Endocrine Glands and Hormones — NEET Biology
📚 Practice ConceptEndocrine glands lack ducts and are hence, called ductless glands. Their secretions are called hormones. The classical definition of hormone as a chemical produced by endocrine glands and released into the blood and transported to a distantly located target organ has current scientific definition as follows: Hormones are non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts. The new definition covers a number of new molecules in addition to the hormones secreted by the organised endocrine glands. Invertebrates possess very simple endocrine systems with few hormones whereas a large number of chemicals act as hormones and provide coordination in the vertebrates. The human endocrine system is described here.
Which of the above statements are correct? S1: Hormones are non-nutrient chemicals that act as intercellular messengers and are produced in trace amounts. S2: The classical definition of hormones emphasizes their secretion by ductless glands and subsequent transport through blood to distantly located target organs. S3: The neural system, unlike the endocrine system, is primarily responsible for the continuous regulation of cellular functions throughout all cells of the body. S4: Hypothalamic hormones that regulate the anterior pituitary reach it through direct neural regulation, while the posterior pituitary is regulated by a portal circulatory system. S5: The endocrine systems of invertebrates are typically more complex and diverse than those found in vertebrates.
View solution & NCERT explanation
Correct answer: A — S1, S2
The core concept involves the definition, transport, and general characteristics of hormones. S1: Correct. The modern definition states that "Hormones are non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts." (NCERT Page 239) S2: Correct. The classical definition describes hormones as "a chemical produced by endocrine glands and released into the blood and transported to a distantly located target organ." (NCERT Page 239) S3: Incorrect. The NCERT states, "As the nerve fibres do not innervate all cells of the body and the cellular functions need to be continuously regulated; a special kind of coordination and integration has to be provided. This function is carried out by hormones." This indicates that continuous regulation of all body cells is a role for hormones where neural innervation is lacking, making the statement false. S4: Incorrect. The regulation is reversed. "These hormones [hypothalamic, regulating anterior pituitary] reach the pituitary gland through a portal circulatory system and regulate the functions of the anterior pituitary. The posterior pituitary is under the direct neural regulation of the hypothalamus." (NCERT Page 240) S5: Incorrect. The statement is reversed. NCERT states, "Invertebrates possess very simple endocrine systems with few hormones whereas a large number of chemicals act as hormones and provide coordination in the vertebrates." This means invertebrate systems are simpler, not more complex. Therefore, statements S1, S2, and S5 are correct, while S3 and S4 are incorrect. The correct option is A. The question tests the understanding of both classical and modern definitions of hormones, their transport, and comparison with neural coordination.
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