Bioenergetics and Digestion

We’ll be discussing Trends and Various Strategies Used by Organisms to Process Food Process of Digestion in Man Disorders of the Human Digestive System

Core Concepts Nutritional requirements Animals are heterotrophs that require food for fuel, carbon skeletons, and essential nutrients. Metabolic rate provides clues to an animal’s bioenergetic strategy.  Evolutionary adaptations of feeding mechanisms and digestive systems Diverse feeding adaptations have evolved among animals. Structural adaptations of digestive systems are often associated with diet. Symbiotic microorganisms help nourish many vertebrates.  Overview of food processing The four main stages of food processing are ingestion, digestion, absorption, and elimination. Digestion occurs in specialized compartments. The oral cavity, pharynx, and esophagus initiate food processing. The stomach stores food and performs preliminary digestion. The small intestine is the major organ of digestion and absorption. Reclaiming water is a major function of the large intestine. Hormones regulate digestion. Nutrition and disorders of the human digestive system A healthful diet provides both fuel and building materials. Nutritional disorders damage health.

Keywords absorption alimentary canal amebocytes anorexia bile bolus brush border bulimia cecum chyme complete digestive tract crop digestion duodenum elimination endocytosis enzyme esophagus essential nutrient extracellular digestion filter feeders gallbladder gastrovascular cavity gizzard heterotroph ileum incomplete digestive tract ingestion intracellular digestion jejunum large intestine liver malnutrition microvilli minerals nutrition obesity pancreas peptic ulcers peristalsis phagocytosis pharynx salivary glands small intestine sphincters stomach undernutrition vesicles villus vitamins

Bioenergetics of an animal Food Fuel C-skeletons essential nutrients ATP resting metabolism activity temperature regulation Excess for biosynthesis 85-90% of energy from food is lost as heat

Metabolic rates Metabolism Resting/ Basal Metabolic Rate (BMR) Anabolism Catabolism Resting/ Basal Metabolic Rate (BMR) energy/unit mass/hr Size and relative metabolic rate are inversely proportional

Do plants have digestive systems? Pitcher plant – Heliamphora nutans Sundew– Drosera capensis Venus fly trap– Dionaea muscipula Carnivorous plants with primitive digestive systems Habitats with N-poor soils Adaptation: occasionally feed on animals Insect traps Glands in trap secrete digestive enzymes Nutrients absorbed by leaves Flypaper trap – Pinguicula gigantea

Evolution of digestion Different types depending on diet and lifestyle All must accomplish Ingestion Digestion Mechanical breakdown Chemical breakdown Absorption Elimination Digestion occurs in specialized compartments

Intracellular digestion (evolved in single-celled protists, retained in simplest animals) Paramecium

Intracellular digestion (Protists, Porifera) SPONGES

Extracellular digestion FUNGI Sedentary heterotrophs living in or on food supply Saprotroph/parasites No internal cavity  release digestive enzymes Image from http://www.aber.ac.uk/fungi/graffeg/decomp/digestion-by-hypha.jpg

Extracellular and intracellular digestion Incomplete digestive system Image from http://www.anselm.edu/homepage/jpitocch/genbio/digesthydra.jpg Extracellular and intracellular digestion Incomplete digestive system CNIDARIANS Hydra gastrovascular

Extracellular and intracellular digestion Incomplete digestive system PLATYHELMINTHES Planaria Extracellular and intracellular digestion Incomplete digestive system

Extracellular digestion Animals with complete digestive systems NEMATODA to VERTEBRATES Earthworms Extracellular digestion Animals with complete digestive systems 20 cm long with ~ 100 segments 1st – mouth Last – anus Eats its way through soil

Feeding adaptations for ingestion Suspension-feeders Deposit-feeders Substrate feeders Fluid feeders Bulk feeders Vertebrate dentition

Comparison of vertebrate digestive systems

Mammalian digestion General plan Organs of the GI tract ACCESSORY DIGESTIVE ORGANS

Comparison of mammalian digestive systems (Diet plays an important role in the length and structure) Esophagus – no sphincter valve, two-way contraction of esophagus muscles Rumen and reticulum – low partition, intermix, main fermentation <synthesis of vitamins and proteins, breakdown of fibrous feeds> vat teeming with microorganisms (before exposing to gastric juices) Omasum – filter pump to sort food (absorption) Abomasum – true stomach (gastric juices)