Digestive System Review Unit # 4 Lesson 4 -5
t 1. Differentiate between physical and chemical digestion
_ and state the function of each.
t Physical digestion is where the food is physically broken down into smaller pieces,
h such as in the mouth. This is done to increase surface area, and also because
substances have to move across a cell's membrane to get inside of it. The
e substance must be small enough to pass through the membrane, and also be in
_ solution. Physical digestion serves to break down food into smaller pieces and also
t mix it with gastric juices so the food can be in solution. This thick liquid is called
o chyme Chemical digestion is when the food is chemically broken down into smaller
m molecules by the aid of acids and enzymes for the absorption of nutrients. It serves
a to break complex molecules in the food into smaller ones so that they can pass
c through cell membranes, where they are used as needed.
_ 2. Define ingestion, digestion, absorption, and elimination.
f - ingestion: refers to how food is taken in and broken down inside the mouth. In
r humans, food is broken down in the mouth physically by teeth and chemically by
o saliva. In teeth, the incisors aid in cutting, canines aid in tearing, premolars aid
m grinding, molars aid crushing the food. Saliva moistens and lubricates food so it
_ passes down easily into the esophagus.
- digestion: refers to the chemical breakdown of large food molecules into smaller
i molecules that can be used by cells.
g - absorption:absorption takes place in the small intestine. The intestines walls are
e covered with villi which maximize the surface area available to absorb nutrients.
s Once nutrients are absorbed across the intestinal walls, nutrients enter the
t circulatory system and are delivered to the rest of the body.
i - elimination:elimination removes toxic waste from our bodies. Indigestible material
that remains at the end of digestion is called feces. The material passes into the
g rectum and anal canal. From there, the feces passes out of the body through the
t 3. Why are you able to swallow water while standing on
e your head?
l Food moves by the process of peristalsis. Circular and longitudinal muscles contract
f to push the food forward. Once the water is in your throat, peristalsis pushes/
moves it to the stomach; regardless of which way you are standing, it has no effect
# on peristalsis.
z 4. How do the teeth and tongue function in digestion?
1 As I mentioned previously, the teeth aid in the physical digestion of food by
d chewing (cutting, grinding, and crushing food so it can be broken down into smaller
pieces. The tongue aids in positioning the food inside the mouth as we chew it. It is
E muscular and pushes food to the back of the mouth where it is swallowed. The
V upper surface of the tongue is also covered with structures called papillae, which
d house our taste buds and allow us to tell whether our food is sweet, bitter, salty,
5. What prevents food from entering the trachea?
When you swallow, the esophagus and the trachea move up against a covering
called the epiglottis, a flap-like structure. This actions seals off or closes the
epiglottis and food is prevented from entering the trachea.
6. What is the purpose of saliva?
Saliva is a mixture of water and amylase, which is an enzyme that breaks down
starch into smaller disaccharide sugar molecules. Saliva also moistens and
lubricates food when it enters the mouth so it can be passed down to the next part
of the digestive system more readily. There is a continuous secretion of amylase to
keep the mouth moist.
7. What prevents self-digestion of the stomach?
The stomach contains a thick mucus lining. This protects the stomach from the
harmful effects of the acidic environment of the stomach and stops the stomach
8. What is the combined effect of sphincter muscles and
peristalsis in the stomach?
When the sphincters muscles are closed, food is confined to remain inside the
stomach and is subjected to churning and gastric juice. Peristalsis pushes the food
down and along the stomach by wavelike muscular contractions and relaxations, as
it is broken down and mixed with gastric juices.
9. What would be the result if the stomach did not have
If the stomach did not have sphincter muscles, food would not remain long enough
inside the stomach to be digested. Food would keep entering the stomach from the
esophagus and since there would be no pyloric sphincter to control the flow of food
leaving the stomach, the food would not remain inside the stomach for a long
enough time. Also, a cardiac sphincter prevents food in the stomach from
reentering into the esophagus. Without the splinter, the food (mixed with acid)