Epithelial Tissue

Epithelial Tissue Epithelial tissue is characterized by cellularity, that means that we will see many cells packed closely together. Remember that when you are naming epithelia, you first determine whether there is one layer of cells (simple) or more than one layer (stratified). Next, look at the shape of the cells in the apical (unattached) layer to decide whether it is squamous, cuboidal or columnar. Finally remember that pseudostratified and transitional (not shown) epithelia do not quite follow the naming convention! The following slides were provided by Dr. Heather Townsend The text was written by Eylana Goldman Goffe

This epithelial tissue is a simple cuboidal. Notice that one layer of square-shaped cells is surrounding a space. This space is called the lumen (L). The apical (A) surface of the tissue is against the lumen (unattached), while the basal (B) surface is along the opposite (attached) side of the tissue. The nuclei are centered within each cell. If you look carefully, you can see some connective tissue along the basal side of the tissue (CT). The basement membrane (though not stained here) is located at this junction. CT B A A L CT

This epithelial tissue is a simple columnar. Notice that one layer of elongated cells is surrounding a space. This space is called the lumen (L). The apical (A) surface of the tissue is against the lumen (unattached), while the basal (B) surface is along the opposite (attached) side of the tissue. The nuclei are located along the basal end of each cell. If you look carefully, you can see some connective tissue along the basal side of the tissue (CT). The basement membrane (though not stained here) is located at this junction. B A CT L

This epithelial tissue is a psuedostratified columnar epithelium. This tissue looks like it has more than one layer of cells, because some of the cells are shorter than others and do not reach the apical surface. However, because all of these cell begin at the basement membrane, it is truly only a single layer. As before, the apical surface opens into a lumen (L), while the basal (B) surface is along the opposite (attached) side of the tissue. You can observe cilia on its apical surface. The nuclei are located along the basal end of each cell, but not in a straight line due to the differences in cell height. You can clearly see the connective tissue along the basal side of the tissue (CT). L A short cell B CT

This epithelial tissue is a stratified squamous epithelium. It clearly has multiple layers of cells (i.e. stratified). You can examine the shape of the cells in the apical surface to see that they are squamous (i.e. flattened). Remember that you may see cuboidal cells in the basal layers, but you have to use the cells in the apical layer to name the tissue. As before, the apical surface (A) opens into a space, which could be the lumen of an organ or the surface of the body. The basal (B) surface is along the opposite (attached) side of the tissue. The nuclei are visible throughout the layers of the tissue. They appear flattened in the squamous cells and round in the cuboidal cells. You can clearly see the connective tissue along the basal side of the tissue (CT). L A B CT

Connective Tissue The following slides were provided by Dr. Heather Townsend The text was written by Dr. Cindy Hansen

This does not look like epithelium, so you need to decide whether it is connective, muscle or nervous tissue. We see lots of fibers and relatively few cells; this is characteristic of connective tissue. Is this loose connective tissue or dense connective tissue? It is loose because we can see a lot of space between the fibers. This is areolar connective tissue. The thick purple fibers are collagen, the thin purple ones are elastin, and the purple dots are the nuclei of the scattered cells.

More connective tissue. The thick pink bands that you see are collagen fibers. The dark purple dots are the nuclei of the fibroblasts. Is this loose connective tissue or is it dense connective tissue? There is little to no space between adjacent fibers, so this would be a dense connective tissue. Is it dense regular or dense irregular ? Look at the collagen fibers. Do you see that they are all running in the same direction or running parallel to each other? That is characteristic of dense regular connective tissue.

Compare this to the previous slide. Again we are looking at connective tissue. There are pink collagen fibers and dark pink dots which are the nuclei of the fibroblasts. Is this dense or loose connective tissue? Look back at the areolar connective tissue if you are having trouble deciding. This is dense…there is relatively little space between fibers…it is densely packed. Is this dense regular or irregular? Look at the fibers. Are they running neatly, all in the same direction? No. There is a suggestion of whorls here. This is dense irregular connective tissue.

Here we again have an abundance of extracellular material and relatively few cells, so this looks like an example of connective tissue. We don’t see individual fibers, though. The extracellular matrix has a smooth, glassy appearance. This is a special type of connective tissue known as cartilage. We see holes called lacunae and we can see chondrocytes within the lacunae. This is hyaline cartilage.

Here again, we see lacunae and chondrocytes within the lacunae. The extracellular material is not smooth and glassy. We see clumps of fibers that stain dark purple. These are elastic fibers. Look back at the hyaline cartilage slide. Do you see the similarities and differences between these two slides? The presence the of the elastic fibers in the matrix allows us to identify this as elastic cartilage.

More connective tissue. There is relatively a lot of extracellular material, and the small dark spots are the nuclei of scattered cells. There are several “tree trunks” or osteons present. Therefore, this is bone tissue, specifically, compact bone tissue. The dark circle at the center of the osteon is the central canal where nerves and blood vessels travel. The rings around the central canal are lamellae, or layers of bone. The osteocytes are found in lacunae between the lamellae.

Muscle Tissue

Here we see parts of cells running across this slide….these must be very long cells indeed! Notice that each cell has multiple purple, oval nuclei. Note also the prominent “stripes” called striations running across the cells. This has to be…….skeletal muscle tissue.

1 More muscle tissue, but this looks quite different from the previous slide. We see many complete cells; they are not as long as the skeletal muscle cells. Arrow #1 is pointing out a nucleus. There are not multiple nuclei per cell here. If you look carefully in some areas, you can see striations. The cells are branching. Where 2 cells meet, you can see a dark pink line called an intercalated disc. (arrow #2) This must be…cardiac muscle tissue. 2

More muscle tissue. We can see that it is arranged in two layers. The layer in the right portion of the slide has been cut longitudinally while the layer in the left portion of the slide has been cut transversely. Therefore, this is muscle tissue that is usually found with a longitudinal layer and a circular layer. The cells are densely packed together, and there are no striations to be seen. This must be…..smooth muscle tissue.

Nervous Tissue

This looks quite different from any of the other tissues we have looked at. It is our fourth and final tissue type…..nervous tissue. The fairly large purple “splotches” are the cell bodies of individual neurons or nerve cells. You can see multiple purple “strings” extending away from the cell bodies. These are processes. Some of them are dendrites and others are axons, but we will not try to distinguish between them here.

Epithelial Tissue