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Digestive System Purpose • The digestive system is the organ system that breaks down food into carbohydrates, proteins, fats, vitamins, and nutrients for the body to use for energy Nutrients • A nutrient is a substance that the body breaks down and uses to grow, repair, and function 6 Processes of Digestion • • • • • • Ingestion Secretion Mixing & Movement Digestion Absorption Excretion Alimentary Canal • Also called the Gastrointestinal (GI) Tract • A long, hollow, twisted, and coiled tube that runs through the body • It includes: • Mouth, throat, esophagus • Stomach, small intestine, large intestine, rectum, anus 1. Ingestion • Food enters the digestive system through the mouth • eating 2. Secretion • Process by which a substance is released from an organ or gland to assist in digestion • The body secretes almost 2 gallons of digestive fluids per day! – Saliva – Mucus – Hydrochloric acid – Bile Saliva: • produced by salivary glands • Watery mixture with digestive enzymes – Enzymes speed up a reaction • Speeds up the break down of food into simpler substances • Moistens food Hydrochloric acid • strong acid that breaks food down in the stomach Mucus • Lubricant: helps food to slide down esophagus easily • Protection: mucus lines the stomach walls to protect it from the strong acid inside • Produced by liver Bile • Stored in gallbladder • Released into the small intestine • Thick green fluid • Breaks down large fat droplets in the small intestine 3. Mixing & Movement • Mixing begins with the chewing muscles in the mouth • Tongue(large muscle) helps to form the bolus: soft, round mass of chewed food 3. Mixing & Movement (cont) • The tongue helps to move the food into the pharynx • Movement continues as the food moves through the digestive tract 3. Mixing & Movement (cont) • Most of the mixing happens in the stomach • Food is mixed with gastric juice – Gastric juice is a mixture of mucus, hydrochloric acid and enzymes, especially pepsin Protease • A protease is an enzyme that breaks down proteins • Pepsin is a protease in gastric juice 4. Digestion • Digestion is the actual breaking down of complex food into basic building blocks 2 types of Digestion A)Chemical digestion: the breakdown of food by chemical means through enzymes • It happens in – The mouth (saliva) – Stomach( protease & hydrochloric acid) – Small intestine (enzymes from pancreas and bile from gallbladder) – Large intestine (gut flora) Gut Flora • Symbiotic bacteria that break down some materials 2 types of Digestion (cont) • B) Mechanical Digestion: the physical breaking down of food. • It involves: chewing, churning, & segmentation 5) Absorption • This is the process by which substances are passed from the digestive tract into the blood. • The blood transports them to other parts of the body • Mostly occurs in the small intestine • Nutrients are absorbed into capillaries 6)Excretion • This is the removal of waste products • Digestive waste products accumulate in the large intestine • Remaining water is absorbed • Solid wastes (feces) are stored in the rectum and eliminated through anus. Organ Systems related to Digestion • 1) Nervous System: prepares for food by contracting stomach or triggering salivary glands Organ Systems related to Digestion (cont) • 2)Endocrine System: releases hormones that regulate body functions. • Some of these hormones determine production of digestive juices, control stomach muscle contractions, control absorption rate of nutrients The Mouth • Both chemical and physical digestion takes place in the mouth • It contains the teeth, tongue, and salivary glands Teeth • Adult jaw contains 32 teeth • 4 types of teeth Incisors • 8 total (4 top, 4 bottom) • Chisel shaped • Biting large pieces. Cuspids • Also called canine teeth • 2 upper, 2 lower • Cone-shaped • For grasping & tearing food Bicuspids • • • • Also called premolars 4 top, 4 bottom Flat surfaces For grinding food Molars • Similar to premolars, but larger • 6 on bottom, 6 top A tooth is made of…. • • • • Enamel: hard tissue on outside of tooth Crown: the part of tooth above gum Root: part of tooth that anchors it into gum Cementum: a thin, bony material that fixes the root to the jaw • Dentin: largest part of tooth, hard bone-like tissue under enamel Salivary Glands • Three sets of glands • Release saliva for chemical digestion Tongue • Tongue: primary organ of taste • Taste buds: send taste information to brain where it is processed • Shapes food into the bolus and directs it into the pharynx Esophagus • Movement of muscle contractions which push the food is called peristalsis Structure of the Stomach • • • • • Hollow, muscular sac Below the diagram, left side Can expand to about 2 liters Food remains in stomach for 1-2 hours Muscle contractions cause the bolus to mix with gastric juice • Now the bolus is called chime. Small Intestine • Long, hollow, muscular tube • Between 18-23 feet • Length provides surface area and time for the absorption of nutrients. Villi • Small folds in the small intestine • Contain artery, vein, and capillaries • The capillaries absorb nutrients into the blood Duodenum: • entrance to small intestine from stomach • This is where the bile and other enzymes from pancreas an gallbladder Large Intestine • Has a larger diameter than small intestine • Less than 5 feet long • Function: 1) to absorb any remaining water, electrolytes, and vitamins in the colon • 2) remove wastes through rectum and anus. Liver • 2nd largest organ • Under right rib cage