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Semester 4 (NME) > Thyroid > Flashcards

Thyroid Flashcards

1
Q

What percentage of hormone secreted from the thyroid is T3/T4?

A 
T3 = 7%
T4 = 93%
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2
Q

Which cell in the thyroid secretes T3 and T4? How are these cells arranged?

A

Folicle cells

Arranged into lobules of 20-40 evenly distributed cells

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3
Q

Which receptor allows TSH to act on the thyroid, how does it do this?

A 
Thyrotropin receptor (on thyroid epithelial cells)
G-protein coupled receptor is activated when bound to TSH, converts GTP to GDP increasing cAMP levels (therefore increasing T3+T4 production)
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4
Q

What is the name of the lumen in each thyroid lobule?

A

The colloid

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5
Q

What is thyroglobulin?

A

A carbon chain consisting of many tyrosine molecules

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6
Q

What type of epithelium lines the colloid?

A

Cuboidal epithelium

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7
Q

What is the major constituent of the colloid?

A

Thyroglobulin

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8
Q

Thyroid follicules store enough thyroid hormone to supply to body for how long?

A

3-4 months

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9
Q

What is RT3?

A

Reverese T3
Where diiodotyrosine joins monoiodotyrosine (with the diidotyrosine first)
Functionally insignificant in humans

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10
Q

Which hormone is more potent, T3 or T4?

A

T3 (by around 10x)

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11
Q

What is the main protein which carries T4 and T3 in the blood?

A

Thyroxine-binding globulin

Much lesser extent also thyroxine-binding prealbumin and albumin

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12
Q

How do T3 and T4 travel in the blood, why must they travel this way?

A

Travel bound to proteins

As they are lipids so not soluble

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13
Q

What is the main protein which carries T4 and T3 in the blood?

A

Thyroxine-binding globulin (binds most of the T3)
(Much lesser extent also thyroxine-binding prealbumin and albumin)
Albumin binds majority of T4 but T4 is much less abundant than T3

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14
Q

What is Hashimoto’s thyroiditis?

A

A primary hypothyroidism disease
Autoimmune cause- TCell infiltration
(Blocks thyroperoxidase)- Anti-TPO antigen

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15
Q

High TSH level and low T4 level indicates what?

A

Hypothyroidism

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16
Q

Low TSH level and high T4 level indicates what?

A

Hyperthyroidism

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17
Q

In iodine deficiency what happens to the thyroid?

A

Low T3/T4 detected
Hypothalamus detects and releases more TRH and TSH which leads to receptor overload
This leads to a goitre

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18
Q

Where is calcitonin produced?

A

In the C-Cells which are interspersed with the columnar epithelium

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19
Q

What is the role of the c-cells?

A

They are interspersed with the follicular epithelium and produced the hormone calcitonin
(Also known as parafollicular cells)

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20
Q

What is the role of calcitonin?

A

Lowers blood calcium (counteracts PTH)
Inhibits Ca intestinal absorbtion
Inhibits osteoclasts and stimulates osteoblasts

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21
Q

What is graves disease?

aka toxic diffuse goiter

A

An autoimmune disease which affects they thyroid. It results in hyperthyroidism and goitre

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22
Q

Where is thyroglobulin synthesized and then processed?

A

Synth: Endoplasmic reticulum
Processed: Golgi apparatus

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23
Q

How does Iodide enter the follicle cell? Where does the energy for this come from and what is the process called?

A

IODIDE TRAPPING
Enters via the 2Na/I symporter
Energy comes from concentration gradient (low intracellular Na) created by Na/K ATPase pump

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24
Q

How is iodide moved from the folicle cell into the colloid?

A

Via the PENDRIN I/Cl antiporter

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25
Q

What converts iodide to iodine?

A

Peroxidase enzymes

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26
Q

What happens to free iodine in the colloid?

A

It joins with the tyrosine residues on thyroglobulin, creating either monoiodotyrosines or diodotyrosines

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27
Q

What is the name of the process of moving MIT/ DIT’s/T3/T4 into the follicle cells from the colloid?

A

Pinocytosis

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28
Q

How are T3 and T4 created in the colloid?

A

By joining of MIT’s and DIT’s

Mono/diidotyrosines

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29
Q

When does T3/T4 seperate from thyroglobulin and how does this occur?

A

When taken back into follicle cells

Done by lysosomes

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30
Q

How do T3 and T4 get back into the blood and what happened to them once the reach the blood?

A

Lipid soluble so go through basolateral membrane

Carrier mostly by carrier proteins

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31
Q

How does the body stabilise T3 and T4 levels?

A

Bind to intracellular proteins for storage over days/ weeks

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32
Q

How does the body stabilise T3 and T4 levels?

A

Bind to intracellular proteins for storage over days/ weeks (T4 binds more strongly)

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33
Q

T4 can be classed as a pro- form of T3, how is it converted and where does this happen?

A

By diodinase enzymes
Type 1- In liver, thyroid, kidney (low affinity)
Type 2- In pituitary/ brain/ brown fat/ thyroid (high affinity)
Type 3- Inactivates T3 and T4

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34
Q

How does T3 have its effect on the cell?

A

Binds to nucelic receptors (thyroid hormone receptor and retinoid X receptor)
This changes gene transcription and mRNA leaves the nucleus

35
Q

What affects does increased thyroid hormone levels have on body

A

CNS development
Growth of skeletal muscle
Increased cardiac output/ heart rate/ resp rate
Increase O2 consumption/ gluconeogenesis/ protein synth

36
Q

Where are the parathyroid glands located?

A

Usually 4 glands

Found behind the thyroid

37
Q

What is the difference between thyrotoxicosis and hyperthyroidism?

A

Thyrotoxicosis- Increased levels of thyroid hormone (any cause e.g. hyperthyroidism or levothyroxine over dose)
Hyperthyroidism- Excessive production of thyroid hormone by thyroid gland

38
Q

What is the lifetime risk of hyperthyroidism and what is it’s most common cause? What is the most common age of presentation?

A

Presents most commonly 20-50
Lifetime risk F: 2% / M: 0.2%
70% cases due to graves disease

39
Q

What are the risk factors (5) for hyperthyroidism?

A

Family history, high iodine intake, smoking, childbirth, multinodular goitre

40
Q

What are the symptoms (11) of hyperthyroidism?

A

Weight loss despite increased appetite (10% have weight gain) or appetite changes
Anxiety/ nervousness/ irritability
Tremor/ sweating/ palpitations/ heat intolerance
Weakness/ fatigue/ changes in menstruation

41
Q

What are the signs (8) of hyperthyroidism?

A

Fine tremour/ tachycardia/ goitre
Warm, sweaty palms/ palmar erythema
Hair thinning/ hyperreflexia/ muscle weakness or wasting

42
Q

What are the additional 3 signs and symptoms seen in graves disease?

A 
Hyperthyroid symptoms 
Eye bulge (exophthalmos)
Pretibial myxedema (waxy/ orange peel skin)- Rare ~3% of P
43
Q

What are the signs and symptoms of thyrotoxic crisis (aka thyrotoxic storm/ hyperthyroid crisis)? How should it be treated?

A

Fever >38.5/ Tachycardia/ delirium/ coma/ seizures
Vomiting/ diarrhoea/ Jaundice
25% mortality (arrhythmia’s etc)
TREAT WITH propylthiouracil

44
Q

What is the name of the autoantibody in Graves disease?

A

Thyroid-stimulating immunoglobulin

45
Q

What are the three most common causes of thyrotoxicosis?

A

Graves
Multinodular goitre (surgery)
Solitary nodule

46
Q

What are the risks associated with thyoidectomy?

A

2% relapse rate (take T4 post surgery)
1% vocal cord paralysis
5% permenant parathyroid damage
(very surgeon dependant)

47
Q

What is the difference in what is monitored when treating with thyroxine for hypothyroidism or carbimazole for hyperthyrodism?

A

Titrate dose against:
Carbimazole: T4 levels
Thyroxine: TSH levels

48
Q

What is myxedema?

A

Hypothyroidism (severe)

Also describes dermatological changes

49
Q

What is goitre and what can cause diffuse goitre?

A

Its and enlarged thyroid

Cause (diffuse): Graves/ hashimoto hypothyroidism/ colloid goitre/ iodine deficiency/ drugs

50
Q

What should you do about nodules found on the thyroid?

A

V.common (Increases with age)

For >1cm do ultrasound or fine needle aspiration

51
Q

What is the most accurate blood test to diagnose hypo/hyperthyroidism?

A

TSH

52
Q

What is subclinical hyperthyroidism?

A

Normal T3/T4

Low TSH

53
Q

Which foods provide the best iodine sources?

A

Seaweed (like kelp)- Best
Seafoods (cod, shrimp)
Meat/ egg/ milk

54
Q

What hyperthyroidism do to pulse pressure?

A

Increases pulse pressure

raised systolic/ decreased diastolic

55
Q

What does T3 do to mitochondia levels?

A

Increases them and causes growth of mitochondria

56
Q

Which hormone (T3/T4) is most stable in blood?

A

T4

57
Q

What would happen to a child with hypothyroidism in relation to their growth?

A

FTT

58
Q

What would happen to a child with hyperthyroidism in relation to their growth?

A

Initially grow very fast but then not reach full potential as epiphesis plates close earlier?

59
Q

Which of the two types of cellular receptors (membrance/ nuclear) has a quicker response time?

A

Membrane

As nuclear need to use transcription to have effects which takes longer

60
Q

How does TSH act on the cell to increase T3/T4?

A

Binds to membrane receptor and activates cAMP
Faster breakdown of thyroglobulin
Growth of thyroid cell
Increased concentration of

61
Q

What % of T4 is unbound and which type of T4 is active?

A

T4 is only active when unbound

0.03% is ‘free’ in blood

62
Q

What temperature issues do patients with hyper and hypothyroid experience?

A

Hyperthyroid: Heat intolerance
Hypothyroid: Cold intolerance

63
Q

Why do patients with hyperthyroidism experience nervousness?

A

Because TSH increases sympathetic stimulation (and increased release from all endocrine glands)

64
Q

What effect does thyroid hormone have on cholesterol?

A

Lowers serum cholesterol levels

65
Q

What antibody is involved in Graves disease?

A

TSI- thyroid stimulating immunoglobulin

66
Q

What is derbyshire neck?

A

Goitre caused by lack of iodine in the diet

67
Q

What is the difference between PTU (propylthiouracil) and carbimazole?

A

Carbimazole inhibits TPO centrally but PTU does this and also inhibits conversion of T4 to T3 peripherally

68
Q

Roughly how long are drugs such as carbimazole given?

A

18months

69
Q

Which isotopes of I are used for treatment and diagnostic imaging?

A

Diagnosis: I(123)
Treatment: (131)

70
Q

What are the similarities between the epidemiology of Graves and anxiety?

A

Both affects F much more than M

Around 20-50 peak age

71
Q

Where would you find the TPO enzyme?

A

On the luminal membrane of the thyroid follicule cells

72
Q

What do low T4 levels do to TSH levels?

A

Raise TSH

73
Q

Graves disease is most like to affect what age group and gender? Whereas multinodular goitre is most likely to affect…?

A

Graves: F (younger age)
MG: M (older age)

74
Q

What is the general mechanism of carbimazole and propylthiouracil?

A

Block iodine organification

Stops TPO enzyme iodinating tyrosine residue on thyroglobulin

75
Q

What is the most common SE of carbimazole and propylthiouracil?

A

Rash and itching

76
Q

Where are C-cells found and what is there role?

aka parafollicular cells

A 
Interspersed with columnar epithelium 
Make calcitonin (lowers blood calcium)
77
Q

What use does T3 have in diagnosing hypothyroidism?

A

Very little use as levels don’t drop until disease is severe

TSH is used instead

78
Q

What is the unit MBq used to measure?

A

Megabecquerel

Disintergrations per second (radioactivity)

79
Q

What causes exophthalmos in graves disease?

A

TSH receptor antibodies also go into the tissues of the orbital muscles and cause inflammation

80
Q

What is the most common malignancy of the thyroid?

A

Papillary carcinoma

81
Q

What is the pathophysiology of Graves disease?

A

Autoimmunie- antibodies produced to TSH receptor

These antibodies bind to the TSHr and chronically stimulate it

82
Q

What is the role of the Na+/K+ ATPase pump?

A

Pumps Na+ out of cells and K+ into cells

Uses ATP as both molecules are moving against their concentration gradient

83
Q

What does TSI stand for?

A

Thyroid stimulating immunoglobulin

84
Q

All diiodinase enzymes contain which amino acid?

A

Selenocysteine

Semester 4 (NME) (24 decks)

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