Transcript Ruminants and Complex Stomachs

“Health food makes me sick!
-Calvin Trillin
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Ruminants only have one true stomach
(abomasum), but have 3 forestomachs (reticulum,
rumen, and omasum).
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The act of swallowing food, then regurgitating
it to chew it some more then swallow it again.
◦ How does regurgitation differ from vomiting?
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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.
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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.
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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
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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.
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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.
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Proteases- breakdown proteins to amino
acids and peptides
◦ Then can be broken down further to ammonia and
VFA’s.
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Ruminant is dependent on microbes to digest
nutrients.
Very delicate balance
◦ Changes in diet can upset this balance
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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
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Functions very similar to that of
mongastric stomach.
Only glandular part of the stomach.
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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
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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.
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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 sphinctermuscle that regulates movement of materials
from small intestine into colon or the cecum
(blind pouch of the large intestine).
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Similar to other segments of GI tract.
Thickness changes depending of area of GI
tract.
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Inner mucosal layer
Submucosal layer
Muscular layer
Serosal layer
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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.
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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.
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Ileus- decreased movement of ingesta.
◦ May be caused by disease or stress.
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Cholecystokinin (CCK)
◦ Stimulates intestinal motility (opposite of gastric
motility)
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Prostaglandins
◦ Increase GI motility and secretions.
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Absorbed intact into small intestinal wall
are:
◦ Sodium
◦ Chloride
◦ Postassium
 The above are collectively known as electrolytes
◦ Vitamins
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Must be chemically broken down to absorb
in small intestine are:
◦ Carbohydrates
◦ Proteins
◦ Fats
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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
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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.
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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
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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.
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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
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Consists of 4 sections:
◦ Cecum
◦ Ventral colon
 Right and left halves
◦ Dorsal colon
 Right and left halves
◦ Small colon
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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
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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.
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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
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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.
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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
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Storage compartment for bile.
Will force bile down bile duct to duodenum.
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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.