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Processes of Digestion:
- 1. Food ingested: by mouth
- 2. Mechanical digestion: chewing
- 3. Chemical digestion: Salivary amylase begins chemical breakdown of starch
- 4. Propulsion: initiated by swallowing
- 5. Pharynx and Esophagus: pass food from mouth to stomach
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Pharynx
- passes food and fluids to esophagus and gives air to trachea
- -lined with stratified squamous epithelium and mucus glands
- -two skeletal muscle layers for swallowing
- 1. inner longitudinal
- 2. outer pharyngeal constricters
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Deglutition
Swallowing: involving 22 seperate muscle groups and involves 3 phases
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Buccal Phase:
- (within deglutition)
- bolus is forced into oropharynx
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Pharyngeal-esophageal phase:
- (within deglutition)
- -controlled by medulla and lower pons
- routes sealed off except into digestive tract (probably so we don't choke)
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Peristalsis:
- (within deglutition)
- moves food through pharynx and esophagus
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Esophagus
- muscular tube going from laryngopharynx to stomach
- travels through mediastinum and pierces diaphragm
- joins stomach at cardiac orifice
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Esophageal mucosa
nonkeratinized stratified squamous epithelium
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What happens when the esophagus is empty?
its folder longitudinally and flattened
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The muscle changes from what to what in the esophagus?
skeletal (superiorly) to smooth muscle (inferiorly)
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When does a Hiatal Hernia occur?
- when the cardiac (gastroesophageal) Sphyncter does not close when food is in stomach
- -causes pregnancy, obesity, weak sphyncter
- -superior stomach can move into thoracic cavity
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Gastro Esophageal Reflux Disease (GERD)
- is a result with acid irritating the esophagus
- -if chronic then esophageal cancer can result
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What does the salivary gland secrete?
- Amylase: carbs-glucose
- Lingual Lipase: fats-fatty acids
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What does the Stomach secrete?
- Pepsin: proteins-polypeptides
- HCl: pepsinogen-pepsin, destroys pathogens
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What does the Liver secrete?
Bile Salts: fats-fatty acids
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What does the Pancreas secrete?
- Amylase: carbs-glucose
- Trypsin: polypeptides-peptides
- Lipase: fats-fatty acids
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What do the small intestines secrete?
- peptidase: peptides-amino acids
- sucrase: sucrose-glucose
- maltase: maltose-glucose
- lactase: lactose-glucose
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What happens when bolus goes into stomach?
chemical breakdown of proteins and food is converted into chyme
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Cardiac Region
surrounds cardiac orifice and cardic sphincter
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Fundus
dome shaped region beneath diaphragm
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Pyloric Region:
- made of antrum and canal whih terminates at pylorus
- -pylorus extends to duodenum
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What does the greater omentum help with?
holding the small intestines in place
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What is the Nerve Supply like in the Stomach?
sympathetic and parasympathetic fibers of autonomic nervous system
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Blood Supply in the stomach comes from where?
- celiac trunk (gastric artery
- corresponding veins (gastric veins)
part of hepatic portal system
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What does the Muscularis layer do in the Stomach?
- allows stomach to churn, mix, and pummel food physically
- breaks down food into smaller fragments
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What is the Epithelial lining in the Stomach composed of?
Goblet cells: produce double layer coat of alkaline insoluble mucus with bicarbonate in between
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Gastric Pits:
contain gastric glands that secrete gastric juice, mucus, and gastrin
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Mucous Neck Cells (Gastric Pit)
secrete acid mucus
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Parietal Cells (Gastric Pit)
secrete HCl and intrinsic factor needed for Vitamin B12 (nucleic acid metabolism and RBC maturation) absorption in small intestines
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Chief Cells (Gastric Pit)
produce pepsinogen
(pepsinogen activated to pepsin by HCl in stomach and pepsin breaks down proteins to polypeptides)
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Enteroendocrine cells (Gastric Pit):
- Secretes:
- -Gastrin: stimulates gastric glands to increase there secretion, stimulates gastric emptying
- -Histamine: activates parietal cells to release HCl
- -Serotonin: stimulates gastric muscle contractions
- -Cholecystokinin (CCK): allows pancreatic and bile enzymes to be released
- -Ghrelin: release when stomach is empty stimulating hunger and appetite
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