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RW Endocrinology > Thyroid > Flashcards

Thyroid Flashcards

1
Q

How many parathyroid glands are found on each lobe of the thyroid?

A

2 on each (4 total)

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2
Q

Which vertebral levels and cartilage rings does the thyroid span?

A

C5-T1 and 2nd-4th tracheal rings

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3
Q

When does the thyroid gland naturally increase in size?

A

Pregnancy and menstruation

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4
Q

What is the sympathetic and parasympathetic innervation of the thyroid gland?

A

Parasympathetic: vagus Sympathetic: superior, middle, and inferior ganglia of the sympathetic trunk

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5
Q

What is the blood supply of the thyroid gland?

A

Superior and inferior thyroid arteries (branch of external carotid) +/- thyroidea ima

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6
Q

What is the venous drainage of the thyroid gland?

A

• Superior/ middle thyroid vein > internal jugular • Inferior thyroid vein> brachiocephalic veins

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7
Q

Which ligament supports the thyroid gland?

A

Posterior suspensory ligament (Berry ligament) which attaches the posteromedial aspect of the gland

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8
Q

What 2 main things make up the structure of the thyroid gland?

A

Follicles and parafollicular C cells

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9
Q

What do the parafollicular cells secrete?

A

Calcitonin

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10
Q

What are follicles made up of?

A

Follicular cells surrounding colloid (which is essentially tyrosin- containing thyroglobulin filled spheres)

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11
Q

What is the main fuel for the thyroid?

A

Iodine

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12
Q

What is the synthesis and storage stages of T3 and T4?

A

1) Iodide and tyrosine are taken up by follicular cells, via Na/iodide symporter 2) Thyroglobulin (protein rich in tyrosine residues) is synthesised within follicular cells: - Secretion of iodide/thyroglobulin into the colloid. - In the colloid, iodide is oxidised to iodine which attaches to tyrosine residues to form monoiodotyrosine (MIT) and diiodotyrosine (DIT) - Conjugation/coupling of 2 DITs form T4 and MIT with DIT forms T3. 3) They are stored in the colloid thyroglobulin until they are required. 4) Mature iodinated thyroglobulin is endocytosed into follicular cells and proteolytically cleaved to liberate free TH.

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13
Q

How does Carbimazole and Propylthiouracil treat hyperthyroidism?

A

It prevents iodine from attaching to tyrosine residues, preventing formation of MIT and DIT

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14
Q

When iodine is in short supply, what does the reaction favour the formation of more, T3 or T4?

A

It favours MIT formation and therefore T3

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15
Q

What is the main regulator of the thyroid gland?

A

TSH (causes the release of T3/T4)

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16
Q

What are the 3 main plasma proteins T3/T4 bind to for transport?

A

• Thyroxine binding globulin (TBG) - main • Thyroxine binding prealbumin (TBPA) • Albumin

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17
Q

What is the biologically active form of T3/T4 - bound or unbound?

A

Unbound

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18
Q

What important roles does thyroid hormones have?

A

Increase metabolism and thermogenesis, growth (via GHRH), foetal development, aids sympathetic action

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19
Q

What is the thyroid acts?

A

Hypothalamus release thyroid releasing hormone (TRH), which then stimulates the anterior pituitary to release thyroid stimulating hormone (TSH) which stimulates the thyroid to release T3 and T3. These then act back on the hypothalamus in a negative feedback loop

20
Q

What are deiodinase enzymes?

A

Subfamily of 3 enzymes (type 1, 2 and 3) important in the activation and deactivation of thyroid hormone.

21
Q

What is the specific function of Deiodinase Type 2?

A

Activates T4 to T3 in tissues

22
Q

Which nerve can potentially be damaged during thyroid surgery?

A

Recurrent laryngeal

23
Q

True or False: goitre only occurs in hypothyroidism

A

False, it occurs in both

24
Q

Low TSH and and high T4/T3 indicates…

A

Primary Hyperthyroidism

25
Q

High TSH and low T4/T3 indicates..

A

Primary Hypothyroidism

26
Q

High TSH and high T4/T3 indicates…

A

Secondary hyperthyroidism

27
Q

Myxoedema coma occurs in hypothyroidism or hyperthyroidism?

A

Severe hypothyroidism

28
Q

Pretibial myxoedema occurs in hypothyroidism or hyperthyroidism?

A

Hyperthyroidism, specifically Grave’s

29
Q

Where is the problem in Primary hypothyroidism?

A

Problem with the thyroid

30
Q

Where is the problem in Secondary hypothyroidism?

A

In the pituitary/hypothalamus

31
Q

What is the commonest cause of primary hypothyroidism?

A

Chronic autoimmune thyroiditis (Hashimoto’s)

32
Q

Which antibodies are present in Hashimoto’s thyroiditis?

A

Thyroid peroxidase antibodies

33
Q

Subclinical hypothyroidism

A

High TSH but no symptoms

34
Q

Low TSH and T3/T4

A

Secondary Hypothyroidism

35
Q

What is the starting dose of thyroxine?

A

1.6micrograms/kg/day levothyroxine (~50micrograms). Lower dose if elderly patients.

36
Q

What is the embryological development of the thyroid gland?

A

Develops from evaginatiion of pharyngeal epithelium and then descends from foramen caecum to normal location along thyroglossal duct

37
Q

What can occur of the thyroid descends abnormally?

A
  • Failure of descent – lingual thyroid (back of the tongue)
  • Excessive descent – retrostenral location in mediastinum
  • Thyroglossal duct cyst
    • Normally the thyroglossal duct fuses and regresses in adults
    • However somethimes portions of the duct can sometimes remain patent and cant present as a mass in the neck
38
Q

What is the a pyramidal lobe?

A

Continuation of the distal portion of the thyroglossal duct. Present in 50% of individuals and has no clinical consequence

39
Q

What are the two main autoimmine diseases of the thyroid and which causes hypofunction and which causes hyperfunction?

A
40
Q

Is a diffuse goitre symmetrical or asymmetrical?

A

Symmetrical (whole thyroid is enlarged)

41
Q

What are thre 4 types of thyroid carcinoma, and which is the most common and the most aggressive?

A
  1. Papillary (most common - 75-85%)
  2. Medullary (10-20%)
  3. Follicular
  4. Anaplastic (most aggressive)
42
Q

In parathyroid adenoma, how many glands are normally affected?

A

Normally only a single gland (of the 4 total)

43
Q

In parathyroid hyperplasia, how many glands are normally affected?

A

Normally all glands

44
Q

Which genetic syndrome is hypoparathyroidism associated with?

A

DiGeorge Syndrome

45
Q

What are Chovsteks and Trousseau sign and what do the indicate clinically?

A
  • Chovsteks sign (tapping over facial nerve)
  • Trousseau sign (carpopedal spasm
  • They indicate hypocalcaemia (hypoparathyroidism?)
46
Q

What are two main questions to consider with thyroid nodules?

A
  • Does it move on swallowing?
  • Does it move on sticking out the tongue? - thyroglossal cyst
47
Q
A

RW Endocrinology (9 decks)

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