTHESIS AND STORAGE OF THYROID HORMONE

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20
Q

where does thyroid hormone synthesis take place

A

within the colloid

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21
Q

where is thyroglobulin produced

A

by the endoplasmic reticulum of the thyroid follicular cell

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22
Q

what happens to tyrosine containing thyroglobulin once it is exported from follicular cells

A

goes into the colloid by exocytosis

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23
Q

how does iodide get into the colloid

A

via the iodide pump

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24
Q

how does the iodide pump work

A

symporter driven by Na+ / K+ pump

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25
Q

what happens in the iodide pump

A

transports Na+ into the follicular cells and I- into the cell

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26
Q

where is iodide mostly in the body

A

in the thyroid cells

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27
Q

what happens to iodide in the follicular cells

A

is it oxidised to ‘active’ iodide

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28
Q

how is iodide oxidised

A

by thryoperoxidase (TPO)

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29
Q

how does active iodide get into the colloid

A

exits through a channel in the luminal membrane to enter the colloid

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30
Q

once iodide enters the colloid what happens

A

TPO attaches iodide to a tyrosine

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31
Q

what odes attachment of iodide to tyrosine form

A

monoiodotyrosine (MIT).

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32
Q

what does attachment of two iodine to tyrosine form

A

di-iodotyrosine (DIT)

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33
Q

what happens once MIT and DIT are formed

A

coupling process occur which forms the thyroid hormones

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34
Q

1 MIT + 1 DIT forms

A

tri-iodothyronine (T3)

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35
Q

1 DIT + 1 DIT =

A

tetraiodothyronine (T4) = thyroxine

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36
Q

can 2 MIT molecules join

A

no

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37
Q

where do T3 and T4 remain

A

stored in the colloid until they are split off and secreted

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38
Q

SECRETION OF THYROID HORMONE

A

SECRETION OF THYROID HORMONE

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39
Q

what happens to secrete thyroid hormones from the colloid

A

the follicular cells internalise a portion of the thyroglobulin complex by phagocytosing part of the colloid

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40
Q

what happens when the colloid is internalised

A

T3 and T4 are split by lysosomes into free T3 and T4 as well as MIT and DIT

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41
Q

are thyroid hormones lipophilic

A

yes so can pass the membrane of follicular cells and into the blood

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42
Q

are MIT and DIT of value

A

no

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43
Q

what happens to MIT and DIT

A

follicular cells have an enzyme called iodinate that removes the iodine from MIT and DIT

44
Q

what happens to the free iodine

A

they are recycled for synthesis of more hormone

45
Q

what is the majority of T3 and T4 transported by

A

thyroxine-binding globulin

46
Q

is most T3 or T4 free or bound

A

bound

47
Q

is bound T3 and T4 able to bind to receptors

A

no only the free form

48
Q

T4 CONVERTING TO T3

A

T4 CONVERTING TO T3

49
Q

what is secreted more T4 or T3

A

T4

50
Q

what is more potent T3 or T4

A

T3

51
Q

what happens to most of T4

A

it is converted into T3

52
Q

how is T4 activated to T3

A

it is stripped of one of its iodide outside the thyroid gland

53
Q

where is T4 converted to T3

A

liver and kidneys

54
Q

what happens when thyroid hormone crosses the plasma membrane

A

binds to a nuclear receptor bound to the thyroid-response element of DNA - this alters transcription of mRNA

55
Q

what does the receptor have a higher affinity for T3 or T4

A

T3

56
Q

does thyroid hormone affect all body cells

A

yes it can in one way or another

57
Q

how dose thyroid hormone affect metabolic rate

A

increases it

58
Q

what does thyroid hormone do to catecholamines

A

stimulates them

59
Q

effect of thyroid hormone on cardiovascular status

A

increase heart rates and force of contraction therefore increase cardiac output

60
Q

is thyroid hormone essential for normal growth

A

yes

61
Q

does thyroid hormone stimulate growth hormone secretion

A

yes

62
Q

does excess thyroid produce excess growth

A

no

63
Q

does thyroid hormone play an essential role in normal development of nervous system

A

yes

64
Q

REGULATION OF THYROID HORMONE

A

REGULATION OF THYROID HORMONE

65
Q

what its het most important regulator of thyroid hormone secretion

A

thyroid stimulating hormone

66
Q

what produces thyroid stimulating hormone

A

the anterior pituitary

67
Q

what does thyroid stimulating hormone increase

A

cAMP in the thyrotropes

68
Q

what is every step of thyroid hormone synthesis stimulated by

A

TSH

69
Q

other than enhancing thyroid hormone secretion what else does TSH have a role in

A

maintaining the structural integrity of the thyroid gland

70
Q

what happens to the thyroid gland in the absence of TSH

A

atrophies (decreases in size)

71
Q

how does excess TSH affect the thyroid gland

A

hypertrophy and hyperplasia i

72
Q

what turns on TSH secretion

A

thyrotropin releasing hormone

73
Q

what turn off TSH secretion

A

thyroid hormone

74
Q

how does TRH function via

A

the IP3/DAG/ Ca2+ pathway

75
Q

what is the only factor that increase TRH secretion

A

exposure to cold in newborn infants

76
Q

what factors inhibit TSH and thyroid hormone secretion

A

stress starvation infection

77
Q

ABNORMALITIES IN THYROID FUNCTION

A

ABNORMALITIES IN THYROID FUNCTION

78
Q

what are the 2 main thyroid disorders

A
  • hypothyroidism - hyperthyroidism
79
Q

how can hypothyroidism occur

A
  • primary failure of thyroid gland - secondary to a deficient TRH, TSH or both - inadequate dietary supply of iodine
80
Q

symptoms of hypothyroidism

A
  • reduced BMR - poor tolerance to cold - gain excessive weight - easily fatigued - slow, weak pulse - slow reflexes - diminished alertness - slow speech - poor memory - puffy appearance in face and hands (myxoedema)
81
Q

what develops if someone has hypothyroidism from both

A

cretinism

82
Q

what is cretinism characterised by

A
  • dwarfism - mental retardation
83
Q

treatment of hypothyroidism

A

replacement therapy by administering thyroid hormone

84
Q

what is the most common cause of hyperthyroidism

A

Graves disease

85
Q

what is Graves disease

A

autoimmune disease in which the body produces excess thyroid stimulating immunoglobulin (TSI)

86
Q

what does TSI stimulate

A

secretion and growth of the thyroid

87
Q

does TSI affect the negative feedback loop

A

nope it has no effect on negative feedback

88
Q

symptoms of hyperthyroidism

A
  • elevated BMR - increased heat production - excessive perspiration - poor tolerance to heat - weight loss - muscle weakness - palpitations - irritable - tense - anxious
89
Q

prominent features of Graves disease

A
  • exophthalmos
90
Q

what is exopthalamos

A

bulging eyes - the eye may bulge so much that they cannot close their eyes

91
Q

treatment of hyperthyroidism

A
  • antithyroid drugs - surgical removal of a portion of the over secreting thyroid gland - administration of radioactive iodine
92
Q

what happens when radioactive iodine is administered

A

destroys thyroid glandular tissue

93
Q

GOITER

A

GOITER

94
Q

what is a goiter

A

enlarged thyroid gland

95
Q

is a goitre palpable

A

yes

96
Q

can goitre be present in hypothyroidism and hyperthyroidism

A

yes

97
Q

when is a goitre present in hypothyroidism

A
  • thyroid gland failure - lack of iodine
98
Q

why is there a goitre in hypothyroidism

A

as its a negative feedback system there is little thyroid hormone so TSH is being produced this increases the size of the thyroid gland

99
Q

if there is still TSH why may there not be thyroid hormone

A

due to lack of iodine or enzymes

100
Q

why is there a goitre in hyperthyroidism

A
  • excessive TSH secretion - Graves disease (TSI promotes growth)
101
Q

when would there be hyperthyroidism but no goitre

A

thyroid tumour

102
Q

why is there no goitre in thyroid tumour

A

as there is excessive amounts of T3 and T4 it inhibits TSH so there is no input to promote growth of the thyroid

103
Q

look at diagram of anatomy and histology

A
104
Q

diagram

A
105
Q

diagram

A

endocrine (6 decks)

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