Thyroid Flashcards
What is the histology of the thyroid
single layer of cuboidal cells surrounded by basement membrane
composed of thyroid follicles, which are lined by follicular cells that make iodine
Innactive follicular cell- simple flat columnar
active follicular cells- simple tall columnar
paarafollicular cells- synethsise calcitonin
What is the process for TSH production
paraventricular nucleus in hypothalamus release TRH onto ant. pitiutary. Thyrocytes in the gland then stimulated to release TSH, which then enters circulation. TSH binds to Gs on thyroid gland to make…. PKA, which causes production of thyroglobulin. Iodide then enters gland which is oxidised via TPO to iodine. TPO then iodinates thyroglobulin by attaching iodine to tyrosine AA. TPO then fuses DIT-DIT (T4) and MIT-DIT (T3), which are then endocytosed out of cell
How does thyroid hormone control basal metabolic rate
hormone increase BMR, rate of O2 comsumption. BMR directly proportional to cellular metabolism
How does thyroid hormone effect Na+/K+ pumps
thyroid hormone stimulates synthesis of additional Na+/K+ pumps, which require ATP to pump Na+ from cytosol into ECF. Release of ATP is exothermic reaction, therefore more heat given off, body temp rises causing a calorigenic effect
How does thyroid hormone regulate metabolism
stimulates protein synthsis and increase glucose and FA use in ATP production
Increase lipolysis and cholesterol excretion, which reduces cblood cholesterol levels
How does thyroid hormone effect catechalamine
thyroid hormone upregulates β-receptors thus enhancing actions of nor/epinerphrine to increase BP
How does thyroid hormone effect body growth
It can stimulate synthesis of type 1 collagen, ALP and osteoblast activity which can cause accelerated body growth esp nervous and skeletal system
What is hypothyroidism
primary hypothroidism- underactive thyroid, where not enough thyroxine is produced for body causing decreased T3 and T4 and high levels of TSH. Hashimoto’s most common disease as immune response to thyroid autoantigens leading to depletion of thyroid epithelial cells (lymphocyte infiltration and fibrosis) mediated by CD8+ cytotoxic killing T cells and cytokine mediated death
How does hypothyroidsm clinically present
painless enlargement of thyroid, increased cold sensitivity, poor conc, depression, constipation , muscle cramps, skin cool and pale, non-pitting oedema due to accumulation of matrix substances e.g GAGs, hylaruronic acid
What are other types of hypothyroidism
secondary due to problems with pituitary release and tertiary problems with hypothalamic release
What is hyperthryoidism
excess free T4/3 due to thyroid gland overactivity resulting in thyrotoxicosis
Primary hyperthryoidism causes
Grave’s disease (IgG antibodies similar structure to TSH continues activation)
Toxic multinodular goitre or adenoma will produce excess thyroid hormone
How can thyrotoxicosis occur without hyperthyroidism
Excessive T4 administration
Postpartum- after pregancy causes inflammed thyroid due to thyroid antibody production
What are the clinical features of hyperthyroidism
weight loss, increased apetite, heat intolerance, fatigue, hyperactivity ,tremor, lid-lag, hyper-feflexia, tachycardia
MOA Carbimazole
it inhibits TPO so no thyroxine is made or thyroglobulin therefore no T4, T3
