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ENDOCRINOLOGY > The thyroid gland > Flashcards

The thyroid gland Flashcards

1
Q

Hypothryoidism symptoms and treatment

A
  • Drowsy
  • Skin + hair changes
  • Thickened dry skin
  • Puffiness
  • Iv with thyroid hormone for underactive thryoid
  • Hormone tablet a day
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2
Q

Thryoid gland made up of :

A
  • Multiple follicles - surrounded by follicular cells
  • the colloid (sticky xtracellular fluid)
  • Parafollicular cells produce hormone Calcitonin -regulates calcium and phosphate in blood opposing the action of parathyroid hormone.
  • Parathyroid glands embedded in thyroid - produce parathyroid hormone
  • left recurrent laryngeal nerve runs close (supplies vocal cords)
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3
Q

What is risky about operation to remove thyroid gland

A

Recurrent laryngeal nerve - can risk damage to these

Can cause problems with heart rhythm and Ca+

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4
Q

Embryology of thyroid gland

A
  1. Originates from base of tongue (floor of pharynx)
  2. Development of thyroglossal duct
  3. Divides into 2 lobes
  4. Duct disappears before leaving foramen caecum
  5. Last position - Week 7
  6. Thyroid gland develops
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5
Q

thyroid histology

A

****

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6
Q

How is thryoid hormone produced

A
  • TSH-1 produced by thyrotroph cells
  • Receptors on cell memb
  • TSH-1 arrives via blood to TSH recep, Binds to it on follicular cell
  • Sodium and iodine ions enter cell via sodium iodide transporter
  • Iodide ions go across cell and Go thru other transporter into colloid, They’re oxidised into iodine (called iodination)
  • Production of prohormone thyroglobulin, Released and enters colloid as well
  • TSH activates an enzyme - TPO (thyroid peroxidase) when it binds ot TSH receptor - important in production of throid
  • Oxidase enz and hydorgen peroxide Catalyses iodination reactions
  • Iodine : in collioid, thyoglobulin , bind these two together in iodination : two products :MIT and DIT (mono iodothyrine and diodothyrinine)- which join to Give you thyroid hormone (still bound to thyroglobulin
  • Enters cell and in lysosomes the protein bonds are broken down
  • Thyoid hormone enters bloodstream
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7
Q

Thyroid hormones

A
  • About 100 tyrosine residues on thyroglobulin
  • Approx 20 are capable of being iodinated (can put iodine onto it )
  • Add iodine to tyrosine you iodinate it
  • MIT and DIT - coupling to form T3
  • DIT and DIT - coupling forms T4 (thyroxine)
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8
Q

Deiodination of T3

A
  • T4 is main hormone product of thyroid gland
  • ITs a prohormone converted by deiodinase enz into T3 ( its bioactive form in target tissues) (deiodination)
  • deiodinated in diff position to produce reverse T3 (inactive)
  • Circulating T3 - 80% from deiodination of T4, 20 % from thyroidal secretion
  • T3 provides almost all thyroid hormone activity in target cells
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9
Q

How is thyroid transported around blood

A

Mostly bound to plasma proteins:

  • thyroid binding globulin (TBG) (70-80%)
  • albumin (10-15%) ,
  • prealbumin (aka transthyretin)
  • only 0.05% T4 and 0.3 % T3 is unbound (bioactive components)
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10
Q

Effects on gene expression

A
  • Almost every cell requires thryroid hormone
  • T4 is deioniated after it enters cell via cell surface recpetors
  • T3 enters nucleus
  • T3 binds to hormone receptor
  • Thyroid hormone affects gene expression
  • Effect depends on tissue it is acting on
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11
Q

Why is thyroid hormone important

A

Essential for fetal growth + development especially CNS

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12
Q

What happens if problems with thyroid hormone production in foetus

A

Untreated congenital hypothyroidism - cretinism - baby born without thyroid gland

TSH measured in new born infacnts heel prick test

Thyroid treatmetn lifelong

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13
Q

ACtion of thyroid hormone and can baby be affected if it does not develop thyroid

A
  • increases metab
  • Affects sympathetic nervous system , Increases power of catecholamines) tachcardia , lipolysis)
  • Can affect how quickly bowels move, effects on GI, CNS, and reproductive system
  • Can affect maturation of brain
  • Thyroid hormone crosses placenta so baby protected in womb
  • Only when baby is delivered something appears wrong
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14
Q

Control of thryoid hormone production and what happens if overproducing thyroid

A
  • Production of T3 and T4
  • Whole process called Hypothalamo pit access
  • TRh released by hypo
  • TSH released into circ
  • Acts on thyroid gland
  • Stimulate release T3 and T4 and when there is enough they send signals telling hypo to stop producing TRH
  • homeostasis everything kept in balance
  • Iodide can inhib production of T3 and T4
  • Overproducing - hyperthyroid - can give them large amount of potassium iodide - called Wolff- Chaikoff effect
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15
Q

Is thyroid disorders more common in men or women adn why

A
  • Women had to evolve because they carry babies - exposed to antigens that men are not exposed to
  • Their immune system is different - more likely to develop glitches in system so more likely to develop immune disorders
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16
Q

Is overactive thryoid gland or underactive thyroid gland more common in men or womwn

A

The same

17
Q

Primary hypothyroidism

A
  • Automimune damage to thyroid
  • thyroxine decrease
  • TSH increase
  • Commonest forms : Hashimoto’s throiditis and Graves’ disease
  • Hashimotos usually associated with hypthyroidism
  • Presence of autoimmune disease increases risk of others
18
Q

Symptoms and signs of hypothyroidism

A
  • Deepening voice
  • Depression and tiredness
  • Cold intolerance - may feel hot and ask for windows to be opened
  • Weight gain and reduced appetite
  • constipation
  • Bradycardia
  • Eventual myoxodema coma - needs urgent treatmebt
19
Q

LEvothyroxine as treatment

A
  • Levothyroxine almost identical to T4 and can be deiodinated into T3 - given in tablet form
  • Can treat hypo and hyper thryoidism
  • Radioactive iodine can cause hyperthyroidism
  • Overactive hyperthyroidism - block thyroxine and replace
  • T4 is good indicator of thyroid status -
  • Try to get TSH into norm range , common dose is 100 micrograms
  • Only use iv when they cant ingest it
  • Weight loss , headache , Can become tachycardic - all complications are very rare and only happens when taking too much thyroxine
20
Q

Combined thyroid hormone replacement

A
  • T4 - prohormone - coonverted by deiodinase action to T3
  • Combo of T4 and T3 - some say improvement in wellbeing
  • Complicated by symptoms of toxicity - palpatations , tremor, anxiety - often combo of treatm suppresses TSH - because of too much thryoid hormone - may have ‘overreplaced’
21
Q

Hyperthyroidism

A
  • Thyroid MAkes too much thyroxine
  • Thyroxine increases
  • TSH decreases
  • CAsues : GRAVES disease - whole gland smootly enlarged adn whole gland overactive
  • Toxic multinodular goitre
  • Solitary toxic nodule
22
Q

Hyperthyroidism symtpoms

A
  • Nervousness, irritability, insomnia, depression, mood swings
  • Weight loss , feeling of hunger, diarrhea
  • Fragile fingernails, shaking hands
  • Warm moist skin, increased body temp
  • Broken hair, hair loss
  • Enlarged thyroid gland
  • INcreased heart rate , arrhythmia, high blood pressure, myopathy, palpitations
  • Muscle cramps , muscle weakness
  • Misclellaneous : cycle disorders
  • Sore eyes , goitre
23
Q

Graves disease

A
  • autoimmune
  • Ab bind to and stimulate TSH receptor in thyroid
  • Results in production of T4 and T3
  • Smooth goitre
  • Diffuse enlargement and engorgement of thyroid gland
  • Other ab bind to muscles behind eye - exophthalmos and cause thryoid eye disease
  • Should not be able to see white around iris - normal
  • But here eyes are bulging and white around eyes is very visible
  • Eyes feel gritty and don’t close at night
  • May need surgery or steroids to treat the eyes because of complications
  • Other ab stimulate growth of soft tissue of shins - pretibial myxoedema
24
Q

What is thyroid eye disease associated witg

A

smoking

ENDOCRINOLOGY (5 decks)

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