Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

*Diabetes & Endocrinology > Thyroid Gland > Flashcards

Thyroid Gland Flashcards

1
Q

What are the 2 physiologically active forms of thyroid hormone?

A

T3 (triiodothyronine) and T4 (thyroxine)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What 2 cell types does the thyroid gland contain?

A

C (clear) cells

Follicular cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What do C cells secrete?

A

Calcitonin (Ca2+ secreting hormone)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the function of follicular cells?

A

Support thyroid hormone synthesis and surround hollow follicles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the structure of thyroid follicles?

A

Spherical structures whose walls are made of follicular cells; centre is filled with colloid (sticky glycoprotein matrix)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How much supply of TH do thyroid follicles contain?

A

2-3 months

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What do follicular cells manufacture?

A

Enzymes that make thyroid hormones as well as thyroglobulin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is thyroglobulin?

A

A large protein rich in tyrosine residues

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What happens once the enzymes and thyroglobulin produced by follicular cells are made?

A

They are packaged into vesicles and exported from follicular cells into the COLLOID

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What do follicular cells do with iodide?

A

Actively concentrate it from plasma and transport it into colloid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What does iodide do once it is transported into the colloid?

A

Combines with tyrosine residues to form thyroid hormones

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Where are tyrosine and iodide derived from?

A

Diet

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How does iodide enter follicular cells from the plasma?

A

via a Na+/I- transporter (symport); the coupling to Na+ enables the follicular cells to take up iodide against a concentration gradient

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Via what transporter is iodide sent into the colloid?

A

Pendrin transporter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Enzymes exocytosed into the colloid, along with the thyroglobulin, catalyse what?

A

Addition of iodide to tyrosine residues on the thyroglobulin molecule

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What happens to iodide in the process of being added to tyrosine residues?

A

Loses an electron to become iodine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Addition of one iodine to tyrosine =

A

MIT (monoiodotyrosine)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Adding a second iodine =

A

DIT (diiodotyrosine)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

MIT + DIT =

A

triiodothyronine or T3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

DIT + DIT =

A

tetraiodothyronine or T4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What enzyme are these reactions catalysed by?

A

Thyroid peroxidase (aka thyroperoxidase)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What happens in response to TSH?

A

Portions of the colloid are taken back up into the follicular cell by endocytosis
Within the cell they form vesicles which contain proteolytic enzymes that cut the thyroglobulin to release thyroid hormones

23
Q

What is the nature of T3 and T4?

A

Lipid soluble

24
Q

What do T3 and T4 bind to in the plasma?

A

Plasma proteins (mainly thyroxine-binding globulin)

25
Q

Where do both T3 AND T4 circulate?

A

the plasma

26
Q

Where are the thyroid hormones stored when their release is not stimulated by TSH?

A

the colloid

27
Q

Where is TSH released from?

A

Pituitary gland

28
Q

Which thyroid hormone does TBG have a particularly high affinity for?

A

T4 - releases it slowly into plasma giving it a longer half life than T3

29
Q

Which hormone is released from the hypothalamus to stimulate TSH production?

A

TRH

30
Q

What exerts an inhibitor effect on TSH and TRH

A

ONLY free hormone

31
Q

How much of TH in the plasma is free, unbound and physiologically active?

A

0.2%

32
Q

Which TH hormone do TH receptors have a higher affiinity for, making it more physiologically active?

A

T3

33
Q

What catalyses the deiodination of T4 to T3?

A

Deiodinase enzymes

34
Q

How much of T4 is deiodinated in plasma? And where is the remaining fraction deiodinated?

A

Around half

Inside target cells

35
Q

In what conditions is TRH release boosted?

A

Cold
Exercise
Pregnancy

36
Q

What do somatostatins inhibit in terms of thyroid?

A

TSH

TH required for GH action

37
Q

What do glucocorticoids inhibit in terms of thyroid?

A

TSH and conversion of T4 to T3

38
Q

Where do THs bind in target cells?

A

Nuclear receptors

39
Q

What effect do THs have once bound to receptors?

A

They change transcription and translation to alter protein synthesis

40
Q

Give 6 functions of TH in the body

A
  • raises metabolic rate and promotes thermogenesis (futile cycles)
  • increases hepatic gluconeogenesis (tho no effect on BG if pancreas functional)
  • net increase in proteolysis
  • net increase in lipolysis
  • critical for growth (stimulates GH receptor expression)
  • essential for brain development in utero
41
Q

What can maternal iodine deficiency result in?

A

Congenital hypothyroidism/cretinism

42
Q

2 causes for hyperthyroidism

A
  • Graves disease (common)

- Thyroid adenoma (rare)

43
Q

Describe the mechanism of Graves

A

antibodies produced that mimic TSH + continually activate thyroid gland; increased release of TH switches off TSH release from pituitary = TSH plasma v low

44
Q

What happens to thyroid gland as result of Graves

A

may be 2-3x normal size due to hyperplasia

45
Q

What is a thyroid adenoma?

A

Hormone-secreting thyroid tumour

46
Q

4 symptoms of hyperthyroidism and the mechanism behind?

A
  1. Increased metabolic rate + heat production =
    weight loss/heat intolerance
  2. Increased protein catabolism
    = muscle weakness/weight loss
  3. Altered nervous system function
    = hyperecitable reflexes + psychological disturbance
  4. Elevated cardiovascular function
    = increased HR/contractile force, high output, cardiac failure
47
Q

Give 3 causes of hypothyroidism

A
  • Hashimoto’s disease (autoimmune attack of thyroid gland)
  • Deficiency of dietary iodine
  • Idiopathic
48
Q

4 symptoms of hypothyroidism and mechanism behind (same but opposite to hyper)?

A 
1. Decreased metabolic rate + heat production
= weight gain/cold intolerance
2. Disrupted protein synthesis
= brittle nails/thin skin
3. Altered nervous system function 
= slow speeches/reflexes, fatigue
4. Reduced cardiovascular function
= slow HR/weaker pulse
49
Q

What is seen in BOTH hyper- and hypo- thyroidism?

A

Goitre

50
Q

What is goitre caused by in hypothyroidism?

A

Increased trophic action of TSH on thyroid follicular cells

51
Q

What is goitre caused by in Graves?

A

Over-activity as result of autoimmune disease

52
Q

What is primary thyroid disease?

A

When the TG is not working

53
Q

What is secondary thyroid disease?

A

When the problem is with the PG

54
Q

What is tertiary thyroid disease?

A

When the problem is in the hypothalamus

*Diabetes & Endocrinology (24 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions