资源描述
,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,Digestion and Nutrition,Obtaining Energy,All organisms require energy to maintain their complex structure.,The ultimate source of energy is the sun.,Green plants utilize energy in sunlight to make glucose.,Autotrophs,(,phototrophs,),A few autotrophs are,chemotrophs, gaining energy from inorganic chemical reactions.,Animals are Heterotrophs!,Animals are,heterotrophs, depending on other organisms for food.,Animals fall into one of three dietary categories:,Herbivores,eat mainly autotrophs (plants and algae).,Carnivores,eat other animals.,Omnivores,regularly consume animals as well as plants or algal matter.,Saprophagous,animals feed on decaying organic matter.,Why We Eat,Regardless of what an animal eats, an adequate diet must satisfy three nutritional needs:,Fuel for all cellular work.,The organic raw materials for biosynthesis.,Essential nutrients, substances such as vitamins that the animal cannot make for itself.,Feeding Mechanisms,Very few animals absorb nutrients directly from the environment.,Exceptions include parasites that absorb nutrients that have been digested by the host,：,e.g.,，,Protozoan parasites,Blood parasites,Tapeworms,（绦虫,无口及肠）,Feeding Mechanisms Particulate Matter,（颗粒物质）,The upper portion of lakes and oceans contains very small animals and plants (,plankton,浮游生物,) that drift with the water currents.,Along with plankton, there is also organic debris floating in the water column and mixed in with the sediment,(,沉积物,),.,Many organisms feed on this particulate matter.,Feeding Mechanisms Particulate Matter,Feeding Mechanisms,Fluid feeders,may bite and rasp,(,锉,),at host tissues and suck fluid (such as blood).Many have specialized, tubelike mouthparts.,Feeding Mechanisms,Herbivorous animals have evolved special devices for crushing and cutting plant material.,Snails have a radula,(,齿舌,),for scraping algae or plant material.,Insects have grinding & cutting mandibles,(,大颚,) .,Mammals have wide corrugated,(,起皱褶的,) molars for grinding.,Feeding Mechanisms,Predators have evolved a variety of ways to capture, hold, and swallow prey.,Many swallow food items whole.,Some have specialized teeth, beaks, or tooth-like structures.,Some have highly elastic jaws and distensible stomachs to accommodate large meals.,Feeding Mechanisms,Only mammals can actually chew their food.,Mammals have teeth that are specialized for different functions.,Incisors, biting, cutting.,Canines, seizing, piercing, tearing.,Premolars,&,molars, grinding and crushing.,The Main Stages of Food Processing,Ingestion,is the act of eating.,Digestion,is the process of breaking food down into molecules small enough to absorb.,Involves enzymatic hydrolysis of polymers into their monomers.,The Main Stages of Food Processing,Absorption,is the uptake of nutrients by body cells.,Elimination,occurs as undigested material passes out of the digestive system.,Intracellular Digestion,In,intracellular digestion, food particles are engulfed by,endocytosis,and digested within,food vacuoles,.,Protozoa, sponges.,Extracellular Digestion,Extracellular digestion,is the breakdown of food particles outside cells.,Digestion occurs in the alimentary canal(,消化道,).,Cells lining the lumen(,腔,) of the alimentary canal are specialized for secreting enzymes or absorbing nutrients.,Extracellular Digestion,Radiates, flatworms, & ribbon worms practice both intracellular and extracellular digestion.,Extracellular digestion became emphasized with the appearance of a complete digestive tract.,Digestion is almost entirely extracellular in arthropods and vertebrates.,Digestive Systems,Animals with simple body plans have a gastrovascular cavity that functions in both digestion and distribution of nutrients.,Digestive Systems,Animals with a more complex body plan have a digestive tube with two openings, a mouth and an anus.,This digestive tube is called a,complete digestive tract,or an alimentary canal.,Digestive Systems,The digestive tube can be organized into specialized regions that carry out digestion and nutrient absorption in a stepwise fashion.,食道,砂囊,嗉囊,盲道,胃盲囊,直肠,腺胃和肌胃（砂囊）,Mammalian Digestive System,The mammalian digestive system consists of the,alimentary canal,and various accessory,glands,that secrete digestive juices through ducts.,腮腺，舌下腺及颌下腺,i,leum,回肠,盲肠,阑尾,十二指肠,贲门,幽门,Digestive Enzymes,Enzymes,are essential in the breakdown of food into small, absorbable units.,Digestive enzymes are hydrolytic enzymes.,Food molecules are split by,hydrolysis,.,R-R + H,2,O,digestive enzyme,R-OH + H-R,Digestive Enzymes,Proteins are broken down into individual amino acids.,Complex carbohydrates are broken down into simple sugars.,Fats are reduced to glycerol(,甘油,), fatty acids, and monoglycerides (,甘油单酯,).,Motility in Alimentary Canal,Food moves through the alimentary canal by,cilia,纤毛, specialized,musculature,肌肉组织, or both.,Gut musculature is present in coelomates,真体腔动物,.,Motility in Alimentary Canal,The gut is lined with opposing layers of smooth muscle: a circular layer and a longitudinal layer.,浆膜,粘膜,粘膜下层,肠系膜,Motility in Alimentary Canal,Two types of gut movement:,Segmentation,involves alternate constriction of rings of smooth muscle that move the contents around, mixing with enzymes.,Peristalsis,involves waves of contraction behind the food mass that move it through the gut.,分节运动,蠕动,Organization - Five Major Regions,Reception,Conduction & Storage,Grinding & early digestion,Terminal digestion and absorption,Water absorption and concentration of solids.,前胃,Receiving Region,The receiving region consists of devices for feeding and swallowing.,Mouthparts,&,Buccal cavity,(,口腔,mouth) mandibles(,颚,), jaws, bills, teeth, radula(,齿舌,), tongue.,Muscular,pharynx, throat,Salivary glands, produce lubricating,润滑,secretions that may also contain toxic enzymes or salivary enzymes to begin digestion.,Amylase,淀粉酶,begins hydrolysis of starches,淀粉,.,Receiving Region,The vertebrate tongue assists in food manipulation and swallowing.,Also used as a chemosensor.,会厌软骨,Conduction and Storage Region,The,esophagus,食道,transfers food to the digestive region.,In many invertebrates (annelids, insects, octopods) the esophagus is expanded into a,crop,嗉囊,used for storage.,Birds also have a crop that serves to store and soften food.,Region of Grinding & Early Digestion,The,stomach,provides initial digestion as well as storing and mixing food with gastric juice.,For further grinding of food, terrestrial oligochaetes (,寡毛纲,),and birds have a muscular,gizzard,砂囊,that is assisted by stones or grit (,沙砾,),swallowed with food.,The Stomach,The lining of the stomach is coated with mucus,粘液, which prevents the gastric juice from destroying the cells.,Pepsin,胃蛋白酶,is a protease that splits specific peptide bonds.,主细胞 壁细胞,The Stomach,Gastric ulcers,胃溃疡,are caused mainly by the bacterium,Helicobacter pylori,幽门螺杆菌,.,Region of Terminal Digestion and Absorption,The,small intestine,is the longest section of the alimentary canal.,It is the major organ of digestion and absorption.,Region of Terminal Digestion and Absorption,Increasing the surface area of the intestine increases the area available for absorption.,Longer intestine,Villi,绒毛, fingerlike projections of intestinal tissue in birds and mammals,Microvilli,微绒毛, tiny processes on intestinal cells.,乳糜管,乳糜管：吸收脂肪的淋巴管,The Small Intestine,The first portion of the small intestine is the,duodenum,十二指肠, where acid chyme,酸性食糜,from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and intestine itself.,The Small Intestine,The pancreas produces:,Proteases, protein-digesting enzymes.,Lipases,for breaking up fat.,Amylase,for hydrolyzing starches.,Nucleases,which degrade RNA & DNA into nucleotides.,胆盐（,Bile salt),是由肝细胞分泌的胆汁酸与甘氨酸或牛磺酸结合而形成的钠盐或钾盐。它是胆汁中参与脂肪消化和吸收的主要成分。,The Small Intestine,The,liver,secretes,bile,into the bile duct which drains into the duodenum.,Bile is stored in the,gallbladder,between meals.,Bile salts are important for digestion of fats.,The Small Intestine,Enzymatic digestion is completed as peristalsis moves the mixture of chyme and digestive juices along the small intestine.,Absorption of Nutrients,The small intestine has a huge surface area due to the presence of,villi,and,microvilli,that are exposed to the intestinal lumen.,The enormous microvillar surface is an adaptation that greatly increases the rate of nutrient absorption.,Absorption of Nutrients,The core of each villus contains a network of blood vessels and a small vessel of the lymphatic system called a,lacteal,.,Absorption of Nutrients,Amino acids and simple sugars pass through the epithelium of the small intestine and enter the bloodstream.,Initial absorption occurs by facilitated transport, later by active transport.,Region of Water Absorption,The large intestine, or,colon,结肠,is connected to the small intestine.,Region of Water Absorption,A major function of the colon is to recover water that has entered the alimentary canal.,The wastes of the digestive tract, the,feces, become more solid as they move through the colon.,The terminal portion of the colon is the,rectum,where feces are stored until they can be eliminated.,Region of Water Absorption,The colon houses various strains of the bacterium,Escherichia coli.,Some produce various vitamins.,Regulation of Food Intake,Hunger centers,in,hypothalamus,regulate food intake.,A drop in blood glucose level stimulates a craving for food.,Homeostatic mechanisms control the bodys storage and metabolism of fat.,Regulation of Food Intake,Undernourishment occurs in animals when their diets are chronically deficient in calories.,Can have detrimental effects on an animal.,Overnourishment results from excessive food intake.,Leads to the storage of excess calories as fat.,Regulation of Food Intake,Mice that inherit a defect in the gene for the hormone,leptin,瘦素,become very obese.,leptin,具有调节体内脂肪储存量和维持能量平衡的作用，可直接作用于脂肪细胞抑制脂肪的合成，促进分解，避免肥胖发生。,Regulation of Digestion,Hormones,help coordinate the secretion of digestive juices into the alimentary canal.,胆囊收缩素,肠促胰液素,Glucose Regulation as an Example of Homeostasis,Animals store excess calories as,glycogen,in the liver and muscle.,Glycogen is made up of many glucose subunits.,Glucose,is a major fuel for cells.,Glucose Regulation as an Example of Homeostasis,Blood glucose levels rise, the pancreas produces,insulin,.,Insulin enhances transport of glucose into body cells and stimulates storage of glucose as,glycogen,.,Results in lower blood glucose levels.,Glucose Regulation as an Example of Homeostasis,Lower blood glucose levels stimulates the pancreas to secrete,glucagon,.,Glucagon promotes breakdown of glycogen in the liver back into glucose which is released into the blood.,Nutritional Requirements,An animal must obtain organic carbon (from glucose) and organic nitrogen (from amino acids obtained during digestion of protein) in order to build organic molecules such as carbohydrates, lipids and proteins.,Nutritional Requirements,An animals diet must also supply essential nutrients in preassembled form.,An animal that is,malnourished,is missing one or more essential nutrients in its diet.,Nutritional Requirements,Herbivorous animals may suffer mineral deficiencies if they graze on plants in soil lacking key minerals.,Vitamins,Vitamins,are organic molecules required in the diet in small amounts.,To date, 13 vitamins essential to humans have been identified.,Vitamins are grouped into two categories:,Fat-soluble,Water-soluble,Minerals,Minerals,are simple inorganic nutrients that are usually required in small amounts.,Essential Fatty Acids,Animals can synthesize most of the,fatty acids,they need.,The essential fatty acids are certain unsaturated fatty acids.,Deficiencies in fatty acids are rare.,Essential Amino Acids,Animals require 20,amino acids,and can synthesize about half of them from the other molecules they obtain from their diet.,The remaining amino acids, the essential amino acids, must be obtained from food in preassembled form.,Essential Amino Acids,A diet that provides insufficient amounts of one or more essential amino acids causes a form of malnutrition called protein deficiency.,Malnutrition is much more common than undernutrition in human populations.,Essential Amino Acids,Most plant proteins are incomplete in amino acid makeup.,Individuals who eat only plant proteins need to eat a variety to ensure that they get all the essential amino acids.,
展开阅读全文