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regub 5: thyroid hormone 2 (actions of thyroid hormones (essential for…
regub 5: thyroid hormone 2
thyroxine 5'-deiodinase
converts T4 ro T3
in liver + kidneys
T3 vs T4 synthesis
monoiodotrysine coupled diiodotyrosine via thyroid peroxidase = T3
diiodotrysine coupled diiodotyrosine via thyroid peroxidase = T4
TH release
thyrocytes ingest colloid by endocytosis
endosome + lysosome fuse to digest thyroglobulin
hormones released
99.5% bind to carrier proteins
not biologically available
TH carrier proteins
thyroxine binding protein
high affinity, low capacity
70% of T4, 38% of T3
thyroxine binding pre-albumin
low affinity, high capacity
10% T4, 27% T3
albumin
low affinity, high capacity
20% T4, 35% T3
action of TSH on follicular cells
increases iodide transport
increases production + iodination of thyroglobulin
increases colloid endocytosis
thyroid hormone R
nuclear
hormone-R complex regulates gene expression by binding to the hormone response element via the retinoid X R
retinoid X R activated by binding to 9-cis-retinoic acid
conformational change: corepressors displaced, coactivators recruited
coactivators recruit RNA polymerase for protein synthesis
present in all tissues except spleen, brain, testes, uterus, thyroid gland
expression inhibited by TH
actions of thyroid hormones
increases O2 consumption, CO, HR, contractility, SV ventilation, rest rate
increases food intake, mobilisation of carbs,protein,fat
increases CO2, urea, renal function, thermogenesis, sweating
decreases muscle (more protein degradation) + adipose tissue (more glycogen breakdown)
essential for normal tissue growth... esp NS
increases speed + amplitude of peripheral N reflexes
increases alertness, memory, learning capacity
stimulates BMR
required for GH+prolactin secretion
increases intestinal glucose absorption
increases oxidative phosphor - ATP production
increases activity of adrenal medulla
induces enzyme synthesis
decreases protein synthesis, increases glucose production
upregulation of catechol Rs
downregulation of insulin Rs
increases bone, epidermis, hair follicles, nails growth + maturation
increases tooth development + eruption
increases rate + force of skeletal muscle contraction
hyperthyroidism
lack of TSH, excess TH
heat intolerance, tachycardia (heart failure risk), increases BMR, weightloss, muscle wasting, proptosis, goitre
hypothyroidism
excess TSH, lack of TH
early onset causes delayed/incomplete development
cretinism
short stature
mental deficits
adult onset
tiredness
weight gain
decreases BMR
slow mental + motor function
cold intolerance
alopecia
dry skin
risk of coma