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Small Intestine Blood Vessels

Large intestine

Cecum

(of large intestine)

Figure 17.2

The alimentary canal is a muscular tube about 9 meters long.

Large intestine

Cecum

(of large intestine)

Figure 17.2

The alimentary canal is a muscular tube about 9 meters long.

Parasympathetic impulses generally increase the activities of the digestive system. Some of these impulses originate in the brain and are conducted through branches of the vagus nerves to the esophagus, stomach, pancreas, gallbladder, small intestine, and proximal half of the large intestine. Other parasympathetic impulses arise in the sacral region of the spinal cord and supply the distal half of the large intestine.

Sympathetic nerve impulses' effects on digestive actions usually are opposite those of the parasympathetic division. That is, sympathetic impulses inhibit certain digestive actions. For example, such impulses inhibit mixing and propelling movements, but contract sphincter muscles in the wall of the alimentary canal, blocking movement of materials through the tube.

So extensive are the nerve plexuses of the gastrointestinal tract that it is sometimes said to have a "second brain." The small intestine, for example, has at least 100 million neurons, many glial cells, and abundant and diverse neurotransmitters, neuropeptides, and growth factors.

What are the general functions of the digestive system?

Which organs constitute the digestive system?

Describe the wall of the alimentary canal.

Name the two types of movements that occur in the alimentary canal.

How do parasympathetic nerve impulses affect digestive actions? What effect do sympathetic nerve impulses have?

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