Digestion All animals are heterotrophs Different modes of feeding evolved Modes of feeding (structure-function) can be used as an evolutionary evidence Compartmentalization

Intracellular vs. Extracellular Intracellular- occurs within food vacuoles E.g. food vacuoles in Paramecium, amoebocytes of sponge Extracellular- occurs within specialized compartments Incomplete vs. complete

Incomplete A single opening is present for both entrance of food and exit of wastes Gastrovascular cavity of Cnidarians Gastrodermis- has specialized cells that secrete digestive enzymes Hydrolysis of macromolecules is intracellular

Incomplete Obelia sp.

Complete Opening of food is different from exit of waste materials Specialized regions of the alimentary canal Complexity varies in each phylum Extracellular hydrolysis of food

Complete Bos taurus

Modes of feeding Herbivore Carnivore Omnivore Dentition Alimentary canal

Modes of Feeding Suspension feeders Substrate feeders Fluid feeders Bulk feeders

Modes of Feeding

Symbiotic Relationship Vertebrates acquired symbiotic relationship with microscopic organisms in processing food E.g. Ruminants, Humans, termites

Four Main Stages of Food Processing Ingestion Large oral cavity Digestion Mechanical vs. Chemical Absorption Elimination

Digestion in Humans Primary organs of digestion Mouth, pharynx, esophagus, stomach, small intestine, large intestine Accessory glands of digestion Salivary glands, pancreas, liver, gall bladder

Digestion in Humans Mouth- functions: ingestion and digestion Digestion begins in the Oral Cavity Mechanical and Chemical digestion Salivary amylase- breaks down polysaccharide and glycogen Saliva- also fxns as antibacterial agent and neutralizes acidity of foods

Pharynx Upper portion of the throat Where air and digested food meet Digested ball (bolus) of food enters Epiglottis- acts as a seal to prevent food from entering the air passages

Esophagus Upper portion- striated muscle Lower portion- smooth muscle Connects the pharynx to the stomach Peristalsis Goblet cells- specialized cells that lines the esophagus Release mucus that covers the bolus

Peristalsis Wave-like motion responsible for the movement of digested food in the alimentary canal

Stomach Stores and digests food Cardiac sphincter- prevents backflow Pyloric sphincter- regulates entrance of acidic chyme to the small intestine Secretes digestive juice Mixed with food through churning of the stomach through smooth muscle contractions

Stomach Chief cells- secretes pepsinogen Parietal cells- secrete HCl HCl- disrupts the extracellular matrix of plant and animal cell Pepsin- active form of pepsinogen Hydrolyzes proteins Works best in an acidic environment

Stomach Stomach lining is protected product- acid chyme First, pepsinogen is only activated when secreted into the lumen due to the action of the acidic HCl (pepsinogen activation-positive feedback) Secondly, presence of goblet cells that secrete mucus product- acid chyme

Stomach

Small Intestine Major organ of digestion and absorption Longest section of the alimentary canal Divided into three sections:duodenum, jejunum, ileum Duodenum- site of mixing of acidic chyme and other digestive juices (digestion) Jejunum and Ileum- absorption

Small Intestine Carbohydrate digestion Protein Digestion Nucleic Acid Digestion Fatty Acid Digestion

Carbohydrate digestion Starch, glycogen and other polysaccharides that were digested in the mouth is further digested Pancreatic amylase Maltase- splits maltose into its glucose units Disaccharides- absorbed by intestinal epithelium

Protein digestion Trypsin and Chymotrypsin- breakdown large polypeptide chain like pepsin Dipeptidase- split small peptides Carboxypeptidase- breakdown polypeptides in its carboxyl end Aminopeptidase- breakdown peptidase in its nitrogenous end Enteropeptidase- activates pancreatic enzymes

Protein digestion Intestinal enzymes- aminopeptidase, enteropeptidase Pancreatic enzymes- Trypsinogen, Procarboxypeptidase, Chymotrypsinogen Enteropeptidase- activates Trypsinogen Trypsin- activates Procarboxypeptidase, Chymotrypsinogen

Nucleic Acid Digestion Nucleases- hydrolyze nucleic acids Exonucleases- hydrolyze nucleic acids on its terminal Endonucleases- hydrolyze nucleic acids within Other enzymes hydrolyze the nucleotides into its components

Fatty acid digestion Bile salts- emulsify undigested fats in the duodenum Emulsification- inc SA of fat molecules Lipase- digests fat molecules

Absorption Villus- folds found in the small intestine Microvillus- microscopic fingerlike projections that increases the absorption of materials Each villus is connected to a capillary (BV) network and lacteals(Lymphatic system)

Transport of nutrients Passive Diffusion Active transport Nutrients that were absorbed are transformed into what the body needs Chylomicron- small globule that is a combination of fats, cholesterol, coated with proteins

Hormones that regulate digestion Gastrin-stimulated by gastric juices Inhibited by low pH stimulates secretion of gastric juice Enterogastrones- group of enzymes found in the duodenum Cholecystokinin (CCK)- stimulated by fats and amino acids Stimulates gall bladder to release bile Secretin- stimulated by the acidic chyme Stimulates pancreas to release bicarbonates If chyme is rich in fats, it stimulates the duodenum to release other enzymes to slows down digestion in the stomach

Large Intestine Also called the colon Cecum – small pouch that has different fxns Appendix- small cecum found in man Rectum- portion of the large intestine that temporarily stores feces Main fxn of colon is to reabsorb water Feces- waste that was formed after digestion Compactness depends on water that was reabsorbed

Large Intestine Intestinal Bacteria- common example is E. coli Have mutualistic relationship with host Generate methane or hydrogen sulfide Some produce vitamins that are needed by the body

Nutrition Nutritionally adequate diet composed of: fuel (chemical energy) organic raw materials (carbon skeletons) essential nutrients (substances the animal cannot make)

Balancing the fuel Homeostatic mechanism balances the animal’s fuel ATPs that were produced are budgeted depending on the energy requirements Fats have the highest amount of ATP Glucose conversion is an example of homeostatic mechanism

Caloric Imbalance Undernourishment Overnourishment Malnourishment Calorie deficiency Overnourishment Excessive calorie intake- results to obesity Malnourishment Deficient in any essential nutrients

Essential Nutrients Essential Amino Acids Essential Fatty Acids Vitamins Minerals

Essential Amino Acids Tryptophan, methionine, Valine, Threonine, Phenylalanine, Leucine, Isoleucine, Lysine, Histidine (infants) Deficiency in one of these may result into protein deficiency

Essential Fatty Acids Essential Fatty Acids belong to the unsaturated fatty acid groups An example is linoleic acid Deficiencies are rare

Vitamins Organic molecules that are required relatively in small amount Two types: Water-soluble B vits, C Fat-soluble A, D, E, K

Minerals Inorganic nutrients that are required in small amounts E.g. Calcium, Phosphorous, Sodium, etc.

Balance diet what enters= what leaves It is easier to take in calories in the body than to burn it The food pyramid serves as a guide in the kind of foods that should be taken in