Steps of Digestion
1. Food enters the mouth, mucous protects mouth
-mechanical breakdown: teeth
-chemical breakdown: salivary amylase
2. Food passes down the esophagus via
peristaltic muscle contractions, epiglottis tips
over the glottis, preventing food from entering
the trachea. Sphincters prevent backflow.
3. Stomach: Chemical breakdown
-Gastric juice (HCl) secreted by Parietal cells
-Pepsinogen secreted by chief cells
Pepsinogen + Hcl → active Pepsin → cleaves
proteins and breaks them down.
4. Small Intestine
a. Duodenum: chemical breakdown
Receives secretions from
Pancreas: secretin increases basicity,
neutralizes stomach acidic chyme, trypsin + chymotrypsin digest proteins, pancreatic
amylase digests carbs, pancreatic lipase helps break down lipids.
Liver: produces bile, releases it into the gallbladder
Gallbladder: stores bile, releases into pancreas, emulsifies fat for lipase to further break
down lipids.
b. Jejunum + Ileum: absorption of nutrients
Intestinal Villi and microvilli increase Surface Area, transport blood from SI → hepatic
portal vein → Liver
5. Large Intestine: water absorption compacts feces
-Colon→ rectum → anus
-cecum: fermenting undigested plant material, protective layer of mucous prevents
pathogens from entering, fermenting fiber produces Short Chain Fatty Acids (SCFAs) which are
protective against heart disease, obesity,
-appendix: storage for good gut bacteria, immune response
Mouth
Starch breakdown
Stomach
Protein breakdown
Small Intestine - duodenum
Protein, starch, lipid breakdown
Large intestine
Fiber breakdown by mutualistic microbes
