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Chapter 11

Living body chapter 11.docx

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Natural Science
NATS 1610
Barbara Czaban

Living Body – Chapter 11 Notes -The digestive system is a long tube which food is broken down and from which the nutrients food contains are absorbed • This tract continues on to the anus and is called the gastrointestinal tract -when we eat, food advances in one direction, from the mouth through the pharynx, the esophagus, stomach, small intestine, large intestine (ends in the rectum, anal canal, and anus) -The digestive tube have 4 layers (from the esophagus on the digestive tube wall has 4 layers) 1. Innermost: mucosa (lines the lumen) 2. Submucosa (layer of connective tissue with blood and lymph vessels and nerve cells) 3. Smooth muscle usually two layers (one circling the tube other lengthwise) 4. Serosa very thin serous membrane -Sphincters: circular arrays of smooth muscles found in the junctions between sections in the GI -The digestive system’s part carries out five types of tasks 1. Mechanical processing and motility: movements of various parts (EX. Mouth, tongue, etc) 2. Secretion: glands and accessory organs release enzymes or other chemicals 3. Digestion: food is chemically broken down to nutrient molecules small enough to be absorbed 4. Absorption: Digested nutrients and fluid pass across the tube wall and into blood or lymph 5. Elimination: undigested and unabsorbed residues are excreted from the end of the GI tract -in your oral cavity food begins to be torn apart by chewing -adults have 32 teeth, where children have only 20 primary teeth (all teeth are coated with enamel) -shape of your teeth fit its function (EX. Chisel shaped food incisors bite off chunks of food) -chewing mixes food with saliva from several salivary glands -saliva is mostly water, but it includes other substances (important enzyme is salivary amylase, breaks down starch) • A buffer keeps the pH of your mouth between 6.5 -11.5 • Saliva also contains mucins which helps bind food together in ball like shape • Once it is swallowed the ball is called a bolus -behind the upper teeth is a bone reinforced section of the palate (roof of the mouth) -Pharynx: throat • This connects with the windpipe or trachea which leads to the lungs • Or connects to the esophagus which leads to stomach -swallowing has both voluntary and involuntary phases -Waves of muscle contractions called peristalsis help push food bolus along Stomach -The stomach has three functions 1. Mixes and stores ingested food 2. It produces secretions that help dissolve and break down food particles, especially proteins 3. By the way of a sphincter, it helps control the passage of food into the small intestine -surface of the stomach is lines with the glandular epithelium -each day gland cells release HCL (hydrochloric acid) mucus and other substances • Includes pepsinogens, precursors of digestive enzymes called pepsins -Gastric juice: stomachs strongly acidic substance -the acidity changes swallowed bolus into chyme -Gastric mucosal barrier: lines the stomach to protect against the acidic substance -When the stomach is empty its walls crumble into folds called rugae -water and alcohol are two substances that begin to be absorbed across the stomach wall • Liquids on an emprty stomach move quickly into the small intestines • Effects of alcohol are more gradual when drinking accompanies and meal especially fatty ones Small intestine -the structure of the small intestine wall is the key to its ability to absorb nutrients -inch and half diameter and meters (20 feet) long -mucosa is folded and stick out like ruffles into the lumen. Each fold has even smaller hair like projections (each finger is villus) • A lymph vessel in each villus move substances to and from the bloodstream • Gland cells in the mucosal lining release digestive enzymes - most cells in the epithelium covering a villus have a threadlike projection of their plasma membrane called the microvillus -each epithelial cell has about 1700 microvilli - a dense array that gives the epithelial of villi its common name, the brush border Accessory organs: the pancreas, gallbladder, and liver -the pancreas nestles behind and below the stomach -it contains exocrine cells that release digestive enzymes into the duodenum (first section of small int.) -there are four types of pancreatic enzymes (complex carbs, proteins, lipids, nucleic acids) -making bile is the digestive role of the liver • Bile is a blend of water and bile salts synthesized from cholesterol -bile is stored in the gallbladder (small sac behind the liver) -besides the digestive function of the liver, it processes incoming nutrient substances the body requires -a system of blood vessels called the hepatic portal system diverts blood from the small intestine to the liver -liver functions • Forms bile used in fat digestion, rids body of excess cholesterol, and bilirubin from dead red blood cells • Synthesizes important proteins in blood plasma,. Converts potentially toxic ammonia to urea • Stores some excess glucose as glycogen • Removes hormones that served their function from blood • Removes ingested toxins, such as alcohol from blood • Stores some vitamins and minerals Di
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