The Digestive System,
Nutrition, and
Metabolism
E
atingissomethingyou do every day without
thinking much about it. After you eat that deli-
cious breakfast of waffles, sausages, and eggs, its
nutrients (including sugars, fats, and proteins) are
absorbed by your digestive system and whisked
away to provide fuel for your daily activities.
However, the nutrient molecules must be
broken down to their most basic form prior
to their absorption in the digestive system.
This process requires mechanical actions
to physically break down the food particles
and numerous secretions from the diges-
tive organs to chemically break down
the food molecules. After absorption,
nutrients are further processed by a
variety of cells in the body— converted
into cellular components and secre-
tions or used to form ATP (the cell's
energy-storing molecule).
The digestive system is composed
of a number of organs, many of which
are joined as a large tube. The remain-
ing accessory organs produce the
majority of the secretions that are used
to process the foods we eat. In this
chapter, we examine what happens as
you eat a meal and how the nutrients are
processed after they get to your cells. By
the end of this chapter, you should be able
to answer a wide variety of questions related
to the seemingly simple process of eating
your breakfast: How is food digested? How is it
absorbed? What is the fate of each type of nutri-
ent? How are those nutrients stored or broken
down? How do problems with metabolism lead to
diseases and, on the flip side, how do diseases lead
to problems with metabolism?
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