PY 105 Chapter Notes - Chapter 12: Esophagus, Pylorus, Canine Tooth
Gastrointestinal Tract
• Mouth
o Three roles in digestion
• Fragmentation
▪ Mastication (chewing)
▪ Incisors (front teeth) are for cutting
▪ Cuspids (canine teeth) are for tearing
▪ Molars are for grinding
• Lubrication
▪ Accomplished by saliva
▪ Contains salivary amylase (ptyalin) - hydrolyzes starch, breaking it into
fragments
▪ Contains lingual lipase for fat digestion
▪ Contains lysozyme - attacks bacterial cell wall
• Some enzymatic digestion
• Pharynx and esophagus
o Pharynx - throat
o Floppy thing that hangs down in the back of the throat is the uvula
o Pharynx contains opening to two tubes: trachea and esophagus
o Trachea - cartilage lined tube at the front of the neck which conveys air to and from the
lungs
o Esophagus - muscular tube behind the trachea which conveys food and drink to the stomach
o Solids and liquids are excluded from the trachea by the epiglottis
o The upper esophageal sphincter near the top of the esophagus and the lower esophageal
sphincter end of the esophagus
• Stomach
o Large hollow muscular organ
o Partial digestion of food
o Regulated release of food into small intestine
o Destruction of microorganisms
• Acidity
o Gastric pH is about 2
o Secretion of HCl by parietal cells
o Destruction of microorganisms
o Acid-catalyzed hydrolysis of many dietary proteins
o Conversion of pepsinogen to pepsin
• Pepsin
o Enzyme secreted by chief cells
o Pepsin is secreted as pepsinogen
o The inactive form is known as a zymogen
• Motility
o Stomach churns food
o Breaks up food particles
o Food mixed with gastric secretions is known as chyme
• Sphincters
o The lower esophageal sphincter prevents reflux of chyme into esophagus
o Pyloric sphincter prevents the passage of foo from the stomach into the duodenum
o Stretching or excess acidity in the duodenum inhibits further stomach emptying
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