Thyroid Physiology Flashcards
Are T3/T4 hytrophobic or philic?
hydrophobic, so bind to plasma proteins
What is the biologically active form in plasma protein binding?
unbound
Which, T3 or T4 is more avidly bound by Thyroid binding globulins?
T4
What is measured at Ninewells, bound or free T4/T3?
free
Increased Thyroid binding globulins leads to what happenening to T4?
increases total T4 but not free T4
Decreased Thyroid binding globulins leads to what happenening to T4??
decreases total T4 but not free T4
Name some conditions where there is increased TBG?
pregnancy newborn state Hep A Chronic active hepatitis Biliary cirrhosis Acute intermittent porphyria
Name some conditions where there is decreased TBG?
androgens
large doses of glucocorticoids, Cushings
Chronic liver disease
Nephrotic syndrome
List 5 thyroid hormone effects related to metabolism.
BMR Thermogenesis Carbohydrate metabolism lipid metabolism protein metabolism
What effect do thyroid hormones have on growth and development?
Growth hormones requires thyroid hormones
Development of foetal and neonatal brain - myelinogenesis and axonal growth
Maintains normal CNS
What is permissive sympathomimetic action?
Thyroid hormones increase responsiveness to adrenaline and sympathetic NS neurotransmitter, noradrenaline, by increasing numbers of receptors
also causes cardiovascular responsiveness
What is used to treat symptoms in initial stages on therapy for hyperthyroidism due to increased cardiovascular responsiveness?
propranolol
What causes TSH to be released from the anterior pituitary?
TRH
What causes T3 and T4 to be released from the thyroid gland?
TSH
What exert negative feedback control of release of TRH and TSH?
T3 and t4
In babies and young children, exposure to cold environments stimulates what?
TRH release, so TSH and then T3 and T4
What does stress do to TRH and TSH release?
inhibits
What is circadian rhythm?
thyroid hormones highest late at night, lowest in morning
Which type of gland failure, primary or secondary, may be associated with an enlarged goiter?
primary
If hypothyroidism is secondary to TRH or TSH, is there a goiter?
no
May hypothyroidism caused by iodine deficiency be associated with a goiter?
Yes
Give 5 symptoms of hypothyroidism.
reduced BMR, slow pulse rate, fatigue, cold intolerance, tendency to put on weight easily
What sign is seen in adults with hypothyroidism?
myxoedema (puffy face, hands and feet)
What sign may be seen in babies with hypothyroidism?
cretinism (dwarfism and limited mental function)
