Simple Epithelial Tissues

Simple epithelial tissues consist of a single layer or sheet of cells that is exposed to a lumen on the apical side and anchored to the basement membrane on the basal side. Because they are a single layer of cells in thickness, simple epithelial tissues are found in organs where substances are passed across the layer by processes such as diffusion, absorption, filtration, or secretion.

Simple Epithelial Tissues are Named According to Cell Shape

Squamous – scale-like, flattened cells that resemble the scales on a fish with a flat disc nucleus

Cuboidal – roughly cube-shaped cells (or as cube-shaped as a water balloon can be!) with a round nucleus

Columnar – tall, rectangle cells with an egg-shaped nucleus located near the basal side

As you learn how to recognize each type of epithelial tissue, remember to look at the shape of the nucleus and the number of cells layers!

Simple squamous epithelium

Simple squamous epithelium can be found in many locations in the body (e.g., lining blood vessels, lining the alveoli (air sacs) of our lungs, and in Bowman’s capsule of the kidney). To help you understand how to identify simple squamous epithelium, we have included two examples of this tissue. Table 1 and Figure 1 show simple squamous epithelium in the alveoli of the lung, while Table 2 and Figure 2 show simple squamous epithelium in Bowman’s capsule of the kidney. In both organs, you will see that this epithelium is made of a single layer of flattened cells.

Table 1: Simple squamous epithelium of the alveoli 

Tissue Type Simple Squamous Epithelium
General Description         Single layer of flattened, disc-shape cells
Location Alveoli of the lung
Function Allows for gas exchange between lungs and blood vessels
Helpful Hints This tissue is easily confused with adipose tissue – look for the flattened nuclei lined up in a row

Figure 1: Simple squamous epithelium of the alveoli with and without illustration overlay

Table 2: Simple squamous epithelium of Bowman’s capsule of the kidney

Tissue Type Simple Squamous Epithelium
General Description Single layer of flattened, disc shape cells
Locations Bowman’s capsule in the nephron of the kidney
Function Forms a thin boundary which gives structure to the cup-like structure
Helpful Hints Bowman’s capsule looks like a round bowl – look for the single row of flattened nuclei that touch the white space

Figure 2: Simple squamous epithelium of Bowman’s capsule of the kidney with and without illustration overlay

Check out our YouTube videos to help you understand simple squamous epithelium:

YouTube Video – Alveoli of the Lung

YouTube Video: Bowman’s Capsule of the Kidney

SPECIALIZED SIMPLE SQUAMOUS EPITHELIUM – ENDOTHELIUM

Simple squamous epithelium also forms the lining of all of our blood vessels, where it is called endothelium. The picture below shows the cross-section of a blood vessel. The small pink dots are red blood cells (RBC) inside the vessel. The single layer of nuclei surrounding that space (lumen) is the layer of simple squamous epithelium called the endothelium.

Figure 3: Simple squamous epithelium, endothelium, lining a blood vessel lumen 

Simple squamous epithelium (endothelium) lining the lumen of a blood vessel. Red blood cells (erythrocytes) fill the lumen of the vessel.

Simple cuboidal epithelium

Simple cuboidal epithelium can look a little different depending on the direction the tissue has been sectioned. To help you understand how to identify simple squamous epithelium, we have included two examples of this tissue. While both figures show simple cuboidal epithelium of the renal tubules in the kidney, Figure 4 shows a cross section and Figure 5 shows a longitudinal section. In both examples, you will see that this epithelium is made of a single layer of cube-shaped cells with round nuclei.

Table 3: Simple cuboidal epithelium

Tissue Type Simple Cuboidal Epithelium
General Description Single layer of cube-shaped cells with round nuclei
Locations Tubules of kidney, follicles of the thyroid gland, salivary gland, surface of ovaries
Function Absorption and/or secretion 
Helpful Hints Cells surround the lumen (inside) of the kidney tubule, so they may not look perfectly cube-shaped – look for the round nuclei

Figure 4: Simple cuboidal epithelium of the renal tubule of the kidney (cross section) with and without illustration overlay

Figure 5: Simple cuboidal epithelium of the renal tubule of the kidney (longitudinal section) with and without illustration overlay

Check out our YouTube videos to help you understand simple cuboidal epithelium:

YouTube Video: Simple Cuboidal Epithelium

Simple columnar Epithelium

Table 4: Simple columnar epithelium 

Tissue Type  Simple Columnar Epithelium
General Description Single layer of column (rectangular)-shaped cells with oval nuclei usually located near the basal side of the cell
Location Lining of intestines, stomach, and gallbladder
Function Absorption and/or secretion
Special Features May contain goblet cells to secrete mucus, often cells have microvilli which appear as a fuzzy apical edge (called the brush border in the small intestines)
Helpful Hints Depending on the direction of the tissue section, the appearance of the tissue may change. Longitudinal section will have a long row of cell with empty space at the apical side. Cross section will have a ring of cells with empty space in the center where the apical side touches the lumen.

Figure 6: Simple columnar epithelium of the small intestine (ileum) with and without illustration overlay

Check out our YouTube videos to help you understand simple columnar epithelium:

YouTube Video – Simple Columnar Epithelium

Chapter Illustrations By:

Juan Manuel Ramiro-Diaz, Ph.D.

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Anatomy and Physiology I: An Interactive Histology Atlas Copyright © 2024 by Karen Wiles; Christina Wilson; Juan Manuel Ramiro-Diaz; Georgios Kallifatidis; and Soma Mukhopadhyay is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

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