Digestion And Absorption Revision Notes For NEET

 DIGESTION AND ABSORPTION

        Digestion is the process of converting complex food into simple forms to provide energy and nutrition to the body.

        Nutrients are the substances which provide nutrition to body. Macronutrients are carbohydrates, protein, lipids and fats. Micronutrients are vitamins, minerals and water.

        Alimentary canal is a long tube structure containing mouth, buccal cavity, pharynx, oesophagus, stomach, small intestine and large intestine.

        Mouth is slit-like structure ventrally, guarded by pair of movable lips.

        Buccal cavity contains palate, tongue and teeth. Anterior palate has palatine rugae, posterior palate has velum palate.

        Tongue a muscular organ is attached to buccal cavity floor via frenulum linguae. It is unequally divided into pharyngeal and papillary (taste receptors) by sulcus terminals.

     Teeth are diphyodont and thecodont in humans. The dental formula in humans is .

        Pharynx is divided into oropharynx, nasopharynx, and laryngopharynx. Tonsils are lymphoid tissue of pharynx and oral cavity, classified into tubal, nasopharyngeal, palatine and lingual.

        Oesophagus or food pipe transfer food into stomach by peristaltic movement. Cardiac sphincter prevents back flow of acidic contents.

        Stomach J-shaped and divisible into cardiac, fundus, corpus and pyloric parts. HCl along with gastric enzymes secreted helps in digestion of food (protein and simple sugars) and converts it into chyme.

        Small intestine longest part of alimentary canal, divided into duodenum (main digesting organ) jejunum and distal ileum.

        Large intestine contains

        Caecum

        Colon

        Rectum

        Caecum - Contains vermiform appendix.

        Colon - Longitudinal bands, i.e. taeniae coli are present, colon is divided into ascending, transverse, descending and sigmoid parts.

        Rectum - Terminal part of intestine and digestive tract.

        External and internal sphincter regulates opening of the anus, i.e. the outermost opening of the digestive tract.

        Alimentary canal histology the walls of alimentary canal possess four layers, from outside to inside, i.e. serosa, muscularis, submucosa and mucosa.

        Digestive glands salivary, gastric and intestinal glands along with pancreas and liver.

        Salivary glands in mouth, major glands are parotid which secretes serous-like substance salivary amylase, submandibular gland secretes mucus, some enzymes, sublingual, open via duct of Rivinus, infraorbital glands present in dogs and cats. Accessory mucus secreting glands are goblet cells. Nuhn’s gland and weber’s gland.

        Gastric glands in stomach epithelium, cardiac gland (mucus), oxyntic (main gastric glands) and pyloric (mucus, HCl and enzymes). Gastrin secreted by G cells present in pyloric gland.

        Intestinal glands formed by surface epithelium of small intestine. Crypts of Lieberkuhn (digestive juices) and Brunner’s glands in duodenum secretes an alkaline fluid.

        Liver the largest gland divided into two hepatic lobes, connected by falciform ligament. It secretes bile, helps in digestion of fats.

        Gall bladder bile secreted by hepatic cells is stored in gall bladder.

        Pancreas mixed gland with endocrine and exocrine functions. The exocrine part secretes pancreatic enzymes in acini cells, while endocrine part made of alpha, betta and delta-cells secrete glucagon, insulin, somatostatin, etc.

        Process of digestion the digestion of food starts in the mouth, where the teeth masticate the food and the tongue mixes it with saliva.

        The saliva contains starch digesting enzymes. Thus, the digestion of food starts in mouth itself.

        The food then passes into the pharynx and enters the oesophagus in the form of bolus, which is then further carried down into the stomach by peristalsis, where the digestion of protein and absorption of simple sugars takes places.

        The food in the stomach forms chyme, upon mixing with acidic gastric juices. It enters the duodenum part of small intestine.

        The duodenum contains pancreatic juices and bile released from the pancreas and gall bladder, respectively. Here, major portion of the food is digested.

        As the digestion gets completed, the digested end products are absorbed into the body through the epithelial lining of the intestinal villi.

        Afterwards the undigested food enters into caecum of the large intestine, where most of the water is absorbed from it. This makes it semisolid in nature.

        Lastly, this semisolid digestive wates get ejected out of the body through anus.

        Nutritional and digestive disorders every organism requires adequate supply of nutrients in their diet for proper growth and development. Any change in this leads to either a nutritional or a digestive disorder.

        Various nutritional disorder includes hypercholesterolemia, fluorosis, kwashiorkor, marasmus, obesity, etc.

        Various digestive disorder includes indigestion, constipation, vomiting, jaundice, diarrhoea, etc.

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