Brainscape's Knowledge GenomeTM

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


See full index

BRS Endocrinology > The Thyroid Gland > Flashcards

The Thyroid Gland Flashcards

1
Q

Label these diagrams of the thyroid gland.

A

Pyramid= pyramidal lobe

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

Where are parathyroid glands embedded?

A

In the thyroid

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

What supplies the vocal cords?

A

Left recurrent laryngeal nerve and it runs close to the thyroid gland

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

Describe the embryology of the thyroid gland.

A

Midline outpouching from floor of pharynx (originates from base of tongue)

Development of thyroglossal duct

Divides into 2 lobes

Duct disappears leaving foramen caecum

Final position by week 7

Thyroid gland then develops

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

What is it called when the thyroid fails to develop at all?

A

thyroid agenesis
- it can also remain in tongue leading to a lingular thyroid

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

Label this diagram.

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

What stain is used to check thyroid histology?

A

H and E stain

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

What is the small white spaces in this thyroid histology?

A

Where reactions take place to make thyroid hormone

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

How does TSH work on the thyroid gland?

A

TG=> thyroglobulin
TPO=> thyroperoxidase
MIT and DIT=> monoiodotyrosine and diiodotyrosine

Sodium iodide transporter

lysosome break bonds in thyroglobulin holding T3 and T4 so they can released into blood stream

Iodination occurs colloid

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

What are the thyroid hormones?

A

Iodothyronines

coupling reactions from T3 and T4

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

What is the main product of the thyroid gland?

A

T4= thyroxine

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

Why is T3 formed and how does T4 turn into T3?

A

Deiodinated to triiodothyronine (T3), its bioactive form, in target tissues by DEIODINASE ENZYME

Also can deiodinated in a different position to produce reverse T3 (inactive)

T4-> T3 can happen within target tissue

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

What is T4?

A

tetraiodothyronine is a prohormone

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

What is the half life of T3 and T4?

A

T4 is roughly 7-9 days
T3 is roughly 2 days

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

How much of circulating T3 is from the thyroid gland?

A

80% from deiodination of T4
20% from direct thyroidal secretion

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

What does T3 provide?

A

T3 provides almost all the thyroid hormone activity in target cells.

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

How is T3 and T4 transported in the blood?

A

Mostly bound to plasma proteins

a) thyroid-binding globulin: TBG (70-80%)
b) albumin (10-15%)
c) prealbumin (aka transthyretin)

Only 0.05% T4 and 0.5% T3 is unbound (bioactive components)

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

What does T3/ T4 do once inside the cell?

A

First T4 is converted to T3

T3 then enters the nucleus and binds to TR (thyroid hormone receptor) on TRE gene

Leading to altered gene expression

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

What are the actions of thyroid hormone in babies?

A

Essential for fetal growth & development, in particular that of the central nervous system
Untreated congenital hypothyroidism: cretinism
TSH measured in new-born infant’s heel-prick test

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

What is untreated congenital hypothyroidism called?

A

Untreated congenital (present since birth) hypothyroidism: cretinism

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

How is TSH measured in a new-born infant?

A

TSH measured in new-born infant’s heel-prick test

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

What does a baby with hypothyroidism look like?

A

swollen and drowsy

23
Q

What are the actions of thyroid hormone?

A

↑ Basal metabolic rate
Protein, carbohydrate & fat metabolism
Potentiate actions of catecholamines (e.g. tachycardia, lipolysis)
Effects on the GI, CNS, Reproductive systems

24
Q

What happens when thyroid hormone binds to nuclear receptor?

A

Synthesis of new proteins

25
Q

How is thyroid hormone production controlled?

A

Somatostatin also inhibits TSH

26
Q

What is the effect called of the control of thyroid hormone production?

A

Wolff-Chaikoff effect (inhibits production of T3 and T4)

27
Q

What sex are thyroid disease more common in?

A

Women 4:1 ratio

28
Q

Why are women thought to be more prone to thyroid disease?

A

Because it is though to be related to differences in immune system between men and women
Most thyroid disorders are auto-immune

29
Q

Is an overactive thyroid gland or an underactive thyroid gland more common?

A

The same

30
Q

What happens when there is autoimmune damage to the thyroid?

A

Thyroxine levels decline
TSH levels climb (because of negative feedback)

31
Q

What are the commonest forms of autoimmune thyroid disease?

A

Hashimoto’s thyroiditis and Graves’ disease.

32
Q

What is Hashimoto’s usually associated with?

A

Hashimoto’s is usually associated with hypothyroidism

33
Q

What does the presence of one autoimmune disease increase the risk of?

A

Having others

34
Q

What are the symptoms of hypothyroidism? (7)

A

Deepening voice
Depression and tiredness
Cold intolerance
Weight gain with reduced appetite
Constipation
Bradycardia
Eventual myxoedema coma (if not treated)

35
Q

What is a treatment for hypothyroidism?

A

Levothyroxine (synthetic T4)

36
Q

What is the proposed mechanism of action?

A
37
Q

What are the indications and dosing of levothyroxine?

A

30 mins before eating

38
Q

What are the potential complications of levothyroxine?

A

the headache is rare and well tolerated

39
Q

What other therapy can be used but is not recommended?

A

Liothyronine (T3)

40
Q

What is combination therapy for hypothyroidism?

A

T4 = prohormone, converted by deiodinase action to T3

Combination T4 / T3 – some reported improvement in wellbeing

Complicated by symptoms of ‘toxicity’ – palpitations, tremor, anxiety - often combination treatment suppresses TSH
- risk of cardiovascular issues
- bone issues etc.

41
Q

What happens with hyperthyroidism?

A

Thyroid makes too much thyroxine
Thyroxine levels rise
TSH levels drop

42
Q

What are the causes of hyperthyroidism?

A

Graves’ disease – whole gland smoothly enlarged and whole gland overactive

Toxic multinodular goitre

Solitary toxic nodule

43
Q

What are symptoms of hyperthyroidism? (8)

A

Heat intolerance
Weight loss with increased appetite
Myopathy
Mood swings
Diarrhoea
Tremor of hands
Palpitations
Sore eyes, goitre

44
Q

What is Grave’s disease?

A

Autoimmune disease

  • Antibodies bind to and stimulate TSH receptor in the thyroid
    = Diffuse enlargement and engorgement of thyroid gland
    = Smooth goitre
  • Other antibodies bind to muscles behind eye
    = Exophthalmos
  • Other antibodies stimulate growth of soft tissue of shins
    = pretibial myxoedema
45
Q

What is exophthalmos?

A

proptosis= bulging of eyes

46
Q

What is another word for follicular cells?

A

Thyrocytes

47
Q

How would you describe follicular cells?

A

Bipolar cells (apical and basolateral side)
basolateral= closer to blood vessel
apical= closer to colloid

48
Q

What does colloid contain?

A

precursor hormone thyroglobulin

49
Q

What is on the membrane of the basolateral side of follicular cells?

A

sodium-iodide symporter
pump 2Na+ into follicular cells down electro-chenical gradient
In order to pump 1 I- into cells

50
Q

How is iodine pumped into the colloid space?

A

From the apical side through pendrin an ion transporter
- exchanges iodide for chloride

51
Q

What happens to the iodide once in the colloid?

A

When the iodide is in the colloid it undergoes oxidation with the enzyme thyroperoxidase
This turns it into an iodine atom

Then it attaches to tyrosine residues which are attached to thyroglobulin
Iodination process
- forming monoiodotyrosine or diiodotyrosine (MIT or DIT)

52
Q

How are MIT and DIT bound together and what do they form?

A

These molecules are bound together by thyroperoxidase making T3 or T4
- These are still bound to thyroglobulin until they are cleaved inside the cell by lysosome

53
Q

What does T3 do?

A

Speed up basal metabolic rate

BRS Endocrinology (12 decks)

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