The digestive system ingests and digests food, absorbs released nutrients, and excretes food components that are indigestible. The six activities involved in this process are ingestion, motility, mechanical digestion, chemical digestion, absorption, and defecation. These processes are regulated by neural and hormonal mechanisms.
absorption
passage of digested products from the intestinal lumen through mucosal cells and into the bloodstream or lacteals
chemical digestion
enzymatic breakdown of food
chyme
soupy liquid created when food is mixed with digestive juices
defecation
elimination of undigested substances from the body in the form of feces
ingestion
taking food into the GI tract through the mouth
mastication
chewing
mechanical digestion
chewing, mixing, and segmentation that prepares food for chemical digestion
peristalsis
muscular contractions and relaxations that propel food through the GI tract
propulsion
voluntary process of swallowing and the involuntary process of peristalsis that moves food through the digestive tract
segmentation
alternating contractions and relaxations of non-adjacent segments of the intestine that move food forward and backward, breaking it apart and mixing it with digestive juices
Visit this site for an overview of digestion of food in different regions of the digestive tract. Note the route of non-fat nutrients from the small intestine to their release as nutrients to the body.
Answers may vary.
1. Which of these processes occurs in the mouth?
A) ingestion
B) mechanical digestion
C) chemical digestion
D) all of the above
D
2. Which of these processes occurs throughout most of the alimentary canal?
A) ingestion
B) propulsion
C) segmentation
D) absorption
B
3. Which of the following stimuli activates sensors in the walls of digestive organs?
A) breakdown products of digestion
B) distension
C) pH of chyme
D) all of the above
D
4. Which of these statements about reflexes in the GI tract is false?
A) Short reflexes are provoked by nerves near the GI tract.
B) Short reflexes are mediated by the enteric nervous system.
C) Food that distends the stomach initiates long reflexes.
D) Long reflexes can be provoked by stimuli originating outside the GI tract.
A
1. Offer a theory to explain why segmentation occurs and peristalsis slows in the small intestine.
The majority of digestion and absorption occurs in the small intestine. By slowing the transit of chyme, segmentation and a reduced rate of peristalsis allow time for these processes to occur.
2. It has been several hours since you last ate. Walking past a bakery, you catch a whiff of freshly baked bread. What type of reflex is triggered, and what is the result?
The smell of food initiates long reflexes, which result in the secretion of digestive juices.