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Lecture 2

Digestion (week 2).docx

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Queen's University
Health Studies
HLTH 230
Jeffery Lalonde

Digestion  Process by which food is broken down into absorbable units Obstacles of Digestion  Mouth o Eat, breath drink  Diaphragm below the lungs o Separates upper half form lower half o Food must pass the diaphragm  Gastro Intestinal Tract o Flexible emuscular tube from the mouth to anus  Digestion and absorption occurs  Digestion occurs when the food enters the GI tract through the mouth  Materials inside should be moving slowly to allow reaction to occur  Food must be lubricated to move  Too much – moves too fast  Too little – moves too slow  Water must also pass to eliminate waste  Most is retained to prevent dehydration o Lumen  Space within a vessel  Eg, Intestines  Enzymes o Digest protein, fat, carbs  Body is made of these things Mouth  Where digestion beings  Food is crushed into smaller pieces  Bolus is formed o Foods blend with fluids  Fluids start to dissolve food particles to allow for tasting  Enzyme action begins o Amylase  Starts carb digestion Taste  Mouth contains 9,000 – 10,000 taste buds that are replaced every 10 days o 4 basic tastes  Sweet  Sour – organic acids – vinegar  Salty – sodium  Bitter – no specific chemical structure – quinine – tonic water  Umami – Savoury  Taste associated with MSG  Children have the most discriminating taste o Number of taste buds decline with age  Taste buds are not specialized o Have different receptor sites that respond to different taste sensations  Taste o Sweet, sour, etc.  Flavour o Total sensory impression when food is eaten o Combination of taste, odour, and feel  Tongue o Tastes food o Moves food around for chewing and swallowing  Dysphagia  Difficulty in swallowing  Saliva o Secretion of salivary glands o Contains water, salts, mucus, enzymes o Also flushes away food residue  Protects the teeth and linings of mouth and esophagus o Salivary amylase  Breaks polysaccharides into disaccharides o Mucus  Holds bolus of chewed foods together and lubricates o Lysozyme  Destroys bacteria  Xerostomia  Difficulties in chewing a swallowing  Decrease in saliva production When bolus is swallowed, it passes through the pharynx and into the esophagus  Pharynx o Short tube that is shared by the respiratory system and digestive system  Epiglottis o Cartilage in the through which helps protect the airway from fluids and food during swallowing  Trachea – to the lungs  Esophagus – stomach  People choke on food when it goes through the trachea instead of esophagus Esophagus  Muscular tube that extends between pharynx and the stomach  Has sphincters at both ends  Upper Esophagael Shpincter opens to allow food into the esophagus  Lower Esophagael Sphincter relaxes to allow foods to enter the stomach o Peristalisis  Ringlike contractions of the muscles in the esophagus pushing bolus towards the stomach  Occurs through entire GI tract to push contents along Digestive Problems in the Esophagus  Heartburn/ Gastroesophageal reflux o Backflow of gastric contents o Failure of lower sphincter to contract appropriately  Achalasia o Failure of the lower sphincter to relax during swallowing o Build up food in the esophagus o Bloated Stomach  Sac between esophagus and small intestine  3 sections o Fundus  Lies above esophageal opening o Body  Middle of the stomach o Antrum  Lower part of the stomach  Volume of aprox 50ml when empty o Increase to 1 litre after a meal  Stomach has the thickest walls and strongest muscles of the GI tract  3 types of muscles in the stomach o Longtitudinal (long) o Circular o Diagonal  Bolus moves from esophagus to stomach o Lower sphincter closes to prevent stomach contents from returning back into the esophagus  Stomach keeps bolus in the upper portion  Food is transferred little by little into lower portion when gastric juice is added  Gastric juices include mucus, pepsinogen, hydrochloric acid, and gastrin  Mucus  Slippery substances secreted by cells of GI linig  Protects against gastric mucosa  Could cause acidic damage  Pepsinogen  Gastric enzyme inside of pepsin  Begins protein digestion  Hydrochloric acid  Activates pepsinogen  Break down of foods  Kills microorganisms  Intrinsic Factor  Glycoprotein in the stomach  Joins B12 in small intestine  Gastrin  Hormone secreted by the stomach wall which acts on glands  Leads to increased secretion of HCL  Once PH level is 1.5 gastrin is turned off  Stomach contents form into semi liquid texture called chyme o 3 sets of muscles force chyme downward  Pyloric Sphincter  Remains closed when stomach releases gastric juices  When chyme is completely liquefied, sphincter opens to let chyme into small intestine  Chyme passes through sphincter into the top of small intestine  Bypasses bile duct  No food or water is absorbed from the stomach o Absorbed from the blood  Aspirin can be absorbed in the stomach  Acetylsalicylic acid Small Intestine  3 Sections o Duodenum o Jejunum o Ileum  Aprox 10 feet (21-25 ft when stretched)  Segmentation o Squeezing of the intestine along its length by circular muscles o Mixes chyme o Promotes contact with digestive juices and absorbing of cells  Secretin o Released from duodenum wall o Stimulated by chyme o Secretes into the blood o Secretin stimulates pancreases o Released bicarbonate rich juices o Neutralizing acidic chyme Liver  Storage of fats, iron, vitamins  Activation of vitamin D  Main contribution to digestion is secretion of bile o Bile aids in fat digestion o Between meals bile is stored in gall bladder Gall Bladder  Bile storage  Opening of the bile duct is guarder by sphincter of Oddi o Sphincter prevents bile from enter duodenum (stomach)  Except when digestion is occurring o When sphincter is closed the bile is stored in the gall bladder o Pancreas  Lies beneath stomach  Above duodenum  Secretes pancreatic juice o NACHO3  Sodi
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