Title Digestion and Absorption_(1-52).pdf ✅

NARAYANA GROUP 1 NEET ZOOLOGY VOL-I DIGESTION AND ABSORPTION * The reductionist approach to study of life forms resulted in increasing use of physico- chemical concepts and techniques. * Majority of these studies employed either surviving tissue model or straightaway cellfree systems. * An explosion of knowledge resulted in molecular biology. * Molecular physiology became almost synonymous with biochemistry and biophysics. However, it is now being increasingly realised that neither a purely organismic approach nor a purely reductionistic molecular approach would reveal the truth about biological processes or living phenomena. * Systems biology makes us believe that all living phenomena are emergent properties due to interaction among components of the system under study. * Regulatory network of molecules, supra molecular assemblies, cells, tissues, organisms and indeed, populations and communities, each create emergent properties. * ALFONSO CORTI, Italian anatomist, was born in 1822. Corti began his scientific career studying the cardiovascular systems of reptiles. Later, he turned his attention to the mamma- lian auditory system. * In 1851, he published a paper describing a structure located on the basilar membrane of the cochlea containing hair cells that convert sound vibrations into nerve impulses, the organ of Corti. He died in the year 1888. Human Physiology INTRODUCTION Unit -V
NEET ZOOLOGY VOL-I 2 NARAYANA GROUP DIGESTION AND ABSORPTION CO N T E N TS NEET SYLLABUS Digestion and Absorption * Introduction * Digestive System * Digestion of Food * Absorpt ion of D igested Products * Disorders of Digestive System  Vitamins & Minerals  Alimentary canal and digestive glands  Role of digestive enzymes and gastrointestinal hormones  Peristalsis, Digestion, absorption and assimilation of proteins, carbohydrates and fats.  Calorific value of proteins, carbohydrates and fats.  Nutritional and digestive disorders - PEM, Indigestion, Constipation, vomiting, Jaundice and Diarrhoea. 16
NARAYANA GROUP 3 NEET ZOOLOGY VOL-I DIGESTION AND ABSORPTION INTRODUCTION * Food is one of the basic requirements of all living organisms. The major components of our food are carbohydrates, proteins and fats. Vitamins and minerals are also required in small quantities. * Food provides energy and organic materials for growth and repair of tissues. The water we take in, plays an important role in metabolic processes and also prevents dehydration of the body. * Biomacromolecules in food cannot be utilised by our body in their original form. They have to be broken down and converted into simple substances in the digestive system. This process of conversion of complex food substances to simple absorbable forms is called digestion and is carried out by our digestive system by mechanical and biochemical meth- ods.  Modes of nutrition:  Autotrophic - The process of synthesising their own food material. Depending upon the source of energy, autotrophs can be classified into photoautotrophs and chemoautotrophs.  Heterotrophic - The process of feeding on other organisms. It includes holozoic, saprobic, parasitic, etc.,  In holozoic nutrition the solid food is ingested, digested and then absorbed into the cells. eg: man  In saprobic nutrition, organisms obtain nutrients from decaying organic materials after digesting the same with the help of enzymes eg: Decomposers. DIGESTIVE SYSTEM * The human digestive system consists of the alimentary canal and the associated glands. THE HUMAN DIGESTIVE SYSTEM
NEET ZOOLOGY VOL-I 4 NARAYANA GROUP DIGESTION AND ABSORPTION Alimentary Canal * The alimentary canal begins with an anterior opening – the mouth, and it opens out posteri- orly through the anus.  It develops from mesoderm and endoderm.  Length of alimentary canal is 8-10 mts. * The mouth leads to the buccal cavity or oral cavity. This cavity is divided into vestibule and oral cavity proper.  Vestibule is a space found between lips, gums and cheeks.  The oral cavity has a number of teeth and a muscular tongue.  A small median fold of mucous membrane connecting the upper lip to the gum is called superior labial frenulum. Inferior labial frenulum connects the middle lower lip with gum.  Ventral surface of hard palate contains transverse ridges called palatine rugae which provide grip during mastication( palatine rugae are thick in carnivores).  One pair of nasopalatine ducts are present at the anterior part of hard palate, these connect the buccal cavity to the nasal passage.  Free end of the soft palate hangs down as a small conical flap into the pharynx called uvula. At the time of swallowing, the soft palate and uvula move up and close the internal nostrils. Teeth * Each tooth is embedded in a socket of jaw bone This type of attachment is called thec- odont * Majority of mammals including human being forms two sets of teeth during their life, a set of temporary milk or deciduous teeth replaced by a set of permanent or adult teeth. This type of dentition is called diphyodont. * An adult human has 32 permanent teeth, which are of four different types (Heterodont dentition), namely, incisors (I), canines (C), premolars (PM) and molars (M). * Arrangement of teeth in each half of the upper and lower jaw in the order I, C, PM, M is represented by a dental formula which in human is 2123 2123  Root formula for different teeth in the order I,C,PM,M 1123 is I,C,PM,M 1112 * The hard chewing surface of the teeth, made up of enamel, helps in the mastication of food.  Teeth are ecto – mesodermal in origin.  Incisors are long, chisel like teeth for cutting the food. They are well developed in Lagomorphs, Rodents, etc.  Canines are sharp pointed dagger like teeth meant for tearing the food. Canines are well developed in carnivorous animals. Canines are absent in herbivorous animals e.g. Rabbit. In herbivores, the space of canine in gum is empty and this empty space is called diastema.  Pre molars are meant for chewing and crushing of food. They are triangular in shape.  Molars (cheek teeth) are meant for chewing and crushing of food. They are rectangular in shape. Premolar and molar help in the mastication of food.