Like the stomach, the small intestine carries on mixing movements and peristalsis. The major mixing movement is called segmentation, in which small, ringlike contractions occur periodically, cutting the chyme into segments and moving it back and forth. Segmentation also slows the movement of chyme through the small intestine.
Peristaltic waves propel chyme through the small intestine. These waves are usually weak, and they stop after pushing the chyme a short distance. Consequently, chyme moves slowly through the small intestine, taking from three to ten hours to travel its length.
As might be expected, parasympathetic impulses enhance both mixing and peristaltic movements, and sympathetic impulses inhibit them. Reflexes involving parasympathetic impulses to the small intestine sometimes originate in the stomach. For example, food filling the stomach distends its wall, triggering a reflex (gas-troenteric reflex) that greatly increases peristaltic activity in the small intestine. Another reflex is initiated when the duodenum fills with chyme, stretching its wall. This reflex speeds movement through the small intestine.
If the small intestine wall becomes overdistended or irritated, a strong peristaltic rush may pass along the entire length of the organ, sweeping chyme into the large intestine so quickly that water, nutrients, and electrolytes that would normally be absorbed are not. The result is diarrhea, a condition in which defecation becomes more frequent and the stools become watery. Prolonged diarrhea causes imbalances in water and electrolyte concentrations.
The ileocecal sphincter joins the small intestine's ileum to the large intestine's cecum. Normally, this sphincter remains constricted, preventing the contents of the small intestine from entering the large intestine, and at the same time keeping the contents of the large intestine from backing up into the ileum. However, eating a meal elicits a gastroileal reflex that increases peristalsis in the ileum and relaxes the sphincter, forcing some of the contents of the small intestine into the
Describe the movements of the small intestine.
How are the movements of the small intestine initiated?
What is a peristaltic rush?
What stimulus relaxes the ileocecal sphincter?
The large intestine is so named because its diameter is greater than that of the small intestine. This portion of the alimentary canal is about 1.5 meters long, and it begins in the lower right side of the abdominal cavity where the ileum joins the cecum. From there, the large intestine ascends on the right side, crosses obliquely to the left, and descends into the pelvis. At its distal end, it opens to the outside of the body as the anus.
The large intestine absorbs water and electrolytes from the chyme remaining in the alimentary canal. It also reabsorbs and recycles water and remnants of digestive secretions. The large intestine also forms and stores feces.
Was this article helpful?
This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.