Chapter 45 & 46 Digestive System Key Concepts Animal nutrition general principles of digestion and absorption of food overview of vertebrate digestive systems mechanisms of digestion and absorption in vertebrates Intro to nutrition nutrient any substance taken in by an organism that is needed for: survival growth development tissue repair or reproduction nutrition process of consuming and using food for nutrients animals receive nutrients by consuming food Dietary categories basic similarities in organ system function lead to similarities in nutritional requirements different animal physiologies can have different nutrient demands   Herbivores eat only plants digestive system contains micro-organisms that help digest cellulose Carnivores eat only animal flesh or fluid  Omnivores eat both Animals are heterotrophic Heterotrophs ingest feeders cannot manufacture more food require already synthesized organic compounds of plants of other animals to supply materials survival maintenance growth reproduction Gut Tracts Two types Blind Gut no cavity between gut and body wall one opening primitive form tube-within-a-tube flow through digestive tube body cavity between git and body wall separate opening (mostly) Digestion the breakdown of large molecules into smaller ones Digestive enzymes (hydrolases) carbohydrases proteases lipases nucleases Food processing in animals Occurs in Five phases Ingestion food is taken into the body and moves into a digestive digestion food is broken down into smaller molecules chemical and mechanical transport absorption ions, water, and small molecules are transported into the circulatory system egestion undigested materials and other waste are passed from the body elimination or exceretion Alimentary canal digestive tract or tube Gastrointestinal tract Five regions of food processing Single tube with opening at each end contains smooth muscles in walls lined with epithelial cells synthesize and secrete digestive enzymes secrete hormones transport digestive materials several specialized regions different structures for different processes storage area Structure of GI Tract some general structure from midpoint of esophagus, to the anus or cloaca lumen lined by epithelial and glandular cells  secretory cells release a protective layer of mucus other cells release hormones glands release enzymes, acids, water, and ions Epithelial cells linked by tight junctions and surrounded by layers of tissue made of smooth muscle, neurons, connective tissues, and blood vessels neurons activated by sight and smell of food and presence of food in tract Region of Reception Buccal cavity mouth and accessory structures ingestion site and digestion site chemical and mechanical jaws, teeth, cheek muscles, tongue, and salivary glands (saliva) Pharynx back of mouth cavity point that respiratory and digestive system cross paths Region of Conduction Esophagus tube carrying materials from mouth cavity to the rest of the alimentary canal forces/pushes good down conducts food from pharynx to stomach Peristalsis rhythmic wave-like contractions which propel food forward in the GI tract No new digestion here only chemical continuation from buccal cavity Region of digestion and storage Stomach (mostly) saclike organ evolved for storing food muscular nature helps break up food partial protein digestion regulates rate of emptying into small intestine Secretions hydrochloric acid kills microbes dissolves particulate matter secreted by parietal cells Pepsinogen converted to pepsin to begin protein digestion secreted by Chief cells Epithelium coated with an alkaline mucus carbohydrate digestion continues from mouth little lipid digestion happens lumen (cavity) stomach pepsinogen + HCL -> pepsin (for protein breakdown) Region of terminal digestion and absorption Small intestine near