Tiêu đề Chemical-Coordination-and-Integration.pdf ✅

1. Chemical Coordination and Integration Chemical Coordination and Integration INTRODUCTION y For control and coordination in higher animals, besides nervous system, there is Endocrine System. y Endocrine system consists of endocrine glands which secrete their secretions directly in the blood stream, unlike exocrine glands which have ducts to deliver their secretion. y Thus, endocrine glands are ductless glands which secrete hormones. Hormones are informational molecules which are secreted in response to changes in the environment inside or outside the body. y There is a considerable coordination between nerves and hormones. Synthesis and release of hormones are regulated by nerves, hormones may also influence nerve activities. HORMONES y These are the non-nutrient chemicals (chemical messengers) produced by the endocrine glands, transported via blood to the distantly located target organs. y These are messengers, required for regulating different metabolic and physiological functions which help in maintaining homeostasis in the body. y Some of the hormones also control the production of other hormones by the various endocrine glands (like hormones secreted by hypothalamus and pituitary body). Types of Hormones y On the basis of chemical nature hormones are of three types- ○ Peptide or proteins hormones: These are made up of short polypeptide chain, small proteins or large glycoproteins. For example, antidiuretic hormone, oxytocin, growth hormone, insulin and follicle stimulating hormone. Definition Gland: A cell or an aggregation of cells specialized to secrete or excrete materials. Rack Your Brain Who called hormones as chemical messengers? Definition Hormones: These are chemicals which act as intercellular messengers and are produced in minute amounts by the endocrine glands. Gray Matter Alert!!! The term hormone was introduced by Starling in 1905.
Chemical Coordination and Integration 2. ○ Amino acid derivatives: These are relatively small molecules that are derived from amino acids, tyrosine and tryptophan. When a hormone is derived from an amino acid its name ends with ‘-ine’. For example, epinephrine and norepinephrine. ○ Lipid derived hormones: These are derived from cholesterol. Chemically the hormones are either ketones or alcohols and their chemical names end with ‘-ol’ for alcohols or ‘-one’ for ketones. For example, estradiol (estrogen), testosterone, aldosterone, cortisol, etc. Note: Steroids are lipid soluble hormones so can easily pass through the plasma membrane while peptide or amino acid hormones are water soluble so cannot pass through the plasma membrane therefore, their receptors are found on the cell membranes. Difference between Hormones and Enzymes Hormones Enzymes Hormones may or may not contain proteins. These are either amino acids, peptides, proteins, phenolic compounds or steroids. Enzymes invariably contain proteins (few exceptions are there i.e ribozyme). These have low molecular weight. These have high molecular weight. These are carried via blood to the target tissues. These are used either locally or reach the target organ by ducts of the glands. These are diffusible through cell membrane. These are non-diffusible through the cell membrane. Rack Your Brain Hormones may be ............, ............ and ............ derivatives. Gray Matter Alert!!! Secretin was the first hormone discovered by Bayliss and Starling in 1903. Previous Year’s Question Which pair is tryrosine derivatives? (1) Calcitonin and insulin (2) FSH and GH (3) Thyroxine and adrenaline (4) Insulin and glucagon
3. Chemical Coordination and Integration Hormones Enzymes These are synthesised by the endocrine glands. These are produced by exocrine glands. These are not catalysts and after participating in specific biochemical reactions their chemical composition changes. These are catalysts so at the end of the biochemical reaction remains unchanged. These are used up during the biochemical reactions. These are not used up during the biochemical reactions. These are either excitatory or inhibitory in their actions. These accelerate the rate of biochemical reaction. Biochemical reactions controlled by hormones are irreversible. Biochemical reactions controlled by enzymes are irreversible. SITES FOR HORMONE ACTION Three sites of action for hormones can be postulated. The Cell Membrane y By altering permeability or active transport mechanisms for a particular molecule. For example, increase in glucose uptake by the target organs of TSH and LH. y By activation of some membrane bound enzyme system which can then produce an intra-cellular metabolic controller. Pre-Existing Intracellular Enzyme System y Hormones may activate or inhibit specific enzyme or enzyme systems within the cell. For example, insulin secreted by pancreatic cells forms complex with hexokinase. Previous Year’s Question A molecule acting as ‘second messenger’ in biological system is (1) c- RNA (2) c-AMP (3) t-RNA (4) hn- RNA Gray Matter Alert!!! Father of endocrinology is Thomas Addison.