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MEH > Thyroid gland > Flashcards

Thyroid gland Flashcards

1
Q

describe the structure of the thyroid gland

A

2 lobes joined by the isthmus

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2
Q

location of the thyroid gland

A
  • lies against and on front of larynx + trachea
  • below thyroid cartilage
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3
Q

describe the embryological development of thyroid gland

A
  • originates from foramen caecum
  • thyroid diverticulum grows down > thyroglossal duct
  • as thyroid descends the thyroglossal duct breaks down
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4
Q

describe the microscopic structure of thyroid glands

A
  • thyroid follicles - follicular cells in spheres
  • filled with colloid - deposition of thyroglobin
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5
Q

what do thyroid follicular cells produce?

A

thyroid hormone

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6
Q

what do parafollicular cells produce?

A

calcitonin

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7
Q

what are the principal cells of the parathyroid gland?
what do they produce?

A

chief cells
parathyroid hormone

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8
Q

how are thyroid hormones formed?

A

2 tyrosine molecules are linked together with iodine at 3 or 4 positions on aromatic rings

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9
Q

what is iodine used for in the body?

A

making thyroid hormone

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10
Q

what is needed to make T3?

A

monoiodotyrosine + diiodotyrosine > triiodotyrosine

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11
Q

what is needed to make T4?

A

diiodotyrosine + diiodotyrosine > tetraiodotyrosine/thyroxine

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12
Q

what is the role of thyroglobulin in thyroid hormone formation?

A

acts as a scaffold on which thyroid hormones are produced

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13
Q

what is thyroid peroxidase?

A

membrane bound enzyme that regulates thyroid hormone synthesis

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14
Q

what does thyroid peroxidase regulate to thyroid hormone synthesis?

A
  • oxidation of iodide to iodine
  • addition of iodine to tyrosine acceptor residues on thyroglobulin
  • coupling of MIT/DIT to generate thyroid hormones
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15
Q

outline the absorption of dietary iodine in the thyroid gland

A
  • dietary iodine reduced to iodide
  • iodide absorbed by small intestines
  • iodide taken up from blood by thyroid epithelial cells via Na/I- symport
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16
Q

sources of iodine

A

dairy products
meat
vegetables
eggs
grains

17
Q

where is T4 converted to T3?

A

liver + kidneys

18
Q

how are thyroid hormones transported in the blood?

A

lipid soluble
bound to thyroxine-binding globulin

19
Q

what thyroid hormone is more biologically active?

A

T3

20
Q

what are the effects if T3 and T4?

A
  • effects on cellular differentiation + development
  • effects of metabolic pathways
21
Q

describe the structure of TSH

A

glycoprotein hormone
composed of 2 non-covalently bound subunits aB

22
Q

what does TSH stimulate?

A
  • iodide uptake
  • oxidation of iodide to iodine
  • thyroglobulin synthesis
  • thyroglobulin iodination
  • colloid pinocytosis into cells
  • proteolysis of thyroglobulin
  • cell metabolism + growth
23
Q

actions of thyroid hormone

A
  • increase in BMR + heat production
  • stimulation of metabolic pathways
  • sympathomimetic effects
24
Q

how do thyroid hormones increase BMR + heat production?

A
  • increase number + size of mitochondria
  • stimulate synthesis of enzymes in respiratory chain
25
Q

what metabolic pathways are stimulated by thyroid hormone?

A
  • lipid metabolism - lipolysis + B-oxidation
  • carb metabolism - gluconeogenesis, glycogenolysis, insulin dependent entry of glucose into cells
26
Q

what are the sympathomimetic effects of thyroid hormones?

A

increases target cell response to catecholamines

27
Q

effect of thyroid hormones on CVS

A
  • increases hearts responsiveness to catecholamines:
  • increase CO (HR and force of contraction) + peripheral vasodilation
28
Q

effect of thyroid hormones on nervous system

A
  • increased development of neurones
  • increased myelination of nerves
29
Q

what type of receptors are thyroid hormone receptors?
what is their function?
what is their action?

A
  • nuclear receptors
  • hormone-activated transcription factors
  • modulating gene expression
30
Q

what is goitre?

A
  • enlargement of thyroid gland due to overstimulation
31
Q

What affect would lack of dietary iodine have on?
- T3+4
- TSH
- goitre present?

A
  • decreased T3+4
  • increased TSH
  • yes, goitre present

MEH (23 decks)

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