The Small Intestine • The small intestine is the longest section of the alimentary canal • It is the major organ of digestion and absorption
Feb 24, 2016
The Small Intestine
• The small intestine is the longest section of the alimentary canal
• It is the major organ of digestion and absorption
LE 41-19
Stomach
Pancreas
Liver
Gall-bladder
Duodenum ofsmall intestine
Intestinaljuice
Bile
Acid chyme
Pancreatic juice
• The pancreas produces proteases, protein-digesting enzymes that are activated after entering the duodenum
LE 41-20
Pancreas
Lumen of duodenum
Membrane-boundenteropeptidase
Inactivetrypsinogen
Other inactiveproteases 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 41-21
Oral cavity,pharynx,esophagus
Stomach
Lumen ofsmall intes-tine
Smaller polysac-charides, maltose
Polysaccharides DisaccharidesCarbohydrate digestion
Salivary amylase
PolysaccharidesPancreatic amylases
Maltose and otherdisaccharides
Epitheliumof smallintestine(brushborder)
Disaccharidases
Monosaccharides
Protein digestion Nucleic acid digestion
Proteins
Fat digestion
Fat globulesDNA, RNA
Fat dropletsNucleotides
Bile salts
Pancreatic lipase
Pancreaticnucleases
Nucleotidases
Glycerol, fattyacids, glycerides
Nitrogenous bases,sugars, phosphates
NucleosidesNucleosidasesand phosphatases
Dipeptidases, carboxy-peptidase, and aminopeptidase
Amino acids
Amino acids
Small peptides
Pancreatic carboxypeptidase
Pancreatic trypsinand chymotrypsin
Smaller polypeptides
Polypeptides
Small polypeptidesPepsin
LE 41-22
Pancreas
Stomach
Entero-gastrone
Gall-bladder
Liver
DuodenumSecretin
CCK
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 41-23
Key
Nutrientabsorption
Microvilli(brush border)
Epithelial cellsLacteal
Lymphvessel
Villi
Largecircularfolds
Epithelialcells
Bloodcapillaries
Vein carrying bloodto hepatic portalvessel
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 dropletscoated withbile salts
Fat globule
Bile salts
Micelles madeup of fatty acids,monoglycerides,and bile salts
Epitheliumof smallintestine
Epitheliumof 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 41-26
Incisors
Carnivore
CaninesPremolars
Molars
Herbivore
Omnivore
Stomach and Intestinal Adaptations
• Herbivores generally have longer alimentary canals than carnivores, reflecting the longer time needed to digest vegetation
LE 41-27
Smallintestine
Stomach
Cecum
Colon(largeintestine)
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 41-28
Intestine Rumen
Reticulum
Omasum
EsophagusAbomasum