Video Transcript
Which of the following organs has
an outer layer of stratified squamous epithelial cells that function to protect the
body from entry by pathogens and are routinely shed and replaced? (A) Kidneys, (B) lungs, (C) heart,
(D) skin, or (E) liver.
To answer this question, first
let’s clarify what a stratified squamous epithelial cell is. Epithelial cells are those that
cover the surfaces of our body and organs. And as indicated in the question,
one of their main functions is to protect these internal and external surfaces.
The structure of epithelial tissue
consists of epithelial cells attached to a basement membrane with connective tissue
beneath it. Epithelial tissue is characterized
by the number of layers it possesses and by the shape of the cells in the outermost
layer. Epithelial tissue with only one
layer of cells is called simple epithelial tissue. Epithelial tissue with multiple
layers of cells is called stratified epithelium.
Now that we understand what a
stratified epithelial cell is, we just have to understand what the term squamous
refers to. The shape of epithelial cells have
various forms. If cells found in the outermost
layer of the epithelium are about as wide as they are tall, they are referred to as
cuboidal. If the cells in this outer layer
are taller than they are wide, we refer to them as columnar. If the cells in this top layer are
flat and irregular, we refer to them as squamous. So stratified squamous epithelial
cells are flat cells in the top layer of a tissue with multiple layers of cells that
cover our body and organs.
Now, let’s return to the question
and its answer options. Which option is the organ with a
layer of these specific cells that protects the body from the entry of
pathogens? The kidneys, lungs, heart, and
liver are all internal organs. So if a pathogen arrived at the
outer layer of these organs, it would already be inside the body. Therefore, none of these options
can be the correct answer to this question. The correct answer must be an
external surface of the body and one that is constantly shed and replaced. This is describing option (D),
skin.
