生理学中英文DigestionandNutrition消化和营养

1、生理学中英文DigestionandNutrition消化和营养Obtaining EnergyAll 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 ch

2、emical 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

3、matter.Saprophagous animals feed on decaying organic matter.Why We EatRegardless 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

4、 make for itself.Feeding MechanismsVery few animals absorb nutrients directly from the environment.Exceptions include parasites that absorb nutrients that have been digested by the host：e.g.，Protozoan parasitesBlood parasitesTapeworms（绦虫,无口及肠）Feeding Mechanisms Particulate Matter （颗粒物质）The upper por

5、tion 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 Pa

6、rticulate MatterFeeding MechanismsFluid feeders may bite and rasp(锉) at host tissues and suck fluid (such as blood).Many have specialized, tubelike mouthparts.Feeding MechanismsHerbivorous animals have evolved special devices for crushing and cutting plant material.Snails have a radula(齿舌) for scrap

7、ing algae or plant material.Insects have grinding & cutting mandibles(大颚) .Mammals have wide corrugated (起皱褶的 ) molars for grinding.Feeding MechanismsPredators have evolved a variety of ways to capture, hold, and swallow prey.Many swallow food items whole.Some have specialized teeth, beaks, or tooth

8、-like structures.Some have highly elastic jaws and distensible stomachs to accommodate large meals.Feeding MechanismsOnly mammals can actually chew their food.Mammals have teeth that are specialized for different functions.Incisors biting, cutting.Canines seizing, piercing, tearing.Premolars & molar

9、s grinding and crushing.The Main Stages of Food ProcessingIngestion 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 ProcessingAbsorption is the uptake of nu

10、trients by body cells.Elimination occurs as undigested material passes out of the digestive system.Intracellular DigestionIn intracellular digestion, food particles are engulfed by endocytosis and digested within food vacuoles.Protozoa, sponges.Extracellular DigestionExtracellular digestion is the b

11、reakdown 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 DigestionRadiates, flatworms, & ribbon worms practice both intracellular and extracellul

12、ar digestion.Extracellular digestion became emphasized with the appearance of a complete digestive tract.Digestion is almost entirely extracellular in arthropods and vertebrates.Digestive SystemsAnimals with simple body plans have a gastrovascular cavity that functions in both digestion and distribu

13、tion of nutrients.Digestive SystemsAnimals 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 SystemsThe digestive tube can be organized into specialized regions that car

14、ry 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 SystemThe 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ileum 回肠盲肠阑尾十二指肠贲门 幽门Digestive EnzymesEnzy

15、mes are essential in the breakdown of food into small, absorbable units.Digestive enzymes are hydrolytic enzymes.Food molecules are split by hydrolysis.R-R + H2Odigestive enzyme R-OH + H-RDigestive EnzymesProteins are broken down into individual amino acids.Complex carbohydrates are broken down into

16、 simple sugars.Fats are reduced to glycerol(甘油), fatty acids, and monoglycerides (甘油单酯).Motility in Alimentary CanalFood 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 CanalThe gut is lined w

17、ith 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 CanalTwo 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 con

18、traction behind the food mass that move it through the gut.分节运动蠕动Organization - Five Major RegionsReceptionConduction & StorageGrinding & early digestionTerminal digestion and absorptionWater absorption and concentration of solids.前胃Receiving RegionThe receiving region consists of devices for feedin

19、g and swallowing.Mouthparts & Buccal cavity (口腔 mouth) mandibles(颚), jaws, bills, teeth, radula(齿舌), tongue.Muscular pharynx throatSalivary 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

20、.Receiving RegionThe vertebrate tongue assists in food manipulation and swallowing.Also used as a chemosensor.会厌软骨Conduction and Storage RegionThe 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

21、 storage.Birds also have a crop that serves to store and soften food.Region of Grinding & Early DigestionThe 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

22、 is assisted by stones or grit (沙砾) swallowed with food.The StomachThe 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 StomachGastric ulcers 胃溃疡 are caused mainly by the b

23、acterium Helicobacter pylori 幽门螺杆菌.Region of Terminal Digestion and AbsorptionThe small intestine is the longest section of the alimentary canal.It is the major organ of digestion and absorption.Region of Terminal Digestion and AbsorptionIncreasing the surface area of the intestine increases the are

24、a available for absorption.Longer intestineVilli 绒毛 fingerlike projections of intestinal tissue in birds and mammalsMicrovilli 微绒毛 tiny processes on intestinal cells.乳糜管 乳糜管：吸收脂肪的淋巴管 The Small IntestineThe first portion of the small intestine is the duodenum十二指肠, where acid chyme 酸性食糜from the stomac

25、h mixes with digestive juices from the pancreas, liver, gallbladder, and intestine itself.The Small IntestineThe 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

26、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 IntestineThe 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 IntestineEnzymatic digestion is completed as peristalsis

27、moves the mixture of chyme and digestive juices along the small intestine.Absorption of NutrientsThe 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 t

28、he rate of nutrient absorption.Absorption of NutrientsThe core of each villus contains a network of blood vessels and a small vessel of the lymphatic system called a lacteal.Absorption of NutrientsAmino acids and simple sugars pass through the epithelium of the small intestine and enter the bloodstr

29、eam.Initial absorption occurs by facilitated transport, later by active transport. Region of Water AbsorptionThe large intestine, or colon 结肠 is connected to the small intestine.Region of Water AbsorptionA major function of the colon is to recover water that has entered the alimentary canal.The wast

30、es 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 AbsorptionThe colon houses various strains of the bacterium Escherichia coli.Some produce various

31、 vitamins.Regulation of Food IntakeHunger 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 IntakeUndernourishment occurs in animals when their diets are c

32、hronically 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 IntakeMice 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

33、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 DigestionHormones 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 HomeostasisAnimals store excess calories as glycogen in the liver and muscle.Glycogen is made up of many

34、 glucose subunits.Glucose is a major fuel for cells.Glucose Regulation as an Example of HomeostasisBlood 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.Glucos

35、e Regulation as an Example of HomeostasisLower 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 RequirementsAn animal must obtain organic carbon (from glucose) and orga

36、nic nitrogen (from amino acids obtained during digestion of protein) in order to build organic molecules such as carbohydrates, lipids and proteins.Nutritional RequirementsAn 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 RequirementsHerbivorous animals may suffer mineral d