True about thyroxine are all except-
Ans. is 'c' i.e., Decreases rate of respiration * The various actions of thyroid hormone are: -i) Calorigenic effect:# Thyroid hormones enhance oxygen consumption, and hence the basal metabolic rate (BMR). This may be at least partly due to increase in the activity of membrane Na+/K+ ATPase.# Thyroid hormones also increase the number and activity of mitochondria, which may be the cause or the effect of increase in oxygen consumption.# By increasing the BMR, thyroid hormones raise body temperature, loss of body weight and increase urinary nitrogen loss.ii) Growth and development:# Thyroid hormones are essential for normal growth and development.iii) Carbohydrate metabolism:# Thyroid hormones have both hypoglycemic and hyperglycemic effects.# The hypoglycemic effect is the increased glycolysis. The hyperglycemic effects are stimulation of glycogenolysis and glucoconeogenesis.# The net effect is hyperglycemia and depletion of glycogen.iv) Fat metabolism:# Thyroid hormone stimulates both lipogenesis and lipolysis. The lipolysis exceeds lipogenesis. Thus thyroid hormones moblize fat from adipose tissue, leading to an increase in plasma concentration of FFAs.v) Protein metabolism :# Thyroid hormone has a protein anabolic effect but in large doses, it has a protein catabolic effect. Thus thyroid hormone increases both protein synthesis and protein degradation.vi) Cardiovascular effects:# The thyroid hormones increase the heart rate, cardiac contractility, stroke volume and cardiac output, and consequently also the systolic BP. But the diastolic BP may fall due to vasodilatation in several vascular beds with decrease in peripheral vascular resistance.# The cardiovascular effects of thyroid hormones are partly mediated by potentiation of effects of catecholamines.vii) GIT:# Thyroid hormones increase GI secretion, absorption and motility.viii) Nervous system :# Thyroid hormones are essential for normal formation of synapses and myelination in the developing brain.ix) Respiratory system:# Thyroid hormones increase the rate and depth of respiration.
Increases BMR
Increases oxygen consumption
Decreases rate of respiration
Causes lipolysis
Endocrinology and Reproduction