Biochemical Foundations of Human Vital Activity - Volkov N.I., Nesen E.N. 2000

Biochemical Foundations of Human Vital Activity
Hormones as Metabolic Regulators
General Concept of Hormones

Numerous biochemical processes in various Organs and Tissues proceed in a strictly orderly and coordinated manner thanks to regulatory systems that orchestrate these processes. Regulatory systems play an especially crucial role in maintaining metabolic Homeostasis during muscular activity, when The rate of energy utilization increases and METABOLISM changes.

The main Regulatory Systems of The Human Body are the Central Nervous system (CNS) and the hormonal, or endocrine, system. They are closely interrelated and hierarchically linked: the CNS controls metabolism through the Endocrine System, while the latter, in turn, influences this control. The coordinating center for both systems is the Hypothalamus. Together, these systems ensure The regulation of all biochemical and physiological processes associated with muscular activity. The Nervous System exerts a rapid, localized regulatory effect, whereas the endocrine system provides a slower and more sustained response. The endocrine system exerts its regulatory effects through BIOLOGICALLY ACTIVE SUBSTANCES known as Hormones.

Hormones are organic substances synthesized in specialized secretory Cells and organs. Carried by the bloodstream to various target tissues, they exert a regulatory influence on the body's metabolism and physiological Functions. Hormones themselves do not participate in metabolic reactions; rather, they act as specific regulators of these processes. Under hormonal control are Protein Synthesis, The activity of numerous Enzymes, the permeability of Cell membranes to various energy substrates, Coenzymes, and minerals. This influence plays a vital role in maintaining the constancy of the internal environment (homeostasis) during Physical Exercise and other external stressors, ensuring high physical performance and adapting the body to systematic physical loads.

Highly specialized organs or groups of cells that synthesize hormones (secretion) and release them directly into the Blood, intercellular fluid, or Lymph are called Endocrine glands. Lacking excretory ducts, they are referred to as ductless glands (endo meaning "inner"). Individual endocrine glands are not anatomically connected to one another and are located at a considerable distance apart (Fig. 45). Nevertheless, they are all functionally interconnected to form a unified endocrine system.

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Fig. 45 Main human endocrine glands and their anatomical Location

A distinction is made between central glands (hypothalamus, Pituitary Gland, Pineal Gland) and peripheral glands (thyroid, parathyroid, Pancreas, Adrenal Glands, Gonads). The central glands are located at the Base of the Brain and are directly linked to CNS activity. They secrete neurohormones and hormones that regulate the Functions of the peripheral endocrine glands. A close interrelation also exists among the peripheral glands: hormones from one gland can enhance or suppress the secretory function of another. Certain hormones produced in endocrine glands (Insulin, Glucagon, thyroxine) can also be synthesized in the walls of The Stomach or intestines. Humoral factors, known as tissue hormones, exert a regulatory effect similar to that of hormones.

Tissue hormones are biologically active substances synthesized in various Tissues of the body that exert localized regulatory effects. Many of these are synthesized in digestive organs to regulate their activity. Examples include gastrin (which stimulates gastric secretion), secretin (which enhances duodenal secretion), and cholecystokinin (which enhances Small Intestine secretion), among others. Tissue hormones such as histamine, serotonin, bradykinin, and Prostaglandins influence blood vessel tone and the excitability of the nervous system. Brain cells produce gamma-aminobutyric acid (GABA), which regulates inhibitory processes in the nervous system and acts as a fatigue factor. The pituitary gland can produce endorphins, which possess analgesic properties and, at high concentrations, induce a sense of euphoria similar to narcotic drugs.

Currently, about 100 hormones and Neurotransmitters have been isolated and studied, varying in their site of synthesis, chemical Structure, and mechanisms of regulatory action. These three criteria are most commonly used to classify hormones. This textbook employs the traditional yet convenient Classification of hormones based on the endocrine glands in which they are synthesized.