Transcript Digestion
Digestion & Nutrition chapter 50 We need to eat! • Since we as animals cannot produce our own food, we must EAT it. • Classifying organisms by what they eat… – Herbivores: eat autotrophs – Carnivores: eat other animals – Omnivores: eat both autotrophs and animals – What are we?? Classifying Animals by HOW They Get Their Food • Suspension feeders: – Sift small food particles from the water – Examples: clams, oysters, whales • Substrate feeders: – Live on (or in) their food source – Example: leaf miners, eat their way through leaves Classifying Animals by HOW They Get Their Food • Fluid-feeders – Suck nutrient-rich fluids from a living host – Example: mosquitoes, hummingbirds • Bulk-feeders – Eat relatively large pieces of food – That’s us! The 4 Stages of Food Processing 1. Ingestion The act of eating 2. Digestion The process of breaking down food into molecules small enough for the body to absorb (physical & chemical) This involves hydrolysis, which you should know well PolymersMonomers This has to occur in a specialized compartment… why?? The 4 Stages of Food Processing 3. Absorption – The animal’s cells absorb the small molecules broken down during digestion – Only monomers (monosaccharides, amino acids, glycerol & fatty acids) can be absorbed 4. Elimination – Undigested material passes out of the digestive compartment Gastrovascular Cavities • Gastrovascular cavities are the digestive systems in simple animals (Cnidarians, Platyhelminthes) • Incomplete Digestive Systemone opening Digestion in Alimentary Canals • Complex animals – An “Entrance” and an “Exit” – This is a complete digestive system. • Mouth = site of ingestion • Anus = site of elimination • What phyla have complete digestive tracts? • (Nematoda, Mollusca, Annelida, Arthropoda, Echinodermata, Chordata) Alimentary Canals/Complete Digestive System The Mammalian Digestive System The Mammalian Digestive System • Consists of: – – – – – – Oral cavity (mouth) Pharynx Esophagus Stomach Small Intestine Large Intestine • Food moves through the digestive system by peristalsis, rhythmic waves of contraction by the smooth muscles Accessory Organs • Salivary glands – Secrete saliva • Liver – Secretes bile • Gallbladder – Stores and concentrates bile • Pancreas – Secretes digestive enzymes Oral Cavity • The mouth • Chewing cuts, smashes, and grinds food to facilitate swallowing • Saliva is secreted into the mouth by the salivary glands – Saliva contains salivary amylase – This enzyme breaks down starch and glycogen into smaller pieces Specialized Teeth • Structure of teeth reflects feeding behavior • Antelope brush teeth against dirt as they eat; wear down crown. ANTELOPE MOLAR HUMAN MOLAR crown crown root root Pharynx • The pharynx is the intersection that leads to both the esophagus (digestive system) and the trachea (respiratory system) • The epiglottis makes sure that food doesn’t enter the trachea Esophagus • The esophagus carries food from the pharynx into the stomach • Where is your stomach? Stomach • Our stomachs are stretchy – they expand to fit our food! • The inside of the stomach contains gastric juice, which has a pH of about 2 – HCl – kills most bacteria swallowed with food -activates the enzyme pepsinogen – Pepsin (active form) – breaks down proteins to smaller polypeptides – Why must pepsinogen be secreted in an inactive form????????? Stomach • The pyloric sphincter closes off the stomach from the small intestine, the next stop on our tour • The pyloric sphincter lets in small amounts of acid chyme at a time Small Intestine • Most digestion and absorption occurs in the small intestine • In humans, the small intestine is about 6 meters long – It’s called the “small intestine” because it has a small diameter Small Intestine • First section of the small intestine is the duodenum responsible for digestion – Acid chyme enters from the stomach – Pancreatic enzymes and bile from the liver are mixed with the food here. Pancreatic Enzymes • Secreted into duodenum • Pancreatic amylase- breaks down polysaccharides to disaccharides • Trypsin and chymotrypsin- breaks down proteins to smaller polypeptides • Carboxypeptidase- breaks down proteins to amino acids. • Lipase-breaks down lipids to fatty acids and glycerol • Pancreatic nucleases-breaks down DNA & RNA to nucleotides Fat Digestion • Liver produces bile • Bile is stored in gallbladder, then secreted into duodenum • Bile emulsifies fats; breaks them into small droplets • This gives enzymes a greater surface area to work on Small Intestine • The digestion occurs in the duodenum • Disaccharidases- break disaccharides down into monosaccharides. • Aminopeptidases-break polypeptides down into amino acids. • Intestinal nucleases-break down nucleotides into nucleotide bases and monosaccharides. • The absorption of nutrients occurs in the jejunum and ileum (sections 2 & 3 of small intestine) Small Intestine • The jejunum and ileum have a brush border – The jejunum and ileum have villi (that look like fingers) and microvilli. WHY?? – This gives them more surface area, which facilitates absorption of nutrients • Classic example of structure & function (form follows function)! The Small Intestine Absorption of Nutrients • What diffuses where? • All nutrients except glycerol & fatty acids diffuse directly into capillaries. • Glycerol & Fatty Acids (from fats) diffuse into LACTEALS (part of lymphatic system) and eventually dump into the circulatory system at ducts under the clavicles. INTESTINAL LUMEN Absorption Mechanisms carbohydrates monosaccharides Monosaccharides & proteins amino acids are actively transported across plasma EPITHELIAL CELL membrane of epithelial cells, then from cell into internal environment Figure 41.11 Page 734 INTERNAL ENVIRONMENT amino acids Fat Absorption bile salts bile salts + micelles fat globules (triglycerides) emulsification droplets fatty acids, monoglycerides triglycerides + proteins EPITHELIAL CELL chylomicrons Figure 41.11 Page 734 INTERNAL ENVIRONMENT Hormones and Digestion • Gastrin –secreted by stomach lining; causes acid secretion. • Secretin- causes pancreas to secrete bicarbonate • Cholecystokinin (CCK)-controls secretion of pancreatic enzymes & bile release from gall bladder • GIP (glucose insulinotropic peptide)-causes cells to take in more glucose by stimulating insulin secretion Large Intestine (Colon) • The major function of the colon is to reabsorb water • The wastes of the digestive tracts are called feces, and they become more solid as they are moved along the colon – If it moves through too quickly, not enough water is reabsorbed diarrhea – If it moves through too slowly, too much water is reabsorbed constipation • The waste is stored in the rectum until it can be eliminated through the anus • Fecies are not considered “excretion.” Why not? Evolutionary Adaptations • Evolutionary adaptations of the digestive system exist among animals, primarily based on their diet • Herbivores have less specialized teeth than do carnivores • Herbivores have longer alimentary canals than carnivores…why?? Evolutionary Adaptations The Mammalian Digestive System Food Pyramid added fats and simple sugars milk, yogurt, cheese group fruit group bread, cereal, rice, pasta group legume, nut, poultry, fish, meat group vegetable group Carbohydrates • Body’s main energy source • Foods high in complex carbohydrates are usually high in fiber; promote colon health • Simple sugars lack fiber as well as minerals and vitamins of whole foods; intake should be minimized • 4 Cal/g Proteins • 20 Total Amino Acids • 8 Essential Amino Acids (Body can’t make these, so they must be ingested in foods) • Plant proteins are incomplete; must be combined to get all 8 essential a. acids. • 4 Cal/g Lipids • Most fats can be synthesized • Essential fatty acids must be obtained from food • Fats should be about 30 percent of diet • Excess saturated fats can raise cholesterol level and contribute to heart disease • 9 Cal/g • So why do we want to cut lipids if we want to lose weight? Dietary Essentials • Vitamins (Coenzymes: helps enzymes function) – Essential organic substances • Minerals (Cofactors: help enzymes function) – Essential inorganic substances