21.2: Structures of the Endocrine System
The intricate framework of the endocrine system encompasses a diverse array of glands, with their target tissues and organs strategically distributed throughout the body. Central to this network are the endocrine glands, specialized structures that lack ducts and release hormones directly into the interstitial fluid. Notably, the hypothalamus, a vital neuroendocrine organ situated in the brain, governs neural functions and serves as a potent source of hormonal regulation. Near the hypothalamus are the pituitary and pineal glands in the head region.
The thyroid and parathyroid glands in the neck region play pivotal roles in metabolism and calcium homeostasis, respectively. In the upper chest, the thymus influences immune system development. The adrenal glands are positioned above the kidneys. They contribute to stress response and electrolyte balance. The gonads, comprising the testes in males and ovaries in females, generate reproductive hormones.
In addition, the pancreas, nestled near the stomach, showcases versatility by functioning as both an endocrine gland regulating glucose levels and an exocrine gland aiding digestion. Beyond these recognized glands, cells within various organs and tissues—including the heart, adipose tissue, skin, and placenta—can release endocrine signals, expanding the system's influence across the body's diverse physiological domains. This intricate spatial distribution underscores the holistic nature of the endocrine system, working in concert to maintain balance and coordination throughout the organism.
