Full Title: Canine Large Intestine
Author: Ted Clark
Date of Publication: November 20, 2014
Research Paper Text:
The large intestine of the dog extends from the small intestine to the anus. Although connected it functions less a significant role in digestion than the small intestine. By example it’s about sixteen inches in length in a forty-pound dog and is larger in diameter than the small intestine. Its primary function is to absorb water from chyme which is partially digested food and gastric secretions that are in a semi solid form. As water is absorbed the resulting feces is in more of a solid form. Its other function is to store fecal matter awaiting passage from the body.
**Circular muscles line the inside and longitudinal muscles outside. Pacemaker cells*** receive neurologic messages causing those involuntary muscles and tissues to contract or dilate for transmission. It also contains lymph nodes and mucosal glands important for lubrication. Equally important to the nerves function, local (within the intestine) and vagally (cranial) are chemicals that send signals cell to cell; paracrine (for neighboring cells around the intestine) and endocrine (that flow with the blood throughout the body).
The large intestine has three distinct parts. *The cecum a small, finger-like projection near the junction of the small intestine; responsible for microbial fermentation, absorption and transportation every three to five minutes. It moves chyme to the colon. Blood is supplied by the cranial artery.
The colon is the longest portion of the large intestine and is divided by three portions. Ascending is closest to the small intestine, transverse goes from the right side to the left of the abdomen, descending terminates within the pelvic cavity just inside the anus to the final portion of the large intestine called the rectum. Its blood supply comes from the caudal artery. It functions like the cecum responsible for microbial fermentation, absorption yet a more important part of transportation. The terms colon and large intestine are commonly used interchangeably.
The rectum stores feces and when filled stimulates pressure sensitive cells within the walls of the rectum initiating the reflex for defecation. Two sphincter muscles control the aperture.*
* McGavin DM & Zachary, JF: Pathologic Basis of Veterinary Disease 4th edition pp.301-393
** Strombeck’s small animal Gastroenterology, 3rd edition pp.889-910