Digestion Notes (Biology 12) I. Introduction/Overview • Digestion: Breakdown of food into small, soluble molecules • Occurs physically and chemically • Absorption: The process of taking specific compounds into the body • Elimination: Expulsion of materials not absorbed into the body • Excretion: Removal of waste from metabolic processes II. Location of Parts and Function A. Teeth • Type of teeth depends on diet: • Carnivores: Sharp teeth for grasping prey and severing meat • Herbivores: Flat teeth for crushing plant fibers • Omnivores: A combination of tooth types for eating both meat and plants • Structure: • Enamel: Hard outer layer • Dentin: Bony layer under enamel • Pulp: Living part of the tooth (contains nerves and blood vessels) • Teeth are embedded in sockets in the jaw B. Tongue • Functions: • Taste: Detects salt, sour, sweet, and bitter flavors • Positioning food for chewing C. Salivary Glands • Three pairs: • Parotid (side of face; swells with mumps) • Sublingual (under tongue) • Submandibular (lower jaw) • Produce saliva, which contains enzymes for digestion D. Palates • Located at the top of the mouth • Hard palate: Front, separates the mouth from the nasal cavity • Soft palate: Back, ends in the uvula E. Pharynx • Area between mouth and esophagus • Used for both breathing and eating • Epiglottis: Closes over the glottis when swallowing to prevent choking F. Esophagus • Muscular tube that pushes food into the stomach using peristalsis • Composed of five tissue layers: 1. Mucosa (epithelial lining) 2. Submucosa (connective tissue) 3. Muscularis (two muscle layers: circular and longitudinal) 4. Serosa (outer epithelial layer; secretes fluid for lubrication) G. Cardiac Sphincter • Muscle at the junction of the esophagus and stomach • Opens to allow food into the stomach H. Stomach • J-shaped organ, located left of the body’s center • Capacity: About 1 liter • Inner lining contains gastric glands: • Parietal cells → Produce HCl • Chief cells → Produce pepsinogen, activated by HCl into pepsin • Epithelial cells → Produce mucus (protects stomach lining) • Functions: • Storage of food (empties in 2-6 hours) • Digestion using pepsin and salivary amylase • Absorption of water, ethanol • Regulation of pepsin production by the hormone gastrin I. Pyloric Sphincter • Muscle at the junction of the stomach and small intestine • Opens to allow chyme (partially digested food) into the small intestine J. Small Intestine • Length: ~ 3 meters (10 feet) • Highly convoluted to increase surface area for absorption • Interior folds covered with villi (tiny projections that increase surface area) • Divided into three parts: 1. Duodenum (first 25 cm): Produces lactase, peptidase, maltase, nuclease 2. Jejunum 3. Ileum • Functions: • Completes digestion • Absorbs nutrients into the bloodstream K. Liver • Largest organ in the body • Monitors blood composition via the hepatic portal vein L. Pancreas • Produces pancreatic juice (digestive enzymes and sodium bicarbonate to neutralize stomach acid) • Produces insulin (regulates blood glucose) M. Ileo-Caecal Opening • Joins the small intestine to the large intestine N. Caecum • Blind pouch at the end of the small intestine • No function in humans (vestigial), but in herbivores, it helps digest cellulose O. Large Intestine • Parts: 1. Ascending colon 2. Transverse colon 3. Descending colon 4. Rectum (stores feces) 5. Anus (controls feces release) • Functions: • Reabsorbs water (~95% of 10L daily intake) • Forms feces • Produces vitamins B and K using E. coli bacteria III. Digestive Enzymes Enzyme Source pH Digested Food Product Salivary Amylase Salivary Glands 7 Starch Maltose Pepsin Stomach 2 Protein Peptides Pancreatic Amylase Pancreas Basic Starch Maltose Trypsin Pancreas Basic Protein Peptides Lipase Pancreas Basic Fat Glycerol & Fatty Acids Peptidases Small Intestine Basic Peptides Amino Acids Maltase Small Intestine Basic Maltose Glucose Nuclease Pancreas Basic DNA/RNA Nucleotides IV. Swallowing and Peristalsis • Swallowing: Food forms a bolus (food ball) and is moved down the esophagus • Peristalsis: Rhythmic contractions of smooth muscle that push food through the digestive tract V. The 7 Functions of the Liver 1. Detoxifies harmful substances (e.g., alcohol) 2. Stores glucose as glycogen 3. Destroys old red blood cells (recycling heme into bile) 4. Produces urea from amino acid breakdown 5. Makes blood proteins 6. Stores iron and vitamins A, D, E, K 7. Converts amino acids to glucose if needed (gluconeogenesis) VI. Digestive Juices & Hormones Gastric Juice (Stomach) • Contains HCl, pepsinogen (activated into pepsin), and mucus • Helps digest proteins into peptides Pancreatic Juice • Contains sodium bicarbonate (neutralizes acid) • Enzymes: Pancreatic amylase, trypsin, lipase, nuclease Bile (Liver & Gallbladder) • Breaks down fats into small droplets for lipase to act on VII. Control of Digestive Gland Secretions • Nervous Reflex: Presence of food triggers digestion • Conditioned Reflex: External stimuli (e.g