Ch 4 Digestive System
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Transcript of Ch 4 Digestive System
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DIGESTIVE
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SYSTEM
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Chapter - 4
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Objectives
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Describe the three main functions of the digestive system. Identify the organs of the digestive system and their functions. Digestive System Disorders
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CareerIAS.in
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Introduction
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Process of conversion of complex food substances to simple absorbable forms is called digestion.
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(i) Intracellular: When the process of digestion occurs within the cell in the food vacuole. Examples: Protozoa, Porifera, Coelenterata and free living Platyhelminthes (iii) Extracellular: When the process of digestion occurs outside the cell, Examples: Coelenterates and phylum Platyhelminthes to phylum Chordata.
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Human Digestive System
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The human digestive system is a complex series of organs and glands that processes food. It converts ingested food so that it can be assimilated by the organism. On the basis of the embryonic origin, the alimentary canal of vertebrates can be divided into three parts– (1) Fore gut / Stomodaeum: Ectodermal. It includes buccal cavity / oral cavity, pharynx, oesophagus, stomach and small part of duodenum. (2) Mid gut/Mesodaeum: Endodermal. It includes small intestine, and large intestine. (3) Hind gut/Proctodaeum:Ectodermal. It includes anal canal and anus.
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Mouth is also known as the oral cavity or buccal cavity. It is the first portion of the alimentary canal. Food and saliva are received by mouth. Mouth has inner lining of mucous membrane epithelium.
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It is the opening of oral and nasal cavities. It is classified as: - 1) Nasopharynx 2) Oropharynx 3) Laryngopharynx Oesophagus connects pharynx with stomach. Opening of oesophagus is regulated by gastro-oesophageal sphincter.
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Muscles contract in waves to move the food down the esophagus. This means that food would get to a person's stomach, even if they were standing on their head.
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Parts of Digestive System
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Mouth
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Pharynx
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It is a J-shaped, muscular, hollow and dilated part of the digestive system. It is located between the oesophagus and the small intestine. It has 1 liter capacity. It secretes protein-digesting enzymes (proteases) and strong acids which aid in food digestion.
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The stomach has three parts: Cardiac: The part of the stomach into which oesophagus opens. Fundus: It is the air filled portion of stomach. Pyloric: The portion of the stomach that opens into the small intestine.
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1. An adult's stomach can hold approximately 1.5 liters of material. 2. Stomach rumbling can happen at any time, not just when you're hungry.
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It is the part of the gastrointestinal tract that comes after the stomach and is followed by the large intestine.
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Small intestine distinguished into three parts: (a) Duodenum: It is ‘U’ shaped first part of the small intestine. (b) Jejunum: It is the longer, coiled middle portion. (c) Ileum: Ileum is the highly coiled posterior part of the small intestine.
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Stomach
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Small Intestine
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Large intestine consists of three parts: (a) Caecum: It is a small blind sac. Vermiform appendix is a finger-like blind tubular projection of caecum. (b) Colon: The Caecum opens into colon. Colon has three distinct parts- - Ascending colon - Transverse colon - Descending colon (c) Rectum: It is the final straight portion of the large intestine.
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Every day 11.5 liters of digested food, liquids and digestive juices flow through the digestive system, but only 100 mls is lost in feces
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A.) We eat about 500kg of food per year. B.) 1.7 liters of saliva is produced each day.
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Large Intestine
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(i) These are the exocrine glands that produce saliva. (ii) These are the glands with ducts which also secrete amylase. (iii) Amylase is an enzyme that breaks down starch into maltose.
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Three types of salivary glands are: - 1) Parotid gland 2) Submandibular gland 3) Sublingual gland
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(i) The gastric glands (fundic gland) secrete acids and digestive enzymes. (ii) Secretion of gastric gland is called gastric juice. (iii) There are approximately 35 million gastric glands present in human stomach.
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Intestinal glands:- (i) Intestinal glands in mammals is a collective name for crypts of Liberkuhn (secretes alkaline enzymatic juice) and Brunner’s glands (secrete mucous). (ii) Intestinal glands secrete intestinal juice or sucus entericus.
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(i) Pancreas has two different kind of tissue- exocrine and endocrine. (ii) Pancreatic secretion is stimulated by cholecystokinin and secretinboth. (iii) Complete digestive juice is pancreatic juice as it contains amylolytic, lipolytic and proteolytic enzymes. (iv) It produces several important hormones like insulin, glucagon, somatostatin and pancreatic polypeptide.
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Digestive Glands
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Salivary Gland
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Gastric Gland
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Intestinal glands
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Pancreas
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(i) Liver is the largest digestive gland of the body, weighing about 1.2 to 1.5 Kg in an adult human. (ii) It is situated in the abdominal cavity, just below the diaphragm and has two lobes (small left and large right lobe). (iii) The liver has a wide range of functions to perform in the body: a) It detoxifies various metabolites b) It helps in protein synthesis.
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Amount: 1.0-1.5 litre/day Chemical nature: Slightly acidic. pH: 6.3 - 6.8 Control of secretion: Autonomic reflex parasympathetic nervous system increases salivation while sympathetic nervous system inhibit secretion) Chemical composition; Water (99.5%), mucous acts as lubricant), salts (NaCl, NaHCO3 etc.), enzymes (ptyalin, lysozyme) etc
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Amount: 2-3 liters/ day. Chemical nature: Highly acidic pH: 1.0 - 3.5 (due to presence of HCI) Control of secretion: By gastrin hormone: Chemical composition: Water (99%), mucous, morganic salts, castle's intrinsic factor, HCI (0.5%, cone.) and enzymes prorennin and pepsinogen and gastrin lipase. Succus entericus (intestinal juice) Amount: 1.5 - 2.0 1/day. Chemical nature: Alkaline. pH: 7.6-8.3 Control of secretion: Nervous and hormonal (Enterocrinin, Duocrinin etc.)
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Chemical composition: Water (99%), mucous, inorganic salts, enzymes etc.
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Liver
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Juices
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Salivary Glands
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Gastric juice
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Amount: 1-1.5 1/day Chemical nature: alkaline pH: 7.1-8.2 Control of secretion: Hormonal and normal mechanism Secretin hormones stimulate the production of more alkaline pancreatic juice but low in enzyme content. Pancreozymin or Cholecystokinin stimulates the production of enzyme rich pancreatic juice. Chemical composition: Water (99%), enzymes and salts. Bile/chole Amount: 800-1000 ml daily. On the average about 700 ml. Source: Secreted by hepatic cells Storage' site: Gall bladder Colour: Greenish-blue Chemical nature: Alkaline pH: 7.6-8.6
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An adult's stomach can hold approximately 1.5 liters of material.
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Pancreatic juice
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The Summary of Absorption in Different Parts of Digestive System:
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Gastrointestinal hormones
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Some animals such as cows, giraffes and deer have stomachs with multiple compartments. While others like seahorses, lungfishes and platypuses have no stomachs at all.
