Mechanisms of hormone action

Answer 1

Hormones exert their effects on target tissues and cells through various mechanisms of action. Here are some of the key mechanisms:

1. Receptor-mediated signaling: Many hormones bind to specific receptors on the surface or inside target cells. This binding triggers a signaling cascade that ultimately leads to cellular responses. Examples of hormones that use this mechanism include insulin, glucagon, and growth hormone.

2. Nuclear receptor signaling: Some hormones enter target cells and bind to specific nuclear receptors. This hormone-receptor complex then enters the cell nucleus and binds to specific DNA sequences called hormone response elements (HREs). This interaction leads to changes in gene expression and protein synthesis. Steroid hormones, such as estrogen and testosterone, primarily use this mechanism.

3. Second messenger systems: Some hormones bind to receptors on the cell surface, initiating a series of intracellular events mediated by second messengers. Second messengers, such as cyclic adenosine monophosphate (cAMP), calcium ions, or inositol trisphosphate (IP3), amplify the hormonal signal and trigger cellular responses. Examples of hormones that use second messenger systems include adrenaline, glucagon, and parathyroid hormone.

4. Activation of enzyme activity: Certain hormones can directly activate or inhibit enzymes within target cells. For example, insulin stimulates glycogen synthesis by activating glycogen synthase, while glucagon activates glycogen breakdown by activating glycogen phosphorylase.

5. Feedback regulation: Hormones often exert negative feedback control on their own production and secretion. When hormone levels rise above a certain threshold, they inhibit their own production to maintain physiological balance. This mechanism helps regulate hormone levels in the body and prevent excessive or insufficient hormone action.

These mechanisms of hormone action work together to maintain homeostasis and regulate various physiological processes in the body, including metabolism, growth, reproduction, and stress response.