Tiêu đề CHEMICAL COORDINATION & INTEGRATION.pdf ✅

 Digital www.allendigital.in [ 243 ] 1. Introduction : • The neural system and the endocrine system jointly co-ordinate and regulate the physiological functions in the body. • The neural co-ordination is fast very exact and short lived, whereas chemical co-ordination is usually slow, widespread and long lasting. • All cells of our body are not innervated by nerve fibres but the cellular function need to be continuously regulated so a special kind of coordination and integration has to be provided. This function is carried out by hormones. 2. Endocrine Glands and Hormones : • Endocrine glands lack ducts and are hence, called ductless glands. Their secretions are called hormones. • Classical definition of hormone – A chemical produced by endocrine glands and released into the blood and transported to a distantly located target organ. • Current scientific definition of hormones – 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. CHEMICAL NATURE OF HORMONES TABLE Human Endocrine System : • 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 bodies in our body. Water soluble Lipid soluble Types of Hormones Amine Peptides and protein Hormones e.g. Epinephrine nor epinephrine e.g. Oxytocin, Vasopressin (ADH), MSH, PTH, TSH, FSH Steroid Hormones Thyroid Hormones e.g. Mineralocorticoids, Glucocorticoids, Testosterone, Estrogen, Progesterone e.g. Thyroxine Chemical Coordination 06 and Integration
NEET : Biology [ 244 ] www.allendigital.in  Digital • In addition to these, some other organs, e.g., gastrointestinal tract, liver, kidney, heart also produce hormones. A brief account of the structure and functions of all major endocrine glands and hypothalamus of the human body is given in the following sections. Organised endocrine gland : Where hormone producing cells are present in cluster/tissue form called organised endocrine gland. Examples : Pituitary, Pancreas, Parathyroid, Pineal, Thyroid, Thymus, Adrenal and Gonads (Testis in males and Ovary in females. Non-organised endocrine gland : Where hormone producing cells are present in scattered form called non-organised or diffused endocrine tissue. Example : Heart, Liver, Kidney, Gastrointestinal tract 3. Mechanism of Hormone Action : • Hormones are two types : (i) Water soluble hormones (ii) Lipid soluble hormones • Hormones produce their effects on target tissues by binding to specific proteins called hormone receptors located in the target tissues only. • Hormone receptors present on the cell membrane of the target cells are called membrane- bound receptors and the receptors present inside the target cell are called intracellular receptors. Mostly nuclear receptors (present in the nucleus). Binding of a hormone to its receptor leads to the formation of a hormone-receptor complex. • Each receptor is specific to one hormone only and hence receptors are specific. • Hormone-Receptor complex formation leads to certain biochemical changes in the target tissue. Target tissue metabolism and hence physiological function are regulated by hormone (A) Water Soluble Hormones : Hormone which interact with membrane bound receptor normally do not enter the target cell, but generate secondary messenger (e.g. cyclic GMP / cyclic AMP, IP3, Ca++ etc.) which in turn regulate cellular metabolism. Response 1 (Generation of second messenger) (Cyclic AMP or Ca++) Biochemical responses Physiological responses (e.g. ovarian growth) Hormone (e.g. FSH) Receptor Ovarian cell membrane
Chemical Coordination and Integration  Digital www.allendigital.in [ 245 ] (B) Lipid Soluble Hormone : Hormone which interact with intracellular receptor (Steroid, iodothyronine) mostly regulate gene expression or chromosome function by the interaction of hormone receptor complex with the genome. Cumulative biochemical action results in physiological and developmental effects. On the basis of their chemical nature, hormones can be divided into groups : (i) Peptide, polypeptide, protein hormones (e.g., insulin, glucagon, pituitary hormones, hypothalamic hormones, etc.) (ii) Steroids (e.g., cortisol, testosterone, estradiol and progesterone) (iii) Iodothyronines (thyroid hormones) (iv) Amino-acid derivatives (e.g., epinephrine). 1. Following are the example of organised gland except (1) Pituitary (2) Pineal (3) Thyroid (4) Kidney 2. Which of the following characteristics is not mentioned in current scientific definition of hormone? (1) Non-antigenic substance (2) Non-nutrient chemical (3) Act as intercellular messenger (4) Produced in trace amount 3. A hormone which binds with membrane bounded receptor except one : (1) Insulin (2) Thyrocalcitonin (3) Oxytocin (4) Progesterone Nucleus mRNA Proteins Physiological responses (Tissue growth and differentiation) Hormone receptor complex Hormone (e.g. estrogen) Uterine cell membrane Genome BEGINNER’S BOX-1 MECHANISM OF HORMONE ACTION
NEET : Biology [ 246 ] www.allendigital.in  Digital 4. Which of the following hormone not binds with cytoplasmic or nuclear receptor? (1) Cortisol (2) Aldosterone (3) Insulin (4) Oestrogen 5. Body co-ordination is exhibited by- (1) Blood vascular system (2) Nervous system (3) Endocrine system (4) Nervous and endocrine system 6. Hormones may be- (1) Amino acid derivatives (2) Peptides (3) Steroids (4) All of the above 7. Endocrine glands produce or Action of endocrine glands is mediated through- (1) Hormones (2) Enzymes (3) Minerals (4) Vitamins 4. Hypothalamus : • The hypothalamus is the basal part of diencephalon (forebrain) and it regulates a wide spectrum of body functions. • It contains several groups of neurosecretory cells called nuclei which produce hormones. These hormones regulate the synthesis and secretion of pituitary hormones. • However, the hormones produced by hypothalamus are of two types, the releasing hormones (which stimulate secretion of pituitary hormones) and the inhibiting hormones (which inhibit secretions of pituitary hormones). For example : • A hypothalamic hormone called Gonadotrophin releasing hormone (GnRH) stimulates the pituitary synthesis and release of gonadotrophins. • On the other hand, somatostatin from the hypothalamus, inhibits the release of growth hormone from the pituitary. • These hormones originating 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 and regulate the functions of the anterior pituitary. • The posterior pituitary is under the direct neural regulation of the hypothalamus. 5. Pituitary Gland : • On the basis of development pituitary gland is completely ectodermal. • It is located in the sella.tursica (bony cavity) of sphenoid bone. • This gland is attached to the hypothalamus through a stalk which is called as infundibulum. • It is divided anatomically into an adenohypophysis (anterior pituitary) and a neurohypophysis (posterior pituitary). • Adenohypophysis consists of two portions, pars distalis and pars intermedia. Hypothalamus