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