Hypo and hyper activity of endocrine glands and related disorders

Because hormone secretion has to be kept within a narrow working range, both too little (hyposecretion) and too much (hypersecretion) of any hormone can cause serious disease.

Growth hormone disorders: Dwarfism results from GH hyposecretion in children — skeletal growth and sexual maturity are arrested, and adult height is capped at about 4 feet (Figure 11.8). Gigantism is the opposite — GH hypersecretion in children causes overgrowth of the skeleton, up to about 8 feet, with the visceral organs failing to grow in matching proportion to the limbs (Figure 11.9). Acromegaly is GH hypersecretion occurring in adults (after the growth plates have fused), causing disproportionate overgrowth of the hand, foot and jaw bones, along with enlargement of internal organs — the viscera, tongue, lungs, heart, liver, spleen — and malfunctioning gonads (Figure 11.10).

Thyroid disorders: Grave's disease (thyrotoxicosis, or exophthalmic goitre) is caused by thyroid hypersecretion — the thyroid enlarges, BMR rises by 50–100%, respiratory and excretory rates climb, heart rate and blood pressure rise, body temperature increases, the eyeballs protrude (exophthalmos) with weakened eye muscles, and weight is lost (Figure 11.13). Simple (endemic) goitre is the opposite pattern, from thyroxine hyposecretion: the thyroid enlarges to compensate, serum thyroxine falls, and TSH secretion rises (Figure 11.14). Cretinism is hypothyroidism present from infancy: retarded skeletal growth, absent sexual maturity, retarded mental ability, thick wrinkled skin, an enlarged protruding tongue, a bloated face, and thick short limbs, together with low BMR, a slow pulse, subnormal body temperature and elevated blood cholesterol (Figure 11.11). Myxedema (Gull's disease) is the adult-onset equivalent: decreased mental activity, memory loss, slowed movement and speech, general weakness, dry coarse skin, scarce hair, a puffy appearance, disturbed sexual function, low BMR, poor appetite, and subnormal body temperature (Figure 11.12).

Parathyroid disorders: Tetany results from PTH hyposecretion — falling serum calcium (hypocalcemia) and rising serum phosphate cause generalised convulsions, locked jaws, a raised heart rate, raised body temperature and muscular spasms. Hyperparathyroidism, excess PTH, causes bone demineralisation, cyst formation, softened bone, loss of muscle tone, general weakness and renal disorders.

Adrenal cortex disorders: Addison's disease results from hyposecretion of glucocorticoids and mineralocorticoids — muscular weakness, low blood pressure, loss of appetite, vomiting, skin hyperpigmentation, a low metabolic rate, subnormal temperature, reduced blood volume and weight loss; reduced aldosterone specifically increases urinary loss of sodium chloride and water while retaining potassium, driving dehydration (Figure 11.15). Cushing's syndrome, excess cortisol, causes facial and truncal obesity, redness of the face, hands and feet, thinning skin, excess hair growth, bone mineral loss (osteoporosis), high blood pressure, and suppressed sexual function with gonadal atrophy (Figure 11.16). …