The diagram provided shows the
villi that line the ileum of the small intestine. What is the main purpose of the
villi? (A) To trap pathogens, dust, and
other unwanted substances and move them toward the stomach to be broken down. (B) To increase the surface area of
the epithelial lining so the maximum amount of substances can be absorbed. (C) To decrease blood flow to the
small intestine as part of the thermoregulation of the body. (D) To secrete mucus and provide a
protective lining for the small intestine.
The small intestine is a digestive
organ specialized in digesting food and absorbing nutrients. Let’s describe how this happens in
more detail by using the provided diagram.
The provided diagram shows a
magnified section of the small intestine. As you can see, it is coated in
little bumps called villi, which increase the surface area of the small
intestine. This increased surface area is
important, because it gives nutrients more room to diffuse into the cells of the
villi so they can enter the bloodstream. Each villi is made up of multiple
epithelial cells called enterocytes, which we can see here.
Nutrients can diffuse into the
enterocytes, and from there, they can diffuse into the capillaries of the
bloodstream or the lymphatic system. Water-soluble nutrients can enter
the bloodstream though the capillary network as shown here, and fat-soluble
nutrients can enter the lymphatic vessels by the lymph capillaries as shown
here. These are sometimes called
lacteals, and will enter the bloodstream later in the process.
These villi collectively make up
the mucosa or the mucous membrane of the small intestine. Because there are so many villi
present within the small intestine, this greatly increases its surface area to
absorb nutrients. Now that we understand the purpose
of the small intestine and how villi contribute to its function, we can answer the
The main purpose of the villi is
given by answer choice (B), to increase the surface area of the epithelial lining so
the maximum amount of substances can be absorbed.