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DIGESTIVE SYSTEM
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DIGESTIVE TRACT Tube in which digestion occurs
Also called alimentary canal, gastrointestinal tract (GI) Entire canal is about 9 meters along (30 feet) in a cadaver. Shorter in a live person
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FUNCTIONS Ingest food Break down nutrients to a form that can cross plasma membranes Absorb nutrients Eliminate undigested parts
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PARTS
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ORAL CAVITY Mouth - receives food Lips (labia) protects opening
Tongue – taste buds, pushes food to back of throat fermium – a fold of mucous membrane that secures the tongue to the floor of the mouth Roof of mouth – contains made up of: hard palate -anterior portion is bone Soft palate posterior portion is muscle
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Parts continued Uvula – finger-like projection that closes off nasopharynx keeps food from entering the nasal cavity Tonsils – protects against injection
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SALIVARY GLANDS 3 pairs secrete saliva
contains enzyme salivary amylase starts digestion of starch feel flaps under tongue and cheeks – where ducts are located Contains substances that inhibit bacteria growth Dissolves food chemicals so they can be tastes
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Teeth – mechanical digestion
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PHARYNX – region that receives food and air
Trachea – also called windpipe lies in front of esophagus Swallowing is a reflex Glottis – opening to the larynx Epiglottis – spoon shaped tissue covering a piece of cartilage covers glottis so food/liquids do not enter trachea
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ESOPHAGUS Muscular tube Connects to stomach
Remains collapsed until bolus enters Peristalsis – rhythmic contractions that push food along digestive tract No chemical digestion occurs
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LAYERS OF GI TRACT Mucosa – inner most – moist membrane that lines the lumen Submucosa- beneath mucosa- made up of connective tissue, and lymph vessels Muscularis external - smooth muscles Serosa – outermost layer
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Esophagus continued Sphincters – muscles that encircle a tube act as valves located at point where stomach and esophagus meet when open – food passes into stomach closed – keeps acid from entering esophagus
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STOMACH Thick muscular wall Wall has deep folds called rugae
Holds 4 liters when full Stores food Empties in 2/6 hours Mechanical digestion – churns and mixes food with gastric juices pyloric sphincter connects to small intestine Cardioesophageal sphincter – connects to esophagus
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REGIONS OF STOMACH Fundus – expanded part of the stomach
Body – the midportion Pylorus – terminal part of stomach
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GASTRIC JUICES Pepsin – digests protein
HCL – hydrochloric acid pH kills bacteria breaks down connective tissue of meat activates pepsin Mucus Intrinsic factor – substance needed for the absorption of vitamin B12 in the small intestine
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MUCUS Thick layer of mucus Protects stomach from HCL
Produced by goblet cells Ulcer – open sore in wall of stomach exposed to gastric juices bacterial infection interferes with mucus production
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STOMACH CONTINUED Chyme – contents of stomach thick soupy liquid enters small intestines in small squirts No absorption of food occurs in stomach Alcohol absorption only
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SMALL INTESTINE Major site of digestion Has small diameter
About 3 meters (9 feet) long
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THREE PARTS OF SMALL INTESTINE
Duodenum – 1st part of small intestine sphincter muscles control chyme entering receives enzymes from liver and pancreas Jejunum Ileum – terminal part of intestine Ends with the ileocecal valve
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WALL OF SMALL INTESTINE
Fingerlike projections called villi Microscopic microvilli absorb sugars and amino acids directly into blood stream Components of fats enter smooth ER where they are rejoined and enter the lacteal (small lymphatic vessels)
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LARGE INTESTINE 1.5 Meters Absorbs water, salts, and vitamins
Parts: cecum colon rectum
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CECUM Lind end of large intestine
Appendix – small projection may help fight infection subject to inflammation
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COLON Ascending Transverse Descending Sigmoid colon – enters rectum
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RECTUM 20 cemeters Anus – opening to outside expels feces
Stretching of rectal wall sends nerve impulses to spinal cord causing relaxation of anal sphincters Bacteria found in some feces produce vitamins that are reabsorbed by our body
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PANCREASE Endocrine functions involves insulin and glucagon
Exocrine function involves the secretion of pancreatic juices
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PANCREATIC JUICES Sodium bicarbonate Pancreatic amylase Trypsin Lipase
NaHCO3 Neutralizes chyme Pancreatic amylase Digest starch Trypsin Digest proteins Lipase Digest fats
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LIVER Responsible for maintaining homeostasis of blood
Removes poisonous substances Removes Fe and stores it Removes Vitamins A,D,E and K and stores them Makes plasma proteins to maintain osmotic pressure
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LIVER CONTINUED Makes cholesterol and regulates amount in blood
Maintains blood glucose levels Produces bile which emulsifies fat Produces fact
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GALL BLADDER Sac attached to undersurface of liver
Stores bile until needed in the duodenum Gall stones - cholesterol comes out of bile solution forming crystals
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Feces – more or less solid product delivered to the rectum
Resident bacteria of large intestine metabolize the remaining material Gases are released Methane and hydrogen sulfide produce the odor – more gas is produced when food is high in carbohydrates Bacteria make vitamin K and some B vitamins
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DISEASES OF THE GI TRACT
Acid reflux Appendicitis Cirrhosis Colorectal cancer Colostomy Constipation Diarrhea Gallstones Hemorrhoids Hepatitis Hernia IBS Jaundice Lactose intolerance Mumps Peritonitis Ulcer Vomiting
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