Animal Nutrition II (Ch. 41) Guest lecturer: Letitia Reichart (Letty)

Keywords Roles of mouth, stomach, sm.&lg. Intestine in digestion Pepsin, pepsinogen Villi, microvilli Cecum Cellulose Cellulase Acid chyme Enzymatic hydrolysis Peristalsis

Mammalian Digestive System Alimentary canal Accessory glands –Salivary glands, pancreas, liver, gallbladder Food moved by peristalsis

Mouth (oral cavity) Mechanical –Teeth –Saliva Enzymatic –Salivary amylase – breakdown of starch and glycogen

Throat (pharynx) & Esophagus Throat – junction to esophagus & trachea –Epiglottis Esophagus – uses peristalsis to move food to stomach

Stomach Stores food Secretes gastric juices –Acid chyme Relaxed muscles Contracted muscles Stomach

Digestive mechanisms in stomach Mechanical Chemical Enzymatic Esophagus Stomach Pyloric sphincter Cardiac orifice Liver Gall- bladder Pancreas

Mechanical Mixing and churning –Smooth muscle –Every 20 seconds Esophagus Stomach Pyloric sphincter Cardiac orifice

Chemical Hydrochloric acid (HCl) pH around 2 –Also breaks food down

Enzymatic Pepsin –Breaks down proteins

Chief cells Mucus cells Parietal cells Interior surface of stomach Gastric gland Why doesn’t pepsin digest stomach? Gastric pit

Activation of pepsin Pepsin (active enzyme) Pepsinogen HCl Parietal cellChief cell

Stomach After mechanical and enzymatic digestion: -Acid chyme (nutrient- rich broth) - Pyloric sphincter to the small intestine Stomach Pyloric sphincter Cardiac orifice

Small intestine Small intestine Most of: – Enzymatic digestion occurs here –Absorption of nutrients into the blood stream occurs here

Figure p. 859 in Campbell 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

Stomach Pancreas Liver Gall- bladder Duodenum of small intestine Intestinal juice Bile Acid chyme Pancreatic juice Figure p. 858 in Campbell

Pancreas Secretes proteases into duodenum Inactive formActive form TrypsinogenTrypsin ProcarboxypeptidaseCarboxypeptidase ChymotrpsinogenChymotrypsin

Why doesn’t the small intestine digest itself? Pancreas Active proteases Fig Lumen of duodenum Membrane-bound enteropeptidase Inactive trypsinogen Other inactive proteases Active proteases Trypsin

Liver Produces bile that is stored in gallbladder Bile contain bile salts Bile salts aids digestion and absorption of fats

Large circular folds Vein carrying blood to hepatic portal vessel Muscle layers Villi Intestinal wall Most nutrient absorption occurs in small intestine

Structure of small intestine Lacteal Lymph vessel Villi Epithelial cells Blood capillaries

Microvilli (brush border) Epithelial cells Aid in nutrient transport across epithelial cells of sm. intestine into bloodstream

Large intestine (colon) Major function is to reabsorb water Ascending portion of large intestine Ileum of small intestine Rectum Anus Appendix Cecum Large Intestine

Here are a few review questions

What would happen if you had a defect in pepsin production?

A. carbohydrate would not be digested well B. meat would not be digested at all C. perhaps decreased absorption of protein

What would happen if you had a defect in salivary amylase production?

A. You would die B. You would be unable to digest starch C. The pH of the stomach would be affected D. None of the above What would happen if you had a defect in salivary amylase production?

Which of the following would you least like to donate to science while you are still alive? A. Cecum B. Pancreas C. Reproductive organs

What would happen if you had a defect in small intestine enteropeptidase?

A. Pancreatic enzymes would not be activated B. Liver enzymes would increased C. Your small intestine would become blocked D. None of the above

Variations of vertebrate digestive system Herbivorous mammals –Specialized fermentation chambers

Coyote vs. Koala Small intestine Stomach Cecum Colon (large intestine) Carnivore Herbivore Small intestine

Why does herbivory require specializations? Plant tissue –Harder to break up –Contains cellulose –Nutrients less concentrated than meat

Structure of cellulose

Only bacteria and protozoa can break down cellulose Via the enzyme cellulase

Cecum Pouch at junction between lg and sm intestine Large cecum in rabbits, some rodents, koala, horses Full of symbiotic bacteria Stomach Cecum Colon (large intestine) Herbivore Small intestine

Symbiosis “living together”

Cecum function Fermentation chamber Bacteria breakdown cellulose Feces must be reingested Stomach Cecum Colon (large intestine) Herbivore Small intestine