Fuel Storage Glucose is major fuel Stored in the liver, and excess is stored as fat.Stored in the liver, and excess is stored as fat. Diet needs essential nutrients in addition to fuel

Feeding Mechanisms Herbivores Carnivores Omnivores Suspension feeders Substrate feeders Fluid feeders Bulk feeders

Four stages of Food Processing 1.Ingestion 2.Digestion (enzymatic hydrolysis) 3.Absorption 4.Elimination

Intracellular Digestion Lysosomes fuse with food vacuoles Digestion occurs within the cell Sponges only digest food intracellularly

Extracellular Digestion Breakdown of food outside of cells Gastrovascular cavities serve as digestive sacs Enzymes in cavity begin extracellular digestion After absorption, digestion is completed intracellularlyAfter absorption, digestion is completed intracellularly Animals with alimentary canals organize digestion in stepwise fashionAnimals with alimentary canals organize digestion in stepwise fashion

Mammalian Digestion Peristalsis- smooth muscle contraction, moves food along digestive tract Sphincters regulate passage of food Accessory glands: –Salivary glands –Pancreas –Liver –Gallbladder

Hormonal regulation Many hormones regulate digestion Gastrin Enterogasterones: –CCKCCK –SecretinSecretin –Other enterogasteronesOther enterogasterones

Absorption Very little is absorbed from stomach and large intestine Most absorption is from SI Large SA of microvilli enhance absorption capacity Capillaries from villi converge into hepatic portal vein Cecum is an extension of LI E. coli live in LI and generate gas and vitamins Water is reabsorbed from SI and LI Diarrhea and constipation result from abnormal water reabsorption

Hepatic Portal System