BIO 203 Lecture Notes - Lecture 22: Gastrointestinal Tract, Gastric Glands, Small Intestine
18 Jun 2019
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Stomach: functions: storage : the stomach is a large distensible organ. Small intestine not overwhelmed with food: initial chemical digestion of proteins (and some lipids via gastric lipase, mechanical break down of food particles, absorption of hydrophobic substances (e. g. ethanol) In the stomach, surface area is increased by invaginations called gastric glands. Stomach: protein digestion: the acidic environment of the stomach (ph ~1-2): Disrupts the extracellular matrix that binds cells together. Creates more surface area on food particles, more interactions between enzymes and substrates. Pepsinogen has an additional 44 amino acids that maintains the zymogen in an inactive form: pepsinogen (inactive) is converted to pepsin (active) after release from chief cells into the lumen of the stomach. Low ph environment of the stomach lumen causes the catalytic conversion of pepsinogen to pepsin. Hcl causes pepsinogen to unfold and autocatalytically cleave the inhibitory 44 amino acids, generating functional pepsin. Pepsin also cleaves pepsinogen to generate more pepsin.
