INDULGE!

1. INDULGE! “Health food makes me sick! -Calvin Trillin

2. Ruminants and Complex Stomachs • Ruminants only have one true stomach (abomasum), but have 3 forestomachs (reticulum, rumen, and omasum).

3. Rumination • The act of swallowing food, then regurgitating it to chew it some more then swallow it again. • How does regurgitation differ from vomiting?

4. Reticulum • Smallest and most cranial compartment. • Separated from rumen by ruminoreticular fold. • Interior is a honeycomb type arrangement to increase absorption. • Muscle wall is continuous with the rumen • Rumen and Reticulum work together and produce Reticulorumen contractions. • Hardware disease is associated with the reticulum.

5. Rumen • Series of muscular sacs separated by pillars (long, muscular folds of rumen wall). • Sacs can close off to allow more mixing to take place • Fermentation takes place here • Reticuloruminal contractions allow: • Regurgitation to take place • Eructation-Expulsion of built up carbon dioxide or methane gas • If build up continues, may cause bloat.

6. Rumen • Gastric motility is controlled by: • Vagus nerve primarily • Rate and strength of contractions is controlled by other factors: • pH (ideal is 5.8-6.4) • Presence of volatile fatty acids • Consistency of foodstuffs • Stretch receptors

7. Fermentative Digestion • Enzymes are produced by bacteria and protozoa. • How does this differ from monogastric animals? • Rumen bacterial surfaces produce cellulase • Allows for the breakdown of plant cell walls into simpler monosaccharides and polysaccharides.

8. Fermentative Digestion • Volatile Fatty Acids (VFA’S)- • Produced when glucose is absorbed by microbes and converted. • VFA’s are by-products of the anaerobic fermentation process • They are rapidly absorbed by host animal • In host animal, liver converts the VFA propionic acid into usable glucose. • Other volatile fatty acids can be used to produce fat tissue, milk fat.

9. Fermentative Digestion • Proteases- breakdown proteins to amino acids and peptides • Then can be broken down further to ammonia and VFA’s. • Ruminant is dependent on microbes to digest nutrients. • Very delicate balance • Changes in diet can upset this balance

10. Omasum • When reticulorumen contractions occur, ingesta moves to omasum. • Omasum is muscular with interior full of parallel, longitudinal muscular folds. • Breaks down food particles and carry these particles to the abomasum. • Omasumabosrbs remaining VFA’s and removes bicarbonate ions

11. Abomasum • Functions very similar to that of mongastric stomach. • Only glandular part of the stomach.

12. Young Ruminant Digestive Tract • Newborn’s stomach functions mainly as a monogastric digestive system. • Rumen and reticulum are small and non-functional • Development of rumen and reticulum is dependant on diet • Milk in rumen can disrupt fermentation process so is carried directly to omasum. • Reticular groove (Esophageal groove)- allows liquids to be carried from esophagus to omasum. • Initiated by suckling, can not drink from pail • As calf ages, groove disappears.

14. Small Intestines • Where majority of nutrients are absorbed into the bloodstream. • Divided into: • Duodenum • Short, first segment that leaves stomach. • Jejunum • Longest portion, makes up majority of small intestines. • Ileum • Short section that enters the colon (large intestine). • Separated from colon by ileocecal sphincter- muscle that regulates movement of materials from small intestine into colon or the cecum (blind pouch of the large intestine).

16. Small Intestine Structure • Similar to other segments of GI tract. • Thickness changes depending of area of GI tract. • Inner mucosal layer • Submucosal layer • Muscular layer • Serosal layer

18. Mucosa of Small Intestines • Provides large surface area for absorbing nutrients. • Folds in intestinal wall called villi are present • Villi- tiny, cylindrical, fingerlike projections that help with absorption. • Each villus contains very small villi called microvilli (brush border). • Crypts- small invaginations in the intestinal mucosa that help with replenishing cells of villus.

19. Small Intestine Motility • Vagus nerve and some sacral-vertebral nerves of parasympathetic system provide stimulation for motility, secretions, and blood flow. • Intestinal tract is constantly functioning and is never at rest. • Peristalsis • What type of contractions are associated with peristalsis? • How does diarrhea occur? • Antidiarrheal meds decrease secretion and increase segmental contractions.

20. Small intestine motility • Ileus- decreased movement of ingesta. • May be caused by disease or stress. • Cholecystokinin (CCK) • Stimulates intestinal motility (opposite of gastric motility) • Prostaglandins • Increase GI motility and secretions.

21. Small Intestine Digestion • Absorbed intact into small intestinal wall are: • Sodium • Chloride • Postassium • The above are collectively known as electrolytes • Vitamins

22. Small Intestine Digestion • Must be chemically broken down to absorb in small intestine are: • Carbohydrates • Proteins • Fats • Chemically digested in 2 steps: • Enzymes in lumen of intestine • Enzymes of microvilli • Once digested, a “unit” of foodstuff can be transported or diffused across intestinal tract membrane

23. Carbohydrate Digestion • Amylase- converts starch into smaller sugar segments (in lumen of small intestine) • Then sucrase, maltase, isomaltase and lactase found in cell membrane of microvilli convert sugar segments down further. • Finally, units of foodstuff are transported across microvilli into the body • Types of enzymes present is dependent on diet. • Changes in diet produce diarrhea because enzymes necessary to digest new diet may not be present in sufficient quantities.

24. Protein Digestion • Gastric pepsin can help break apart some protein chains, but this is not sufficient for complete protein digestion. • Pancreas secreted 5 basic Proteases: • 1. Trypsin • Precursor is trypsinogen • Trypsin activates other enzyme precursors • Break apart bonds in middle of protein • 2. Chymotrypsin • Break apart bonds in middle of protein • 3. Elastase • Break apart bonds in middle of protein • 4. Aminopeptidase • Break apart proteins at amino `ends • 5. Carboxypeptidase • Break apart proteins at carboxyl ends • Peptidases embedded in the cell membrane of brush border cells

25. Fat Digestion • Fats in water environment form globules. • Globules are broken down by emulsificaton (mixing of fat and water by agitation or shaking) and micelle (fat surrounded by hydrophilic molecules that allow it to readily move in small intestine) formation. • Bile acids (secreted by liver to make fat more water soluble) combine with droplets to keep from returning to globular state. • Have a hydrophobic and hydrophilic end • Pancreatic lipases penetrate and digest fat • Fat soluble vitamins (A, D, E, and K), are incorporated into the micelles and absorbed with them.

26. Large Intestine • General functions are to recover fluid and electrolytes and to store feces until it can be eliminated. • Consists of: • Cecum • Blind sac at ileocecal junction • Fermentation in horses • Poorly developed in carnivores • Colon • Rectum

27. Horse Hindgut • Consists of 4 sections: • Cecum • Ventral colon • Right and left halves • Dorsal colon • Right and left halves • Small colon

28. Horse Hindgut • Ingesta from small intestine passes through ileocecal sphincter and enters cecum. • Cecum is composed of: • Base • Main body • Apex • Cecum and dorsal and ventral colons have longitudinal bands that separate the structure into a series of sacs called haustra • Cecum is separated from colon by cecocolic orifice

29. Ingesta flow in horse hindgut • Ileocecal sphincter►Cecum►Right ventral colon►sternal flexure►left ventral colon►Pelvic flexure►left dorsal colon►diaphragmatic flexure►Right dorsal colon►small colon. • Colonic impaction is most common form of colic in horse • VFA’s absorbed from cecum and colon provide energy needs in animals with hindgut fermentation. • Guinea pigs, rats, rabbits, swine.

30. Rectum • Terminal portion of the large intestine • Extension of colon • Secretions similar to colon to help lubricate feces as they pass through colon. • Capable of more expansion than colon • Has sensory receptors that detect stretching or distention and stimulates defecation response. • Defecation- process of expelling feces

31. Anus • Composed of: • internal sphincter • Under autonomic control • Parasympathetic system causes relaxation • Sympathetic system causes constriction • external sphincters. • Under voluntary control • When material makes contact with anal mucosa of internal sphincter, increases conscious need for defecation. • Anal abnormalities can result in fecal incontinence.

32. Liver • Produces bile acids that help to digest fat. • Helps to filter materials absorbed from GI tract before they reach blood. • Hepatic portal system- is blood vessel system that transports blood from capillaries in the intestine to liver. • Some nutrients are stored or metabolized by the liver. • Bile is produced in liver and leads to gallbladder. • Source of blood proteins • Albumin

33. Gallbladder • Storage compartment for bile. • Will force bile down bile duct to duodenum.

34. Pancreas • Exocrine gland(secretes substances to outside of body through a duct) as well as Endocrine gland (secretes hormones directly into the blood without going through a duct). • Insulin and glucagon help regulate blood glucose • Beta cells (located in pancreatic islets or islets of langerhans) produce insulin which lowers glucose levels in blood • Lack of insulin leads to Diabetes mellitus • Glucagon produced by alpha cells in pancreas dos the opposite insulin by working to increase blood glucose when the body is running low.