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Gastrointestinal Tract
Part 2
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
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.
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
Gastric Layers and Glands
PERISTALSIS: involuntary, wavelike movement of the intestinal tract propelling contents through the GI tract.Produced by circular and longitudinal muscle fibers of tubular structures.
PERISTALSIS: involuntary, wavelike movement of the intestinal tract propelling contents through the GI tract.Produced by circular and longitudinal muscle fibers of tubular structures.
• CHYME = viscous, highly acidic, semiliquid contents of stomach after digestion. Moves through digestive tract via peristalsis.
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).
Ruminant Stomach
4 CHAMBERS: Reticulum
RumenOmasumAbomasum
Three forechambers to true stomach are called diverticula. They help ferment food by soaking it and subjecting it to digestive microorganisms.
Rumination
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
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 animal’s
body weight• Made up of numerous long
papillae.• Divided into the ventral and
dorsal sac.
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
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.
Other Structures of the Abdomen
• PERITONEUM – membrane that lines the abdominal cavity and holds organs in place– Visceral peritoneum– Parietal peritoneum
OMENTUM • Fold of peritoneum,
extending from stomach, overlying organs (like an apron).
• Lace-like in appearance
MESENTERY• Peritoneal fold that attaches the
intestines to the dorsal abdominal wall
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
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.
Parts of Small Intestine • 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
Large Intestine
• Provides fermentation for monogastric animals
• Recovers fluid and electrolytes
• Stores feces• Made up of cecum,
colon, and rectum
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
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.
Species Variations in Colon
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)
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).
Pancreas
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
Liver
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.
Gallbladder
Liver & Gallbaldder