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Semester 4 > Case 9 > Flashcards

Case 9 Flashcards

1
Q

The isthmus of the thyroid is usually at the level of what?

A

the second and third tracheal cartilage

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2
Q

The thyroid originates as a median outgrowth of the tongue then migrates to its place in the neck. What two anatomical structure are the result of this?

A

The foramen cecum of the tongue shows the thyroids origin, and the thyroglossal duct shows its path of migration

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3
Q

What is the pyramidal lobe of the thyroid?

A

An additional lobe of the thyroid along the path of the thyroglossal duct present in only 50% of people

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4
Q

What is the lingual thyroid?

A

Thyroid tissue associated with the tongue not present in everyone

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5
Q

What is the name of the fluid that fills the follicle of the thyroid?

A

colloid

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6
Q

What lines the follicle of the thyroid?

A

coidal epithelial cells

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7
Q

What is thyroglobulin?

A

a large glycoprotein that contains all thyroid hormones within itself

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8
Q

What are the two main arteries that supply the thyroid gland?

A

The superior and inferior thyroid arteries

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9
Q

What vessel does the superior thyroid artery originate from? what is its course to the superior pole of the lateral gland?

A

The superior thyroid artery is the first branch of the external carotid artery, it descends along the lateral margin of the thyrohyoid muscle

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10
Q

What does the superior thyroid artery split into once it reaches the superior pole of the lateral gland?

A

The anterior and posterior glandular branches

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11
Q

Where does the inferior thyroid artery originate from?

A

It is a branch of the thyrocervical trunk which arises from the subclavian artery

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12
Q

What is the course of the inferior thyroid artery?

A

It branches off the thyrocervical trunk, ascends along the medial edge of the anterior scalene muscle and passes posterior to the carotid sheath

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13
Q

What does the inferior thyroid artery branch into at the inferior pole of the lateral gland?

A

The inferior and ascending branches.

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14
Q

What are the three veins that drain the thyroid what do they drain into?

A

The superior and middle thyroid veins that drain into the internal jugular vein and the inferior thyroid vein that drains into the right and left brachiocephalic veins

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15
Q

What embryological structures are the inferior and superior parathyroid glands derived from respectively?

A

The third and fourth pharyngeal pouches

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16
Q

What is the blood supply for the parathyroid glands?

A

The inferior thyroid arteries

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17
Q

What controls thyroid secretion?

A

thyroid stimulating hormone secreted by the anterior pituitary gland

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18
Q

As well as T3 and T4 what else does the thyroid secrete and what is its purpose?

A

calcitonin that aids calcium homeostasis

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19
Q

What are the relative amounts of T3 and T4 secreted by the thyroid?

A

93% T4 and 7% T3

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20
Q

What is the relative potency of T3 and T4?

A

T3 is roughly four times as potent as T4

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21
Q

How much of ingested iodine (in the form of iodides) is used to form T3 and T4 each week and year respectively?

A

1mg/week and 50mg a year

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22
Q

What proportion of the circulating iodine is used to make thyroid hormone and filtered in urine respectively?

A

one fifth is used to produce thyroid hormone the other four fifths is filtered out

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23
Q

What is the most important amino acid in thyroglobulin? How many molecules of this are in each molecule of thyroglbulin?

A

tyrosine is the most abundant amino acid each thyroglobulin contains roughly 70

24
Q

What is iodide trapping? What regulates it?

A

Iodide trapping is the transport of iodides out of the blood into the interior of thyroid cells.The concention of TSH influences the amount of this that happens

25
Q

How does TSh increase the rate of iodide trapping?

A

It stimulates the iodide pumps in thyroid cells

26
Q

iodide is converted to what form when it enters thyroid cells?

A

either nascent iondine (I0) or I3-

27
Q

What type of reaction converts iodide to nascent iodine or I3- when it enters thyroid cells. What catalyses this?

A

It is an oxidation reaction catalyzed by peroxidase and its associated hydrogen peroxide

28
Q

What is organification of thryroglobulin? How is it catalyzed?

A

It is the addition of iodine to a thyroglobulin molecule. It is catalyzed by iodinase which the oxidized iodine is attached to

29
Q

What are the alternatenames for T3 and T4 respectively?

A

triiodothyronine and thyroxine

30
Q

Why might thyroid disfunction not display for several months?

A

The thyroid glands store enough throxine and triiodothyronine to last 2-3 so symptoms cannot present until this reserve is depleted

31
Q

How much of iodinated tyrosine in thyroglobulin becomes thyroid hormones?

A

only a quarter

32
Q

What enzyme is capable of converting thyroxine to triodothyroxine?

A

deiodanase enzyme

33
Q

What three things in the blood do thyroid hormones combine with?

A

Mostly thyroxine bindine globulin but also with thyroxine-binding prealbumin and albumin

34
Q

What do thyroid hormones typically make a dimer with? Where does this happen

A

retinoid X receptor (RXR). This happens as specific response elements on the DNA

35
Q

How much can the metabolic rate be raised under the influence of thyroid hormones?

A

by 60%-100% above normal

36
Q

Why might hyperthyroidism stunt growth?

A

While it causes increased skeletal growth hyperthroidism also increases the rate of bone maturation closing off epiphyseal growth plates earlier

37
Q

What is the effet of thyroid hormones on carbohydrate metabolism?

A

it increases uptake of glucose, the absorption from the GI tract and the release of insulin and enhances glycolysis and gluconeogenesis

38
Q

What are thyroid hormones’ effect on plasma concentrations of cholesterol, phospholipids and triglycerides. What association of hypothyroidism is this related to?

A

Thyroid hormones decrease plasma conc of cholesterol, phospholipids and triglycerides. This is why atherosclerosis is more common in hypothyroid patients

39
Q

What is the other name for TSH/thyroid stimulating hormone?

A

thyrotropin

40
Q

What are the five main effects of TSH/thyrotropin ?

A

increased proteolysis of thyroglobulin, increased activity of the iodine pump increasing rate of iodine trapping, increased iodination of tyrosine, increased size and secretory activit of thyroid cells and incrased number of thyroid cells/change from cuboidal to columnar, increasing infolding on border of follicles

41
Q

What are the two effects of calcitonin?

A

inhibition of osteoclasts and stimulation of calcium excretion

42
Q

What cells of the thyroid produce calcitonin?

A

C cells or parafolllicular cells

43
Q

What are the three effects of parathyroid hormone (PTH)

A

stimulation of osteoclasts, increased GI absorption through the activation of vitamin D/calcitriol and promoting of calcium conservation by the kidneys

44
Q

What is secondary hyper thyroidism?

A

hyperthyroidism caused by excessive stimulation of the thyroid by TSH

45
Q

What are the relative likelyhoods of men and women having hyperthyroidism? What is prevalence of hyperthyroidism in women?

A

women are 10 times more likely than men to have hyperthyroidism, 1 in 50 women in the uk are thought to live with an overactive thyroid gland

46
Q

When do the majority of hyperthyroid cases start ?

A

between the ages of 20-40

47
Q

What ethnicities are effected more and less by hperthyroidism?

A

white and asian peopleare effected more, african caribbean people are effected less

48
Q

What is neutropenia?

A

An abnormally low number of neutrophils in the blood leading to a higher risk of infection

49
Q

What is agranulocytosis?

A

An abnormally low number of granulocytes in the blood leading to a higher risk of infection

50
Q

What are the main two anti-thyroid drug used to treat hyperthyroidism? How do they work? What causes the majority of their side effects?

A

Carbimazole and to a lesser extent propylthiouracil are the main anti-thyroid drugs they inhibit the formation of thyroid hormones but also have an immunosuppresive effct that account for the majority of their side effects

51
Q

what isotope of iodine is used in radiotherapy treatments for hyper thyroidism?

A

iodine 131

52
Q

What are the two forms of radiation caused by iodine 131 decay howdo each effect the thyroid?

A

gamma rays are formed that pass through bodily tissue with no effect and beta particles that cause the destruction of the thyroid follicular cells

53
Q

What nerve palsy can be caused by a thyroidectomy? What is the prevalence?

A

Laryngeal nerve palsy can be caused effecting 1% of patients

54
Q

Why are beta blockers useful in the treatment of hyperthyroidism?

A

Because a lot of the symptoms of hyperthyroidism e.g. palpitations trembling anxiety etc are mediated by increases of beta andrenergic receptors

55
Q

What are the two isomers of propanolol? how does each help treat hyperthyroidism?

A

L-propanolol that causes beta blockage alleviating the symptoms of hyper thyroidism that a beta adrenergic receptor mediated and D-propanolol which inhibits thyroxine deiodinase blocking conversion of T4 to T3

56
Q

What is thought to trigger de quervain’s thyroidittis?

A

viral infection

Semester 4 (10 decks)

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