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BRS > The Thyroid Gland > Flashcards

The Thyroid Gland Flashcards

1
Q

The thyroid gland location

A

Within neck, surrounding trachea

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2
Q

How many lobes does the thyroid gland have?

A

2

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3
Q

What is the thymus made up of?

A

Multiple follicles made up of follicular sides round the outside and colloid in the centre

Parafollicular cells

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4
Q

Parathyroid glands are embedded where?

Which nerve runs close to the thyroid and what does it supply?

A

Within the thyroid

Left current laryngeal nerve runs close and supplies vocal cords

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5
Q

Where does the thyroid gland start and how does it develop embryologically?

A 
Floor of pharynx (base of tongue)
Develops into thyroglobulin duct
Divides into 2 lobes
Duct disappears leaving foramen caecum
Final position by week 7
Thyroid gland then develops
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6
Q

What is colloid?

A

Sticky mucous in middle of follicles where the thyroid hormone is made

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7
Q

How is thyroid hormone made?

A

TSH released by anterior pituitary gland binds TSH receptor (thyroid stimulating hormone) adjacent to blood vessel.

Iodide ions are essential
Through sodium iodide transporters it is transported into follicular cell and then into colloid

TPO is also transported into follicular cell and into colloid

Iodisation makes iodine in the colloid

Thyroglobulin (prohormone) contains

Tyrosine residues which can be ionidated - stick iodine onto it, giving MIT and ….. which take part in a coupling reaction to produce hormones T3 and T4.

T3 and T4 are still bound to thyroglobulin, enter follicular cell and then blood circulation

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8
Q

What does MIT stand for?

What does DIT stand for?

What is produced if MIT and DIT are joined together?

What about if two DIT are joined together?

A

3-monoiodotyrosine

3,5-diiodotyrosine

3,5,3 triiodothyronine

3,5,3’,5’ tetraiodothyronine

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9
Q

Which is the main product of the thyroid gland?

In target tissues what happens?

A

T4

Deiodinated to form T3.

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10
Q

How is T4 (thyroxine) a prohormone converted into T3 (triiodothyronine)?

A

Deiodinase enzyme

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11
Q

Where is thyroglobulin made?

What is thyroid binding globulin?

A

Only in thyroid gland, it is a prohormone that forms T3 and T4

Plasma protein found in blood

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12
Q

What percentage of thyroid hormones are unbound?

What does this mean?

A

1%

Only 1% are active

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13
Q

Why do we need thyroid hormone?

A

Fetal growth and development
In particular that of the central nervous systemi

Increases basal metabolic rate

Protein, carbohydrates and fat metabolism

Potentiate actions of catecholamines (eg. Tachycardia,
Iipolysis)

Effects on GI, CNS, reproductive systems

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14
Q

What is untreated congenital hypothyroidism called?

A

Cretinism

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15
Q

What test is done to measure thyroid stimulating hormone?

A

Heel-prick test measures TSH in new borns

If it is high, the baby is not producing enough of its own thyroid hormone

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16
Q

Half life of T4?

Half life of T3?

A

7-9 days

2 days

17
Q

How is thyroid hormone production controlled?

A

Thyrotropin releasing hormone is released by hypothalamus

Goes to anterior pituitary and stimulates thyrosome cells which release thyroid stimulating hormone

Thyroid releases T3 and T4

Creates a negative feedback loop - T3 and T4 negatively inhibit release of TRH and TSH

SS inhibits release of TSH

18
Q

How much more common is thyroid disorders in women than men?

Why do we think this is?

A

4:1

Autoimmunity - antibodies made to various parts of your thyroid gland which destroy it, women are more at risk because of pregnancy and the way their immune systems have had to adapt to the foetus.

19
Q

Is an overactive or underactive thyroid gland more common?

A

They’re the same

20
Q

What can cause primary hypothyroidism

A

Autoimmune - destroys part of thyroid
Surgery - remove part of thyroid

if you take out/ destroy part of it, negative feedback loop changes, TSH goes up to produce more thyroxine and T4 and T3 but you can’t make the T4 so T4 goes down.

Always measure TSH and T4 - TSH goes up, T4 goes down

21
Q

Describe some symptoms and signs of someone with hypothyroidism

A 
Lethargic - feeling tired
Depression
Deepening voice 
Swelling around eyes
Cold intolerance
Weight gain
Reduced appetite
Constipation
Bradycardia
Weakness
Dry skin
Hypothermia
Low libido
Problems with periods
Eventual myxoedema coma
22
Q

What does levothyroxine do?

A

Produces T4

Even if the thyroid is taken out

All the target tissues contain deiodinase enzymes which convert T4 to T3

23
Q

Why do we give levothyroxine to some people with hyperthyroidism

A

Block their thyroid hormone production and replace it with levothyroxine ie. only the minimum that they need

24
Q

How do you adjust the dose of levothyroxine?

A

Adjusted according to TSH (aim to get into normal range)

Common does 100 micrograms

Given orally

25
Q

Potential complications of levothyroxine?

A

Weight loss, headache

Rapid heart rate, heart attack

26
Q

Combined thyroid hormone replacement

What can it cause?

A

Combination T4 and T3 - found on market without prescription

Toxicity

27
Q

What happens during hyperthyroidism?

What are the symptoms

A

Thyroxine levels rise
TSH levels drop

Nervousness
Irritability 
Insomnia 
Depression
Anxiety
Broken hair, hair loss
Increased heart rate
Weight loss despite increase in appetite
Arrhythmia
High blood pressure
Weight loss
Strong feeling of hunger
Diarrhoea
Muscle cramps
Muscle weakness
Warm, moist skin, increased body temperature
Palpitations
Nodules within thyroid gland
Enlarged thyroid gland
28
Q

Causes of hyperthyroidism?

A

Grave’s disease - whole gland smoothly enlarged and whole gland overactive

Toxic multinodular goitre

Solitary toxic nodule

29
Q

What is Graves’ disease?

What happens?

What are the symptoms?

A

Autoimmune disease

Antibodies bind to and stimulate TSH receptor in the thyroid

Smooth goitre (enlargement of thyroid gland)

Other antibodies bind to muscles behind eye

This is exophthalmos - you can see white ring around iris and a bulging eyeball and the whites of the eye become red and angry looking

Other antibodies stimulate growth of soft tissue of shins

This is pretibial myxoedema - thickening and growth of shins

30
Q

What connects the two lobes of the thyroid gland?

A

Isthmus

31
Q

Where is the thyroid gland’s embryological origin?

A

Floor of pharynx

32
Q

Which form of the thyroid hormone is active and which is inactive?
Which is the prohormone?

A

T4
T3
Thyroglobulin - produced by follicular cells combined with iodine from blood to create T3 and T4 in presence of thyroperoxidase

T4–> T3 in presence of deiodinase

33
Q

Hyperthyroidism causes

A

Autoimmune (Grave’s disease) or nodule- related

34
Q

What connects the two lobes of the thyroid gland?

A

Isthmus

35
Q

Where is the thyroid gland’s embryological origin?

A

Floor of pharynx

36
Q

Which form of the thyroid hormone is active and which is inactive?
Which is the prohormone?

A

T4
T3
Thyroglobulin - produced by follicular cells combined with iodine from blood to create T3 and T4 in presence of thyroperoxidase

T4–> T3 in presence of deiodinase

37
Q

Hyperthyroidism causes

A

Autoimmune (Grave’s disease) or nodule- related

BRS (19 decks)

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