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Endo > thyroid gland > Flashcards

thyroid gland Flashcards

wk 5

1
Q

What is the secondary role of the thyroid gland? and what does it do?

A

secretion of calcitonin (regulates calcium concentration in the blood)

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2
Q

What does the combination of two DIT molecules create?

A

T4

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3
Q

What does the combination of one DIT and one MIT create?

A

T3

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4
Q

What are the first 4 steps of thyroid biosynthesis?

A

Na+/I- symporter rbinsg I into cell

Pendrin transporter moves I- into blood

Follicular cell synthesises enzymes + thyroglobulin = colloid

Thyroid peroxidase adds iodine to tyrosine to make T3 and T4

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5
Q

What are the last 4 steps of thyroid biosynthesis?

A

Thryoglubin is taken back into cell in vesciles

Intracellular enzymes separte T3 and T4 from protein

Free T3 and T4 enter circulation

stored in veciles for 2-3 months

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6
Q

describe the actions of thyroglobulin when stimulated.

A

Iodianted thyroglobulin is taken into follcilar cell via endocytosis

Lysosomal enzymes digest thyroglobulin to release T4 and T3

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7
Q

Does T4 or T3 have a stronger binding affinity to proteins?

A

T4

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8
Q

How are thyroid hormones released into tissue cells?

A

slowly by plasma proteins

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9
Q

Is T3 or T4 more biologically active?

A

T3 (3-4 times more potent)

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10
Q

Does T3 of T4 have a longer half life?

A

T4

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11
Q

Where is the receptor that the thyroid binds to?

A

in DNA strands or close proximity

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12
Q

What GPCR pathway does thyroid use?

A

cAMP

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13
Q

What are the effects of TH on Basal Metabolic rate?

A

Increases cellular metablic acivity

Maintains optimal levels for metabolism (Plasma concentration of thyroid is major factor in BMR)

Increases 60-100% above normal when large quantities of TH

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14
Q

What are the effects of TH on calorigenic Action

A

Increases synthesis of Na and K ATPase = increase oxygen consumption. (NaK-ATPase consumes ATP= heat)

Influences rate of food utilisation for energy (increased)

Increases amount and activity of mitochondria

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15
Q

What are the main areas of metabolism that TH impacts?

A

Protein, carbohydrate and fat metabolism

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16
Q

What is the impact of low thyroid levels on protein synthesis?

A

increased protein synthesis

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17
Q

What is the impact of high thyroid levels on proteins?

A

increased protein degradation

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18
Q

What is the impact of excessive TH for proteins

A

protein catabolism (due to high metabolic rate) = weight loss and nitrogen excretion

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19
Q

What are the effects of TH on glucose and carbohydrates?

A

increases glucose absorption from GIT, Increases blood glucose level and worsens diabetes mellitus

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20
Q

What is the effect of TH on fat metabolism?

A

increases release of fatty acid from adipocytes

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21
Q

What is the effect of TH on cholesterol metabolism?

A

lowers cholesterol levels, stimulates adipocyte proliferation and increases intracellular lipid accumulation

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22
Q

In regrads to growth and development, what needs TH?

A

maturation of central nervous system and attainement of adult stature

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23
Q

What (in CNS) does TH stimulate the growth of?

A

synapse, myelin formation and axonal growth

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24
Q

What can hypothyroidism during CNS development cause and what are the major parts effected?

A

mental retardation – cerebral cortex, basal ganglia and cochlea damaged.

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25
Q

Describe the impact of TH for bone growth

A

Acts synergistically with GH and somatomedins to promote bone function

Stuimulates bone maturation

Accelerates turnover of material in bone

Increased growth via chondrocytes and osteoblast stimulation

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26
Q

Describe the mechanims of action of Th via cAMP AC pathway

A

– increases iodide transport into follicular cells
– increases production and iodination of thyroglobulin
– increases endocytosis of colloid from lumen into follicular
cells
– TSH increases both the synthesis and secretion of thyroid
hormones

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27
Q

What are three hyperthyroidism disorders?

A

Graves disease, TSH-producing adenoma and Toxic multinodular goiter.

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28
Q

What are some symptoms indicating hyperthyroidism?

A

Increased Basal metabolic rate (weight loss),
increased cardiac output (tachycardia), exophthalmos (bulging eyeballs),

insomnia, heat intolerance, diarrhea, fine tremors and increased heat production

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29
Q

What are the primary hyperthyroidism disorders?

A

Graves’ disease
* Toxic multinodular goiter
* Toxic adenoma
* Functioning thyroid carcinoma metastases
* Activating mutation of the TSH receptor

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30
Q

What are secondary hyperthyroidism disorders?

A
  • TSH-secreting pituitary adenoma
  • Thyroid hormone resistance syndrome
  • Chorionic gonadotropin-secreting tumors
  • Gestational thyrotoxicosis
31
Q

Describe the T3. T4 and TSH levels on hypothyroidism. Usually.

A

T3 and T4 are low but TSH is usually raised.

32
Q

What does raised TSH levels indicate?

A

fault in or above the pituitary gland.

33
Q

what is the most common cause of hypothyroidism?

A

Hashimoto thyroiditis

34
Q

What occurs in Hashimoto’s thyroiditis?

A

Active B lymphocytes produce antibodies that lead to the destruction of thyroid tissue.

35
Q

What is secondary hypothyroidism?

A

pituitary adenoma –> decreased TSH

36
Q

what is tertiary hypothyroidism?

A

hypothalamic disorder –> TRH

37
Q

what are the three types of goiters?

A

nondular, toxic and non-toxic

38
Q

what are the causes of non-toxic goiters?

A

iodine deficencey and soporadic hypothyrodims of unkown origin

39
Q

What is the most common goiter?

A

diffuser goiter

40
Q

what is a nondular goiter?

A

irregulary englarged thyrpid due to nodule formation toxic multinodular goiter

41
Q

What is an example of hypo and hyperthyroidism goiters?

A

Graves disease, Hashimoto thyroiditis

42
Q

What is cretinism?

A

A disorder caused by congenial hypothyroidism that leads to impaired brain and skeleton development and stunts normal growth.

43
Q

What is the action of TH on respiration?

A

Stimulation of the respiratory centre, increases raye and stimulation of red blood cell formation

44
Q

What is the impact of TH on the cardiovascular system?

A

increased cardiac beta-receptors, heart rate, stroke volume and contractibility.

45
Q

What is likely if TSH levels are low?

A

lesion of the hypothalamus or pituitary.

46
Q

What are antithyroid antibodies and what is their action?

A

Thyroid stimulating immunoglobulins (TSI)

antibodies that target one or more components of the thyroid glands. Act against and to stimulate TSH receptors

47
Q

What is the anatomical position of Thryoid to trachea and larynx?

A

Superior to trachea (around it)
inferior to larynax

48
Q

What is the histological structure of the thyroid gland?

A

Organised epithelial cells surrounded by colloid-containing follicles

49
Q

what are the two enzymes involved in thyroid hormone biosynthesis?

A

thyroperoxidase and deiodinase

50
Q

What is the role of thyroperoxidase in biosynthesis

A

oxidose iodide into iodine

51
Q

deiodinase

A

Remove iodine from thyroid hormones, converting T4 to T3

52
Q

What is the mechanism of action for thyroid hormones?

A

Binds to GPCR –> activates G protein–> GTP converted to GDP –> activates AC –> cAMP pathway activates PKA –> phosphorylates protein transcription to produce Thyroglobulin –> thyroglobulin packaged in GA then released in a vesicle –> exocytosis

53
Q

describe the role of Throid hormone on blood pressure

A

thyroid hormones increase β-adrenergic receptors of various tissues = increase blood pressure

54
Q

do increased levels of tH lead to a decrease in Ca ions?

A

yes

55
Q

what do the following symptoms indicate?

slight enlargement of Thyroid gland, delayed tendon reflex and TSH level elevated

A

Hypothyroidism -slow muscle contraction
TSH leves raised due to negative feedback loop

56
Q

Describe Graves Disease?

A

Hyperthyroid disorder: an autoimmune condition where the antibodies (TSI) target one or more components of the gland.

Continuous stimulation by TSI acting against TSH

57
Q

What are the signs of Hyperthyroidism?

A

Tachycardia, increased metabolic function ), warm and moist skin, muscle weakness, tremor and goiter.

58
Q

what are the symptoms of hyperthyroidism?

A

heat intolerance palpitations, fatigue, weakness, diarrhoea, weight loss

59
Q

What are the Tyroxine, free thyroxine and TSH levels in Euthyroidism

A

normal

60
Q

What are the Tyroxine, free thyroxine and TSH levels in Hyperthroidism?

A

high, high and low

61
Q

what are the physiological actions of thyroid hormones on bone growth?

A

TH acts syngetically with GH to promote growth function.

TH stimulates bone maturation via ossification and fusion of growth plates

62
Q

How is TSH secretion regulated?

A

TRH and negative feedback loop

63
Q

what is the impact of TH on muscle proteins?

A

Catabolic: increases protein breakdown

64
Q

Describe what is involved in Iodine trapping.

A

Iodide absorbed form diet by converying to Iodine

Na/K ATPase lowers Na concentartion insde cell

Na/I symporter allows 2 Na to exit and 1 Iodine to enter

Pendrin antipoter transport iodine to colloid

65
Q

What is I2?

A

iodine

66
Q

What is the role of TSH in TH biosynthesis?

A

Increases all aspects of TH biosynthesis= Tropic and Trophic effect

Increases synthesis of TH

67
Q

What do parafollicular cells surround?

A

follicles that secrete calcitonin

68
Q

Where is thyroglobulin found?

A

in colloid

69
Q

what type of protein is thyroglobulin and how is it synthesised?

A

a glycoprotein that is synthesised from tyrosine in follicular cells and extruded into the follicular lumen

70
Q

Where is iodine concentrated?

A

n thyroid epithelial cells by an active,
energy-dependent process mediated by a sodium-iodide symporter located in the basolateral membrane of the follicular
cell

71
Q

what is a myxedema caused by?

A

Myxedema occurs when there is too much fluid in the body’s tissue. T4 and T3 are inhibitors of mucopolysaccharide synthesis, so when limited, causes an accumulation of mucopolysaccharides. This promotes water retention allowing fluid to build up.

72
Q

what is exophthalmos caused by?

A

TSI stimulates mucopolysaccharide synthesis in connective extraocular muscles. resulting in protrusion of eyeballs.

73
Q

what is the difference between the causes of exopththalmos and myxedme?

A

xeophthalmos is due to inflammation induced changes in the retroorbital region and myxedema is due to increased mucopolysaccharides.

Endo (14 decks)

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