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In this article we will discuss about the role of hormones in glucose homeostasis.
Glucose homeostasis is brought about by:
a. Actions of hormones on metabolism and glucostatic role of
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b. Hypothalamus
c. Liver
Actions of Hormones on Metabolism:
Many of the hormones have role to play and there are five hyperglycemic hormones and only one hypoglycemic hormone.
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The hormones having hyperglycemic action are:
1. Growth hormone
2. Thyroxine
3. Glucagon
4. Adrenaline and noradrenaline
5. Cortisol.
The only hormone having hypoglycemic action is insulin.
Glucose homeostasis is brought about by the action of aforementioned hormones on various parts of body, like liver, muscle, and peripheral utilization of glucose in various parts of body.
As far peripheral utilization is concerned, it is not confined to any tissue or organ. This is because most of the times the cells in tissues require constant supply of energy to take care of the metabolic activity which is provided by the metabolism of glucose.
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It is not just the movement of glucose from ECF to ICF (facilitated diffusion) that is important; it should also bring about the activation of the glycolytic pathway to metabolize glucose to supply energy. In case glucose is not available, alternative sources of energy will be looked into.
Gluconeogenesis is brought about only in liver. And hence any of the hormones which either enhance/ inhibit gluconeogenesis should act on the liver and alter the activity of the various enzymes involved in this process. For gluconeogenesis to be brought about, there is requirement of fatty acids and amino acids. These acids are made available for gluconeogenesis by increased lipolysis or proteolysis in various parts of body.
Glycogenolysis can take place either in liver or muscle or both. The stored glycogen in these structures will be broken down to release glucose into circulation. This is aided by enhancing the activity of the enzymes involved in the breakdown of glycogen.
Glycogenesis also occurs in liver. Glucose is removed from circulation, converted to glucose and stored in liver and muscle.
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Hormones having influence on peripheral utilization are:
1. Insulin
2. Thyroxine
3. Cortisol
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4. Growth hormone
Hormones having influence on glycogenolysis are:
1. Insulin
2. Glucagon.
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3. Adrenaline and noradrenaline.
Hormones having role on glycogenesis are:
1. Insulin
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2. Cortisol
Hormones having influence on gluconeogenesis are:
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1. Insulin
2. Thyroxine
3. Cortisol
4. Growth hormone
5. Glucagon.
The role of hypothalamus is equally important in glucose homeostasis. The functioning of both the hypothalamic nuclei and the actions of insulin in tandem is very much essential for normoglycemic situation to prevail. In the hypothalamus, there are two important nuclei that try to maintain glucose homeostasis.
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They are:
1. Ventromedial nucleus
2. Lateral hypothalamic nucleus.
Ventromedial nucleus is also known as satiety center and lateral hypothalamic nucleus is termed as hunger center. The whole of the brain does not require insulin for peripheral utilization of glucose except the ventromedial nuclear area. And another special aspect of these nuclear regions of hypothalamus is the lateral hypothalamic nucleus is believed to be constantly active on its own.
Under normal conditions, when insulin is able to exert its usual action, glucose from ECF enters ICF of neurons of ventromedial nucleus and gets metabolized. This results in ventromedial nucleus to become active. The ventromedial nucleus now inhibits the activity of lateral hypothalamic nucleus and hence the person stops eating.
In diabetes mellitus, since the peripheral utilization of glucose is affected, the ventromedial nucleus is unable to utilize glucose. So the inhibitory influence of this nucleus on the lateral hypothalamic nucleus is lost (there will be disinhibition).
Now the activity of the lateral hypothalamic nucleus goes unopposed, because of which the person develops polyphagia. Hence one of the cardinal symptoms of diabetes mellitus is polyphagia.
