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| Simple Squamous Epithelium: | |
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| Here we see simple squamous epithelium as it would look from a "top" view. These cells are large, but quite thin, and have a prominent, protruding nucleus. A good analogy to their shape is the sunny-side-up fried egg. It has also been called "pavement epithelium, because it can look like like paving stones as seen from above (although paving stones don't have something similar to the nucleus, so I like the fried egg analogy better). This epithelium is called mesothelium (as it is derived from mesoderm) when it is found in certain locations within the body. These include the linings of the peritoneal, pleural and pericardial cavities. Other places simple squamous epithelium can be found include; the glomerulus of the kidney, the walls of capillaries, and the alveoli of the lungs, to name a few. Here they are forming a thin sheet-like layer which allows for minimal resistance to diffusion | Here we see simple squamous epithelium as seen in cross section. This photograph is of the peripheral portion of the chick blastodisc at about 33 hours of incubation. Even though there are several layers of cells visible, they are all distinct and separate simple squamous epithelium layers. In other words, they are each a different structure (here they are membranes), each of which is only one cell layer thick. One of the nuclei of a squamous cell is shown (arrows), which demonstrates how the nuclei can "bulge out" along the simple squamous epithelial layer. The membranes seen here are, from top to bottom: i. ectoderm, ii. somatic mesoderm, iii. splanchnic mesoderm and iv. endoderm (actually simple cuboidal epithelium, but that's hard to see here). |
| Simple Cuboidal Epithelium: | Simple Columnar Epithelium: |
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These are collecting ducts in the medulla of a mammalian kidney. Each duct is lined by simple cuboidal epithelium, whose edges generally aren't apparent, but whose nuclei are quite prominent (you can see how this epithelium got the name "cuboidal," as each cell is almost a perfect cube - a square in cross section, as seen here). This type of epithelium is thicker than simple simple squamous epithelium, so it does not allow for passive diffusion as readily. There are also a couple of squamous cells hanging out in this image. Try to differentiate them from the cuboidal cells present. |
This is a cross section through the small intestine. The tall, vertical cells seen at the top of the tissue are columnar cells (one is shown - red arrow), which make up simple columnar epithelium (the cells at the bottom of the image are connective tissue, which will be discussed later). Since columnar cells are quite thick, they do not readily allow passive diffusion. As a result, these cells use active transport to move nutrients through them from the intestine to the blood. This is what we commonly call "absorption." To help with this, they have numerous microvilli on their apical (lumenal) surface, which increases their surface area to allow for greater absorption. These are seen as a darker pink staining border at their lumenal edge. The black arrow is indicating a goblet cell. These cells show a triangular basal nucleus and a large amount of clear apical cytoplasm. The cytoplasm stains clear due to a large amount of mucus within it that the cell secretes to protect the intestinal cells from digestion by the digestive enzymes (your body wants to digest the food, not itself!). |
| Pseudostratified Columnar Epithelium: | |||||
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Here we see a cross section through the 33 hour chick, which shows the neural tube, mesenchyme and various other labelled structures. The slide on the right focuses on the pseudostratified columnar epithelium associated with the neural tube.
Please see a sketch of pseudostratified columnar epithelium if you find the pictures here confusing. |
Here we see a close up of the cranial neural tube region of the 33 hour chick. The neural tube is composed of pseudostratified columnar epithelium, who's apices surround and delineate the neurocoele. The base of every cell in the neural tube rests on the basal lamina (external limiting membrane) of the neural tube. However, since their nuclei are at differing heights within the cells (unlike simple columnar epithelium who's nuclei were at roughly the same height within the cell), it appears as though there are multiple layers of cells. In reality, though, pseudostratified columnar epithelium consists of only one layer of cells.
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| Stratified Squamous Epithelium: |
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Here we see the epidermis (outer part of the skin) of a frog showing typical stratified squamous epithelium and the dermis showing connective tissue. The cells of the basal layer of the epidermis (closest to the dermis) are cuboidal to columnar in shape. These cells are actively mitotic, producing new cells that get pushed upward into the overlying layers. As these cells are pushed up, they become flatter and longer (just as if you were to squash something), taking on the typical squamous shape. When the cells reach the top, they are sloughed off and replaced by cells from below. The dermis which underlies the epidermis is composed of a dense, irregular connective tissue, which we will see again later.
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Special thanks to Hans Christoffersen for the preparation of this page. Page revised March 7, 2000 by Genevieve Babcock.
Send comments to:
Sandra K. Ackerley (),
Department of Integrative Biology, University of Guelph, Guelph,
Ontario, Canada N1G 2W1.
Last page revision: December 9, 2005