Thyroid Gland Flashcards
Where is the thyroid gland
Sits on trachea - two lobes joined by isthmus
When is the thyroid gland enlarged
Adolescence, pregnancy, lactation, later portion of menstrual cycle
What is the blood supply of the thyroid
superior (from external carotid) and inferior (from subclavian artery) thyroid arteries
Blood flow 4-6 ml/min/g tissue
What does the thyroid gland make
T4 and T3
Calcitonin - involved in Ca2+ metabolism ( opposing action of PTH)
Functions: neural development n foetus, growth in the young child, controls basal metabolic rate
Concentrates iodine for incorporation into thyroid hormones
What does PTH do
secreted in response to low blood serum Ca2+ levels, indirectly stimulates osteoclast activity within bone marrow
Describe thyroid hormone cycle
TRH stimulates thyrotrophs in anterior pituitary to produce TSH. TSH stimulates thyroid gland to synthesise and release thyroid hormones
Main hormone released is T4íT3 in the periphery
T3 more potent at thyroid receptors than T4
T3 acts on the thyrotrophs to decrease release of TSH/decrease release of TRH from hypothalamus
What does the colloid contain
Precursor to thyroid hormones
What does the parafollicular do
Secrete calcitonin
What does the phagosome/lysosome do
break down thyroglobulin to release T3 and T4
How are thyroid hormones synthesised
Active uptake of iodine
Synthesis of glycoprotein thyroglobulin
Organification of iodine by thyroid peroxidase in the presence of hydrogen peroxides
Describe thyroid hormone binding
Thyroid hormones interact with nuclear receptors
Enters cell by diffusion or by specific carrier
T3 enter the nucleus and binds to thyroid receptor
Hormone receptor complex binds to thyroid hormone responsive element on DNA
What are the effects of thyroid hormones
O2 consumption and heat production Cardiac muscle contractility Sensitivity to catecholamines Maintenance of hypoxic and Hypercapnic drive in respiratory centre Gut motility Erythropoiesis Bone turnover Protein turnover - decrease in muscle mass Cholesterol degradation Metabolic turnover of hormones and drugs
What are the signs of hypothyroidism
Cold intolerance, weight gain, constipation, slow reflexes, hypercholesterolemia, hyperprolactinaemia, dry skin, hoarse voice, slow movements, coarse hair and skin, periorbital puffiness
What is the usual range of T4
9-23.8
What is the usual range of TSH
0.49-4.67
What are the serum levels for primary hypothyroid
High TSH, low T4
What are the serum levels for primary hyperthyroid
High T4, low TSH
Describe the types of hypothyroidism
Usually primary autoimmune (destruction of thyroid)
Atrophic thyroiditis: small and shrivelled thyroid
Hashimoto thyroiditis: enlarged thyroid
Thyroid peroxidase antibodies present
What is the treatment for hypothyroidism
Treat with levothyroxine 75-125 mcg per day, check treatment with TFTs blood tests
What is the difference between thyrotoxicosis and hyperthyroidism
Thyrotoxicosis is the clinical syndrome of too much thyroid hormone
Hyperthyroidism is case where thyroid is making too much thyroid hormone
What are the signs of hyperthyroidism
Mood and behavioural changes, restlessness, shaking, sweating, palpitations, breathlessness, diarrhoea, muscle stiffness and weakness
Lid retraction from sympathetic activation
Lid lag
Pre-tibial myxoedema
What is the most common cause of hyperthyroidism
Grave’s disease (most common) - stimulating antibodies to TSH receptor. Can also get tearing of eyes and thyroid acropachy (clubbing of fingernails) and Grave’s dermopathy
What investigations should be done for Grave’s
TFTs, antibodies, thyroid uptake scan, ultrasound of thyroid
What is the treatment for Grave’s
Carbimazole 40mg or propylthiouracil 200mg for 6-12 months
Radio-iodine - avoid in thyroid eye disease
Surgery
What are the other causes of TNG
Unregulated TSH excess
hCG mediated
Excess thyroid hormone medication
Thyroiditis: can fluctuate between hyper, eu and hypo
Painless - lymphocytic thyroiditis (post-partum), Hashimoto’s thyroiditis
Painful - granulomatous thyroiditis, radiation induced thyroiditis
What is a toxic thyroid nodule
Hyper-functioning nodule develops within a longstanding goiter. This results in hyperthyroidism, without the eye bulging effects seen in Grave’s disease
Describe thyroid cancer
Main type is papillary thyroid cancer
Others: follicular, medullary (linked with MEN2, tumour marker is calcitonin), anaplastic
Prognosis of PTC is excellent
What are the side effects of hyperthyroidism treatment
neutropenia and angranulocytosis (severe and dangerous leukopenia)
