Digestive System Overview Quiz

Digestive System Overview

• The gastrointestinal (GI) system includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine.
• Accessory organs that secrete substances into the GI tract include salivary glands, liver, gallbladder, and pancreas.

Anatomy of the GI System

• Mouth: Initiates digestion by chewing and producing saliva.
• Pharynx: Passageway for food and air.
• Esophagus: Transports food from pharynx to stomach via peristalsis.
• Stomach: Stores, mixes, and partially digests food.
• Small Intestine: Major site of nutrient absorption. Composed of the duodenum, jejunum, and ileum.
• Large Intestine: Absorbs water and electrolytes, forms and stores feces. Consists of the cecum, colon, rectum, and anus.
• Salivary Glands: Produce saliva containing enzymes for carbohydrate digestion.
• Liver: Produces bile, processes absorbed nutrients, and performs many other metabolic functions.
• Gallbladder: Stores and concentrates bile.
• Pancreas: Produces enzymes for digestion of carbohydrates, proteins, and fats; also produces hormones.

Functions of GI Organs

• Mouth and Pharynx: Initiation of swallowing, moistening and lubrication of food.
• Salivary Glands: Secretion of amylase (enzyme for carbohydrate digestion).
• Esophagus: Peristalsis to transport food, lubrication.
• Stomach: Mixing and storing food, releasing pepsin (protein digesting enzyme) and HCl (dissolves food and kills microbes).
• Pancreas: Production of pancreatic enzymes and bicarbonate to neutralize acidic chyme.
• Liver: Secretion of bile salts to emulsify fats, and processing absorbed nutrients.
• Gallbladder: Stores and concentrates bile.
• Small Intestine: Major site of digestion and absorption of nutrients.
• Large Intestine: Reabsorption of water from waste and formation of feces for elimination.

Four Processes of Digestion

• Digestion: Breaking down large molecules into smaller ones.
• Secretion: Release of substances into the lumen of the GI tract.
• Absorption: Movement of digested nutrients into the bloodstream.
• Motility: Contractions that mix and propel food through the tract.

Structure of the GI Tract Wall

• Epithelium: Single layer of cells lining the lumen.
• Lamina Propria: Connective tissue layer containing blood vessels and nerves.
• Muscularis Mucosa: Thin layer of smooth muscle.
• Submucosa: Connective tissue layer with blood vessels, nerves and lymphatic vessels.
• Muscularis Externa: Two layers of muscle (circular and longitudinal) that mix and propel contents.
• Serosa: Outermost layer of connective tissue.

Digestion and Absorption (of CHO)

• Carbohydrates in food are either polysaccharides, disaccharides or monosaccharides.
• Fiber is not broken by enzymes, but metabolized by bacteria in large intestine.
• Starch in the mouth is broken down by salivary amylase into disaccharides and small glucose chains.

Digestion and Absorption (of Protein)

• Proteins are digested for the amino acid content, and used to replace cells.
• Proteins in the stomach are converted into peptide fragments by pepsin.
• Peptides are further broken down by trypsin and chymotrypsin (from the pancreas) in small intestine.
• These are broken down into free amino acids which are absorbed.

Digestion and Absorption (of Fat)

• Fats form large lipid droplets in the stomach.
• Emulsification by bile salts and phospholipids increases the surface area of fats.
• Fats are broken down by pancreatic lipase into monoglycerides and fatty acids.
• Monoglycerides and fatty acids are combined to form micelles which pass through the small intestine.
• They enter the epithelial cells and reformed into triglycerides.
• Triglycerides packaged in chylomicrons and pass into lymphatic system.

Regulation of GI Processes

• Neural Regulation: Enteric nervous system (ENS) and central nervous system (CNS).
• Hormonal Regulation: Hormones like gastrin, CCK, secretin, and GIP secreted throughout epithelium of stomach and small intestines.

Other Important Features

• Villi and Microvilli: Increase surface area for absorption in small intestine.
• Lacteals: Absorb fats in the lymphatic system.
• Capillary Network: Absorbs water-soluble nutrients.
• Cell Turnover: Digestive tract epithelial cells constantly replaced by new cells.
• Blood Processing: Nutrients absorbed from capillaries processed by liver before entering general circulation.