Explain biochemical basis of:

MYXEDEMA IN HYPOTHYROIDISM:

Hypothyroidism in the adults is referred to as myxedema, that is it is used to describe a dermatological change that can occur in hypothyroidism, (from Greek, myxa means mucus and oidema means swelling). because of the characteristic mucinous protein deposit in the subcutaneous tissue. Levels of hyaluronic acid are high in proliferating tissue. The enzyme hyaluronidase which splits hyaluronic acid into smaller oligosaccharides. Thyroid hormones stimulate tadpole tissue differentiation, which is paralleled by a decrease in hyaluronic acid levels and an increase in hyaluronidase concentrations. In myxedematous tissue from subjects with hypothyroidism there is an increase in hyaluronic acid. These observations suggest that thyroid hormones stimulate differentiation tissue through stimulation of hyaluronidase production.

BOW LEGS IN RICKETS:

Rickets is a skeletal disorder that is caused by a lack of Vitamin-D,  may therefore develop if the skin does not receive adequate irradiation. Since vitamin D3 (cholecalciferol) is activally produced in the skin of humans by the action of UV light on a precursor molecule, 7-dehydrocholesterol. Due to absence of vitamin D in rickets bone demineralization occurs. Hence people with rickets have weak and soft bones; stunted growth and in severe cases, skeletal deformities. Due to softening of bones, the bones of legs are not able to take the body weight and hence bend due to the weight causing the shape to be bow like.

HYPOPHOSPHATEMIA IN HYPERPARATHROIDISM:

Hypophosphatemia is defined as a serum phosphate level of less than 2.5 mg/dL and in hyperparathyroidism there is an increased parathyroid hormone (PTH) levels in the blood.
Below normal levels of Ca2+ result in enhanced PTH secretion. PTH acts on the number of tissues, in most cases elevating directly or indirectly, plasma levels of Ca2+ and decreasing circulating concentrations of PO43-.In hyperparathyroidism, increased PTH levels cause a rapid increase in urinary PO43- concentration. Increased renal excretion of PO43- , in response to PTH enhances the ionization of plasma Ca2+ through lowering of the [Ca2+]*[PO43-] solubility product. Hence since PO43- is excreted, its concentration in blood decreases below a normal level leading to hypophosphatemia in response to elevated PTH, due to hyperparathyroidism.

POLYDIPSIA IN DIABETES INSIPIDUS:

Polydipsia is the term given to excessive thirst and is one of the initial symptoms of diabetes. Impairment of the neurohypophysial system to synthesize or release AVP (Arginine Vasopressin) results in a diminished ability of the kidney to conserve water, resulting in diabetes insipidus, there is water loss by excretion, since kidney can't conserve water it leads to polydipsia.

COLD FEET AND PALPITATIONS DURING ACUTE STRESS.

Cold feet and thumping heart i.e., palpitations are caused by stress hormones, such as adrenaline (epinephrine), which are released into bloodstream and by overactivity of nervous impulses to various parts of the body. When your body is in flight or fight mode, all the blood goes to the areas that need it most especially heart (leading to palpitation). To do that, blood is taken out of extremities, like feet and hands, leaving them cold. Epinephrine causes constriction in many networks of minute blood vessels but dilates the blood vessels in the skeletal muscles and in liver. In the heart, it increases the rate and force of contraction, palpitations, thus increasing the output of blood and raising blood pressure.