Flashcards in Thyroid: Science and Diseases Deck (131):
Where do the thyroid lobes attach?
thyroid and cricoid cartilages
Which cartilages does the thyroid attach? Which is superior and which is inferior?
Thyroid (superior), Cricoid (inferior)
Where does the isthmus of the thyroid gland lie?
2-3rd tracheal cartilages -- C5-T1 vertebrae
Where does the thyroid gland originally develop?
between the anterior and posterior parts of the tongue, where the foramen caecum is found in adults
How does the thyroid migrate to its adult location?
via the thyroglossal duct - around week 7
Working anteriorly to posteriorly, what is the first level of fascia found at the neck?
What does the superficial fascia of the neck contain?
Working anteriorly to posteriorly, what is found after the superficial fascia in the neck?
anterior investing fascia
What does the anterior investing fascia contain?
the sternocleidomastoid muscles
Working anteriorly to posteriorly, what is found after the anterior investing fascia in the neck?
What is found within the pretracheal fascia? (5)
strap muscles, trachea, oesophagus, recurrent laryngeal nerves, thyroid gland
What is found bilaterally to the pretracheal fascia in the neck?
What is found within the carotid sheath? (4)
internal jugular vein, deep cervical lymph nodes, vagus nerves, carotid arteries
Which fascia is found beyond the pre-tracheal fascia?
What is found within the pre-vertebral fascia?
c-vertebrae, postural neck muscles
What muscle is found within the posterior investing fascia?
the trapezius muscles (bilaterally)
Which arteries supply the thyroid gland? (2)
superior and inferior thyroid arteries
What are the origins of the superior and inferior thyroid arteries?
superior - external carotid; inferior - branch of subclavian
Which veins does the thyroid gland drain? (3)
the superior (2), middle (2) and inferior thyroid (1) veins
Where do the veins from the thyroid gland drain?
superior and middle --> internal jugular --> brachiocephalic; inferior --> brachiocephalic
Which lymph nodes does the thyroid gland drain into? (4)
the inferior pretracheal node; paratrachial nodes; superior deep cervical nodes and deep cervical nodes
Which aortic arch is the subclavian artery formed from?
Which aortic arch is the arch of the aorta formed from?
Name the 4 strap muscles
Omohyoid, sternohyoid, sternothyroid, thyrohyoid
What 3 things does the thyroid gland secrete?
T4 (thyroxine), T3 (triiodothyronine), calcitonin
What naturally causes an increase in the size of the thyroid gland?
menstruation and pregnancy
Innervation of the thyroid gland (2)
ANS including Vagus nerve (Parasympathetic) and the sympathetic trunk
Describe the structure of the thyroid gland
follicles surround by follicular cells; parafollicular C cells found dotted about
What is found within the follicle of the thyroid gland?
colloid - tyrosine containing thyroglobulin
How are T3/T4 secreted into the blood stream?
How is T3 made?
Iodine taken into the follicle is attached to tyrosine residues in the form of mono-iodotyrosine (MIT) or di-iodotyrosine (DIT). T3 is made up of MIT+DIT
How is T4 made?
Iodine taken into the follicle is attached to tyrosine residues in the form of mono-iodotyrosine (MIT) or di-iodotyrosine (DIT). T4 is made up of DIT + DIT
Which thyroid hormone is more potent?
Which thyroid hormone is more biologically active?
Which thyroid hormone is most commonly secreted?
Where is T4 converted to T3?
the liver and kidney
What stimulates the release of T3 and T4 from the follicular cell?
How are T3/T4 carried within the blood stream and why?
T3/T4 are hydrophobic so are carried in the plasma bound to plasma proteins - when they are in the free form they are biologically active
Name the 3 proteins which T3/T4 are most commonly bound to
Thyroxine binding globulin (TBG) ~70%; Transthyretin thyroxine binding pre-albumin (TTR); Albumin (5%)
Which form of T3/T4 is more closely correlated to the metabolic state?
free T3 and free T4
What is the result of increasing TBG?
increased total T4, not free T4
States where there may be increased TBG (4/7)
pregnancy, newborn, hepatitis, biliary cirrohosis, oral contraceptive pill (or other sources of oestrogen), acute intermittent porphyrias, heroin
What is the result of decreasing TBG?
decreased total T4, not free T4
States where there may be a decrease in TBG (4/7)
androgens, large doses of glucocorticoids, active acromegaly, severe systemic illness, chronic liver disease, phenytoin, carbemazepine
Physiological effect of increasing thyroid hormones (5/8)
increased BMR; increased thermogenesis; increased carbohydrate/lipid metabolism; increased protein synthesis; growth; development of foetal/neonatal brain; normal CNS activity
How does thyroid hormone affect the response to adrenaline?
increases responsiveness to adrenaline and NA by increasing the number of receptors --> increase in HR and force
Why is propanolol an initial treatment of hyperthyroidism?
It antagonises the adrenoreceptors to reduce HR and force which can be found in hyperthyroidism
How does thyroid hormone increase BMR?
increases the number and size of mitochondria, increases oxygen use and ATP hyrdolysis and increases the synthesis of respiratory chain enzymes
How much of temperature regulation is affected by thyroid hormone?
How does thyroid hormone affect carbohydrate metabolism?
increased blood glucose through glycogenolysis and gluconeogenesis while increasing insulin dependent uptake into cells
How does thyroid hormone affect growth?
GHRH production and secretion requires TH
How does thyroid hormone affec the development of the neonatal brain?
increases myelinogenesis and axonal growth
How is thyroid hormone release regulated?
Thyrotropin RH is released from the hypothalamus and stimulates TSH release from the anterior pituitary
How do T3/T4 impact the release of TRH?
negative feedback system: T3/T4 inhibit the release of TRH and TSH
What kind of receptor is the TSH receptor?
A GPCR which stimulates cAMP in the follicular cell
When is TH highest in the day?
Late at night; lowest in the morning
How many types of de-iodinase enzymes are there?
Which de-iodinase enzyme is most important for converting T4 to T3 ?
Where is type 2 de-iodinase enzyme mostly found?
within the heart, skeletal muscle, CNS, fat, thyroid and pituitary
Where is type 3 de-iodinase enzyme mostly found?
foetal tissue, the placenta and brain (-pituitary)
Where is type 1 de-iodinase enzyme mostly found?
liver and kidneys
How does T3 activate the TH receptor?
TH receptor is activated and travels to the nucleus of the cell where it binds with the RXR and a transcription factor
What are the 4 thyroid hormone receptor isoforms?
TRa1, TRa2, TRb1, TRb2
Which is the predominant form of thyroid hormone receptor in most tissues?
Which tissues is TRb the predominant form of thyroid hormone receptor?
liver and negative feedback loop
Test results show: high TSH, low fT4...diagnosis is...
Test results show: high TSH, normal fT4...diagnosis is...
Test results show: high TSH, high fT4...diagnosis is...
TSH secreting tumour or TH resistance
Test results show: high TSH, high fT4/ low fT3..diagnosis is...
deiodinase deficiency, TH antibody
Test results show: low TSH, high fT4/T3...diagnosis is...
Test results show: low TSH, normal fT4...diagnosis is...
Test results show: low TSH, low fT4...diagnosis is...
Test results show: low TSH, lowfT4/T3...diagnosis is...
sick euthyroid or pituitary disease
Test results show: normal TSH, abnormal fT4...diagnosis is...
consider TBG, amiodarone, pituitary TSH tumour
Chief cause of hypothyroidism worldwide
Chief cause of hypothyroidism in the UK
Clinical features of hypothyroidism that might be seen in the hair and skin (4+)
coarse, sparse hair; dull expressionless face; periorbital puffiness; pale cool skin that feels doughy
Clinical features involving thermogenesis of hypothyroidism
Cardiac features of hypothyroidism
bradycardia, worsening heart failure
Metabolic features of hypothyroidism
hyperlipidaemia, weight gain, decreased appetite
Common GI feature of hypothyroidism
Common neurological features of hypothyroidism
depression, psychosis, carpal tunnel syndrome and decreased visual acuity
Common gynae features of hypothyroidism
menorrhagia follows by amenorrhoea
Goitrous causes of primary hypothyroidism (4)
chronic thyroiditis (Hashimotos), iodine deficiency, drug induced (lithium, amiodarone), maternally transmitted
Non-goitrous causes of primary hypothyroidism (3)
atrophic thyroiditis (autoimmune), post-ablative, congenital developmental defect
Subclinical hypothyroidism may present with what blood test features?
high TSH, normal T4
Common clinical investigations other than thyroid function tests which may be ordered when considering hypothyroidism
MCV - macrocytosis, increased CK, increased LDL and cholesterol, hyponatraemia, hyperprolactinaemia
Main drug treatment of hypothyroidism
levothyroxine (T4) - taken before breakfast
Why might levothyroxine dose need to be increased in pregnancy?
due to increased TBG produced by the liver
Why is it important to slowly restore normal thyroid function in hypothyroidism?
it may cause cardiac arrhythmias
Dose of levothyroxine in young person?
Dose of levothyroxine in elderly
Antibodies associated with Hashimoto's thyroiditis
anti-TPO - thyroid peroxidase
group most commonly affected by myxoedema coma
elderly women with longstanding or undiagnosed hypothyroidism
Signs of myxoedema coma
bradycardia, type 2 resp failure, hypoxia, hypercarbia, co-existing adrenal failure
cardiac features of hyperthyroidism
palpitations, AF, rarely cardiac failure
General feelings when suffering from hyperthyroidism
anxiety, irritibility, sleep disturbance
How might hyperthyroidism affect the sympathetic nervous system?
sweating and tremors
Visual features of hyperthyroidism
lid retraction (non-specific), diplopia, proptosis - Graves
Gynae features of hyperthyroidism
lighter and less frequent periods
Where might a patient experience weakness in hyperthyroidism?
thighs and upper arms
Thermogenesis in hyperthryoidism
Weight in hyperthyroidism
decreased despite increased appetite
Causes of thyrotoxicosis associated with hyperthyroidism (7)
Graves, Hashitoxicosis, thyrotropinoma, thryoid cancer, toxic solitary nodule, toxic multinodular goitre
Causes of thyrotoxicosis associated with hyperthyroidism (3)
thyroid inflammation (post-partum, sub-acute, drug induced), exogenous TH, ectopic thyroid tissue
Age associated with Grave's disease
younger patients (20-50years)
Is there a genetic component to Graves?
Yes - 70% have susceptibility factors and sisters and children of women with Graves have a 5-8% chance of developing an autoimmune thyroid disease of any kind
Key exacerbating factor in Grave's disease
smoking - more severe and difficult to treat in smokers
Investigations in Graves disease
TSH receptor antibody
Thyroid function test results expected in Graves disease
Decreased TSH and increased fT3/T4
Expected LFTs and calcium results in Graves disease
hypercalcaemia and raised ALP due to increased bone turnover --> association with osteoporosis
Expected WCC in Graves disease
leucopaenia - often milk
TSH receptor antibody is confirmation of diagnosis of Graves - True/False
True - If this is present then there is no need to image the thyroid gland
Clinical signs of Graves disease (4)
Pretibial myxoedema, thyroid acropachy, thyroid bruit, graves eye disease
Graves eye disease occurs in what percentage of patients...what group are particularly high risk?
20%, particularly smokers
confirmation of graves eye disease on MRI
inflammation behind the eye
Which group of patients is most likely to experience nodular thyroid disease?
older patients - occurs with insidious onset
What features suggest a thyroid storm?
resp and cardiac collapse, severe hyperthermia, exaggerated reflexes
Patients at risk of thyroid storm?
those with acute infection or recent surgery
treatment of a thyroid storm?
Lugol's iodine, glucocorticoids, PTU, b-blockers, fluids and monitoring
Brief overview of deQuervains thyroiditis
subacture granulomatous thyroiditis, inflammation of thyroid which may be painful and oftern preceeded by a viral illness
3 phases of deQuervains thyroiditis
thyrotoxicosis, hypothyroid, euthryroid
investigation results confirming deQuervains thyroiditis
raised ESR, CRP and TH levels
First line treatment of hyperthyroidism
mechanism of action of treatment of hyperthyroidism
inhibition of thyroid peroxidase --> blocks TH synthesis
situation where carbimazole is not first line treatment
early pregnancy - may cause aplasia cutis
1st line treatment in early pregnancy for hyperthyroidism
polythiouracil (PTU) - 10x less potent than carbimazole
mechanism of action of PTU
main risk of PTU
1:10000 liver failure
in the first 6 weeks of hyperthyroid treatment, what is the biggest side effect risk
agranulocytosis - warn verbally, get urgent FBC if fever, oral ulcer or oropharyngeal infection