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Human Digestion • This part of the life process of NUTRITION-> process by which an organism obtains and utilizes food Digestive System Food processing occurs in four stages 1. Ingestion: taking in food 2. Digestion: mechanical and chemical breakdown of food so that it can be absorbed by the cells 3. Absorption: cells lining the digestive tract take up (absorb) small nutrient molecules 4. Elimination: undigested material passes out of the digestive tract Two Types of Digestion • 1. Mechanical digestion – physical breakdown of large pieces of food into smaller ones • 2. Chemical digestion – hydrolysis – the splitting of large insoluble molecules in small, soluble molecules with the use of water and enzymes ( in other words; breaking complex molecules into simple ones). Chemical digestion is regulated by enzymes. Examples of chemical Digestion: • 1. Carbohydrates+ water -> simple sugars (glucose for instance) • 2. Proteins+ water -> amino acids • 3. Lipids+ water -> 3 fatty acids +gylcerol HUMAN DIGESTIVE SYSTEM • Human digestive tract = GI (gastrointestinal) Consists of a continuous one way food tube (mouth to anus). • Functions 1. Mouth – mechanical digestion • teeth – break up food – chemical digestion (saliva) • amylase enzyme – digests starch • mucus – protects soft lining of digestive system – lubricates food for easier swallowing • buffers – neutralizes acid to prevent tooth decay • anti-bacterial chemicals – kill bacteria that enter mouth with food All that in spit! HUMAN DIGESTIVE SYSTEM 2. Esophagus: muscular tube that moves food from mouth to the stomach by process of peristalsis: wave of muscular contractions that moves chewed food to stomach Swallowing (& not choking) • Epiglottis – flap of cartilage – closes trachea (windpipe) when swallowing – food travels down esophagus • Peristalsis – involuntary muscle contractions to move food along Ulcers 3. Stomach • Functions –disinfect food • hydrochloric acid = pH 2 – kills bacteria –food storage • can stretch to fit ~2L food –digests protein • pepsin enzyme But the stomach is made out of protein! What stops the stomach from digesting itself? mucus secreted by stomach cells protects stomach lining Ulcers Colonized by H. pylori • Used to think ulcers were caused by stress inflammation of stomach – tried to control with antacids • Now know ulcers caused by bacterial infection of stomach – H. pylori bacteria – now cure with antibiotics Free of H. pylori inflammation of esophagus H. pylori inflammatory proteins (CagA) cell damaging proteins (VacA) cytokines helper T cells neutrophil cells white blood cells Small intestine • Functions – digestion • digest carbohydrates – amylase from pancreas • digest proteins – trypsin & chymotrypsin from pancreas • digest lipids (fats) – bile from liver & lipase from pancreas – absorption • nutrients move into body cells by: – diffusion – active transport This is where all the work is done! Absorption in Small Intestines • Absorption through villi & microvilli – finger-like projections – increases surface area for absorption SMALL INTESTINES 6 meters long, but can stretch to cover a tennis court Pancreas ~ accessory organ • Produces digestive enzymes – digest proteins • trypsin, chymotrypsin – digest starch • amylase – digest lipids • lipase • Buffers – neutralizes acid from stomach small intestine pancreas Liver & Gall Bladder ~accessory organs • Produces bile – breaks up fats – gallbladder only stores bile • that’s why you can have your gall bladder removed bile contains colors from old red blood cells collected in liver = iron in RBC rusts & makes feces brown Large intestines (colon) • Function – re-absorbs water • use ~9 liters of water every day in digestive juices – if don’t reabsorb water would die of dehydration • > 90% of water re-absorbed – not enough water re-absorbed » diarrhea » can be fatal! – too much water re-absorbed » constipation • reabsorb by diffusion You’ve got company! • Living in the large intestine is a community of helpful bacteria – Escherichia coli: E. coli • digest cellulose – digests fruits & vegetables • produce vitamins PEE-YOO! – vitamin K & B vitamins • BUT generate gases – by-product of bacterial metabolism – methane, hydrogen sulfide – STINKY! Rectum • Last section of large intestines – eliminate feces through anus – what’s left over? • undigested materials – mainly cellulose from plants – called roughage or fiber – keeps everything moving & cleans out intestines • masses of bacteria So don’t forget to wash your hands! Appendix Vestigial organ Some Digestive Homeostasis Disorders • 1.Constipation– person has uncomfortable or infrequent bowel movements results from sluggish peristalsis that allows excess water to be removed from feces (fecal matter hardens)- may result from insufficient fiber in diet • 2. Diarrhea– opposite of constipation– associated with intestinal disturbances caused by infections or stress– prolonged diarrhea may result in severe dehydration • 3. Gall stones– small hard particles made of cholesterol which form & collect in gall bladder- may block the bile duct and cause pain • 4. acid reflux -backflow of stomach contents upward into esophagus • 5. appendicitis- inflammation of appendix