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Bioenergetics
and Digestion
We’ll be discussing
1. Trends and Various
Strategies Used by
Organisms to Process
FoodFood
2. Process of Digestion in
Man
3. 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.
– Reclaiming water is a major function of the large intestine.
• 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
• essential nutrient
• extracellular digestion
• filter feeders
• gallbladder
• gastrovascular cavity
• gizzard
• heterotroph
� minerals
� nutrition
� obesity
� pancreas
� peptic ulcers
� peristalsis
� phagocytosis
� pharynx
salivary glands• bulimia
• cecum
• chyme
• complete digestive tract
• crop
• digestion
• duodenum
• elimination
• endocytosis
• enzyme
• esophagus
•• ileum
• incomplete digestive tract
• ingestion
• intracellular digestion
• jejunum
• large intestine
• liver
• malnutrition
• microvilli
� salivary glands
� small intestine
� sphincters
� stomach
� undernutrition
� vesicles
� villus
� vitamins
Bioenergetics of an animal
1. Food
• Fuel
• C-skeletons
• essential
nutrients
2. ATP powers resting 2. ATP powers resting
metabolism, activity,
and temperature
regulation
3. Excess calories can
be used for
biosynthesis
4. 85-90% of energy
from food is lost as
heat
Metabolic rates
• Metabolism– Anabolism
– Catabolism
• Resting/ Basal Metabolic Rate Metabolic Rate (BMR)– energy/unit
mass/hr
• Size and relative metabolic rate are inversely proportional
Do plants have digestive systems?
� Carnivorous plants in marshlands have primitive digestive systems
� Habitats with N-
Pitcher plant –Heliamphora nutans
Sundew–Drosera capensis
Venus fly trap–Dionaea muscipula
Insect traps� Habitats with N-poor soils
� Adaptation: occasionally feed on animals
CH2O � Photosynthesis
N+ minerals � insects, etc.
Flypaper trap –Pinguicula gigantea
Insect traps
Glands in trap secrete digestive
enzymes
Nutrients absorbed by
leaves
Evolution of digestion
� Different types depending on diet and lifestyle
� All must accomplish1. Ingestion
2. Digestion2. Digestion� Mechanical breakdown
� Chemical breakdown
3. Absorption
4. Elimination� Digestion occurs in
specialized compartments
Intracellular digestion ( 1 ) (evolved in single-celled protists, retained in simplest animals)
ProtistsParamecium
Endocytosis of food particle
Fusion with lysosomeFusion with lysosome
Digestion by enzymes
Elimination of waste by exocytosis
Intracellular digestion ( 2 ) (evolved in single-celled protists, retained in simplest animals)
SPONGES
Food obtained by filtering microorganisms
from water
Food is phagocytized by choanocytes (collar cells)
and amebocytes
Waste eliminated into water in the sponge
body
Extracellular digestion
( by fungi )
Fungi
• Sedentary heterotrophs
living in or on food supply
• Saprotroph/parasites
• No internal cavity � release • No internal cavity � release
digestive enzymes
Image from http://www.aber.ac.uk/fungi/graffeg/decomp/digestion-by-hypha.jpg
Food outside the body
Enzymatic hydrolysis outside the body
Absorption by cells across the body surface
Extracellular and intracellular digestion1. In animals with incomplete
digestive systems (1)
CnidariansHydra
Food gathered by cnidocytes
and tentacles
Food enters mouth
Food circulated in gastrovascu-
lar cavity
Hydrolytic enzymes
break down food in GVC
Small food particles
endocytizedinto food vacuoles
Waste materials are
eliminated into the GVC,
out mouth
Image from http://www.anselm.edu/homepage/jpitocch/genbio/digesthydra.jpg
Extracellular and intracellular digestion 1. In animals with incomplete digestive systems (2)
PlatyhelminthesPlanaria and tapeworms
Food enters pharynx
Ingestion via mouth
Enters branched GVC
Secretion of digestive enzymes by intestinal cells
Food phagocytized by intestinal cells
Digestion complete within
food vacuole
Waste eliminated through mouthtapeworms intestinal cellsfood vacuolethrough mouth
Extracellular digestion 2. In animals with complete digestive systems
Nematoda to Vertebrates
Earthworms• 20 cm long with ~ 100 segments
– 1st – mouth
– Last – anus
• Eats its way through soil
Food from mouth to muscular pharynx
Travels through esophagus
Digested in stomach: crop and gizzard
Absorbed through long straight intestine
Waste eliminated through anus
Feeding adaptations for ingestion
Suspension-feeders
Deposit-feeders
Substrate feedersfeeders feeders feeders
Fluid feeders Bulk feedersVertebrate dentition
Comparison of vertebrate digestive systems
Mammalian digestion General plan
Accessory
digestive organs
Organs of the GI tract
digestive organs
Comparison of mammalian digestive systems(Diet plays an important role in the length and structure)