The thyroid gland

Question 1

Hypothryoidism symptoms and treatment

Answer 1

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

Question 2

Thryoid gland made up of :

Answer 2

• 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)

Question 3

What is risky about operation to remove thyroid gland

Answer 3

Recurrent laryngeal nerve - can risk damage to these

Can cause problems with heart rhythm and Ca+

Question 4

Embryology of thyroid gland

Answer 4

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

Question 5

thyroid histology

Answer 5

****

Question 6

How is thryoid hormone produced

Answer 6

• 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

Question 7

Thyroid hormones

Answer 7

• 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)

Question 8

Deiodination of T3

Answer 8

• 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

Question 9

How is thyroid transported around blood

Answer 9

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)

Question 10

Effects on gene expression

Answer 10

• 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

Question 11

Why is thyroid hormone important

Answer 11

Essential for fetal growth + development especially CNS

Question 12

What happens if problems with thyroid hormone production in foetus

Answer 12

Untreated congenital hypothyroidism - cretinism - baby born without thyroid gland

TSH measured in new born infacnts heel prick test

Thyroid treatmetn lifelong

Question 13

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

Answer 13

• 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

Question 14

Control of thryoid hormone production and what happens if overproducing thyroid

Answer 14

• 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

Question 15

Is thyroid disorders more common in men or women adn why

Answer 15

• 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

Question 16

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

Answer 16

The same

Question 17

Primary hypothyroidism

Answer 17

• 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

Question 18

Symptoms and signs of hypothyroidism

Answer 18

• 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

Question 19

LEvothyroxine as treatment

Answer 19

• 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

Question 20

Combined thyroid hormone replacement

Answer 20

• 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’

Question 21

Hyperthyroidism

Answer 21

• 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

Question 22

Hyperthyroidism symtpoms

Answer 22

• 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

Question 23

Graves disease

Answer 23

• 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

Question 24

What is thyroid eye disease associated witg

Answer 24

smoking