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Endocrine > Thyroid > Flashcards

Thyroid Flashcards

0
Q

Histology

A

Cuboidal epithelium (follicular cells) around colloid(external storage)-> follicle
Para follicular cells-> large and pale staining-> calcitonin
Lots of colloid in inactive thyroid

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1
Q

Embryology of thyroid

A

Developes from endodermal down growth of the floor of the pharynx between the anterior two thirds and posterior third of tongue
Grows from foramen cecum to thyroid cartilage-> thyroglossal duct
Ectopic thyroid tissue can be left along migration path

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2
Q

Synthesis and release of thyroid hormones

A

Synthesis in cell
Storage in colloid by exocytosis
Iodinatiin of thyroglobulin
Pseudopod process recaptures by endocytosis
Fusion of lysosomes and hydrolysis of thyroglobulin to active hormones
Released by endocytosis

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3
Q

Parathyroid

A 
Normally 4 glands
Posterior surface of thyroid gland
Also migrate down neck-> ectopic tissue
Chief cells-> calbindin-> increase Ca in blood mid purple staining
Oxytocin cells->darker
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4
Q

Thyroid hormones, biosynthesis and storage

A

Tyrosine+iodine-> mono-iodotyrosine or di-iodotyrosine
DIT+DIT-> thyroxine 4 iodines
MIT+DIT-> tri-iodothyronine
DIT+MIT-> reverse tri-iodothyronine, antagonist at T3 receptor

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5
Q

Synthesis of thyroid hormones

A

Each step stimulated by TSH
Source of iodine-> enters through Na/I-ATPase->I- accumulates->entries colloid via pendrin-> oxidised by thyroid peroxidase-> iodine
Source of tyrosine residues-> thyroglobulin-> into colloid by exocytosis-> many tyrosines on thyroglobulin
Iodination of tyrosine molecules on thyroglobulin->coupling of iodotyrosines-> T3/T4 catalysed by TPO
Stored in colloid

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6
Q

Factors involved in peripheral conversion of T3 to T4 or reverse T3

A

Neonate:
Cold stimulates TSH release to increased heat produced by metabolism by increasing T3 and T4
Stress:
Decreases TRH release from hypothalamus and causes somatostatin production-> decreases TSH-> decreased thyroid hormones-> decreased metabolism

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7
Q

Transport in blood

A

Bound to:
Thyroxine binding globulin 70%
Transthyretin 10%
Albumin 20%

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8
Q

In target cell:

A 
Deiodinase enzymes
T4->T3 by D1 and D2 T3 much more potent 
T4 has less action
Also converted to reverse t3-> antagonist 
T4 functions largely as a prohormone
Free T4 shows thyroid function
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9
Q

Actions of thyroid hormones

A

Increase metabolism in all cells-> increased BMR and metabolism of food
Stimulate growth and development
Important for normal development of the CNS
Syngergistic action with SNS/catecholamines

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10
Q

Mechanism of action of thyroid hormone

A

T3 enters cell
Increase metabolic activity of mitochondria
Binds to nuclear receptors-> mRNA for protiens

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11
Q

Factors that alter peripheral conversion of thyroid hormones

A 
Disease of kidney or liver
Acute stress
Some drugs
Low calorie diet
Starvation-> decreases T3
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12
Q

Roles of parathyroid hormones, PTH

A

Released from chief cells
Stimulates release of Ca from bone
Decreases urinary loss of Ca
Indirectly stimulates Ca reabsorption in small intestine through release of active vit D by kidney

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13
Q

Calcitonin

A 
Released from para follicular cells 
Inhibits osteoclastic bone reabsorption 
Oppose PTH
Inhibits Ca reabsorption by small intestines 
Decreases reabsorption of Ca in kidneys
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14
Q

Hypothyroidism causes

A

Primary thyroid gland failure-> 90% hasimotos thyroiditis
Decrease T3 andT4, increase TSH as nonnegative feedback
Produces a goitre
Or
Secondary to hypothalamic or ant pit failure-> decreased T3 and T4 and decreased TSH. No goitre
Lack of dietary iodine-> can’t make thyroid hormone-> decreased thyroid hormones, increased TSH
Drug induced, anti thyroid, lithium, aminodarone
Radioactive iodine therapy
Surgery
Thyroid hormone resistance

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15
Q

Hasimotos thyroiditis, symptoms

A 
Chorionic autoimmune disease against thyroglobulin and other components
Symptoms:
Weight gain
Dry skin
Hoarse voice, slow speech
Menstural changes
Cold intolerance
Constipation
Lowered BP/HR
depression,confusion, poor memory
16
Q

Test results of hasimotos thyroiditis

A

Primary-> decreased T3 and T4-> increased TSH
Secondary-> decreased T3 and T4-> decreased TSH
Test for TPO (thyroid anti-microsomal), anti-thyroglobulin

17
Q

Management of hasimotos

A

Synthetic thyroid hormones
Levothyroxine T4
Liothyronine T3 emergencies

18
Q

Hyperthyroidism, causes

A

Graves’ disease
Secondary to excessive hypothalamic or anterior pituitary secretion, increase of all three, goitre
Hyper secreting thyroid tumour-> increase thyroid hormones, decreased TSH, toxic goitre and adenoma
Iatrogenic cause-> amioderone, lithium

19
Q

Graves’ disease, symptoms

A 
Autoimmune condition 
Increased T3 and T4, decreased TSH 
Thyroid stimulating immunoglobins active thyroid gland 
Symptoms:
Weight loss
Sweating
Heat intolerance
Palpitations
Tremor bets adrenoceptor response 
Anxiety, emotional, irritable
Restlessness
Exopthalamus
20
Q

Diagnosis of graves

A

Thyroid function test
Primary-> increased T3,T4, decreased TSH
Secondary-> increased T3, T4, increased TSH
Test for thyroid stimulating hormone

21
Q

Management of graves

A

Anti thyroid drugs
Radiotherapy
Surgery

22
Q

Anti thyroid drugs

A

Carbimazole and propylthiouracil
Decrease production of thyroid hormones by inhibiting iodisation and coupling
Takes serval weeks to work because of the colloid stores
50% relapse rate

23
Q

Non selective beta blockers

A

Reduce action of catecholamines-> rapid sympathetic relief of tremor, palpitations and anxiety

24
Q

Radioactive iodine

A

First line for older patients with nodular goitres and hyperthyroidism
Used when thyrotoxocis recurs after drug therapy
Single does
Max effect after 2-4 months

25
Q

Thyroidectomy

A

Used in severe cases
Large goitre or tumour development
Obstructive symptoms
Risk of parathyroid damage

Endocrine (9 decks)

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