The Digestive System -Types of Digestive Systems o Heterotrophs – 3 groups Herbivores, carnivores, omnivores o Intracellular digestion in single celled o Multicellular extracellular digestion o Cnidarians and flatworms – gastrovascular cavity o Specialization when there is a separate mouth and anus Nematodes are most primitive o Ingested food can be stored or fragmented Followed by chemical digestion Pass through epithelial lining into blood Waste excreted from anus -Vertebrate Digestive Systems o Tubular tract and organs o Entry through mouth and pharynx  esophagus  stomach  small intestine large intestine  rectum o Accessory organs: liver (bile maker), gallbladder (store bile), pancreas (juices and enzyme buffero Layered track Mucosa – lines the tract Submucosa – connective tissue Muscularis – smooth muscle layers Serosa – outermost covering external tract -Mouth and Teeth o Used for chewing o Birds: no teeth, two chambered stomach, gizzard pulverizes o Carnivores – pointed teeth without flat grinding surfaces o Herbivores – flat teeth for grinding plant tissues o Humans have carnivore in front and herbivore in back o Inside the mouth Tongue mixes with saliva with amylase to break down starch Nervous system controls salivation-Swallowing o Voluntary but becomes involuntary o Tongue moves to back of the mouth and soft palate seals off nasal cavityo Larynx pushes glottis against epiglottis to keep food out of respiratory-Esophagus o Connects mouth to stomach o Peristalsis o Swallowing center causes one directional contractiono Sphincter allows food to enter stomach, but humans don’t really have a sphincter -Stomach o Allows expansion o 3rd layer of smooth muscles for mixing o secretory cellsmucus secreting parietal cells secrete HCl and intrinsic factor chief cells secrete pepsinogen o low pH denatures food proteins to active pepsin o no digestion of fats or carbs o some water absorption o peptic ulcer can be caused by bacteriao leaves through pyloric sphincter to small intestine -Small Intestine o 4.5 m longo duodenum, jejunum, ileumreceives chime, digestive enzymes, and bile o epithelial wall covered with villi which are covered with microvilli which increase surface area o many adults lack lactase-Accessory Organs o PancreasFluid secreted into duodenumEnzymes -Trypsin and chymotrypsin: proteins into polypeptides -Pancreas amylase: polysaccharides into shorter sugars -Lipase: fats into fatty acids and monoglycerides Bicarbonate neutralizes chime Exocrine and endocrine glands o Liver Largest internal organ Secretes bile pigments (waste products) and salts (emulsifying fats) o Gallbladder Stores and concentrates bile Fatty acids in duodenum and triggers stimulating gallbladder to contract, transporting bile to duodenum -Absorption o Amino acids and monosaccharides transported to blood to liver o Fatty acids and monoglycerides diffuse into epithelial cells Become triglycerides and chylomicrons Enter lymphatic them circulatory systemo Almost all fluid reabsorbed in small intestine -Large Intestineo Shorter but larger diameter o No digestion occurso Absorb water, electrolytes, and K o Prepare waste for expulsion o Bacteriao Feces compacted and pass through anus Smooth (involuntary) and striated (voluntary) -Variations in Digestive Systems o Some digestive tracts contain bacteria that convert cellulose to absorbable substances Minor in humans, but essential in some animals o Herbivores have longer tracts to digest cellulose and enhance digestion o Ruminants have 4 chambers Rumen, reticulum, omasum, abomasum Regurgitated and rechewedo Foregut fermentationConvergentModified lysosome to take on new role of digesting bacteria Same 5 amino acids o rodents, horses, deer, and rabbits digest cellulose in cecum regurgitation isn’t possible o some animals use coprophagy eat feces to absorb nutrients on second passage and can’t remain healthy if they can’t eat their feces o all mammals rely on bacteria to synthesize vitamin k to clot bloodo birds lack bacteria and have to consume vitamin k in diet -Regulation of the Digestive Tract o Coordinated by nervous and endocrine systems o Nervous stimulates saliva and gastric secretions o Proteins stimulate gastrin release to trigger HCl release and pepsinogen o Enterogastrones or duodenal hormones Inhibit contractions and prevent chyme from entering duodenum CCK, secretin, and GIP CCK stimulates gallbladder contraction and pancreatic enzyme secretion Secretin stimulates secretion of pancreatic bicarbonate -Accessory Organ Functiono Modifies substances absorbed from digestive tract o Alcohol and other drugs o Removes toxins, pesticides, and carcinogenso Regulates hormone levelso Produces proteins found in plasma o Regulation of blood glucose Carb rich meal, insulin stimulates removal of blood glucose by liver and muscles When blood glucose levels decrease-Glycogenolysis stimulates liver to break down glycogen and release glucose -Gluconeogenesis converts other molecules into glucose if fasting continues -Food Energy o Purposes: source of energy and raw material o Basal metabolic rate (BMR) – minimal amount of energy consumed under defined resting conditions o Continued ingestion of excess food energy results in accumulation of fat -Regulation of Food Intake o Control metabolism links food intake to energy balance Leptin – peptide hormone -Appetite control -Produced by adipose tissue-Receptor in hypothalamus -Reduced leptin signals brain to intake foodo Other hormones involved in control of feeding and energy Insulin, GIP, CCK signal satiety Ghrelin stimulates food intake Control of feeding -Neuropeptide Y (NPY) induces feeding activity -Melanocyte stimulating hormones suppress it -Essential Nutrients o Animals can’t manufacture these alone so have to obtain in diet o Vitamins Humans can’t synthesize vitamin CHumans require 9 amino acids Long chain unsaturated fatty acids – vertebrates synthesize cholesterol