Video Transcript
Fill in the blank. The walls of the alveoli in the
lungs are made of a very thin epithelium to facilitate gas exchange. This epithelium is mostly composed
of blank cells. (A) Simple squamous, (B) stratified
squamous, (C) simple columnar, or (D) stratified columnar.
An epithelium is a type of tissue
which lines many surfaces of the body and is involved in protection, absorption, and
secretion. Epithelial tissues are made up of
epithelial cells, of which there are three types. These are squamous, columnar, and
cuboidal. Each of these cell types can be
either simple or stratified. Simple just means they are arranged
in a single layer of cells, and stratified means they are in two or more layers of
cells. Squamous cells are thin, flat cells
which can appear polygonal when viewed from above. Columnar cells are, as the name
suggests, column-shaped and elongated cells which are taller than they are wide. And cuboidal cells are cube-shaped
cells which appear square in cross section.
We’re told in the question that the
epithelium which lines the walls of the alveoli is very thin. This is so there is a short
diffusion pathway for the efficient exchange of oxygen and carbon dioxide between
the alveoli and the surrounding blood capillaries. To achieve this, the alveoli are
lined with a single layer of cells. And this layer is composed of the
thinnest, flattest epithelial cell type, squamous cells.
We can now correctly fill in the
blank with answer option (A). This epithelium is mostly composed
of simple squamous cells.