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.

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.

Small intestine Motility

PeristalsisCircular contractions prevent backflow of ingesta, longitudinal

muscles propel ingesta caudallyDilation of bowel with ingesta stimulates peristalsisCCK 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.

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

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)

Food Enzyme Source Broken into Fate Starch Amylase Saliva, Pancreas Disaccharides

lactose sucrose maltose

Lactase Brush border MonosaccharidesSucrase glucose AbsorbedMaltase galactose Absorbed

fructose Absorbed

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

Food Enzyme Source Broken into Fate Protein Pepsin Stomach Polypeptides

Proteases SI (Pancreas) PeptidesPeptidases Brush border Amino acids Absorbed

di-peptides Absorbedtri-peptides Absorbed

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 microvilliVitamins A, D, E, K are often absorbed with the micelles

Food Enzyme Source Broken into Fate Lipids Bile acids SI (Liver) small fat droplets

Lipases SI (Pancreas) glycerol Absorbedfatty acids Absorbedmonoglycerides Absorbed

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

Large Intestines ____________: simple, tubular colon;

poorly developed cecum

__________ __________: very large colon and cecum (hindgut)

Fermentation siteModifications of cecum and

colon allow fermentative digestion in hindgut

similar to rumenVFA’s (produced by microbes)

absorbed from cecum and colon for energy needs (similar to rumen)

Possible areas of impactionFlexures, Small colonCause of colic

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.

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.

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

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

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.

Pancreas’ Role in the GI TractExocrine and endocrine gland

Exocrine functions:

Produces _________, _________, ___________

Secretes _____________ (HCO3-)into

duodenumNeutralizes 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.