Download Digestive System Even when you are sitting still, your body systems

Digestive System
Even when you are sitting still, your body systems are constantly responding to changes within and
around you to maintain homeostasis. In order for your systems to be able to function properly they need the
food you eat to be converted into nutrients that the body’s cells can use. How does the food get to that usable
form?
Digestion is the breaking down of large
food molecules into smaller, more usable ones.
Large food molecules must be broken down both
physically and chemically. The physical
breakdown of food is called mechanical digestion.
This form of digestion begins in the mouth, where
food is chewed into smaller pieces that are easy to
swallow. As the food is chewed, it mixes with
saliva. Saliva moistens the food particles, which
is what makes swallowing easier. This mixture is
called chyme. It also begins chemical digestion by
adding digestive enzymes to the food. The
digestion of starches begins here.
When food is swallowed, it enters the
esophagus, a muscular tube that pushes the food
along with wavelike contractions called
peristalsis. Food is pushed into the stomach,
where the digestion of protein begins. Acid that is
produced in the stomach kills most of the bacteria
that entered with the food, and it acts as a
“switch” to turn on enzymes that will continue
chemical digestion.
From the stomach, food is pushed into the
small intestine. There, bile from the liver and enzymes made by the small intestine and pancreas complete
digestion. The proteins are reduced to amino acids, complex carbohydrates are changed into simple sugars, and
lipids are changed to fatty acids and glycerol. The nutrients can then be absorbed into the blood stream and the
lymph. Millions of tiny, fingerlike projections, called villi, line the small intestine (see diagram). The villi
increase the small intestine’s surface area so that most nutrients
are absorbed by the time the food reaches the large intestine.
The small intestine is 20 feet in length. The undigested
material enters the large intestine, where water, some vitamins,
and minerals are absorbed into the bloodstream. The remaining
materials are eliminated (exit) from the body through the anus
as feces, or as you know it, poop.
Copy and answer the following in your notebook:
1. Define the following: Digestion and peristalsis.
2. Explain the difference between mechanical and chemical digestion. Be sure to include why each is important.
3. What is the role of enzymes in the digestive system? Explain why this is important.
4. Explain how the following is correct: “The digestive system does not give you energy.”
Name: ___________________________________ Class: __________
Regents Practice:
Nutrients in a diet, such as proteins, carbohydrates, and minerals, play an important role in homeostasis
within the human body. Lack of these nutrients can lead to malfunctions that disrupt this internal balance.
Explain how diet can influence homeostasis. In your answer, be sure to:
• select a nutrient from the passage and write it on the line below and state one role this nutrient plays
in the body [1]
• describe, using one specific example, how a decrease in this nutrient can alter homeostasis [1]
Nutrient: ________________________________
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