BIOCHEMISTRY - Textbook - Ostapchenko L. I. - 2012

Chapter 15. INTEGRATION OF METABOLIC PATHWAYS. HORMONES

15.3. Mechanisms of the Endocrine System Functioning

The Synthesis and Secretion of Hormones are stimulated by external and internal signals originating from the Central Nervous system (Fig. 15.4, 1). These neural signals reach the Hypothalamus (Fig. 15.4, 2), which serves as the supreme endocrine center. Its nuclei synthesize releasing factors (liberins) and inhibiting factors (statins) that regulate the function of the anterior Pituitary Gland.

Liberins and statins are transported via the bloodstream to the anterior pituitary, where they respectively stimulate or inhibit the synthesis of adenohypophysial tropic hormones (Fig. 15.4, 3). Pituitary tropic hormones stimulate the synthesis and secretion of hormones by peripheral Endocrine glands (Fig. 15.4, 4), which enter the general Circulation and reach target Cells or Organs (Fig. 15.4, 5). Some Hypothalamic hormones (such as Vasopressin and Oxytocin) are stored in the posterior pituitary before being released into the Blood.

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Fig. 15.4. Mechanism of the Endocrine System functioning

Changes in metabolite concentrations within target cells can inhibit hormone synthesis via negative feedback, acting either on the endocrine glands themselves or on the hypothalamus (Fig. 15.4, b). Furthermore, the synthesis and secretion of tropic hormones are suppressed or stimulated by hormones produced by peripheral glands. The Functions of The Thyroid Gland, Adrenal Glands, and Gonads are regulated through this exact mechanism.

Operating independently of the hypothalamus-pituitary axis are the Parathyroid glands, the C-Cells of the thyroid gland, the islets of Langerhans in the Pancreas, and The adrenal medulla.