Thyroid Physiology Flashcards
What 3 things does the thyroid gland secrete?
thyroxine; tri-iodothyronine; calcitonin
What vertebral ring is the thyroid found at?
between C5 and T1
What tracheal rings is the thyroid found at?
2nd-4th tracheal rings
What is the sympathetic innervation of the thyroid?
superior, middle and inferior ganglia of the sympathetic trunk
What is the parasympathetic innervation of the thyroid gland?
vagus nerve
What artery do the superior and inferior thyroid arteries branch from?
external carotid
What veins do the superior and middle thyroid veins drain into?
internal jugular
What vein does the inferior thyroid vein drain into?
brachiocephalic
What ligament attaches the posteriomedial aspec of the thyroid gland?
Berry ligament
How are T3 and T4 exported from the colloid?
pinocytosis
What are the two units used in T3 and T4?
monoiodotyrosine and di-iodotyrosine
What is the coupling of units in T3?
MIT and DIT
What is the coupling of units in T4?
2 DITs
Where are T3 and T4 stored?
colloid thyroglobulin
What is the basic molecule from which T3 and T4 are synthesised?
thyroglobulin
What attaches to thyroglobulin?
iodine
What drugs inhibit the attachment of iodine to thyroglobulin?
carbimazole and propylthiouracil
What is the name of T4?
thyroxine
What is the name of T3?
triiodothyronine
What is the difference in potency between T3 and T4?
T3 is about 4 times more potent than T4
How do T3 and T4 travel in the blood?
bound to plasma proteins
What plasma proteins do T3 and T4 bind to?
thyroxine binding globulin; thyroxine binding prealbumin; albumin
How do thyroid hormones increase basal metabolic rate?
increase number and size of mitochondria; increase oxygen use and rates of ATP hydrolysis and increase synthesis of respiratory chain enzymes
What do thyroid hormones do in terms of body temperature?
increase thermogenesis
How are thyroid hormones involved in the metabolism of food
stimulate glycogenolysis nad gluconeogenesis and glucose uptake; increase fatty acid oxidation in tissues; increse protein synthesis
What effects does hypo and hyper thyroidism have on CNS actviity?
hypo- slow intellectual functions; hyper- nervousness; hyperkinesis and emotional lability
What is the use of thyroids in foetal develpment?
myelinogensis and axonal growth require thyroid hormones
what is the effect of thyroid hormones on the sympathetics?
increase responsiveness to adrenaline and sympathetic noradrenaline by increasing numbers of receptors
What does this permissive sympathomimetic action ahve on the CVS?
increases force and rate of contraction
What hormone released by the hypothalamus stimulates the anterior pituitary?
thyrotrophin releasing hormone
what hormone does the anterior pituitary release to stimulate T3 and T4 release?
thyroid stimulating hormone
What effect do T3 and T4 have on TRH and TSH
exert negative feedback control
What enzymes are involved in the activati onand deactivation of thyroid hormone?
delodinase enzymes
How do the delodinase enzymes work?
add or remoave an iodine atom from the outer ring
what enzyme converts T4 to T3 in tissues?
D2
Where is D2 found?
in the heart, SK, CNS, fat, thyroid, pituitary
What are symptoms of hypothyroidism?
decreased BMR; slow pulse rate; fatigue; lethargy; slow response times and mental sluggishness; cold-intolerance
How does thryoid stimulating immunoglobulin work?
like TSH but is unchecked by T3 and T4
What are the symptoms of hyperthyroidism?
increased BMR; HR; nervousness and excessively emotional; insomnia; sweating and heat intolerance
