Hormones are steroids or proteins which are released and produced in one part and move to another part of the body to exhibit their effect. Through the process of signal transduction, hormones function. Antagonistic hormones oppose the actions of one another.
Often, the process of maintaining homeostasis necessitates conditions to be restricted to a marginal range. When the state surmounts the upper limit of homeostasis, a particular action, typically hormone production, is triggered. When conditions are stable, the production of hormones is discontinued. In the event of conditions going beyond the lower limit of homeostasis, typically second hormone production is triggered. Those hormones which serve to get back the conditions of the body to standard limits from the contrary extremes are referred to as antagonistic hormones.
Examples of Antagonistic Hormones
1. Parathyroid hormone (PTH) and Calcitonin
Calcitonin and PTH are referred to as antagonistic hormones, as their actions are diametrically opposite. While calcitonin is secreted when blood calcium level is extremely high, PTH is secreted when the blood calcium level is too low. Both these hormones are known to regulate the Ca++ levels in blood. Calcitonin is released and produced by the thyroid gland found in the neck while the parathyroid gland is released and produced by the parathyroid gland seen in the thyroid gland.
PTH from the parathyroid glands raises Ca ++ levels in the blood by increasing the absorption of calcium in intestines and the reabsorption in kidneys, triggering the release of Ca++ from the bones. Calcitonin generates the opposite effect by suppressing the disintegration of bone matrix and reduces the release of calcium in blood.
2. Glucagon and Insulin
Insulin and glucagon are antagonistic hormones. Alpha cells secrete glucagon, beta cells secrete insulin. Glucagon facilitates the release of glucose into the bloodstream from the stored glycogen through a process of signal transduction. Insulin facilitates the elimination of glucose from the bloodstream to store as glycogen through signal transduction.
Blood glucose concentration sharply increases after food is consumed, which contains simple carbohydrates. An increase in the blood glucose levels triggers beta cells found in the pancreas to secrete insulin into blood. Responding to signals by insulin, most of the body cells consume glucose that eliminates it from blood. The blood glucose concentration reverts to the set point.
Later, when hungry, blood glucose concentration drops below the set point, causing the release of glucagon from the pancreas. Glucagon causes release of glucose from the liver cells, which rises the levels of blood glucose. If glucagon did not carry out its function properly, the concentration of blood glucose drops and there are chances of developing hypoglycemia. This relationship between both hormones aids in maintaining the narrow range of concentration of blood glucose.
A chemical signal associates with a membrane protein. Proteins to which hormones attach are referred to as receptor proteins. The association between receptor proteins and hormones can be comprehended as a lock and key model, wherein the receptor protein serves as a lock and hormone the key.
The association of the hormone to the receptor proteins alters the molecular structure, which brings a cellular response. It is deemed that steroid hormones enter the cytoplasm before arriving at the target proteins, while the protein hormones associate with the receptor proteins on the surface of plasma membranes.
This was a brief on Antagonistic Hormones. Learn more about related topics, at BYJU’S.