1 What types of food are most easily digested?
At first glance, the process by which food fuels our daily
activities might seem inexplicable. However, upon closer
examination, 2 digestion—the breakdown of food into
smaller components to provide the body with necessary
nutrients and energy— is a chemical and mechanical
process with a consistent sequence of steps.
3 Chewing first involves putting food inside the
mouth, where the grinding of teeth and secretion of saliva
start to break down the physical and chemical composition
of food. Once the food has been transformed into 4 a
compact mass referred to as a ‘bolus,’ it is swallowed and
passes through the esophagus, a muscular tube connecting
the throat to the stomach. Although the initial act of
swallowing is voluntary, the lower third of the esophagus
is made up completely of smooth muscle, over which
an individual has no conscious control. This lower third
attaches to the stomach—a hollow, muscular organ—which
then 5 digest food both by crushing it mechanically
and 6 secretes digestive enzymes and other fluids that
break down starches and proteins. 7 The contents are
then released into the small intestine.
Although all organs in the gastrointestinal tract are
important for digestion, the majority of nutrient absorption
occurs in the small intestine, which is a long, hollow tube
arranged into a compressed mass around the center of the
abdomen. On the inner surface, this organ is lined with
specialized cells arranged into finger-like “villi” and circular
“plicae” that facilitate the 8 transfer of important nutrients
being transported into the bloodstream. The small intestine
is 9 divided into three parts; the duodenum, the jejunum,
and the ileum. In the duodenum, digestive juices from
the pancreas and gall bladder enter through an opening
referred to as the “ampulla of Vater.” These juices break
down carbohydrates, lipids, and polypeptides into simpler
molecules. The jejunum then links the duodenum to the
ileum, which is where the majority of nutrient absorption
takes place. 10 Instead, the remaining materials move
into the large intestine, where water and salts continue to
be absorbed.
Once in the bloodstream, nutrients from the digestive
tract travel through the cardiovascular network to the liver
and then to many different areas of the body. The
11 energy, from cellular division to muscle contraction,
contained in these molecules can then be used to activate
a number of biological processes. Although we are rarely
aware of it, our bodies are constantly at work to provide us
with the resources necessary to sustain our lives.
At first glance, the process by which food fuels our daily
activities might seem inexplicable. However, upon closer
examination, 2 digestion—the breakdown of food into
smaller components to provide the body with necessary
nutrients and energy— is a chemical and mechanical
process with a consistent sequence of steps.
3 Chewing first involves putting food inside the
mouth, where the grinding of teeth and secretion of saliva
start to break down the physical and chemical composition
of food. Once the food has been transformed into 4 a
compact mass referred to as a ‘bolus,’ it is swallowed and
passes through the esophagus, a muscular tube connecting
the throat to the stomach. Although the initial act of
swallowing is voluntary, the lower third of the esophagus
is made up completely of smooth muscle, over which
an individual has no conscious control. This lower third
attaches to the stomach—a hollow, muscular organ—which
then 5 digest food both by crushing it mechanically
and 6 secretes digestive enzymes and other fluids that
break down starches and proteins. 7 The contents are
then released into the small intestine.
Although all organs in the gastrointestinal tract are
important for digestion, the majority of nutrient absorption
occurs in the small intestine, which is a long, hollow tube
arranged into a compressed mass around the center of the
abdomen. On the inner surface, this organ is lined with
specialized cells arranged into finger-like “villi” and circular
“plicae” that facilitate the 8 transfer of important nutrients
being transported into the bloodstream. The small intestine
is 9 divided into three parts; the duodenum, the jejunum,
and the ileum. In the duodenum, digestive juices from
the pancreas and gall bladder enter through an opening
referred to as the “ampulla of Vater.” These juices break
down carbohydrates, lipids, and polypeptides into simpler
molecules. The jejunum then links the duodenum to the
ileum, which is where the majority of nutrient absorption
takes place. 10 Instead, the remaining materials move
into the large intestine, where water and salts continue to
be absorbed.
Once in the bloodstream, nutrients from the digestive
tract travel through the cardiovascular network to the liver
and then to many different areas of the body. The
11 energy, from cellular division to muscle contraction,
contained in these molecules can then be used to activate
a number of biological processes. Although we are rarely
aware of it, our bodies are constantly at work to provide us
with the resources necessary to sustain our lives.