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The digestive system
- Consists of the alimentary canal that includes
- Mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum and anus
- Accessory organs
- Salivary glands, pancreas, liver, and gallbladder
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The digestive system has two main functions
- Digestion: mechanical and chemical break down of food
- Absorption: transporting the food in to the blood
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The digestive system is location
- the abdominal cavity
- when uncoiled becomes 8m long
- What is food
- Nutrients: substances needed for body growth and maintenance
- Carbohydrates, lipids, proteins, vitamins, minerals, and water
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Where do nutrients come from?
- Carbohydrates,
- Mostly from plants
- Some from milk
- Bread
- Lipids
- Oil from animal products
- Oil from seeds and vegitable oil
- Egg yolks, meats, milk
- Protein
- Mostly from animal
- Legumes and beans
- Vitamins
- Found in all major food
- Minerals
- Found in vegetables, legumes, milk, and some meats
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Histological composition of the alimentary canal
- Consists of four distinct layers
- Mucosa
- Inner most layers that consists of epithelium and connective tissue
- Secretes enzymes
- Submucosa
- Loose connective tissue and blood vessels
- Muscuilaris
- Smooth muscle layer
- Serosa
- Visceral peritoneum
- Made of simple squamous and connective tissue
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Peristalsis
- Movement of food by wave like motion down the alimentary canal
- Achieved by muscularis layer
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Salivary glands
- Three major glands
- Parotid, submandibular, and sublingual
- Secrets mucus
- Secret enzymes AMYLASE which digests carbohydrates
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Stomach
- Medially connected to esophagus and laterally connected to the duodenum
- Has two sphincters which are rings of smooth muscle tissue acting as a valve
- Esophageal sphincter: prevents back flow of food
- Pyloric sphincter: controls the rate of gastric emptying
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Function of the stomach
- Receives food from esophagus
- Mixes food
- Release enzyme that start protein digestion
- Caries limited absorption
- Moves food to the small intestine
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Lining of the stomach
- Gastric pits are folding within the mucosal layer that contains epithelial cells
- Mucous cells secrete mucus
- Parietal cells secret hydrochloric acid
- Chief cells secrete pepsin that digests proteins
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Accessory organs: pancreas
- Associated with the duodenum
- Produces pancreatic juices that consists of many enzymes
- Pancreatic amylase: digest carb
- Lipase: digest fat
- Nuclease: digest nucleic acid
- Trypsin and chymotrypsin: digest proein
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Accessory organs: gallbladder
- Located on the inferior surface of the liver
- Stores and concentrates bile
- Release bile in to the duodenum
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Accessory organs: liver
- Has many important metabolic functions
- Stores glucose
- Responds to insulin and glucagon
- Synthesizes cholesterol
- Synthesizes plasma proteins
- Synthesizes bile
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Bile
- contains water, bile salts, bile pigments, cholesterol, and electrolytes
- function aids digestive enzyme by breaking large fat globules in to small droplets (emulsification)
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Small intestine
- Consists of three portions
- Duodenum, jejunum, ileum
- Contains a double layer membrane called mesentery that holds the small intestine together and support blood vessels
- Intestinal villi are tiny projections of mucous membrane that increase surface area
- Each villus is lined with simple columnar epithelium
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Function of the small intestine
- The site of pancreatic enzymes and bile release
- Synthesizes enzymes needed for carbohydrate digestions
- Site of fat digestion
- Site of absorption
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Large intestine
- Made of many parts
- Cecum: where the ileocecal valve is fund
- Vermiform appendix: lymphatic tissue
- Colon: ascending, transverse, descending, and sigmoid
- Rectum terminates into the anal canal
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Function of the large intestine
- Has little digestive function
- Secretes a lot of mucus to protect the lining from abrasion and to lower the acidity
- Absorbs water and electrolytes
- Absorbs vitamin K, B12, thiamin that are produced by bacteria called intestinal flora found in the large intestine
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