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Digestion

Digestion. Mouth & Stomach. Physical Digestion in The Mouth. Adult humans have 32 teeth (includes 4 wisdom teeth) Teeth are designed to cut, grind and crush food into smaller pieces Incisors, canines: cut Pre/molars: crush, grind. Saliva.

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Digestion

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  1. Digestion Mouth & Stomach

  2. Physical Digestion in The Mouth • Adult humans have 32 teeth (includes 4 wisdom teeth) • Teeth are designed to cut, grind and crush food into smaller pieces • Incisors, canines: cut • Pre/molars: crush, grind

  3. Saliva • Saliva is a solution of mucus, water, and enzymes produced by the salivary glands. • Mucus acts as a lubricant to help swallowing • Water helps dissolve food so you can taste it and moistens food into a ball or bolus so it can be swallowed • Amylase is an enzyme that breaks down carbohydrates: starch disaccharide sugars (this is the only chemical digestion that occurs in the mouth)

  4. Pharynx and Esophagus • The pharynx is the opening toboth the esophagus and the trachea • When swallowing food, the epiglottis covers the trachea, so food is directed down the esophagus. • The esophagus is a long muscular tube • Food stretches the wall of the esophagus and triggers wave-like contractions called peristalsis that push food to the stomach (all all through the digestive system)

  5. Stomach • J-shaped muscular organ that can expand to accommodate 2 L of food. • Movement of food in and out of stomach is controlled by circular muscles called sphincters • Gastroesophageal/cardiac • Pyloric

  6. Stomach (cont) • Stomach contains 4 layers: • Mucosa – innermost layer with extensive folding (rugea) secretes: acid, digestive enzymes, and mucus • Submucosa – Connective tissue, nerves, and blood vessels • Muscle – 3 muscle layers that contract in different directions to mix food with gastric juice to produce chyme (mechanical digestion) • Serosa – outermost layer holds stomach in place and secretes lubricant to reduce friction with other organs

  7. Chemical Digestion in Stomach • The presence of food in the stomach triggers release of hormone gastrin, which causes mucosa to release gastric juice. • pH of stomach acid 2.0 - 3.0 • Kills many harmful microorganisms • Denatures amylase enzyme • Converts pepsinogen enzyme to active form, pepsin (begins breakdown of protein into amino acids)

  8. Disorders of the Stomach & Esophagus • Acid Reflux “heartburn” • if cardiac sphincter does not close completely, acid can splash into esophagus • May also be caused by overfilling stomach • Smoking relaxes cardiac sphincter and increases acid production in the stomach • Stomach Ulcers – open sores • Helicobacter pylori bacteria: produce acid-neutralizing enzymes, burrow into mucosa and prevent cells from producing mucus

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