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hormones of the thyroid

• TRH  -  thyrotropin-releasing hormone • TSH  -  thyroid stimulating hormone • MIT   -  monoiodotyrosine • DIT   -  diiodotyrosine • T3     -  triiodothyronine • T4     -  thyroxine (tetraiodothyronine) • • TG    -  Tg,  thyroglobulin • TBG  -  thyroid binding globulin • D1-D3   deiodinases • TR     -  THR, thyroid receptor • RXR  -  retinoid X receptor (coregulator) thyroid : composed of follicles 

• thyroid hormones synthesised by iodination of tyrosine on thyroglobulin

actions of thryroid hormones

• T3 is much more potent than T4, largely because T4 needs to be converted to T3 for activity at target cells
• increase BMR - increase oxygen consumption, energy expenditure, heat production
• increase turnover of metabolic fuels
• increase food intake
• increase responsiveness to catecholamines eg. tachcardia
• essential for growth, development and maintainance of neural integrity

thyroid disease  Hypothyroidism

• decreased activity
• iodine deficieny (simple goitre) - gland enlargement
• severe forms: cretinism in children, myxoedema in adults
• later stages of hashimotos thyroiditis (autoimmune)
• symptoms- decreased activity, tired, feel cold, slow mentally, decreased CO, weight gain, hair thinning/loss
• treatment - thyroxine sodium 25-200ug

Hyperthyroidism (Graves disease, thyrotoxicosis)

• increased activity
• mostly due to production of antibodies that stimulate excess secretion T3/T4
• may cause modest goitre 
• early stages of Hashimotos thyroiditis (autoimmune)
• symptoms- increased activity, exopthalmos, weight loss despite increased appetite, palpitations, tremor, cold tolerance, muscle weakness, sweating
• treatment - carbimazole 15-40 mg, propylthiouracil 50mg, radioactive iodine 131 mg, partial thyroidectomy

Adrenal glands structure

• cortex - mineralcorticoid (aldosterone), glucocorticoids (cortisol)
• medulla- catecholamines (adrenaline, noradrenaline
• CNS -> CRH -> ACTH -> adrenal -> Glucocorticoids/mineralcorticoids -> Biological effects

steroidgenesis

• zona reticullaris - mainly androgens(DHEA)
• zona fasciculata - glucocorticoids (cortisol)
• zona glomerulosa - mineralcorticoid (aldosterone)

Aldosterone

• mineralcorticoid
• secretion stimulated by:-

decrease ECF vol and/or decrease BP - stretch receptors in atria
decrease ECF osmolarity - direct effect on adrenal increase K+ conc - direct effect on adrenal increase Angiotensin II

• acts on the idney distal cortical principal cells

increase Na+ retention - via ENaC and Na-K ATPase                                                        …