Biology, Eighth Edition (Raven)

Chapter 48: The Digestive System

Reflexes in the Colon

Why are many of the movements in the digestive system not under voluntary control? Much of the activity of the digestive system is influenced by the parasympathetic nervous system. Other activities are controlled by hormones. Very little in the digestive system is under conscious control. There is no need for voluntary control after food has been ingested. The digestive process, once started, will proceed until nutrients and water have been extracted from the food and the waste material is ready for defecation. Conscious control is limited to the intake and physical processing of food and the timing of defecation. These activities impinge on our other activities while internal digestion generally does not.

View the animation below, then complete the quiz to test your knowledge of the concept.


1.	Mass movements in the colon are stimulated by...

		A)	food in the stomach.
		B)	chyme in the duodenum.
		C)	feces in the rectum.
		D)	A and B
		E)	A, B, and C

2.	Mass movements of the colon are integrated by...

		A)	the enteric plexus.
		B)	parasympathetic reflexes.
		C)	local reflexes.
		D)	A and B
		E)	B and C

3.	Defecation is stimulated by...

		A)	the enteric plexus.
		B)	parasympathetic reflexes.
		C)	local reflexes.
		D)	A and B
		E)	B and C

4.	Defecation reflexes are stimulated by the presence of feces in the rectum.

		A)	True
		B)	False

5.	Mass movements of the colon propel its contents toward the rectum.

		A)	True
		B)	False