Hormones are chemical messengers produced by endocrine glands and released into the bloodstream. They travel to specific target cells and regulate many essential physiological processes, helping maintain homeostasis and coordinate the functions of different organs. Major Functions of Hormones Growth and Development: Growth hormone and thyroid hormones regulate body growth, development, and tissue maturation. Metabolism and Energy: Insulin, glucagon, and thyroid hormones regulate glucose metabolism, energy production, and nutrient utilization. Reproduction: Estrogen, progesterone, testosterone, FSH, and LH regulate sexual development, fertility, and reproductive functions. Stress Response: Cortisol and adrenaline help the body respond to physical and psychological stress. Water and Electrolyte Balance: ADH and aldosterone regulate body fluid volume, sodium balance, and blood pressure. Calcium Homeostasis: Parathyroid hormone and vitamin D help maintain normal calcium and phosphate concentrations. Hormones and Biochemistry From a biochemical perspective, hormones exert their effects by binding to specific receptors on or inside target cells. This activates signaling pathways that alter enzyme activity, gene expression, metabolism, and cellular function. Clinical Significance Abnormal hormone production or action can lead to various disorders, including diabetes mellitus, thyroid diseases, growth disorders, infertility, and adrenal abnormalities. Therefore, measuring hormone concentrations is an important part of clinical laboratory diagnosis. Conclusion Hormones act as sophisticated biochemical communication signals that coordinate metabolism, growth, reproduction, stress responses, and internal balance. Understanding hormonal regulation is therefore fundamental to biochemistry, physiology, and modern medicine. Al-Mustaqbal University – Ranked First Among Iraqi Private Universities