Chapter 41 Campbell & Reece Digestion Chapter 41 Campbell & Reece
49-1: Nutritional Requirements Cells need: Water Carbohydrates Lipids Proteins Nucleic acids Vitamins-- Study Table 49-1 pg. 980 Minerals - Table 49-2 pg. 981
Nutrition involves the following steps: Ingestion Digestion Absorption Distribution Digestion: the breakdown of ingested food materials into molecules that can be delivered to and utilized by the individual cells. Can be both mechanical and chemical. human anatomy tutorials, labeled with explanations (all systems) link
The “Gut” (Gastrointestinal Tract): Fig.49-2 pg. 983 Made of 4 layers (see pictures on page 985) Mucosa: (innermost) -epithelial, connective, some smooth muscle Submucosa: connective, nerve fibers, blood & lymph vessels Muscularis Externa: muscle tissue (circular & longitudinal) Serosa: outer covering of connective tissue
Peristalsis: coordinated contractions of circular muscles along digestive tract which move food along Sphincters: thickened, heavy bands of muscle along tract that act as valves by contracting (closing) and relaxing (opening) to control of materials
The Oral Cavity: Initial Processing: Mechanical Digestion Tongue - swallowing (microscopic picture) Teeth: “mastication” (chewing) incisors- cutting, clipping canines- tearing, stabbing premolars- "bicuspids" 2 cusps (points) molars- 4 or 5 cusps (for grinding) Other Animals lack teeth, have alternatives: rasping tongue: ex- snails, lamprey, frogs grinding organ (gizzard): ex- birds, earthworms Chemical Digestion (enzymatic hydrolysis): saliva, mucous 3 pairs of salivary glands and buccal glands in jaw: lubricates, softens food Enzyme- salivary amylase for hydrolysis of starch into smaller sugar molecules; slightly alkaline (sodium bicarbonate)
The Pharynx & Esophagus: Swallowing Swallowing: passage of food to the esophagus ----> stomach begins as voluntary action (striated muscles in upper part of esophagus) lower portion involuntary (smooth muscle)= "peristalsis" Esophagus opens into Stomach Abdominal cavity lined with peritonium / organs are suspended by mesentaries (animation)
The Stomach: Storage & Liquefaction …a collapsible, muscular, j-shaped bag with many folds and ridges mucosal lining folds into gastric pits (microscopic picture) lined with mucous-secreting epithelial cells gastric glands secrete HCl and pepsinogen (precurser to pepsin) pH between 1.5 & 2.5 (mucous barrier between acids + stomach lining )- ulcers?
Stomach acids, enzymes HCl: kills bacteria loosens tissues for digestion converts pepsinogen to pepsin Pepsin: breaks down proteins into smaller peptides Semi-liquid mass "Chyme" moves to lower end of stomach => Pyloric Sphincter (takes about 4 hrs.) Rate of leaving stomach = H2O,carbs, proteins, fat, protein/fat combo The three phases of gastric secretion animation
The Small Intestine: Digestion and absorption lined with VILLI ( microscopic fingerlike projections) and tiny microvilli on surface of epithelial cells about 21 feet long (adult), total surface area about 300 m2 Digestion: Duodenum- 1st 25 cm (10 inches) most digestion takes place here; receives several digestive juices/enzymes from ducts leading from ACCESSORY GLANDS (liver pancreas, gall bladder)
Accessory Glands neutralize stomach acids with alkaline secretions produces several enzymes to chemically digest nutrients
The Pancreas Enzymes made here enter the duodenum via the pancreatic duct Amylase: continues starch digestion Starchesdisaccharidesmonosaccharides Trypsin: breaks down proteins amino acids Lipase: hydrolyzes fats
The Liver: an accessory gland Bile- produced by liver stored in gall bladder contains salts (emulsify fats) sodium bicarbonate (neutralize pH to optimum 7 or 8)
Absorption of Nutrients: food is absorbed through epithelial cells of intestinal mucosa into the bloodstream, for distribution to all cells Active Transport: Monosaccharides, Dipeptides, Amino Acids Diffusion: fatty acids Lipids resynthesize into triglycerides, phospholipids (blood & lymph vessels), Cholesterol
The Large Intestine: Water Absorption & Elimination The Large Intestine (colon)continues absorption of water, sodium, and other minerals (which begins in small intestine) E. coli bacteria: makes Vit.K, amino acid synthesis Appendix: vestigial organ (gastric caecum?) Waste: "fecal matter" water, bacteria, dead cells, indigestible matter (cellulose) lubricated with mucus temporary storage in rectum