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Digestive System
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Organs
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Digestive System Broken Down Into 2 Parts
1. Alimentary Canal – gastrointestinal (GI Tract) – Path that food travels 2. Accessory Organs
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GI Tracts Accessory Organs Oral Cavity Pharynx Esophagus Stomach
Duodenum Jejunum Ileum Cecum Ascending Colon Transverse Colon Descending Colon Sigmoid Colon Rectum Anus Tongue Liver Parotid Gland Sublingual Gland Submandibular Gland Uvula Lingual Frenulum Pancreas Gallbladder Appendix
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Mouth Palate: Hard Soft Uvula Tongue
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Salivary Glands Cleanses Mouth Important for Taste Moistens food
Contains Enzymes
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Major Salivary Glands Parotid gland Submandibular gland
Sublingual gland The average person produces ml a day
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Teeth Masticate = to chew Baby teeth (deciduous)
Full set = 20 teeth Permanent teeth = 32 teeth Incisors Canines Premolars/molars
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Pharynx Longitudinal & Circular layers of Muscles Peristalsis
Peristalsis - is a radially symmetrical contraction and relaxation of muscles that propagates in a wave down a tube
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Esophagus Propels food using muscles (Peristalsis)
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Stomach Mostly Protein Digestion No Absorption***
Mechanically & Chemically Digested Into Chyme Gastric glands produce gastric juice: acidic Walls of Stomach lined with mucus so the acid doesn’t “digest itself”
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Chyme Substance in the stomach that is formed from food and enzymes
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Problems of the Stomach
Ulcers: a hole in the mucus lining of the stomach Heartburn (acid reflux): contents of stomach move into esophagus
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Small Intestine
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Sm. Intestine Chemical digestion of carbohydrates, proteins, nucleic acids, & fats Done with enzymes from pancreas and bile (formed in liver) Pancreatic duct and bile duct empty into duodenum – where enzymes empty into.
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Large Intestine Function: Role of Bacteria: To absorb water
Eliminate residue as feces Absorb vitamins produced by bacteria Role of Bacteria: Digest some nutrients Produce vitamins Produce gas
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Action of L. Intestine Peristalsis
Mass Peristalsis: a strong wave that pushes contents towards rectum Problems: Diarrhea Constipation
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Accessory Organs - Pancreas
Releases enzymes into duodenum Has an endocrine function
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Accessory Organs - liver
Produces bile; leaves through common hepatic duct Bile: part waste produce, part digestive secretion (mechanical digestion of lipids)
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Other Liver Functions Metabolism of carbs, lipids, and proteins
Processing of drugs and hormones Excretion of bilirubin (from hemoglobin of old RBCs)
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Accessory Organs - Gallbladder
Releases bile in response to fatty food entering duodenum Location: underside of liver Gallstones
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Steps of Digestion
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Digestion Major functions of the digestive tract are digestion and absorption
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Essential Activities of the Gi Tract
Ingestion Propulsion Food Breakdown – mechanical digestion Food Breakdown – chemical digestion Absorption Defecation
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1. Ingestion Food must be placed into the mouth before it can be acted on. Active, voluntary process
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2. Propulsion In order for food to be processed by different organs, they must be propelled from one organ to the next. Example: Swallowing – depends on the propulsive process called peristalsis Peristalsis – involuntary and involves alternating waves of contraction and relaxation of the muscles in the organ walls
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3. Food Breakdown – Mechanical Digestion
Mixing of food in the mouth by the tongue Churning food in stomach Segmentation – propels foodstuffs through the small intestine Prepares food for further degradation by enzymes
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4. Food Breakdown – Chemical Digestion
Sequence of steps which large food molecules are broken down to their building blocks by enzymes
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5. Absorption Transport of digested end products from the lumen of the GI tract to the blood or lymph For absorption to occur, digested foods must first enter the mucosal cells by active or passive transport processes Small intestine is major site of absorption
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6. Defecation Elimination of indigestible residues from the GI tract via the anus to form feces
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Neural & Hormonal Control
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Cephalic Phase Occurs before food enters the stomach, especially while it is being eaten Brain is activated by smell, sight, thought, and taste of food Neurons to salivary glands and gastric glands/stomach muscles Autonomic Nervous System
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Gastric Phase Stimulus: Food in stomach
Neural: Stretch receptors activated. Impulse to neurons in submucosa Triggers: Gastric gland production and causes peristalsis Hormonal: Food triggers release of gastrin. Goes in the blood. Triggers: Gastric gland juices Sphincter to prevent acid- reflux Stomach muscles Relaxes lower stomach sphincter
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Intestinal Phase Stimulus: Food in Intestine
Neural: Stretch receptors to medulla oblongata Sympathetic nerves to stomach cause: Decreased stomach movement & increase contraction of pyloric – bottom – sphincter (delays stomach emptying) Hormonal: Cholecytokinin (CCK): stimulates pancreatic juice/squeezes gallbladder
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