Flashcards in Laboratory Investigation of Endocrine Disorders Deck (68)
What is synthesis and release of TH controlled by?
What is the main hormone secreted by the thyroid?
What is the biologically active form of the hormone secreted from the thyroid and how does this occur?
➝ peripheral conversion from T4
Describe the thyroid hormone axis?
➝ Hypothalamus produces TRH
➝ TRH acts on the pituitary gland which produces TSH
➝ TSH acts on the thyroid
➝ thyroid produces T3 and T4
➝ T4 and T3 act on tissues and feedback negatively to the pituitary
➝ in peripheral tissues T4 is converted to T3 which feedsback negatively to the hypothalamus
What are thyroid hormones needed for?
➝ Normal growth and development
What is the effect of thyroid hormone?
➝ increases basal metabolic rate (BMR) and affect many metabolic processes
What are T3 and T4's effects mediated by?
➝ activation of nuclear receptor
What is the normal total and free T4 concentration?
➝ total : 60-150 nmol/L
➝ free : 11-23 pmol/L
What is the normal total and free T3 concentration?
➝ total : 1-2.9 nmol/L
➝ free : 4-8 pmol/L
What is the half life of T4 compared to T3?
➝ T4 6-7 days
➝ T3 0.5-1 day
What is euthyroid?
➝ normal range
What is hypothyroid?
What is hyperthyroid?
What is primary hyper/hypo thyroidism?
➝ dysfunction is in the thyroid gland
What is secondary hyper/hypo thyroidism?
➝ dysfunction is in the pituitary
What is tertiary hyper/hypo thyroidism?
➝ hypothalamus dysfunction
What is hyperthyroidism?
➝ excessive production of thyroid hormones
What are the clinical features of hyperthyroidism?
➝ weight loss
➝ heat intolerance
➝ eye changes
What happens in extreme hyperthyroidism?
➝ thyroid storm
What are the 4 causes of hyperthyroidism?
➝ Graves disease (most common)
➝ toxic multinodular goiter
➝ toxic adenoma
➝ secondary : excess TSH production
What is Graves disease due to?
➝ Due to stimulatory TSH-R antibodies which activate the receptor in the absence of TSH
What is hypothyroidism?
➝ Deficient production of thyroid hormones
What are the clinical features of hypothyroidism?
➝ weight gain
➝ cold intolerance
➝ lack of energy
➝ congenital - developmental abnormalities
What are the biochemistry results for an investigation on hypothyroidism?
➝ Raised TSH
➝ reduced T4
What does reduction in TSH and T4 suggest?
What are the 5 causes of hypothyroidism?
➝ Autoimmune thyroiditis (Hashimotos)
➝ thyroid peroxidase antibodies (anti-TBO)
➝ iodine deficiency
➝ Toxic adenoma
➝ secondary - lack of TSH
if TSH levels are high what does this indicate?
➝ lack of thyroid effectiveness
if TSH is very low and T4 and T3 are very high what does this mean?
➝ the disorder is primary
What does functional zonation of the cortex mean?
➝ different hormones made in each layer