Histology: Epithelial Tissues

As a follow up to my previous entry, here are the final versions of the laboratory photos I took last Monday using the Sony Ericsson K800i. I did away with the large texts produced by the phone’s default Photo DJ editing software and instead tweaked, cleaned and resized the photos using Photoshop CS.

For those who are taking up Histology classes, I hope the photos below will be of great help in your studies.

The specimes were representative samples of the different epithelial tissues found in the different organs and parts of the human body. Epithelial tissue is a diverse group of tissue that cover or line all body surfaces, cavities and tubes. Thus, epithelial tissue perform a myriad of functions since they act as interfaces between different biological compartments and even the outside environment.

Epithelial morphology and physiology, meaning their properties and functions vary depending on their location in the human body. They could be classified into the following:

Shape

  • Squamous: Squamous cells are flat cells with an irregular flattened shape. A one-cell layer of simple squamous epithelium forms the alveoli of the respiratory membrane, and the endothelium of capillaries, and is a minimal barrier to diffusion. Other places where squamous cells can be found include the filtration tubules of the kidneys, and the major cavities of the body. These cells are relatively inactive metabolically, and are associated with the diffusion of water, electrolytes, and other substances.
  • Bowman's capsule

  • Cuboidal: As the name suggests, these cells have a shape similar to a cube, meaning its width is the same size as its height. The nuclei of these cells are usually located in the center.
  • Human stomach

  • Columnar: These cells are taller than they are wide. Simple columnar epithelium is made up of a single layer of cells that are longer than they are wide. The nucleus is also closer to the base of the cell. The small intestine is a tubular organ lined with this type of tissue. Unicellular glands called goblet cells are scattered throughout the simple columnar epithelial cells and secrete mucus. The free surface of the columnar cell has tiny hairlike projections called microvilli. They increase the surface area for absorption.
  • Unirary Bladder

  • Transitional: This is a specialized type of epithelium found lining organs that can stretch, such as the urothelium that lines the bladder and ureter of mammals. Since the cells can slide over each other, the appearance of this epithelium depends on whether the organ is distended or contracted: if distended, it appears as if there are only a few layers; when contracted, it appears as if there are several layers.

Stratification

  • Simple: There is a single layer of cells.
  • Stratified: More than one layer of cells. The superficial layer is used to classify the layer. Only one layer touches the basal lamina. Stratified cells can usually withstand large amounts of stress.
  • Unirary Bladder

  • Pseudostratified with cilia: This is used mainly in one type of classification (pseudostratified columnar epithelium). There is only a single layer of cells, but the position of the nuclei gives the impression that it is stratified. If a specimen looks stratified, but you can identify cilia, the specimen is pseudostratified ciliated epithelium since stratified epithelium cannot have cilia but may be very rarely found in fetal esophagus. A cell that contains hairs will be around ten times stronger than a regular cell

Specializations

Brown Skin

  • Keratinized cells contain keratin (a cytoskeletal protein). While keratinized epithelium occurs mainly in the skin, it is also found in the mouth and nose, providing a tough, impermeable barrier.
  • Trachea

  • Ciliated cells have apical plasma membrane extensions composed of microtubules capable of beating rhythmically to move mucus or other substances through a duct. Cilia are common in the respiratory system and the lining of the oviduct.

From protection from the outside environment via the keratinized skin, to absorption of oxygen in the lungs to helping the egg cell make its way into the uterus, epithelial tissue serves a multitude of roles and functions necessary for our survival.

More about epithelial tissues later on and it will be followed by another important kind of the epithelial tissues, the epithelial glands.

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