The Small Intestine The small intestine is the longest section of the alimentary canal It is the major organ of digestion and absorption

LE Stomach Pancreas Liver Gall- bladder Duodenum of small intestine Intestinal juice Bile Acid chyme Pancreatic juice

The pancreas produces proteases, protein- digesting enzymes that are activated after entering the duodenum

LE Pancreas Lumen of duodenum Membrane-bound enteropeptidase Inactive trypsinogen Other inactive proteases Active proteases Trypsin

The liver produces bile, which aids in digestion and absorption of fats The epithelial lining of the duodenum, called the brush border, produces several digestive enzymes

LE Oral cavity, pharynx, esophagus Stomach Lumen of small intes- tine Smaller polysac- charides, maltose Polysaccharides Disaccharides Carbohydrate digestion Salivary amylase Polysaccharides Pancreatic amylases Maltose and other disaccharides Epithelium of small intestine (brush border) Disaccharidases Monosaccharides Protein digestionNucleic acid digestion Proteins Fat digestion Fat globules DNA, RNA Fat droplets Nucleotides Bile salts Pancreatic lipase Pancreatic nucleases Nucleotidases Glycerol, fatty acids, glycerides Nitrogenous bases, sugars, phosphates Nucleosides Nucleosidases and phosphatases Dipeptidases, carboxy- peptidase, and aminopeptidase Amino acids Small peptides Pancreatic carboxypeptidase Pancreatic trypsin and chymotrypsin Smaller polypeptides Polypeptides Small polypeptides Pepsin

LE Pancreas Stomach Entero- gastrone Gall- bladder Liver Duodenum Secretin CCK Stimulation Inhibition Gastrin Key

Absorption of Nutrients The small intestine has a huge surface area, due to villi and microvilli that are exposed to the intestinal lumen The enormous microvillar surface greatly increases the rate of nutrient absorption

LE Key Nutrient absorption Microvilli (brush border) Epithelial cells Lacteal Lymph vessel Villi Large circular folds Epithelial cells Blood capillaries Vein carrying blood to hepatic portal vessel Muscle layers Villi Intestinal wall

Amino acids and sugars pass through the epithelium of the small intestine and enter the bloodstream After glycerol and fatty acids are absorbed by epithelial cells, they are recombined into fats within these cells Fat droplets coated with bile salts Fat globule Bile salts Micelles made up of fatty acids, monoglycerides, and bile salts Epithelium of small intestine Epithelium of lacteal Lacteal

The Large Intestine The large intestine, or colon, is connected to the small intestine Its major function is to recover water that has entered the alimentary canal

The colon houses strains of the bacterium Escherichia coli, some of which produce vitamins

Concept 41.5: Evolutionary adaptations of vertebrate digestive systems are often associated with diet Digestive systems of vertebrates are variations on a common plan However, there are intriguing adaptations, often related to diet

Some Dental Adaptations Dentition, an animal’s assortment of teeth, is one example of structural variation reflecting diet Mammals have specialized dentition that best enables them to ingest their usual diet

LE Incisors Carnivore Canines Premolars Molars Herbivore Omnivore

Stomach and Intestinal Adaptations Herbivores generally have longer alimentary canals than carnivores, reflecting the longer time needed to digest vegetation

LE Small intestine Stomach Cecum Colon (large intestine) Carnivore Herbivore Small intestine

Symbiotic Adaptations Many herbivores have fermentation chambers, where symbiotic microorganisms digest cellulose The most elaborate adaptations for an herbivorous diet have evolved in the animals called ruminants

LE IntestineRumen Reticulum Omasum Esophagus Abomasum