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The Digestive System Accelerated Biology Functions of the Digestive System • Take in food • Break it down into molecules small enough for the body to absorb • Get rid of undigested molecules and waste • Brainpop animation Stages of Digestion • Ingestion – act of eating or drinking • Digestion – breaking down food into molecules the body can use • Absorption – uptake of small nutrient molecules • Elimination – passage of undigested material from the digestive tract Types of Digestion • Mechanical – chewing in mouth and churning in stomach break food into smaller pieces • Chemical – enzymes break the bonds between molecules – Macromolecules monomer units Pathway through the Digestive System • One long tube, 26 feet! • Mouth pharynx esophagus stomach small intestine large intestine rectum anus • The liver and pancreas are accessory organs that deliver secretions into the digestive tract through ducts. • Passage regulated at each step by sphincters Mouth • Mechanical Digestion – Teeth – rip and chew food into shreds – Tongue – mixes food with saliva Mouth • Chemical Digestion – Salivary glands – secrete saliva which moistens and lubricates food so it can be swallowed more easily – Saliva – contains the enzyme amylase that begins the break down of carbohydrates into monosaccharides Esophagus • A long tube that connects the mouth to the stomach • No digestion takes place • Peristalsis – successive rhythmic waves of smooth muscle contractions move the food to the stomach • Takes 5–10 seconds for food to reach the stomach Peristalsis Stomach • Mechanically breaks down food by using peristaltic waves • Produces gastric juices that is a mixture of HCl acid and the enzyme pepsin • Pepsin – breaks down proteins into amino acids. Only effective in acidic environments Stomach • Food spends 2–6 hours in the stomach • The stomach produces 2 L of HCl a day! Ulcers • A coating of mucous protects the lining of the stomach from the gastric acids • Ulcers result when this lining is damaged Heartburn • Has nothing to do with the heart! • Overtime, the sphincter that separates the esophagus and stomach can become relaxed • Acids from the stomach burn the lining of the esophagus Small Intestine • 6 meters long • Functions in the digestion and absorption of nutrients into the blood • Covered with villi – tiny fingerlike projections that increase the surface area for absorption Villi Small Intestine • Three sections: • Duodenum – first section that receives secretions from the liver, pancreas, and gallbladder • Jejunum – middle section • Ileum – last section connects the small intestine to the large intestine Small Intestine Small Intestine • Bile – produced by the liver and enters duodenum. Breaks up fat globules into tiny droplets • Pancreatic lipase – enzyme secreted by the pancreas and enters the duodenum. Breaks down lipids into fatty acids and glycerol in the small intestine. Large Intestine • • • • Also called the colon No digestion takes place Absorbs minerals & water Prepares wastes for elimination from the body. All food components that are not for energy production are considered waste Large Intestine • Water balance is important! • If food is rushed through you end up with diarrhea (watery feces) • If food remains in the colon too long you become constipated (hard feces) Large Intestine • Most of the contents are dead cells, mucus, secretions. • A colony of bacteria live in the colon and help the body synthesize many compounds you cant get from food – Vitamin K – Several B vitamins Rectum • Rectum – solid waste is stored here until you find a socially acceptable time and place! • Anus – solid waste eliminated through here Liver • Accessory organ • Secretes the bile that aids in the emulsification of fat • Converts extra sugar into glycogen for storage • The liver then breaks down glycogen when it is needed for energy. Liver • The liver also detoxifies poisons • Cirrhosis – scaring of the liver caused by chronic drug use, drinking, viral infections. Liver • Jaundice – a condition in which the eyes, skin, and urine become abnormally yellow as a result of increased amounts of bile pigments in the blood Gallbladder • Concentrated and stores the bile produced by the liver until it is needed in the small intestine Pancreas • Accessory organ • Secretes lipase and protease that aid in the chemical breakdown of lipids and proteins in the small intestine Appendix • A vestigial structure on the the large intestine • Appendicitis – when the appendix becomes inflamed. If immediate medical attention is not received, the appendix may burst. Digestive Enzymes Substrate Organ where breakdown occurs Enzyme Product Carbohydrates (polysaccharides) Mouth Small Intestine Salivary amylase Pancreatic amylase (made by pancreas) Simple sugars Carbohydrates (disaccharides) Small intestine Sucrase, maltase, lactase Monosaccharides Protein Stomach Small Intestine Pepsin Pancreatic protease Amino acids Lipids Small intestine Pancreatic lipase Simple fats Nucleic acids Small intestine Nuclease Nucleotides