1. Small Intestinal Wall Mucosa, submucosa,muscularis, serosa Mucosa – increased surface area due to many villi Each villus contains thousands of ___________ (brush border) Microvilli have both digestive enzymes and carrier molecules for nutrients, vitamins, and minerals embedded in cell membranes _______- invaginations of mucosa around each villus. New cells are produced and pushed from bottom of crypt to replace cells of villus Goblet cells present. Mucus helps with flow of ingesta.

2. Nervous System and Small Intestines _____________ nervous system provides stimulation for intestinal motility, secretions, and blood flow. _____________ nervous system decreases circulation to the intestines. Intestinal tract is constantly functioning and is never at rest.

3. Small intestine Motility Peristalsis Circular contractions prevent backflow of ingesta, longitudinal muscles propel ingesta caudally Dilation of bowel with ingesta stimulates peristalsis CCK and Prostaglandins can both affect motility. Fats/protein in the intestine stimulate the mucosa to release CCK, which increases intestinal motility (opposite of the effect on the stomach) Prostaglandins can increase GI motility and secretions which can lead to colic. Segmental contractions slow the movement of ingesta to allow time for it to be both mixed with intestinal enzymes and absorbed through the intestinal wall. Many times diarrhea is caused not due to increased peristalsis, but lack of segmental contractions.

4. Small Intestine Digestion _____________, _____________, _____________ Absorbed intact across SI wall _____________, _____________, _____________ Chemically digested via enzymes in the lumen and enzymes on the microvilli b/c they are too large to pass through the mucous membrane

5. Carbohydrate Digestion Starch is broken into disaccharides by amylase found in the saliva and from the pancreas Disaccharides are broken down into monosaccharides by enzymes (lactase, sucrase, and maltase) in microvilli Monosaccharides can then be transported across microvilli and absorbed into blood Microvilli enzymes are dependent on diet ( Lactose-intolerant animals/diarrhea) FoodEnzymeSourceBroken into Fate StarchAmylaseSaliva, PancreasDisaccharides lactose sucrose maltose LactaseBrush borderMonosaccharides Sucrase glucoseAbsorbed Maltase galactoseAbsorbed fructoseAbsorbed

6. Protein Digestion Protein chains are broken into smaller polypeptides by pepsin Polypeptides are broken down into peptides (several amino acids) by pancreatic proteases Peptides are broken down into amino acids, dipeptides, and some tripeptides by peptidases are then absorbed FoodEnzymeSourceBroken into Fate ProteinPepsinStomachPolypeptides ProteasesSI (Pancreas)Peptides PeptidasesBrush borderAmino acidsAbsorbed di-peptides Absorbed tri-peptidesAbsorbed

7. Fat Digestion Agitation of the pyloric antrum emulsifies (breaks down) fat globules (triglycerides) into smaller droplets Bile acids from the liver coat the fat droplets in duodenum Keeps them from re-forming into globules again Arranges them to make them more water soluble Pancreatic lipases (fat-digesting enzymes) penetrate bile acid coating Digest triglycerides to form glycerol, fatty acids, and monoglycerides (micelles) which are absorbed through the microvilli Vitamins A, D, E, K are often absorbed with the micelles FoodEnzymeSourceBroken into Fate LipidsBile acidsSI (Liver)small fat droplets LipasesSI (Pancreas)glycerolAbsorbed fatty acidsAbsorbed monoglyceridesAbsorbed

9. Large Intestine Species variation in structure Components 1. ________ - blind sac at ileocecal junction 2. ________ 3. ________ Primary functions - Store feces Recover fluid and electrolytes Hindgut fermentation (non ruminant herbivores) Equine, guinea pigs, rats, rabbits, swine

10. Large Intestines ____________: simple, tubular colon; poorly developed cecum __________ __________: very large colon and cecum (hindgut) Fermentation site Modifications of cecum and colon allow fermentative digestion in hindgut similar to rumen VFA ’ s (produced by microbes) absorbed from cecum and colon for energy needs (similar to rumen) Possible areas of impaction Flexures, Small colon Cause of colic

11. Horse Hindgut Consists of 4 sections: Cecum, Ventral colon ( right and left halves), Dorsal colon (right and left halves), Small colon 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 ________ The role of the small colon is to absorb electrolytes, water, and any VFA’s that were not previously absorbed.

12. Rectum Terminal portion of the large intestine; an extension of colon Capable of more expansion than colon Mucus-secreting glands ___________ feces to aid their passage Has sensory receptors that detect stretching or distention and stimulates defecation response.

13. Anus Internal sphincter under ________ control (Parasympathetic system causes relaxation, Sympathetic system causes constriction) External sphincters under __________ control As rectum distends, stretch receptors cause partial relaxation of internal sphincter. Fecal material moves into the Internal Sphincter Canal which stimulates more stretch receptors increasing urge to defecate. Stretching of Anal mucosal receptors increase the sense or need for defecation Surgery or disease in anal region can damage sphincter muscles and nerves, causing incontinence

14. Liver’s Role in the GI Tract ________, __________, and/or ___________ materials absorbed from GI tract before they reach blood. Removes toxins, infectious agents, old blood cells that enter the body via the GI tract. Glucose, amino acids, and vitamins are stored or metabolized. Glucose absorbed by the GI tract can be stored in the liver as _____________ (glycogenesis). When glucose is needed in the blood, glycogen is broken down by the liver (glycogenolysis). _____________________ is the process of glucose being made in the liver by using amino acids. Major source of blood __________ Albumin

15. Gallbladder The liver produces _______ which contains bile acids, cholesterol, and bilirubin Bile is secreted into bile ducts, which lead to the hepatic duct, which leads to the ____________for storage (not horse) The gallbladder stores bile until it is stimulated by CCK (due to fat in SI), causing it to contract. Contraction forces bile down the common bile duct into the duodenum, where it aids in the digestion of fat.

16. Pancreas’ Role in the GI Tract Exocrine and endocrine gland Exocrine functions: Produces _________, _________, ___________ Secretes _____________ (HCO 3 - )into duodenum Neutralizes acidity of stomach contents and maintains pH in duodenum needed for proper enzyme function Endocrine functions: Produces ___________ & _________ Regulates blood glucose levels: Insulin moves glucose from the blood to the body’s tissues. Glucagon stimulates gluconeogenesis and glycogenolysis in the liver.