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X. MRCS: Pathophysiology > Thyroid > Flashcards

Thyroid Flashcards

1
Q

Embryology of thyroid

A

Develops from foramen cecum (base of tongue)

Descends to anterior neck forming thyroglossal duct

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2
Q

Position of the thyroid

A

Wrapped around cricoid cartilage and superior rings of trachea C5-T1
Within visceral compartment of the neck, surrounded by pre-tracheal fascia
Two lobes

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3
Q

Position of the thyroid

A

Tow lobes
Overlying cricoid cartilage and superior rings of trachea
C5-T1
Visceral compartment of neck, bound by pretracheal fascia

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4
Q

Blood supply to thyroid

A

Superior thyroid artery (1st branch of external carotid)
Inferior thyroid artery (thyrocervical trunk, branch of subclavian)
Thyroid ima artery (in 10%, from brachiocephalic trunk)

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5
Q

Venous drainage of the thyroid

A 
Venous plexus 
Drains into 
Superior thyroid vein (drains into IJV)
Middle thyroid vein (drains into IJV)
Inferior thyroid vein (brachiocephalic)
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6
Q

Lymphatic drainage of thyroid

A

Paratracheal nodes

Deep cervical nodes

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7
Q

Innervation of the thyroid

A

Sympathetic trunk

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8
Q

Anatomical relations of the thyroid

A

Right & left recurrent laryngeal nerves run through tracheoesophageal groove passing deep to thyroid to innervate larynx

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9
Q

Type of thyroid cells

A

Follicular cells: thyroid epithelium: simple cuboidal. Form follicles filled with colloid.
Parafollicular cells.

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10
Q

Function of the thyroid

A

Endocrine gland

Produces: T3/T4 and calcitonin

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11
Q

Hypothalamic-pituitary-thyroid axis

A

Hypothalamus detects low T3/T4 conc and releases thyrotrophin-releasing hormone (TRH) into hypophyseal portal system
TRH binds to receptors on thyrotrophic cells of ant pituitary causing them to release TSH
TSH binds to receptors on basolateral membrane of thyroid and induces synthesis and release of thyroid hormone from follicular cells

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12
Q

Functions of follicular cells

A
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13
Q

Effects of T3/T4

A 
increases BMR
Gluconeogenesis
Glycogenolysis
Lipogenesis
Thermogenesis
Increases expression of B receptors of cardiac tissue
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14
Q

Functions of parafollicular cells

A

Produce calcitonin

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15
Q

Effects of calcitonin

A

Inhibits Osteoclasts, reducing bone resorption
Inhibits renal tubular reabsorption of calcium and phosphate
Opposes effect of PTH
Net effect: reducing Ca2+

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16
Q

Thyroid cancer subtypes

A 
Papillary carcinoma (75%)
Follicular carcinoma (15%)
Medullary carcinoma (3%)
Anaplastic thyroid cancer (5%)
Lymphoma (1-2%)
17
Q

Papillary Carcinoma

A

Most common (75%). Most commonly 40-50 women. RFs: ionising radiation in childhood
Multiple lesions within gland. Rarely encapsulated.
Histology: papillary and colloid-filled follicles. “Orphan Annie Eye nucleus” (little protein/DNA).
Commonly spread to lymphatics
Good prognosis: 90% 10 year survival

18
Q

Follicular carcinoma

A

2nd most common (15%). Usually seen 40-60 women. RF: low dietary iodine.
Focal encapsulated lesions.
Invades blood vessels.
Mets: maematogenous spread: Lungs, liver, bone, brain. Unlikely to invade lymph node.
Subtype: Hurthle cell tumours.

19
Q

Medullary carcinoma

A

Rare (3%). RF: MEN2a/2b
From parafollicular cells (more commonly found in superior 1/3).
Histology: spindle shaped cells with amyloids
Raised calcitonin levels. Can secrete VIP/serotonin.
Lymphatic and medullary spread.
Poor prognosis.

20
Q

Anaplastic thyroid cancer

A

5%. RFs: elderly
Aggressive: Rapidly growing with early local invasion.
Poor prognosis.

21
Q

Signs of thyroid cancer

A

Single hard thyroid nodule.
Local invasion: hoarseness (larynx/RLN), dysphagia (oesophagus).
Usually non-functional (no Sx of hyper/hypothyroid).

22
Q

Investigation of thyroid cancer

A

Initial TFTs. Calcitonin
US neck (micro calcifications, hypoechongenicity, irregular margin)
Fine needle aspiration cytology.

23
Q

Management of thyroid cancer

A

Surg: Hemi-thyroidectomy, total thyroidectomy +/- neck dissection
Non-surg: radioiodine, external beam radiotherapy, chemo.

24
Q

Parathyroid glands location

A

Posterior aspect of the thyroid gland
External to thyroid
Contained within pretracheal fascia

25
Q

Embryology of the parathyroids

A

Superior parathyroids: 4th pharyngeal pouch

Inferior parathyroids: 3rd pharyngeal pouch

26
Q

Blood supply to the parathyroids

A

Inferior thyroid arteries

collaterals from superior thyroid arteries

27
Q

Venous drainage of the parathyroids

A

Superior, middle and inferior thyroid veins

28
Q

Nerve supply to the parathyroids

A

Sympathetic nerves from thyroid branches

29
Q

Lymphatic drainage from parathyroid

A

Paratracheal and deep cervical nodes

30
Q

Parathyroid gland cell types

A

Chief cells: secrete parathyroid hormone

Oxyphil cells - unknown purpose

31
Q

Actions of parathyroid hormone

A

Net effect: increase Ca2+
Bone: Increase resorption (indirectly acts on osteoclasts to increase breakdown of bone)
Kidney: increase Ca reabsorption, increase phosphate excretion (acts in loop of Henle and distal tubules)
Vitamin D synthesis

32
Q

Activation and actions of Vitamin D

A

Skin: Cholecalciferol (D3)
Liver: Converted to calcifediol (25-hydroxycholecalciferol
Kidney: Converted to active form calcitriol (1,25-dihydroxycholecalciferol)

Increases absorption of Ca in GI
Increase renal tubular reabsorption of Ca
Indirectly activates osteoclasts

33
Q

Types of hyperparathyroidism

A

Primary
Secondary
Tertiary
Malignant

34
Q

Primary hyperparathyroidism

A

Direct alterations to parathyroid
Excess secretion of PTH
Elevated calcium
Causes: solitary adenoma, hyperplasia of glands, parathyroid cancer

35
Q

Secondary hyperparathyroidism

A

Physiologically elevated PTH to reduced calcium levels

Causes: chronic renal failure, vitamin D def

36
Q

Tertiary hyperparathyroidism

A

Prolonged secondary hyperparathyroidism
Glands undergo hyperplasia or adenomatous change
PTH remains high inappropriately when Ca normalised
Causes: post-renal transplant for chronic renal failure

37
Q

Malignant hyperparathyroidism

A

Parathyroid related hormone (PTHrP) released by cancers. Mimics PTH
Raised Ca, reduced PTH (intact feedback loop)
Causes: bronchial SCC, breast ca, renal cell ca

X. MRCS: Pathophysiology (13 decks)

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