Final answer:
Hormones function as chemical messengers that influence various physiological processes, with steroid hormones entering cells to affect DNA transcription and non-steroid hormones acting through surface receptors and second messengers. Target cells with specific receptors for a hormone are the only ones affected, thereby regulating body functions and maintaining homeostasis.
Step-by-step explanation:
Hormones are vital chemical messengers that significantly impact physiological processes in our bodies. Specifically, steroid hormones work by diffusing through cell membranes due to their lipid-soluble nature. Once inside the cell, they bind to specific intracellular receptors and form a hormone-receptor complex that can enter the nucleus, influencing DNA transcription and subsequent protein synthesis. This process can alter cell function in various ways, depending on the hormone's role and the cell type involved. On the other hand, non-steroid hormones bind to receptors on the cell surface and work through second messenger pathways to effect change within the cell.
The regulation of hormone receptors is also essential. A target cell's sensitivity to a hormone is determined by the number of receptors it possesses. If a cell has many receptors for a particular hormone, it is more responsive to it. The presence of receptors is what allows hormones to selectively influence only certain cells, even though they circulate throughout the entire body. Receptor numbers can be upregulated or downregulated in response to various signals, which modulates the cell's sensitivity to hormonal signals over time.
Hormonal regulation is crucial for maintaining homeostasis and adapting physiological activity when environmental conditions change. This includes processes such as reproduction, growth, metabolism, fluid and electrolyte balance, and overall body functions.