Esophagus

• The esophagus is a small tube that connects the mouth to the stomach, following a direct path through the neck and chest. The esophageal walls are muscles that undulate, pushing food into the stomach and collapsing when no food is present. It is difficult to perform surgery in this area because it is in the chest and has a slow healing rate.
  
  

Stomach

• A puppy's stomach is a balloon-type structure that stores food during the process of digestion. Food is carried to the stomach from the esophagus and passes through the cardiac sphincter. The outer layers of the canine stomach consist of gastric folds, which crush food and aid in digestion. The lining inside the stomach releases enzymes and acids, breaking down food before it enters the pyloric sphincter en route to the small intestine.
  
  

Small and Large Intestines

• The small intestine is a hose-like structure and is the largest segment of the intestinal tract, generally measuring two and a half times the puppy's length. The small intestine includes the duodenum, which attaches to the stomach as well as the gallbladder and pancreas; the jejunum, which contains finger-like projections that absorb nutrients; and the ileum, which connects to the large intestine. The canine's large intestine connects the small intestine to the anus. Its major function is the absorption of water from feces to help keep the puppy hydrated. It also stores feces prior to evacuation.
  
  

Diarrhea

• Diarrhea is a common ailment that afflicts puppies and is caused when digestive material moves swiftly through the intestine, producing loose stools and frequent bowel movements. Diarrhea has a range of potential causes, including food intolerance, diet change, intestinal parasites, bacterial infections, viral infections and toxins. Puppies are especially prone to intestinal parasites such as roundworms, hookworms, coccidia and giardia. These digestive parasites usually cause symptoms that include diarrhea, vomiting, weight loss, and blood or mucus in the stool. Puppies are also more likely to suffer viral infections such as parvo, distemper and coronavirus. Veterinary attention is generally recommended for puppies suffering from digestive disorders, because wormers, antibiotics and intravenous fluids may be necessary.