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CHEMICAL COORDINATION AND INTEGRATION 113 SCAN CODE Chemical Coordination and Integration CHEMICAL COORDINATION AND INTEGRATION 22
114 CHEMICAL COORDINATION AND INTEGRATION SCAN CODE Chemical Coordination and Integration Chapter 22 Chemical Coordination and Integration 1. Introduction to Hormones The neural system provides a point-to-point rapid coordination among organs. The neural coordination is fast but short-lived. Moreover, the nerve fibres do not innervate all cells of the body and the cellular functions need to be continuously regulated. Hence, a special kind of coordination and integration is required. As a result, the human body has the neural system and the endocrine system that jointly coordinate and regulate the physiological functions in the body. Endocrine system is present in vertebrates and invertebrates as well. The complexity and mechanism of action of different hormones varies from organism to organism. Invertebrate endocrine systems use a variety of hormones, including steroids, peptides, simple amides, and terpenes. The most well-studied hormone systems are the molting and juvenile hormones in insects, the molting hormones in crustaceans, and several of the neurohormones in molluscs and arthropods. (a) (b) Fig. 22.1 (a) Endocrine glands (b) Exocrine glands The endocrine system comprises endocrine glands and hormones. A gland is an organ which produces and releases substances that perform a specific function in the body. On the basis of the presence or absence of ducts, glands can be of two types, exocrine and endocrine:  Exocrine glands: Exocrine glands have ducts and they pour their secretion on epithelial surface directly or through ducts.  Endocrine glands: Endocrine glands lack ducts and are hence called ductless glands. Their secretions are called hormones which are poured directly into blood and lymph.
CHEMICAL COORDINATION AND INTEGRATION 115 SCAN CODE Chemical Coordination and Integration  Heterocrine glands: They are also called mixed glands. These glands have both exocrine and endocrine parts. E.g. Pancreas, ovary and testis. Hormones are chemicals, produced by endocrine glands, released into the blood and transported to a distantly located target organ. Hormones are defined as non-nutrient chemicals which act as intracellular messengers and are produced in trace amounts. DO YOU KNOW? Thomas Addison is known as the father of endocrinology as he was the first person who discovered “Addison’s disease” which is an endocrine disorder. Fig. 22.2 Thomas Addison 1.1 Properties of Hormones  They are synthesized and secreted by living endocrine glandular cells within the body or in vitro.  Hormones are non-nutrient, intercellular messengers that are produced in traces.  They are transported by the blood stream.  Hormones are not building materials and nor do they provide energy.  They are low molecular weight compounds with different types of chemical structures.  They are effective in low concentrations and their excess and deficiency leads to disorders. 2. Human Endocrine System Fig. 22.3 Human Endocrine system
116 CHEMICAL COORDINATION AND INTEGRATION SCAN CODE Chemical Coordination and Integration  The endocrine glands and hormone-producing diffused tissues/cells located in different parts of our body constitute the endocrine system.  Pituitary, pineal, thyroid, adrenal, pancreas, parathyroid, thymus and gonads (testis in males and ovary in females) are the organised endocrine glands in our body.  In addition to these, some other organs, e.g., gastrointestinal tract, liver, kidney, heart, etc. also produce hormones. Endocrinology: It is a branch of biology that deals with the study of the endocrine system and its functions. 2.1 Hypothalamus Fig. 22.4 Hypothalamus Hypothalamus is the basal part of diencephalon, forebrain, and it regulates a wide spectrum of body functions. The hypothalamus is ectodermal in origin and contains several groups of neurosecretory cells called nuclei which produce hormones. These hormones regulate the synthesis and secretion of pituitary hormones. Hence it is called the “supreme commander” of the endocrine system. Hypothalamic hormones originate in the hypothalamic neurons, pass through axons and are released from their nerve endings. These hormones reach the pituitary gland through a portal circulatory system called the hypophyseal portal system and they regulate the functions of the anterior pituitary. Fig. 22.5 Hypothalamic hormones reach pituitary gland through hypophyseal portal system