Digestive System: Mechanical, Chemical Processes & Disorders

Mechanical Digestion

Physical breakdown of food into smaller pieces without altering its chemical composition (e.g., chewing, churning, segmentation).

Chemical Digestion

Enzymatic and chemical breakdown of complex food molecules into absorbable nutrient units.

Mouth - Mechanical Digestion

Mastication (chewing) breaks food down and mixes it with saliva to form a bolus.

Mouth - Chemical Digestion

Salivary amylase begins breaking down starches into smaller carbohydrates.

Esophagus - Mechanical Action

Peristalsis propels the food bolus down to the stomach via rhythmic muscular contractions.

Epiglottis

Flap of tissue that closes off the trachea during swallowing to prevent food from entering the airway.

Stomach - Mechanical Digestion

Churns, mixes, and grinds food with gastric juices to form semi-liquid chyme.

Stomach - Chemical Digestion

HCl denatures proteins and activates pepsin, which breaks down proteins into shorter polypeptides.

Small Intestine - Mechanical Digestion

Segmentation mixes chyme with digestive juices; bile emulsifies fats.

Small Intestine - Chemical Digestion

Pancreatic enzymes and brush border enzymes break down carbohydrates, fats, and proteins into monosaccharides, fatty acids, and amino acids.

Liver - Digestive Role

Produces bile to emulsify fats and processes absorbed nutrients.

Gallbladder - Digestive Role

Stores and concentrates bile before releasing it into the small intestine.

Pancreas - Digestive Secretions

Produces bicarbonate to neutralize acidic chyme, plus amylase, lipase, and proteases.

Gastrin

Stomach hormone that stimulates the secretion of hydrochloric acid (HCl) and increases gastric motility.

Secretin

Small intestine hormone that signals the pancreas to release bicarbonate to neutralize acidic chyme.

Cholecystokinin (CCK)

Small intestine hormone that signals the gallbladder to release bile and the pancreas to release digestive enzymes.

Bile

Fluid produced by the liver and stored in the gallbladder that emulsifies fat globules into smaller droplets.

Passive Diffusion

Nutrients move across the enterocyte membrane from high to low concentration without energy or transport proteins.

Facilitated Diffusion

Nutrients move from high to low concentration using a carrier protein without requiring energy (e.g., fructose).

Active Transport

Nutrients move against a concentration gradient (low to high) using a carrier protein and ATP energy (e.g., glucose, amino acids).

Endocytosis

Cell membrane engulfs a whole nutrient or particle into a vesicle inside the enterocyte.

Cardiovascular System Transport

Transports water-soluble nutrients from enterocytes via the hepatic portal vein directly to the liver.

Lymphatic System Transport

Transports fat-soluble nutrients packaged as chylomicrons through lacteals, bypassing the liver initially.

GERD (Gastroesophageal Reflux Disease)

Caused by a weak lower esophageal sphincter (LES) allowing acid reflux into the esophagus; causes heartburn and chest pain.

Peptic Ulcers

Sores in the stomach or duodenal lining caused by H. pylori infection or NSAID use; cause burning abdominal pain.

Celiac Disease

Autoimmune response to gluten that damages and flattens small intestinal villi, leading to nutrient malabsorption.

Irritable Bowel Syndrome (IBS)

Functional bowel disorder with altered motility and sensitivity; causes pain, cramping, bloating, diarrhea, and constipation.

Gallstones

Hardened deposits formed from high-cholesterol bile in the gallbladder; cause severe upper right abdominal pain.