VPB 121: Veterinary Physiology - II (2+1)

OESOPHAGUS AND STOMACH

• Oesophagus is a muscular tube like structure extends from the pharynx to the stomach. In dog, cattle and sheep, the muscular layer is striated throughout the length of the oesophagus, whereas in pigs and horse, it begins as striated but becomes smooth muscles at caudal oesophagus.
• The pharyngeo – oesophageal junction is normally closed by oesophageal sphincter.
• Vagus is the main motor nerve regulates the motility of the oesophagus.
• During swallowing, the peristaltic wave travels from pharyngeo - oesophageal sphincter towards cardiac sphincter which is located at gastro-oesophageal junction.
• Reverse peristalsis/antiperistalsis is involved in bringing the gastric contents into the oesophagus during belching and regurgitation.
• Peristaltic waves, bucco - phryngeal pressure and gravity are responsible for the movement of food bolus through oesophagus, of which bucco - pharyngeal pressure is important for the passage of liquids.

Cardia

• The point of opening of oesophagus into the stomach is called cardia.
• It is provided with a sphincter muscle known as cardiac sphincter.
• It prevents back flow of food from stomach to oesophagus.
• Cardia is ordinarily closed except during swallowing and regurgitation.
• The cardiac sphincter is well developed and powerful in horse.
• The activity of cardiac sphincter is under the control of CNS.

Stomach

• It functions as a reservoir of food.
• Actively involved in grinding the food to reduce their size
• Initiates enzymatic digestion of food materials
• Controls the rate of passage of food to the small intestine for final digestion and absorption.
• Produces the intrinsic factor for the absorption of vitamin B12 from the intestine, which involves in hematopoiesis.

• Based on structure and function of stomach, domestic animals fall into two general classes.
  • Non-ruminants/ simple stomach animals – Horse, cat, dog, and pig.
  • Ruminants – Cattle, sheep , goat, camel and buffalo
• The stomach of nonruminants is simple consisting of only one compartment, whereas the stomach of ruminants is complex, consisting of four compartments (rumen, reticulum, omasum and abomasum) of which only abomasum secretes the gastric juice
• The stomach is a hollow, sac like organ made up of four layers - serous, muscular, submucosa and mucosa from outside to inside.
• The stomach mucosa of simple stomach animals, is divisible into oesophageal (glandless) region and glandular region. The glandular area includes cardiac, fundic (parietal) and pyloric regions.
  • In horse, oesophageal region is extensive up to 1/3 to 1/5 of the surface area of stomach. In the glandular region, the cardiac gland zone is very narrow, while the fundic gland zone is very wide.
  • In pig, the oesophageal region of the stomach is limited to a small area around the cardia. The cardiac gland zone is very extensive, whereas the fundic and pyloric gland zones are similar to those of horse.
  • In dogs, the oesophageal region is absent, the cardiac glands are found as a narrow zone scattered along the lesser curvature of the stomach around the cardia. The fundic glandular zone is extensive occupying about 2/3 of gastric mucous membrane.