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Endocrine- Thyroid > Physiology > Flashcards

Physiology Flashcards

1
Q

What three things does thyroid gland tissue secrete?

A

T3, T4 and calcitonin

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2
Q

What is required for the synthesis of thyroid hormones?

A

Iodine

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3
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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4
Q

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

A

1 iodine

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5
Q

Iodine is taken up by which cells?

A

Follicular cells

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6
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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7
Q

How do carbimazole and PTU work?

A

They prevent iodination of tyrosine

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8
Q

What units need to be combined to form T3?

A

1 MIT and 1 DIT

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9
Q

What units need to be combined to form T4?

A

2 DITs

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10
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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11
Q

Which is the major biologically active thyroid hormone?

A

T3

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12
Q

Which thyroid hormone is produced in greater amounts?

A

T4

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13
Q

What happens to the majority of T4 produced?

A

It is converted to T3 in peripheral tissues

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14
Q

What chemical process changes T4 to T3?

A

5-monodeiodination (removal of 1 iodine)

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15
Q

What does 3-monodeiodination of T4 form?

A

rT3

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16
Q

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

A

Deiodinase enzymes

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17
Q

Where is deiodinase 1 found?

A

Liver and kidney

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18
Q

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

A

D2

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19
Q

Where is deiodinase 3 found?

A

Foetal tissue ad brain (except the pituitary gland)

20
Q

What is the first step in releasing thyroid hormones?

A

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

21
Q

What type of receptor is the TSH receptor?

A

GPCR

22
Q

What happens when TSH has bound to its receptor?

A

GTP is converted to GDP and cAMP is produced

23
Q

What allows T3 and T4 to be released from cells?

A

Increased cAMP

24
Q

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

A

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

25
Q

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

A

Thyroxine binding globulin

26
Q

What are the less used hormone binding proteins?

A

Thyroid-binding pre-albumin

Albumin

27
Q

Which thyroid hormone is bound less avidly to TBG?

A

T3

28
Q

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

A

Free

29
Q

What type of receptor is the T3 receptor?

A

Nuclear

30
Q

How are thyroid hormones taken into cells?

A

A transmembrane transporter

31
Q

What is the thyroid hormone receptor bound to?

A

Thyroid response element

32
Q

Where are TRalpha thyroid receptors found?

A

Peripheral tissues

33
Q

Where are TRbeta thyroid receptors found?

A

In the feedback loop

34
Q

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

A

TRbeta

35
Q

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

A

Increase it

36
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
37
Q

What effect do thyroid hormones have on thermogenesis?

A

Increase it

38
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
39
Q

Name two effects that thyroid hormones have on lipid metabolism?

A
  • Mobilise fats from adipose tissue

- Increase fatty acid oxidation in tissues

40
Q

What two effects do thyroid hormones have on protein metabolism?

A
  • Increased protein synthesis

- Decreased plasma amino acids

41
Q

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

A

GHRH and GH

42
Q

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

A

They allow myelinogenesis and axonal growth

43
Q

What can inadequately treated hypothyroidism in pregnancy cause?

A

Problems with cognitive development

44
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.

45
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

46
Q

What effect does stress have on thyroid function?

A

Inhibits TRH and TSH release

47
Q

Describe the circadian rhythm of thyroid hormones?

A

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

Endocrine- Thyroid (6 decks)

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