Gastrointestinal Tract

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Gastrointestinal Tract

• Part 2

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The Simple Stomach/ Monogastric

• Main sections
• Fundus rounded section above esophageal opening
• Expands with contents
• Body middle section
• Also distensible
• Pyloric antrum lower, small end

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Sphincter Muscles

• sphincters are muscles in a ring shape that close
  an opening when they contract
• CARDIAC SPHINCTER located between the esophagus
  and stomach.
• Food enters when it relaxes.
• Sphincter tightens when digestion is taking
  place. (Prevents reflux)
• PYLORIC SPHINCTER located between the pylorus
  and the duodenum.
• Contracts to prevent stomach contents from
  escaping during digestion.
• Relaxes to allow contents to leave stomach and
  continue to intestines.

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Gastric Layers and Glands

• Outer serosa layer
• Muscular layer
• Circular muscle
• Longitudinal muscle
• Oblique muscle
• Submucosa
• Contains blood vessels
• Mucosal lining
• Contains many tubular gastric glands that secrete
  digestive enzymes, mucin, and HCl

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Gastric Layers and Glands
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PERISTALSIS involuntary, wavelike movement of
the intestinal tract propelling contents through
the GI tract. Produced by circular and
longitudinal muscle fibers of tubular structures.
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• CHYME viscous, highly acidic, semiliquid
  contents of stomach after digestion. Moves
  through digestive tract via peristalsis.

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Ruminants

• RUMINATION
• regurgitation, remastication, insalivation, and
  reswallowing of partially digested food.
• this process allows fermentation of food by
  bacteria and protozoa which digest cellulose and
  produce energy for the body
• Occurs in RUMINANTS (ex cattle, goats, sheep,
  llamas, camels, deer).

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Ruminant Stomach

• 4 CHAMBERS
• Reticulum
• Rumen
• Omasum
• Abomasum
• Three forechambers to true stomach are called
  diverticula. They help ferment food by soaking
  it and subjecting it to digestive microorganisms.

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Rumination
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The Reticulum

• Smallest, most cranial chamber
• Honeycomb in appearance (increase surface area
  for absorption)
• Separated from heart by diaphragm
• Hardware disease
• Heavy objects drop into reticulum and can pierce
  diaphragm and pericardium

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The Rumen

• Also called the paunch
• Large sac extending from the diaphragm to the
  pelvis
• Left side of abdominal cavity
• Makes up 20 of the animals body weight
• Made up of numerous long papillae.
• Divided into the ventral and dorsal sac.

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The Omasum

• The book stomach
• Round, lined with short, blunt papillae in-folds
  that grind roughage before entering the abomasum
• Squeezes fluid out of ingesta

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The Abomasum

• True stomach
• Only glandular portion of the stomach.
• Functions like a monogastric stomach
• Secretes digestive enzymes to break down food
  particles
• Pylorus opens into small intestines.

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Other Structures of the Abdomen

• PERITONEUM membrane that lines the abdominal
  cavity and holds organs in place
• Visceral peritoneum
• Parietal peritoneum

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OMENTUM

• Fold of peritoneum, extending from stomach,
  overlying organs (like an apron).
• Lace-like in appearance

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MESENTERY

• Peritoneal fold that attaches the intestines to
  the dorsal abdominal wall

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The intestinal digestive juice containing mucus
and enzymes is stimulated by a hormone called
secretin. It is produced by the intestinal
glands as chyme reaches the small intestine. The
digestive process is completed in the small
intestine and the digested food is absorbed
through the intestinal walls by villi. Villi are
small thread like projections, it is these villi
that are sloughed when a dog contracts parvo virus
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SMALL INTESTINE

• Majority of nutrient absorption occurs here
• Entero- refers to intestines
• VILLI of the small intestine (threadlike
  projections that line the mucosa) is where
  absorption takes place.

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Parts of Small Intestine

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• DUODENUM
• Shortest, widest section
• Attaches to the pylorus of the stomach
• Pancreatic and bile ducts empty here
• Digestion and absorption
• JEJUNUM
• Middle section
• Held in place by mesentery
• Vigorous peristaltic wave action moves contents
  into the ileum
• ILEUM
• Empties into cecum at ileocecal valve

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Large Intestine

• Provides fermentation for monogastric animals
• Recovers fluid and electrolytes
• Stores feces
• Made up of cecum, colon, and rectum

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Cecum

• Pouch that forms the first portion of the large
  intestine
• Joins with the colon
• Larger in herbivores (due to fermentation)
• Primary function is to break down fibrous
  material
• Appendix is attached to cecum.
• Home for whipworms

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Colon

• Ascending, Transverse, Descending
• Diameter is wider than small intestine and wall
  is thinner.
• Haustra (a series of pouches), allow expansion
  and elongation of colon (like an accordion).
• Taenia are longitudinal bands of muscle of colon.

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Species Variations in Colon
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Rectum

• Section of descending colon, located within the
  pelvis that dilates to store feces until
  expulsion.
• ANUS termination of the digestive tract - made
  of both smooth and skeletal muscle
• COPROPHAGY-ingestion of fecal material
• Normal activity for rabbits
• Day feces (waste product) Night feces
  (vitamin-rich)

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PANCREAS

• Elongated gland located near the first part of
  the duodenum.
• Exocrine and endocrine gland.
• Exocrine cells secrete pancreatic enzymes needed
  for digestion and transfer them through a duct
  into the small intestine.
• Endocrine cells produce and secrete insulin and
  glucagon directly into the blood (no duct
  required).

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Pancreas
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LIVER

• Hepat/o liver
• largest gland in the body
• Exocrine gland located immediately caudal to
  diaphragm
• Soft, pliable red/brown in color
• Major functions
• Produces and secretes bile for digestion
• Metabolizes protein, fat, and carbs
• Filters and destroys foreign matter and
  neutralizes toxins
• Stores iron, glycogen, and vitamins
• Synthesizes most proteins in the body

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Liver
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GALLBLADDER

• Stores bile from the liver, which is secreted
  into the duodenum during digestion
• Bile is a fluid that aids in the digestion of fat
• Chole - means bile Cholecyst gallbladder
• RATS and HORSES do not have a gall bladder, their
  bile flows continuously from liver into the
  duodenum.

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Gallbladder
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Liver Gallbaldder