Lecture 12 BIO 311D 1st Edition Outline of Last Lecture I Evolution of Animal Size and Shape II Hierarchical Organization of Body Plans III Tissues a Epithelial b Connective c Muscle d Nervous Outline of Current Lecture I Stages of Food Processing II Intracellular Extracellular Digestion III Main Stages of Food Processing IV Digestion in the Stomach and Small Intestine V Pancreas Secretions VI Absorption of the Large Intestine Current Lecture Stages of Food Processing Digestion is the process of breaking food down into molecules small enough to absorb Mechanical digestion including chewing increases the surface area of food Chemical digestion splits food into small molecules that can pass through membranes these are used to build larger molecules In chemical digestion the process of enzymatic hydrolysis splits bonds in molecules with the addition of water Absorption is uptake of nutrients by body cells Elimination is the passage of undigested material out of the digestive system Most animals process food in specialized compartments These compartments reduce the risk of an animal digesting its own cells and tissues Intracellular Digestion In intracellular digestion food particles are engulfed by phagocytosis Food vacuoles containing food fuse with lysosomes containing hydrolytic enzymes Example Phagocytosis Extracellular Digestion Organism has a mouth but no anus Enzymes break down food Extracellular digestion is the breakdown of food particles outside of cells It occurs in compartments that are continuous with the outside of the animal s body Animals with simple body plans have a gastrovascular cavity that functions in both digestion and distribution of nutrients The mammalian digestive system consists of an alimentary canal and accecory glands What are the accessory glands A Stomach liver pancreas B Pancreas liver and gallbladder C Pancreas small intestine and bile salts D Spleen liver and kidneys In humans the first opportunity for ingested food to undergo enzymatic hydrolysis is in the A B C D E Mouth Stomach Liver Small intestine Large intestine Main Stages of Food Processing More complex animals have a digestive tube with two openings a mouth and an anus This digestive tube is called a complete digestive tract or an alimentary canal It can have specialized regions that carry out digestion and absorption in a stepwise fashion The mammalian digestive system consists of an alimentary canal and accessory glands that secrete digestive juices through ducts Mammalian accessory glands are the salivary glands the pancreas the liver and the gallbladder Food is pushed along by peristalsis rhythmic contractions of muscles in the wall of the canal Valves called sphincters regulate the movement of material between compartments The first stage of digestion is mechanical and takes place in the oral cavity Salivary glands deliver saliva to lubricate food Teeth chew food into smaller particles that are exposed to salivary amylase initiating breakdown of glucose polymers Saliva also contains mucus a viscous mixture of water salts cells and glycoproteins The tongue shapes food into a bolus and provides help with swallowing The throat or pharynx is the junction that opens to both the esophagus and the trachea The esophagus connects to the stomach The trachea windpipe leads to the lungs The esophagus conducts food from the pharynx down to the stomach by peristalsis Swallowing causes the epiglottis to block entry to the trachea and the bolus is guided by the larynx the upper part of the respiratory tract Coughing occurs when the swallowing reflex fails and food or liquids reach the windpipe Stomach acid A Splits polypetides into amino acids B Splits fats into fatty acids and glycerol C Activates pepsinogen into pepsin D Initiates the development of stomach ulcers E Inhibits the production of epithelial cells Digestion in the Stomach The stomach stores food and secretes gastric juice which converts a meal to acid chyme Gastric juice has a low pH of about 2 which kills bacteria and denatures proteins Gastric juice is made up of hydrochloric acid HCl and pepsin Pepsin is a protease or protein digesting enzyme that cleaves proteins into smaller peptides Parietal cells secrete hydrogen and chloride ions separately into the lumen cavity of the stomach Chief cells secrete inactive pepsinogen which is activated to pepsin when mixed with hydrochloric acid in the stomach Mucus protects the stomach lining from gastric juice Gastric ulcers lesions in the lining are caused mainly by the bacterium Helicobacter pylori Coordinated contraction and relaxation of stomach muscle churn the stomach s contents Sphincters prevent chyme from entering the esophagus and regulate its entry into the small intestine Digestion in the Small Intestine The small intestine is the longest section of the alimentary canal It is the major organ of digestion and absorption The first portion of the small intestine is the duodenum where chyme from the stomach mixes with digestive juices from the pancreas liver gallbladder and the small intestine itself Pancreas Secretions The pancreas produces proteases trypsin and chymotrypsin that are activated in the lumen of the duodenum Its solution is alkaline and neutralizes the acidic chyme Bile Product by the Liver In the small intestine bile aids in digestion and absorption of fats Bile is made in the liver and stored in the gallbladder Bile also destroys nonfunctional red blood cells Sections Absorptions of the Small Intestine The epithelial lining of the duodenum produces several digestive enzymes Enzymatic digestion is completed as peristalsis moves the chyme and digestive juices along the small intestine Most digestion occurs in the duodenum the jejunum and ileum function mainly in absorption of nutrients and water The small intestine has a huge surface area due to villi and microvilli that are exposed to the intestinal lumen The enormous microvillar surface creates a brush border that greatly increases the rate of nutrient absorption Transport across the epithelial cells can be passive or active depending on the nutrient The hepatic portal vein carries nutrient rich blood from the capillaries of the villi to the liver then to the heart The liver regulates nutrient distribution interconverts many organic molecules and detoxifies many organic molecules Epithelial cells absorb fatty acids and monoglycerides and recombine them into triglycerides These fats are coated with phospholipids