Food fulfills a cat’s basic need for nourishment. The cat’s digestive system takes the food on a journey as it undergoes multiple processing stages, starting the moment it enters the mouth. It has six basic functions: food intake, food transport, food breakdown, nutrient absorption, nutrient storage, and waste elimination. Hunters by nature, their body is well-designed for digesting prey.
During digestion, complex chemical processes take place. Enzymes trigger the breakdown of large pieces of food into simpler compounds, called nutrients, tiny enough to cross cell membranes. These nutrients are what the cell’s need for energy to function properly. Examples of these nutrients are proteins and amino acids, carbohydrates, fats and lipids, minerals, vitamins, and water.
The feline’s digestive system involves the tubular alimentary tract and gastrointestinal tract (GI), running from the mouth to the rectum, as well as the liver and pancreas, both of which play important roles.
The journey begins the moment the cat grabs the food with its teeth and lips. Unlike in humans who have enzyme-filled saliva to start the food breakdown process immediately, cats use the saliva to moisten and lubricate the food. With the help of teeth to cut the food into smaller chunks, the saliva makes it easy for the food to be swallowed.
Once the tongue pushes food back through the pharynx, it enters the esophagus. The esophagus is a small hose-like tube, connecting the mouth to the stomach, and serves to connect the mouth to the stomach. With wave-like contractions, the muscular walls of the esophagus immediately push the food into the stomach within minutes.
In the stomach, positioned in the left side of the abdominal cavity behind the liver, the digestion begins. Inside the sac-like structure are a series of folds called gastric folds. These folds function to help grind and digest the food. The food is also mixed with gastric secretions like hydrochloric acid and digestive enzymes which start the food breakdown process. Other glands secrete mucus that thinly coats the mucosa, or lining of the stomach, to protect it from the damaging acid and enzymes. Once the initial stomach digestive process is complete (approximately 12 hours after eating), the partially digested food exits the stomach through the pyloric sphincter area.
The food then enters the small intestine, which extends between the stomach and the large intestine. On the internal surface, the intestinal mucosa has microscopic, fingerlike projections called villi, which are covered with even smaller microvilli. This arrangement maximizes the surface area of the hollow, mucosa-lined intestinal tubes, providing more absorptive surfaces for nutrients in the cat’s digestive system. It is the longest portion of the GI tract, approximately 2.5 times the animal’s total body length. Because of its length, it is divided into three parts.
First is the relatively short duodenum, which is attached to the stomach. As food passes through, it is mixed with bile and pancreatic enzymes. These are produced by the gallbladder and pancreas, connected by the bile and pancreatic ducts respectively, and help further digest the food. The bible is a fluid that neutralizes the stomach acid, emulsifies and helps absorb fat, and carries some waste. Pancreatic secretions also neutralize stomach acid and enzymes aid in the digestion of carbohydrates, fats, and proteins. Without these enzymes, the body would be unable to absorb nutrients because they would not be broken down enough to pass through the intestinal mucosa into the blood.
Following the duodenum is the jejunum, the small intestine’s longest segment, and
can have up to eight loops. Rich in villis, the jejunum is the portion of the GI tract where the body absorbs the most nutrients. Intestinal contents later empty into the ileum, which links the small intestine and large intestine, into the large intestine.
Larger in diameter than the small intestine, the large intestine has the primary function of absorbing water from feces, keeping the hydration level of the body constant. Its other function is to store fecal matter awaiting passage from the body. The large intestine is divided into the cecum, which is similar to the human appendix, the colon, the site of water resorption and fecal formation, and the rectum, where the feces will pass through.
Diseases in the Gastrointestinal System
- Congenital defects can occur in the GI tract. They may lead to defects in swallowing or movement of food through the esophagus, inability to properly digest food, or inability to defecate.
- Infections: Infectious agents including bacteria, viruses, fungal, and protozoal organisms, as well as parasites are common.
- Inflammation: Can develop anywhere along the GI tract, can be acute or chronic
- Inflammatory Bowel Disease (IBD): It is a microscopic infiltration of the small intestinal wall with inflammatory cells. It is believed to be associated with an abnormal immune response to environmental stimuli, creating a self-perpetuating inflammation that could result in the disease.
- Foreign bodies may result in local inflammation, obstruction, and sometimes perforation of the GI tract.
- Ulcerative gastroenteritis: Interruptions in the lining of the GI tract may develop and be secondary to inflammation, drug administration, neoplasia, or foreign bodies
- Maldigestion and malabsorption disorders.
- Trauma can occur along different segments of the GI tract.
- Tumors can occur anywhere in the GI tract. Different tumors arise in different areas because the types of cells present in each area are unique. Can be benign or malignant and can grow into the cavity of the tract or involve the wall of the tract or the surrounding soft tissues.
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