Peptidihormonijärjestelmän

Peptidihormoni, also known as peptide hormones, are a class of hormones made up of amino acids linked together by peptide bonds. They are produced by endocrine glands and other specialized cells throughout the body. Unlike steroid hormones, which are lipid-soluble, peptide hormones are water-soluble and cannot easily cross cell membranes. Instead, they bind to specific receptors on the surface of target cells, initiating a signaling cascade that alters cellular activity.

The synthesis of peptide hormones begins with the transcription of a gene into messenger RNA (mRNA). This mRNA is then translated into a precursor protein called a preprohormone. The preprohormone undergoes further processing, including cleavage of a signal peptide, to form a prohormone. Finally, the prohormone is cleaved to yield the active peptide hormone and any other associated peptide fragments. These hormones are then stored in vesicles and released into the bloodstream in response to specific stimuli.

Examples of peptide hormones include insulin, glucagon, growth hormone, prolactin, and many hormones of the hypothalamus and pituitary gland. They play crucial roles in regulating a wide range of physiological processes, such as metabolism, growth and development, reproduction, and stress response. Their actions are diverse, influencing everything from blood sugar levels to muscle growth and behavior. The precise mechanism of action for each peptide hormone is specific to its structure and the receptor it binds to, leading to a vast array of biological effects.