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*Epithelial tissue always has a free surface. Cells are close together and attached to basement membrane.
*Epithelial tissue types are named by their shape and number of layers.
Simple | One layer of cells |
|---|---|
Stratified | More than one layer of cells |
Pseudostratified | One layer of cells that appears to be many layers. |
Squamous | Flat cells |
Cuboidal | Cube shaped cells |
Columnar | Column shaped cells, tall and skinny |
Types of Epithelial Tissue
Simple Squamous |
Found in the alveoli of the lungs, lines blood vessels. One layer of flat cells permits filtration and diffusion. |
Stratified Squamous |
Two types: keratinized and non-keratinized. Keratinized found in dry areas like the skin and non-keratinized stratified squamous is found in wet areas like the esophagus and vagina. The many layers of cells offer protection of these areas. |
Simple Cuboidal |
One layer of cube shaped cells. Simple cuboidal lines the kidney tubules. It's function is secretion and absorption. |
Stratified Cuboidal |
Many layers of cube shaped cells. Stratified cuboidal lines the mammary glands and salivary glands. Like stratified squamous, it's function is to offer protection of the areas it lines. |
Simple Columnar |
2 types: ciliated and non-ciliated. Non-ciliated can be found in the GIT. You will also find goblet cells here (which secrete mucus). Ciliated simple columnar lines the fallopian tubes, and the cilia beat to move the oocyte through the tube. |
Stratified Columnar |
Like other stratified epithelial types, it's function is to protect. Also secretion. Rarest epithelial type. |
Pseudostratified Columnar |
Lines the Upper Respiratory Tract where it functions to produce and move mucus. (Has cilia and goblet cells). |
Transitional |
Found in the lining of the urinary bladder. The cells change shape from a rounder appearance to a flatter one as the bladder fills, so their function is to permit distention of the bladder. |
Glandular Epithelium
Endocrine glands: Release their products (hormones) directly into the blood. Examples of endocrine glands are the thyroid, pituitary, and ovary.
Exocrine glands: release product (sweat, oil, ear wax, milk, etc) into a duct.
Holocrine | Apocrine | Merocrine |
The whole cell and contents are secreted into duct. Example: Sebacceous glands | Part of the cell pinches off and is secreted into the duct. Example: mammary glands. | Only the products are secreted into the duct. Most exocrine glands are this type. |
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