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Thyroid Gland Flashcards

1
Q

What is the name of the bit that joins the 2 lobes of the thyroid gland

A

Isthmus

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2
Q

Where are parathyroid glands located

A

Embedded within the thyroid - parathyroid gland produces parathyroid hormone which is responsible for calcium metabolism

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3
Q

Why is it important to be extremely careful when operating on thyroid gland

A

Risk damage to the parathyroid which can cause problems with calcium metabolism and heart rhythm . If there is damage to the recurrent inferior laryngeal nerve ( which also lies close to the thyroid gland ) , there is a risk of damage to the vocals chords

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4
Q

Embryology of the thyroid gland

A

Midline outpouching from floor of the pharynx ( originates from the base of the tongue)
The thyroglossal duct then develops
Divides into 2 lobes
The duct disappears leaving the foremen caecum
Final position by week 7 of gestation
Thyroid gland then develops

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5
Q

What does the colloid contain

A

Contains thyroglobulin . Iodine atoms are incorporated into tyrosine residues on thyroglobulin and forms the bulk of colloid in follicles

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6
Q

Process of thyroid hormone secretion ( complicated diagram )

A

1) TSH arrived and binds to TSH receptors on thyroid glands
2) This also activates the sodium and iodide pump which pumps iodide ions ( e.g. from diet) into the follicular cell
3) Iodination occurs where iodide is oxidised to yield iodine
4) Prohormone thyroglobulin reacts with iodine ( iodination ) to form MIT and DIT
5 ) steps 3 and 4 are catalysed by thyroid peroxidase and Hydrogen peroxidase
7) MIT + DIT = T3 , 2x DIT= T4 ( coupling reaction)
8) packaged into lysosome and then T3 and T4 excreted into blood

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7
Q

Deiodination of triiodothyronine ( T3)

A

Thyroxine ( T4) is the main hormone produced by the thyroid gland
T4 is deiodinated to T3 , its bio active form in the target tissues
T4 may also be deiodinated in a different position to produce reverse T3 ( inactive)

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8
Q

What enzyme converts T4 to T3

A

Deiodinase enzyme

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9
Q

Circulating T3

A

80% comes from the deiodination of T4
20 % comes from direct Thyroidal secretion

T3 provides almost all the thyroid hormone activity in target cells

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10
Q

How is thyroid hormone transported

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 ( bio active components)

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11
Q

Why is thyroid hormone especially important in babies

A

Essential for fetal growth and development in particular that of the CNS
Untreated congenital hypothyroidism ; called Cretinism when the baby is born without thyroid gland or inactive T3 . This required lifelong treatment
At birth TSH is measured in new born infants heel prick test on Day 5 of birth so very rarely seen now

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12
Q

Actions of thyroid hormone

A

Increases basal metabolic rate
Protein , carbohydrate and fat metabolism
Potentials actions of catecholamines ( e.g. tachycardia , lipolysis )
Effects on the GI , CNS and Reproductive systems ( look at diagram)

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13
Q

Half life of T4

A

7-9 days

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14
Q

Half life of T3

A

2 days

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15
Q

How is baby semi protected if has problems with thyroid in utero

A

Thyroid crosses the placenta from the mum so effects of not having enough thyroid is only seen after delivery

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16
Q

Control of thyroid hormone

A

Hypothalamus - TRH- anterior pituitary - TSH- Thyroid Gland - T3 and T4 which negative feedback on hypothalamus and anterior pituitary

Somatostatin released by hypothalamus can inhibit TSH

17
Q

WolffChaikoff effecf

A

Iodine given in large quantities can inhibit T3 and T4

Clinically increased potassium iodide is given to someone with hyperthyroidism to stop the production of thyroid hormone

18
Q

Why are thyroid disorder more common in women ( 4;1 ratio) ?

A

Most defects in the thyroid gland is to do with autoimmunity. Women are more predisposed to autoimmunity due to them needing to carry babies and so they are exposed to more antigen

19
Q

Which is more common , overactive thyroid gland or under active thyroid gland ?

A

Both equal

20
Q

Primary Hypothyroidism changes in thyroxine and TSH

A

Autoimmune damage to thyroid

  • thyroxine levels decline
  • TSH levels climb as a result of negative feedback
21
Q

Commonest forms of hypothyroidism

A

Hashimoto’s thyroiditis ( hypothyroidism ) and Graves’ disease ( normally hyperthyroidism but can also be hypo )

22
Q

Other diseases which can increase risk of hypothyroidism

A

The presence of one autoimmune disease can increase the risk of others ( e.g. vitiligo and pernicious anaemia)

23
Q

Signs are symptoms seen in a patient presenting with hypothyroidism

A 
Deepening voice
Depression and tiredness 
Cold intolerance 
Weight gain and reduced appetite
Constipation 
Bradycardia
Eventual myoxedema coma 
Swollen face 
Dry rough skin
Paresthesia 
Shaggy hair
Hair loss
Low sexual desire
Cycle disorders
BASICALLY SLOWS DOWN EVERYTHING
24
Q

Pharmacology and therapeutics of hypothyroidism

A

Levothyroxine

25
Q

Indications of levothyroxine

A

Hypothyroidism / radioactive iodine treatment

Hyperthyroidism ( blocking and replacement regimen )

26
Q

Dosing of levothyroxine

A

Adjusted according to TSH ( aim to get into normal range) and T4
Common dose is 100 micro grams but may start lower for elderly who are at risk of heart attack

27
Q

Potential complications of levothyroxine

A

Extremely rare and only happens if you take too much

Weight loss
Headache
Heart attach and rapid heart rate

28
Q

Combined thyroid hormone replacement

A

T4 = prohormone , converted by deiodinase action to T3
Combination T4/ T3 - some have reported improvement in well being

Complicated by symptoms of toxicity - palpitations, tremor, anxiety - often combination treatment suppresses TSH

29
Q

Hyperthyroidism

A

Thyroid makes too much thyroxine
Thyroxine levels rise
TSH levels drop

30
Q

Causes of hyperthyroidism

A

Graves’ disease ( autoimmune disease ) where the whole gland is smoothly enlarged and the whole gland is overactive
Toxic multinodular goitre ( many nodules overproducing thyroid hormone )
Solitary toxic nodule ( single nodule overproducing thyroid hormone )

31
Q

Graves’ disease

A

Autoimmune disease
Antibodies bind to and stimulate TSH receptor in the thyroid
- smooth goitre
Other antibodies bind to muscles behind the eye
- exophthalmos ( patients complain of dry or gritty eyes) . Can lead to severe eye complications and can need steroids
Other antibodies stimulate the growth of soft tissue of shins
- pretibial myxoedema

32
Q

Signs and symptoms of hyperthyroidism

A 
Heat intolerance 
Weight loss with increased appetite
Myopathy 
Mood swings
Diarrhoea
Tremor of hands 
Palpitations 
Sore eyes, goitre 
Broken hair 
Hair loss 
Fragile fingernails

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