Final answer:
Local hormones impact nearby cells and are not typically distributed widely through the bloodstream. Hormones can be categorized into two major groups based on their chemical structure: lipid-derived and amino acid-derived, with steroids being a primary group of lipid-derived hormones.
Step-by-step explanation:
Local Hormones
Local hormones are a type of signaling molecule that affect cells in the immediate vicinity of where they are produced. These hormones typically do not travel far in the bloodstream, if at all, and instead influence target cells by diffusing through interstitial fluid. Local hormones include prostaglandins and nitric oxide, among others. They play a crucial role in fine-tuning bodily functions at a cellular level, often in response to immediate environmental changes.
Main Categories of Hormones
The main groups of hormones based on their molecular structure are lipid-derived and amino acid-derived hormones. Lipid-derived hormones include steroids, such as adrenocortical hormones and sex hormones (estradiol and testosterone), which are structurally similar to cholesterol. Amino acid-derived hormones, like the adrenal hormones epinephrine and norepinephrine, are relatively small molecules. The third group, peptide hormones, consists of polypeptide chains or proteins, such as the pituitary hormone oxytocin. The classification of hormones is significant as it influences their mode of action, the type of receptor they bind to, and how they influence the target cells.