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“Health food makes me sick!-Calvin Trillin

Ruminants and Complex Stomachs

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

Rumination The act of swallowing food, then regurgitating

it to chew it some more then swallow it again.

◦How does regurgitation differ from vomiting?

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.

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.

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

Rumen

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.

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.

Fermentative Digestion

Proteases- breakdown proteins to amino acids and peptides◦ Then can be broken down farther to ammonia and

VFA’s.

Ruminant is dependent on microbes to digest nutrients.

Very delicate balance◦ Changes in diet can upset this balance

Fermentative Digestion

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.

Omasum abosrbs remaining VFA’s and removes bicarbonate ions

Abomasum Functions very similar to that of

mongastric stomach. Only glandular part of the stomach.

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.

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).

Small Intestines

Similar to other segments of GI tract.

Thickness changes depending of area of GI tract.◦ Inner mucosal layer◦ Submucosal layer◦ Muscular layer◦ Serosal layer

Small Intestine Structure

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.

Mucosa of Small Intestines

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.

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.

Small intestine motility

Absorbed intact into small intestinal wall are:◦ Sodium◦ Chloride◦ Postassium

The above are collectively known as electrolytes

◦ Vitamins

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

Small Intestine Digestion

Amylase- converts starch into smaller sugar segments

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.

Carbohydrate 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

Protein 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.

Fat Digestion

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

Large Intestine

Consists of 4 sections:◦Cecum◦Ventral colon

Right and left halves◦Dorsal colon

Right and left halves◦Small colon

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

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.

Ingesta flow in horse hindgut

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

Rectum

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.

Anus

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

Liver

Storage compartment for bile. Will force bile down bile duct to duodenum.

Gallbladder

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.

Pancreas

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