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Transcript
Chapter 41 Animal Nutrition Type Producer Also Called Autotroph self Description • energy • gets energy from nonliving resources (like the sun) gets energy from self. Type Also Called Consumer Heterotroph different energy Description • • gets energy by eating other organisms gets energy from a different source. Overview: The Need to Feed • Every meal reminds us that we are heterotrophs, dependent on a regular supply of food • In general, animals fall into these categories: – Herbivores eat mainly autotrophs (plants and algae) – Carnivores eat other animals – Omnivores regularly consume animals as well as plants or algal matter – Detritivores eat dead organic material (... FBI) • An adequate diet must satisfy three needs: – Fuel for all cellular work – Organic raw materials for biosynthesis – Essential nutrients, substances that the animal cannot make for itself • Main feeding mechanisms: suspension (filter) feeding, substrate feeding, fluid feeding, bulk feeding LE 41-2a Baleen LE 41-2b Caterpillar Feces Concept 41.2: An animal’s diet must supply carbon skeletons and essential nutrients • An animal must obtain carbon skeletons from its food to build complex molecules • Besides fuel and carbon skeletons, a diet must supply essential nutrients in preassembled form • A malnourished animal is missing one or more essential nutrients in its diet • Herbivores may suffer mineral deficiencies if they graze on plants in soil lacking key minerals • Malnutrition is much more common than undernutrition in human populations Essential Amino Acids • Animals require 20 amino acids and can synthesize about half from molecules in their diet • The remaining amino acids, the essential amino acids, must be obtained from food in preassembled form • A diet that provides insufficient essential amino acids causes malnutrition called protein deficiency • Most plant proteins are incomplete in amino acid makeup • Individuals who eat only plant proteins need to eat a variety to get all essential amino acids LE 41-10 Essential amino acids for adults Methionine Valine Threonine Phenylalanine Leucine Corn (maize) and other grains Isoleucine Tryptophan Lysine Beans and other legumes • Some animals have adaptations that help them through periods when their bodies demand extraordinary amounts of protein Essential Fatty Acids • Animals can synthesize most of the fatty acids they need • The essential fatty acids are certain unsaturated fatty acids • Deficiencies in fatty acids are rare Vitamins • Vitamins are organic molecules required in the diet in small amounts • 13 vitamins essential to humans have been identified • Vitamins are grouped into two categories: – fat-soluble – water-soluble Minerals • Minerals are simple inorganic nutrients, usually required in small amounts Concept 41.3: The main stages of food processing are ingestion, digestion, absorption, and elimination • Ingestion is the act of eating • Digestion is the process of breaking food down into molecules small enough to absorb • Absorption is uptake of nutrients by body cells • Elimination is the passage of undigested material out of the digestive compartment LE 41-12 Small molecules Pieces of food Mechanical digestion Chemical digestion Nutrient (enzymatic hydrolysis) molecules enter body cells Undigested material Food INGESTION DIGESTION ABSORPTION ELIMINATION Digestive Compartments • Most animals process food in specialized compartments • These compartments reduce risk of self-digestion Intracellular Digestion • In intracellular digestion, food particles are engulfed by endocytosis and digested within food vacuoles Extracellular Digestion • 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 – Mouth – stomach • Animals with simple body plans have a gastrovascular cavity that functions in both digestion and distribution of nutrients Video: Hydra Eating Daphnia LE 41-13 Mouth Tentacles Gastrovascular Food cavity Epidermis Mesoglea Gastrodermis Nutritive muscular cells Flagella Gland cells Food vacuoles Mesoglea • 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 LE 41-14a Crop Gizzard Intestine Esophagus Pharynx Anus Mouth Typhlosole Lumen of intestine Earthworm LE 41-14b Foregut Midgut Esophagus Hindgut Rectum Anus Crop Mouth Grasshopper Gastric ceca LE 41-14c Esophagus Stomach Gizzard Intestine Mouth Crop Anus Bird Concept 41.4: Each organ of the mammalian digestive system has specialized food-processing functions • 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 LE 41-15a Cardiac orifice Tongue Salivary glands Oral cavity Parotid gland Sublingual gland Pharynx Esophagus Submandibular gland Pyloric sphincter Liver Stomach Ascending portion of large intestine Gallbladder Pancreas Ileum of small intestine Small intestine Large intestine Rectum Anus Appendix Cecum Duodenum of small intestine LE 41-15b Salivary glands Mouth Esophagus Gallbladder Liver Pancreas Stomach Small intestines Large intestines Rectum Anus A schematic diagram of the human digestive system The Oral Cavity, Pharynx, and Esophagus • In the oral cavity, food is lubricated and digestion begins • Teeth chew food into smaller particles that are exposed to salivary amylase, initiating breakdown of glucose polymers • The region we call our throat is the pharynx, a junction that opens to both the esophagus and the windpipe (trachea) • The esophagus pushes food from the pharynx down to the stomach by peristalsis LE 41-16_3 Bolus of food Tongue Epiglottis up Epiglottis up Pharynx Glottis Larynx Trachea Glottis down and open Esophageal sphincter contracted Epiglottis down Esophagus Glottis up and closed Esophageal sphincter relaxed Esophageal sphincter contracted Relaxed muscles To lungs To stomach Contracted muscles Relaxed muscles Stomach The Stomach • The stomach stores food and secretes gastric juice, which converts a meal to acid chyme • Gastric juice is made up of hydrochloric acid and the enzyme pepsin • Pepsin is secreted as inactive pepsinogen; pepsin is activated when mixed with hydrochloric acid in the stomach – Digestion of proteins • Mucus protects the stomach lining from gastric juice LE 41-17 Esophagus Cardiac orifice Stomach 5 µm Pyloric sphincter Interior surface of stomach Small intestine Folds of epithelial tissue Epithelium Pepsinogen Gastric gland Pepsin (active enzyme) HCl Pepsinogen and HCl are secreted into the lumen of the stomach. HCl converts pepsinogen to pepsin. Pepsin then activates more pepsinogen, starting a chain reaction. Pepsin begins the chemical digestion of proteins. Mucus cells Chief cells Parietal cells Chief cell Parietal cell • Gastric ulcers, lesions in the lining, are caused mainly by the bacterium Helicobacter pylori LE 41-18 Bacteria 1 µm Mucus layer of stomach The Small Intestine • The small intestine is the longest section of the alimentary canal • It is the major organ of digestion and absorption Enzymatic Action in the Small Intestine • The first portion of the small intestine is the duodenum, where acid chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and the small intestine itself LE 41-19 Liver Bile Gallbladder Stomach Acid chyme Intestinal juice Pancreas Duodenum of small intestine • The pancreas produces proteases, protein-digesting enzymes that are activated after entering the duodenum LE 41-20 Pancreas Membrane-bound enteropeptidase Inactive trypsinogen Other inactive proteases Lumen of duodenum Trypsin Active proteases • The liver produces bile, which aids in digestion and absorption of fats • The epithelial lining of the duodenum, called the brush border, produces several digestive enzymes • Enzymatic digestion is completed as peristalsis moves the chyme and digestive juices along the small intestine LE 41-21 Carbohydrate digestion Oral cavity, Polysaccharides Disaccharides pharynx, Salivary amylase esophagus Smaller polysaccharides, maltose Stomach Lumen of small intestine Polysaccharides Pancreatic amylases Maltose and other disaccharides Epithelium of small intestine (brush border) Disaccharidases Monosaccharides Protein digestion Nucleic acid digestion Fat digestion LE 41-21 Carbohydrate digestion Protein digestion Nucleic acid digestion Fat digestion Oral cavity, Polysaccharides Disaccharides pharynx, Salivary amylase esophagus Smaller polysaccharides, maltose Stomach Lumen of small intestine Polysaccharides Fat globules Pancreatic amylases Bile salts Maltose and other disaccharides Fat droplets Pancreatic lipase Glycerol, fatty acids, glycerides Epithelium of small intestine (brush border) Disaccharidases Monosaccharides • Each villus contains a network of blood vessels and a small lymphatic vessel called a lacteal Fat globule Bile salts Fat droplets coated with bile salts Micelles made up of fatty acids, monoglycerides, and bile salts Epithelium of small intestine Epithelium of lacteal Lacteal Amino acids and sugars pass through the epithelium of the small intestine and enter the bloodstream After glycerol and fatty acids are absorbed by epithelial cells, they are recombined into fats within these cells These fats are mixed with cholesterol and coated with protein, forming molecules called chylomicrons, which are transported into lacteals LE 41-21 Carbohydrate digestion Protein digestion Nucleic acid digestion Fat digestion Oral cavity, Polysaccharides Disaccharides pharynx, Salivary amylase esophagus Smaller polysaccharides, maltose Stomach Proteins Pepsin Small polypeptides Lumen of small intestine Polysaccharides Polypeptides Pancreatic amylases Pancreatic trypsin and chymotrypsin Maltose and other disaccharides DNA, RNA Pancreatic nucleases Nucleotides Pancreatic carboxypeptidase Pancreatic lipase Amino acids Disaccharidases Monosaccharides Bile salts Fat droplets Smaller polypeptides Epithelium of small intestine (brush border) Fat globules Glycerol, fatty acids, glycerides Small peptides Nucleotidases Dipeptidases, carboxypeptidase, and aminopeptidase Nucleosides Amino acids Nucleosidases and phosphatases Nitrogenous bases, sugars, phosphates Absorption of Nutrients • The small intestine has a huge surface area, due to villi and microvilli that are exposed to the intestinal lumen • The enormous microvillar surface greatly increases the rate of nutrient absorption LE 41-23 Key Vein carrying blood to hepatic portal vessel Nutrient absorption Microvilli (brush border) Blood capillaries Epithelial cells Muscle layers Epithelial cells Large circular folds Villi Lacteal Villi Intestinal wall Lymph vessel The Large Intestine • The large intestine, or colon, is connected to the small intestine • Its major function is to recover water that has entered the alimentary canal • Wastes of the digestive tract, the feces, become more solid as they move through the colon • Feces pass through the rectum and exit via the anus • The colon houses strains of the bacterium Escherichia coli, some of which produce vitamins Concept 41.5: Evolutionary adaptations of vertebrate digestive systems are often associated with diet • Digestive systems of vertebrates are variations on a common plan • However, there are intriguing adaptations, often related to diet Some Dental Adaptations • Dentition, an animal’s assortment of teeth, is one example of structural variation reflecting diet • Mammals have specialized dentition that best enables them to ingest their usual diet • Herbivores Incisors Molars Canines Premolars Carnivore Herbivore Omnivore • have large flat teeth for grinding the tough cellulose of plants •Carnivores • Have sharp teeth in order to catch prey Stomach and Intestinal Adaptations • Herbivores generally have longer alimentary canals than carnivores, reflecting the longer time needed to digest vegetation Small intestine Stomach Small intestine Cecum Colon (large intestine) Carnivore Herbivore Symbiotic Adaptations • Many herbivores have fermentation chambers, where symbiotic microorganisms digest cellulose • The most elaborate adaptations for an herbivorous diet have evolved in the animals called ruminants LE 41-28 Intestine Rumen Reticulum Esophagus Abomasum Omasum Concept 41.1: Homeostatic mechanisms manage an animal’s energy budget • Nearly all of an animal’s ATP generation is based on oxidation of energy-rich molecules: carbohydrates, proteins, and fats Glucose Regulation as an Example of Homeostasis • Animals store excess calories as glycogen in the liver and muscles and as fat • Glucose is a major fuel for cells • Hormones regulate glucose metabolism • When fewer calories are taken in than are expended, fuel is taken from storage and oxidized LE 41-3 STIMULUS: Blood glucose level rises after eating. Homeostasis: 90 mg glucose/ 100 mL blood STIMULUS: Blood glucose level drops below set point. Other functions of the liver • Controls concentration of amino acids – Amino acids get deaminated then stored as fats – Uses some amino acids to make proteins of the blood (albumin) • Destroys old red blood cells: recycles iron • Makes bile: breaks down fats into small drops Caloric Imbalance • Undernourishment occurs in animals when their diets are chronically deficient in calories • Overnourishment, or obesity, results from excessive intake, with excess stored as fat LE 41-4 100 µm Obesity as a Human Health Problem • The World Health Organization now recognizes obesity as a major global health problem • Obesity contributes to a number of health problems, including diabetes, cardiovascular disease, and colon and breast cancer • Researchers have discovered several of the mechanisms that help regulate body weight • Over the long term, homeostatic mechanisms are feedback circuits that control the body’s storage and metabolism of fat • Hormones regulate long-term and short-term appetite by affecting a “satiety center” in the brain LE 41-5 Ghrelin Insulin Leptin PYY • The complexity of weight control in humans is evident from studies of the hormone leptin • Mice that inherit a defect in the gene for leptin become very obese Obesity and Evolution • The problem of maintaining weight partly stems from our evolutionary past, when fat hoarding was a means of survival • A species of birds called petrels become obese as chicks due to the need to consume more calories than they burn • Hormones help coordinate the secretion of digestive juices into the alimentary canal Key Liver Stimulation Enterogastrone Inhibition Gallbladder Gastrin CCK Stomach Pancreas Secretin Duodenum CCK Hormonal Control of Digestion • Refer to notes LE 41-3 STIMULUS: Blood glucose level rises after eating. Homeostasis: 90 mg glucose/ 100 mL blood STIMULUS: Blood glucose level drops below set point.
