Digestive System Why do we need to eat? Growth Maintenance (repair tissue) Energy
Nutrients Nutrient = chemical that must be obtained by an organism from it s environment in order to survive; nutrients provide the raw material for growth and repair and may be a source of energy Carbohydrates, proteins, lipids (fats), water, minerals and vitamins Gastrointestinal (GI) Tract The passageway or tube that extends from the mouth to the anus and in which the process of digestion takes place
Mouth Salivary Glands Pharynx Liver Esophagus Stomach Pancreas Gallbladder Small Intestine Large Intestine Rectum Anus Digestive Processes Overview Ingestion: food enters the system Digestion: Further breakdown (chemical/enzymatic) Absorption: Nutrients enter circulatory system Physical and enzymatic breakdown begins Delivered to tissues of the body Egestion: Removal of wastes from body
1. Ingestion Saliva Lubricates food so it can be swallowed Dissolves food particles so food can be tasted Food must be dissolved to be tasted Contains amylase enzymes Breaks down carbohydrates
Saliva On average we produce.75 to 1.5L of saliva per day Most of it is water which moistens the food into a ball or bolus Saliva Amylase Enzymes Break down long, complex carbohydrates (starches) into simpler carbohydrates/sugars Amylases Starch Simpler sugars/carbs
Teeth Physical Digestion Incisors (cutting), canines (tearing), premolars (grinding), molars (crushing), wisdom teeth (annoying) Epiglottis A flap of soft tissue that covers the entrance to the trachea to prevent food from entering the lungs
Esophagus Connects mouth to stomach Composed of smooth muscle (contracts in rhythmic wavelike fashion = peristalsis) Peristalsis (not gravity!) moves bolus down esophagus Peristalsis
2. DIGESTION Stomach site of food storage and initial protein digestion sphincters: constrictor muscles that surround a tube-like structure regulate movement of food to and from the stomach can store about 1.5 L of food
Stomach Millions of cells secrete various stomach fluids, called gastric fluids/juice, that aid digestion. Approximately 500 ml of these fluids are produced following a large meal. Gastric fluid includes mucus, hydrochloric acid (HCl), and pepsinogens. Chyme = a semi-liquid mixture of food and gastric juice Gastric Juices Mucus provides a protective coating. Hydrochloric acid kills many harmful substances that are ingested with food. Also converts pepsinogen into its active form, pepsin (a safety mechanism to prevent stomach from digesting itself!) A VERY strong acid (ph = 3) Pepsin is a protein-digesting enzyme. Breaks the long amino acid chains in proteins into shorter chains, called polypeptides
Stomach Ulcers One specie of bacteria, Helicobacter pylori (H. pylori) is able to survive in the stomach by secreting acid-neutralizing enzymes They prevent mucus-producing cells from producing enough mucus Exposed stomach lining = ulcer Successfully eliminated with antibiotics 3. Absorption of Materials
Importance of absorption Chemical digestion in the stomach and small intestine turned food into nutrients (amino acids, simple sugars, lipids) These nutrients must be absorbed through the lining of the small intestine into the circulatory system so they can be delivered to all cells of the body Absorption in the large intestine also recovers water, minerals, and salts for re-use by the body Small Intestine 2.5cm diameter, 7m in length (in humans) 3 sections: Duodenum Where MOST digestion takes place Jejunum Ileum
Pancreas Secretes enzymes for digestion Lipase = a fat-digesting enzyme Trypsin = a protein-digesting enzyme AND hormones that regulate absorption and storage of glucose Chyme entering small intestine is very acidic, pancreas releases bicarbonate ions to neutralize the acid Goes from ph 3 to ph 9 Macromolecules Broken Down Carbohydrates glucose Proteins amino acids Fats fatty acids and glycerol Smaller sizes allows for absorption and transport
Absorption in the small intestine Ileum and jejunum are the primary sites of nutrient absorption Long finger-like folds/tubes (villi, singular: villus) project from the lining of the small intestine to increase the surface area for absorption Microvilli project from the cell membranes of the villi to increase the surface area even more Villi
Microvillia Absorption in the small intestine Intestinal Villus Microvilli lining the cells of the villus
Absorption in the small intestine Villi/microvilli increase the surface area of the small intestine 10-30x More surface area = more efficient absorption All of these folds give the small intestine a surface area close to that of a tennis court Celiac Disease Inherited disorder of the small intestine Severe immune response to gluten (a protein found in wheat) Ultimately, the villi become inflamed and damaged/blunted which affects their absorptive capabilities Diagnosis: fat/oil droplets present in feces that passed through the small intestine instead of being absorbed Can be controlled with a glutenfree diet Damaged/blunted villi due to celiac disease
Liver and Gall Bladder All blood travelling through the intestines goes directly to the liver before return to the heart Liver involved in the removal and breakdown of toxins (such as alcohol) Liver produces and secretes bile Bile = a substance that emulsifies fats for faster breakdown Gall bladder stores bile until food enters the duodenum
Absorption in the Large Intestine/Colon 7.6cm diameter, 1.5m in length Colon: largest part of the large intestine Water, salts, minerals are re-absorbed here Without this recovery of water, animals could not survive on dry land Nearly 8 L of fluid enters the large intestine only about 0.1 L or so comes out as solid waste Large Intestine - Rectum The lower 20 cm of the large intestine where feces are stored It may take 4 to 72 hours for the undigested material to pass through the large intestine, depending on the types and volume of food eaten
Egestion Inedible components of food such as Cellulose (aka fibre): plant structural carbohydrate that we cannot digest Provides bulk which is sensed by nerves in the colon wall = bowel movement Less fibre less bowel movements toxins spend more time in the body possible link to colon cancer Eat lots of fiber!
Egestion The removal of waste food materials from the body Feces = the undigested material that is eliminated as waste from the body If too much water absorbed = constipation If too little water absorbed = diarrhea Endoscopes endoscope: an instrument to view the interior of the body
Endoscopy Nausea, Vomiting and Diarrhea cha cha cha? Vomiting is a protective mechanisms for removing toxins or foreign substances from the body A strong muscular contraction that forces the contents of the stomach up through the esophagus and out through the mouth (and sometimes the nose)
Causes of Nausea and Vomiting Category of Condition Examples Inner ear Motion sickness Drugs Chemotherapy Alcohol Infection Bacterial, such as food poisoning Viral, such as stomach flu Brain Meningitis Tumours Injury Concussion Hemorrhage Diseases Cancer Ulcers Diarrhea A protective mechanism Inadequate absorption of water in the colon A very common condition, most people experience it 3-4 times a year Usually caused by an infection (bacteria, viruses, or parasites) Kills about 2 million children worldwide each year