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Amylase
An enzyme that breaks down starch; secreted in saliva and by the pancreas.
Lipase
An enzyme that digests fats; secreted by the pancreas.
Pepsin
Active protein-digesting enzyme in the stomach, formed from pepsinogen.
Absorption
Uptake of nutrients from the GI tract into the blood or lymph.
Chyme
Semi-fluid mixture of food and digestive juices formed in the stomach.
Peristalsis
Wave-like muscular contractions that move food through the GI tract.
Microbiome
The community of bacteria in the GI tract, especially the large intestine, is crucial for digestion and immunity.
Ingestion
Intake of food.
Mechanical breakdown
Chewing, churning (stomach), segmentation (small intestine).
Propulsion
Swallowing and peristalsis.
Digestion
Chemical breakdown by enzymes.
Defecation
Elimination of indigestible substances.
Carbs
Broken into monosaccharides and absorbed into capillaries.
Proteins
Broken into amino acids and absorbed into capillaries.
Fats
Broken into fatty acids + monoglycerides and absorbed into lacteals (lymph).
Enteric Nervous System
Intrinsic nerve network controlling GI motility and secretions.
Cephalic phase
Triggered by smell/thought of food.
Gastric phase
Triggered by food in the stomach.
Intestinal phase
Begins when chyme enters the duodenum.
Stomach protection
Mucus coat, tight junctions, and epithelial renewal.
Ulcers
Often caused by Helicobacter pylori (H. pylori).
Small Intestine
Duodenum receives chyme, bile, pancreatic enzymes; jejunum is the main site of nutrient absorption; ileum has limited absorption and connects to large intestine.
Large Intestine
Absorbs water and vitamins; stores feces.
Disorders
IBS, colon cancer.
Microbiome
Helps synthesize vitamins, digest fiber, and regulate immunity.
LDL (Low-Density Lipoprotein)
Bad cholesterol; deposits in arteries.
HDL (High-Density Lipoprotein)
Good cholesterol; removes excess from blood.
Digestive System Organs
Mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, anus; accessory organs: liver, pancreas, gallbladder.
Parietal Cells
Produce HCl (activates pepsinogen).
Chief Cells
Produce Pepsinogen (converted to pepsin to digest proteins).
Mucous Cells
Produce Mucus (protects stomach lining).
Enteric Nervous System
Controls digestive activity (motility, enzyme secretion, blood flow) independently of CNS.
Intestinal Phase
Triggers hormonal and neural responses (e.g., secretin, CCK) that inhibit gastric secretion and motility.
Low pH in Stomach
Activates pepsin, kills microbes, denatures proteins for easier digestion.
Liver Contribution to Digestion
Produces bile, which emulsifies fats to aid fat digestion.
Pancreas Contribution to Digestion
Produces digestive enzymes (amylase, lipase, proteases) and bicarbonate to neutralize acid.
Structures Increasing Absorptive Surface Area
Circular folds, villi, and microvilli.
Regions of the Small Intestine
Duodenum, jejunum, ileum.
Epithelial Lining Protection in Stomach
Mucus secretion, tight junctions between cells, and rapid epithelial regeneration.
Function of the Large Intestine
Absorbs water and vitamins; stores and eliminates feces.
Importance of Bacteria in Large Intestine
They synthesize vitamins, aid digestion, prevent harmful bacteria growth, and support immune function.
Cystic Fibrosis Effect on Digestion
Thick mucus blocks pancreatic ducts → enzymes can't reach intestines → poor digestion and absorption.
Difference between LDL and HDL
LDL: Delivers cholesterol to tissues—can clog arteries; HDL: Removes cholesterol from bloodstream—protects against heart disease.
Phases of Digestion in the Stomach
Cephalic, gastric, and intestinal phases.