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C HD ext. > Thyroid - Pathology > Flashcards

Thyroid - Pathology Flashcards

1
Q

The thyroid gland develops from an invagination of what?

A

Pharyngeal epithelium

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2
Q

Where does the thyroid gland descend to and from?

A

From the foramen caecum of the tongue to the thyroglossal duct

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3
Q

What is known as when the thyroid gland fails to descend normally?

A

Lingual thyroid

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4
Q

If there is excessive descent of the thyroid, where does it end up?

A

Retrosternal in the mediastinum

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5
Q

What is the thyroid gland composed of?

A

Follicles

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6
Q

What cell type are the thyroid follicles surrounded by?

A

Cuboidal follicular epithelial cells

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7
Q

What is the area in the centre of each thyroid follicle known as?

A

Colloid

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8
Q

What does the thyroid colloid contain? What is this?

A

Thyroglobulin- this is the protein on which T3 and T4 are synthesised

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9
Q

What other cell type are found scattered among the thyroid follicles in the upper 2/3rds of the thyroid gland?

A

C-cells (parafollicular cells)

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10
Q

What do C-cells produce?

A

Calcitonin

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11
Q

What does calcitonin do?

A

Decrease serum calcium levels

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12
Q

Calcitonin is a good marker for what?

A

Medullary thyroid cancer

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13
Q

What three things does thyroid gland tissue secrete?

A

T3, T4 and calcitonin

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14
Q

What is required for the synthesis of thyroid hormones?

A

Iodine

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15
Q

What will happen if you live in an area where there is not enough iodine?

A

You won’t make enough thyroid hormones and hence will be hypothyroid

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16
Q

What is the difference, chemically, between T3 and T4?

A

1 iodine

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17
Q

Iodine is taken up by which cells?

A

Follicular cells

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18
Q

What does iodine attach to once it has been taken up? What does this form?

A

Iodine attaches to tyrosine units on thyroglobulin to form MIT and DIT units

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19
Q

How do carbimazole and PTU work?

A

They prevent iodination of tyrosine

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20
Q

What units need to be combined to form T3?

A

1 MIT and 1 DIT

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21
Q

What units need to be combined to form T4?

A

2 DITs

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22
Q

What happens to T3 and T4 molecules once they have been synthesised?

A

They are stored in colloid thyroglobulin until they are required

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23
Q

Which is the major biologically active thyroid hormone?

A

T3

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24
Q

Which thyroid hormone is produced in greater amounts?

A

T4

25
Q

What happens to the majority of T4 produced?

A

It is converted to T3 in peripheral tissues

26
Q

What chemical process changes T4 to T3?

A

5-monodeiodination (removal of 1 iodine)

27
Q

What does 3-monodeiodination of T4 form?

A

rT3

28
Q

Which family of enzymes regulates the conversion of T4 to T3?

A

Deiodinase enzymes

29
Q

Where is deiodinase 1 found?

A

Liver and kidney

30
Q

Which deiosinase enzyme is the major determinant of generating T3 from T4?

A

D2

31
Q

Where is deiodinase 3 found?

A

Foetal tissue ad brain (except the pituitary gland)

32
Q

What is the first step in releasing thyroid hormones?

A

TSH binds to its receptor on the surface of thyroid epithelial cells

33
Q

What type of receptor is the TSH receptor?

A

GPCR

34
Q

What happens when TSH has bound to its receptor?

A

GTP is converted to GDP and cAMP is produced

35
Q

What allows T3 and T4 to be released from cells?

A

Increased cAMP

36
Q

Where is most T3 and T4 found in the plasma? Why?

A

Bound to hormone binding proteins, since they are hydrophobic and lipophilic

37
Q

What hormone binding protein is most of T3 and T4 bound to in the plasma?

A

Thyroxine binding globulin

38
Q

What are the less used hormone binding proteins?

A

Thyroid-binding pre-albumin Albumin

39
Q

Which thyroid hormone is bound less avidly to TBG?

A

T3

40
Q

What type of T3 and T4 should be measured in a thyroid function test?

A

Free

41
Q

What type of receptor is the T3 receptor?

A

Nuclear

42
Q

How are thyroid hormones taken into cells?

A

A transmembrane transporter

43
Q

What is the thyroid hormone receptor bound to?

A

Thyroid response element

44
Q

Where are TRalpha thyroid receptors found?

A

Peripheral tissues

45
Q

Where are TRbeta thyroid receptors found?

A

In the feedback loop

46
Q

Resistance to which type of thyroid receptor causes the biggest problem?

A

TRbeta

47
Q

What effect do thyroid hormones have on the basal metabolic rate?

A

Increase it

48
Q

What are 3 ways that thyroid hormones increase basal metabolic rate?

A
  • Increase the number of mitochondria - Increase oxygen use and rate of ATP hydrolysis - Increase synthesis of respiratory chain enzymes
49
Q

What effect do thyroid hormones have on thermogenesis?

A

Increase it

50
Q

Name two effects that thyroid hormones have on carbohydrate metabolism?

A
  • Increase plasma glucose due to stimulation of glycogenolysis and gluconeogenesis - Increase insulin dependent glucose uptake into cells
51
Q

Name two effects that thyroid hormones have on lipid metabolism?

A
  • Mobilise fats from adipose tissue - Increase fatty acid oxidation in tissues
52
Q

What two effects do thyroid hormones have on protein metabolism?

A
  • Increased protein synthesis - Decreased plasma amino acids
53
Q

What hormones relating to growth require thyroid hormones for their action?

A

GHRH and GH

54
Q

How do thyroid hormones help to develop the foetal and neonatal brain?

A

They allow myelinogenesis and axonal growth

55
Q

What can inadequately treated hypothyroidism in pregnancy cause?

A

Problems with cognitive development

56
Q

What effect do thyroid hormones have on the sympathetic nervous system? What effect does this have on the CV system?

A

They increase responsiveness to adrenaline and noradrenaline by increasing the number of receptors. This increases cardiac rate and force of contraction.

57
Q

What effect do low temperatures have on thyroid function in babies and young children?

A

Stimulate TRH release, hence TSH release, hence T3/4 release

58
Q

What effect does stress have on thyroid function?

A

Inhibits TRH and TSH release

59
Q

Describe the circadian rhythm of thyroid hormones?

A

Thyroid hormone levels are high at night and low in the morning

C HD ext. (5 decks)

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