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Endocrine > Thyroid gland > Flashcards

Thyroid gland Flashcards

1
Q

Wha hormones are synthesised in the thyroid?

A

T3 - tri-iodothyronine

T4 - thyroxine

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2
Q

How are T3 and T4 synthesised? Where does this take place?

A

Iodination of tyrosine on thyroglobulin

Lumen of thyroid follicles

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3
Q

What regulates thyroid hormone synthesis and secretion?

A

TRH - thyrotropin releasing hormone
TSH - thyroid stimulating hormone
Plasma iodide

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4
Q

Is there lots of T3 or T4 in the blood? What is their turnover rate?

A

T3 - small pool, fast turnover rate, intracellular

T4 - large pool in food, slow turnover

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5
Q

Why may T4 be classed as a pro hormone?

A

Converted to T3 in target cells

T3 much more active than T4

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6
Q

What effect do thyroid hormones have?

A

Increase metabolism of carbohydrates, fats and proteins
Normal skeletal development and growth
Maturation of the nervous system
Milk production

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7
Q

What hormones do T3 and T4 work in conjunction with?

A

Insulin
Glucagon
Glucocorticoids
Catecholamines

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8
Q

What can be measured that shows thyroid hormone action?

A

Increased oxygen consumption
Heat production
Increased basal metabolic

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9
Q

What effect does hyperthyroidism (and thyroid hormone drugs) have on the heart?

A

Increases heart rate

Increased arrhythmias

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10
Q

How do thyroid hormones influence growth and developement?

A

Direct action on cells

Indirectly by influencing growth hormone

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11
Q

Which animals are hypothyroidism and hyperthyroidism particularly common?

A

Hyperthyroidism - old cats

Hypothyroidism - dogs

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12
Q

What is goitre? What causes it?

A

Swelling of thyroid gland

Dietary iodine deficiency

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13
Q

What does a dietary deficiency of iodine or goitrogens cause?

A

Reduced thyroid hormone synthesis
Rise in plasma TRH
Increased gland size (goitre)

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14
Q

How is hyperthyroidism diagnosed?

A

History, clinical signs
Total thyroxin
(Cheap, easily available)

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15
Q

How is hyperthyroidism managed?

A 
Diets restricted in iodine
 Surgery 
Drug treatment (thioureylenes and radioactive iodide)
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16
Q

What is a danger when operating on the thyroid gland?

A

Damaging parathyroid gland

17
Q

How can hypothyroidism be diagnosed?

A

History, clinical signs

Total blood thyroxine (not always reliable - false positives)

18
Q

Why is total blood thyroxine often not reliable to diagnose hypothyroidism?

A

Euthyroid sick syndrome
= total blood thyroxine often reduced as a physiological response to other illnesses
Drugs can also reduce tT4

19
Q

What can be used with tT4 in dogs to diagnose hypothyroidism?

A

Elevated TSH - loss of negative feedback

TSH alone is not useful, but useful with tT4

20
Q

How can free T4 (fT4) be used to differentiate euthyroid sick syndrome from genuine hypothyroidism?

A

Free T4 rarely suppressed by other illnesses unlesss severe

High specificity

21
Q

What 2 drugs can be used for hyperthyroidism?

A

Radioiodine

Thioureylenes

22
Q

What 2 drugs can be used for hypothyroidism?

A

Levothyroxine

Liothyronine

23
Q

How does radioiodine work? How long does it take to normal thyroid levels?

A

Rapidly uptaken by thyroid Damages cells by emitting short range beta radiation
1-2 weeks (half life 8 days)

24
Q

How is radioiodine administered? What precautions should be taken?

A

Injection

Treated animals need hospitalisation and isolation for at least 2 wks, need careful handling

25
Q

Radioiodine injections are very expensive!!! Why may some people still use it rather than surgery?

A

Less risk of damage to parathyroid

26
Q

What are the adverse effects and contraindications of radio iodine?

A

Hypothyroidism

Pregnancy

27
Q

Give 2 examples of thioureylenes

A

Carbimazole

Thiamazole

28
Q

How do thiouryelenes work?

A

Metabolised to methimazaole which inhibits synthesis of thyroid hormones

29
Q

How are thioureylenes administered? What are the adverse effects?

A

Orally - once a day

Rare - can decrease GFR and unmask hidden renal failure (CKD)

30
Q

How do levothyroxine and liothyronine work? How do they travel in the blood?

A

Thyroid receptor agonists

Highly protein bound - only free hormone metabolically active

31
Q

How are levothyroxine and liothyronine administered? What are the adverse effects?

A

Orally
Hyperthyroidism
Enhances actions of catecholamines and sympathomimetics

32
Q

What are the symptoms of hyperthyroidism?

A 
Tachycardia
Excitability
Excessive panting 
Weight loss
Increased appetite
33
Q

What are the symptoms of hypothyroidism in the dog?

A

Excess shedding/thinning of fur
Weight gain
Reduced activity

Endocrine (7 decks)

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