 Hello and welcome to physiology open. Try to solve this question on the functions of thyroid hormones. You have to choose all the correct statements in this question. You can pause the video and think about the question. We will come back to it at the end of the video again. Now let's discuss the functions of the thyroid hormones. Well, thyroid hormones act on virtually every cell on the body. In general, the basic function of thyroid hormones is to increase the metabolic rate, except in brain and some other tissues. By virtue of increased oxygen consumption due to this, cardiac and respiratory activity increases. Anyways, apart from this indirect effect on heart and respiration, thyroid hormones also have a direct effect on many organ systems. So now let us consider these actions in detail. First function we will discuss is its effect on basal metabolic rate and thermogenic action. Well, thyroid hormones increase the production as well as utilization of ATP. They increase the oxidative phosphorylation of ADP to ATP in mitochondria by increasing the number of mitochondria and the production of cytochrome oxidases, which are enzymes involved in respiratory change. Utilization of ATP increases because of increased impermeability of membrane to sodium and potassium ions. The change in intracellular concentration of ions causes increase in the activity of sodium-potassium ATPase, which is also directly increased by thyroid hormones. Also, they speed up the synthesis as well as degradation metabolic cycles of carbohydrates, fats and protein. This helps to continuously supply the fuel for ATP production as well as utilization. This increased ATP production and utilization causes increased oxygen consumption and hence heat generation. Thyroid hormones also increase the synthesis of uncoupler protein, which uncouples oxidation and phosphorylation reactions, that is proton movement is uncoupled with the synthesis of ATP. This leads to heat generation without even ATP production and utilization. Now, let us see the specific effects of thyroid hormones on various organ systems. In nervous system, thyroid hormones are essential for differentiation and maturation of neurons. For normal development of nervous system, which starts in fetal life, it is important that precursor cells divide for some time and then the multiplication stops and instead they differentiate and mature after that. Thyroid hormones are essential for making this switch and promoting the differentiation and maturation of neurons. During this time, the dendrites branch and grow, axons grow, myelination of neuron occurs and synapse formation takes place. In later life also, thyroid hormones maintain the mental alertness. Now, thyroid hormones are also essential for normal body growth because thyroid hormones are required for normal production and action of growth hormone and insulin like growth factor 1. They also have a direct effect on bone growth and promote closure of epiphyzes. Another significant direct effect they have is on cardiovascular system. Well, in cardiovascular system, by virtue of increased metabolic activities, there is increase in cardiac activity. However, thyroid hormones also have a permissive action on heart. They basically increase the responsiveness of heart to catecholamines by increasing the expression of their receptors that is beta-hydrogenergic receptors. Not only that, they also increase the expression of proteins involving excitation contraction coupling in heart that is puthendoplasmic reticulum, calcium adipase, sodium potassium adipase and some others. Apart from this, thyroid hormones are essential for normal functions of almost all other systems. For example, normal menstrual cycles, lactation, development of gonads, normal GI function, hematopoiesis. The effect of thyroid hormones on various systems manifests with various signs and symptoms in deficiency and excess of thyroid hormones. For example, excess thyroid hormones causes increase in the cardiac output and hence increases systolic blood pressure. However, because of increased metabolism, there is accumulation of the metabolites, which leads to vasodilation and hence decreased peripheral resistance and hence a decrease in the diastolic blood pressure. These effects, which occur due to excess or deficiency of thyroid hormones, we will see in detail in another video on abnormalities in thyroid function. Okay, now let's come back to the question which we saw at the beginning of the video. I hope now you can easily solve this question. See, first and third statements are straightforward and we discuss them in the video. So they are correct statements. But now you see second statement. We have discussed that thyroid hormone speeds up the metabolic cycles for both the supply as well as the utilization of ATP. So it speeds up both the synthetic as well as big-down limbs of fuel metabolism. So second statement is also correct. The last statement is false. Thyroid hormones increase the differentiation of neurons and are important for making a switch from multiplication to differentiation of neurons and not as mentioned in the statement. Well, thanks for watching the video. If you liked it, do not forget to subscribe to the channel Physiology Open. Thank you.