Two examples of protein hormones are insulin and glucagon.
Protein hormones, also known as polypeptide hormones, are a diverse group of hormones composed of amino acid chains. Because they are not lipid-soluble, they typically bind to receptors on the cell surface, triggering a cascade of intracellular signaling events that ultimately lead to a change in cell function. Insulin and glucagon are crucial for regulating blood glucose levels, demonstrating the important roles protein hormones play in maintaining homeostasis.
Here's a closer look at these two examples:
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Insulin: This hormone is produced by the beta cells of the pancreas. It is released in response to elevated blood glucose levels, such as after a meal. Insulin promotes the uptake of glucose by cells, particularly in the liver, muscle, and adipose tissue. This lowers blood glucose and allows cells to use glucose for energy or store it for later use.
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Glucagon: This hormone is produced by the alpha cells of the pancreas. It is released when blood glucose levels are low. Glucagon stimulates the liver to break down glycogen (stored glucose) into glucose, which is then released into the bloodstream. It also promotes gluconeogenesis, the production of glucose from non-carbohydrate sources. This raises blood glucose levels.
These two hormones work antagonistically to maintain a stable blood glucose level, which is essential for proper bodily function. Other examples of protein hormones include thyrocalcitonin (calcitonin), pituitary hormones such as growth hormone, and hypothalamic hormones like releasing hormones.
