Describe the primary functions and characteristics of epithelial tissue There are three principal cell shapes associated with epithelial cells: squamous. Epithelium is one of the four basic types of animal tissue, along with connective . types are squamous, cuboidal, and columnar classed by their shape. Some columnar cells are specialized for sensory reception. The other basic tissues are connective tissue, muscle tissue, and nervous tissue, There are three types of epithelia, each distinguished by the number of cell.
Three There Kinds Of Epithelial Cells: Basic Are
And just to remind you, exocrine glands will release their substances directly to the target organ. Whereas endocrine glands usually release hormones but into the bloodstream, not to the target organ directly. And epithelial tissue comes in two forms. It can be simple and that means it's one layer thick. Or it can be stratified which means it can have two or more layers.
And where will you expect to find simple epithelium versus stratified epithelium. Well, you'll find simple epithelium in places where substances need to diffuse from two different places. For example the alveoli of the lungs are lined with simple epithelium because carbon dioxide and oxygen need to diffuse from the alveoli into the bloodstream and vice versa. And of course that will be pretty difficult if you had a thick layer of cells.
And you'd expect to find stratified epithelium in places that need to resist chemical or a mechanical stress. For example, the esophagus is lined with stratified epithelium. That's because the esophagus will have food coming through it. The food might be sharp, it might be hot and we want a thick layer of cells to protect the underlying tissue of the esophagus.
A stratified layer epithelium acts as that protective layer. Let's take a look at a section of simple epithelium and epithelial cells are attached to something known as the basement membrane. The basement membrane is not made up of cells but rather it's made up of different types of fibers.
For example one fiber that can be found in the basement membrane is collagen. And the basement membrane is semipermeable to certain substances and that's pretty important because epithelial tissue is avascular. That means that epithelial cells have no blood vessels which then makes us ask the question of how do they get nutrients?
They get nutrients from the underlying tissue. What happens is that nutrients will diffuse from the underlying tissue through the basement membrane to the epithelial cells. And that's how epithelial cells get their nutrients. Let's just recap some of the places that you'd expect to find epithelial cells. We already mentioned the outer layer of the skin, the tissue lining the mouth, esophagus and GI tract and of course this is not an exhaust of list.
In the tissue lining the kidney tubules, and the tissue lining blood and lymphatic vessels. And in fact the tissue that lines blood vessels and lymphatic vessels has a special name. It's known as endothelium. Let's talk about connective tissue.
Connective tissue supports tissues, connects tissues and separates different types of tissues from each other and then there are different types of connective tissue that don't necessarily fall into these neat categories. What are some examples of connective tissue?
Bones, cartilage, blood, lymph, adipose tissue which is fat. The membranes covering the brain and the spinal cord and other types of tissues. What does connective tissue look like?
What are some characteristics of connective tissue? Basically it has three components. It has what's known as a ground substance and then it has fibers.
The ground substance and the fibers together make up a matrix. Let's see what this looks like. Here we have the ground substance which is usually a viscous type of fluid. Then interspersed in the ground substance are fibers and then we have cells, and these cells are usually what is producing the matrix.
Neurons Bipolar neurons e. Muscle tissue is divided into two types based on structure and distribution. Striated muscle Cardiac muscle Skeletal muscle Smooth muscle Epithelium epithelial tissue Surface epithelium Glandular epithelium.
The epithelium is one of four basic types of tissues and is present in almost all organs of the human body as lining and glandular tissue. Classification according to function Surface epithelium Glandular epithelium Distribution: Different types of epithelia are formed from the three germ layers.
A specialized layer of tissue formed by closely aggregated cells that line the outer surface of organs, blood vessels, the skin, and the inner surface of body cavities. Divided into squamous, cuboidal, and columnar types. Surface epithelia are classified according to the number of layers, cell shape, and surface differentiation.
Criteria for classification Layers Simple epithelium: The cell shape of the upper cell layer of a type of epithelium determines the name for the whole epithelium. Characteristics Flat squamous epithelium Appearance: Keratinized epithelium is only found on the skin stratum corneum. The epidermis is a keratinized stratified squamous epithelium. Special surface epithelia Some surface epithelia possess more than one of the criteria mentioned above or occur especially often in a number of different organs.
Keratinized stratified squamous epithelium Keratinized stratified squamous epithelium is only found in the epidermis. Nonkeratinized squamous epithelium Definition: There are three different cell layers: There are three cell layers stratum basale , stratum intermedium, superficial layer between the basement membrane and the surface.
A single cell or group of cells that produce and secrete specific products e. Glandular epithelium commonly invaginates from surface epithelium into other tissue e. Glandular epithelium can be endocrine e. Depending on the type of gland, it secretes: Digestive juices containing enzymes saliva, gastric and pancreatic juices Sweat Sebum Breast milk Mucous mucins Classification: Glandular tissue can be classified according to its location, shape, secretory mechanism, and the type of secretion associated with it.
Classification criteria Location of glandular tissue Based on the location of glandular cells in relation to the surface epithelium , glands can be classified as either intraepithelial located in the surface epithelium or extraepithelial located beneath the surface epithelium. These components are named below in the sequence corresponding to the path of the secretion from formation to the opening: A closed glandular section that is connected to the excretory ducts and is the site of secretion production.
There are numerous types of terminal ends see shapes of the terminal ends of exocrine glands below. Because extraepithelial glands are usually subdivided into lobules or lobuli by connective tissue septa, there are various forms of excretory ducts. There are two special types present in several glands: An intercalated duct drains secretions from the terminal ends that are either transferred into a striated duct if the gland is present or directly into a larger intralobular duct.
The striated duct drains from several intercalated ducts and to an intralobular duct. Shapes of the terminal ends of exocrine glands Acinar glands Form: A portion of the cell membrane buds off with cytoplasm containing the secretory product e. As a result, the gland cell becomes smaller.
The basement membrane connects connective tissue with the following cell types: Epithelium and endothelium Glial cells Adipocytes and myocytes Structure: The basement membrane consists of the basal lamina ; contains two layers and the lamina fibroreticularis.
Basal lamina adjacent to the epithelium Lamina lucida lamina rara Integrins Collagen type XVII BP , or bullous pemphigoid protein Lamina densa Collagen type IV Laminin Lamina reticularis adjacent to the connective tissue Reticular fibers Anchorage with the basement membrane through collagen type III fibrils The basal lamina and lamina reticularis form the basement membrane!
Microscopy of cells and tissues Light microscope: Prepare and succeed on your medical exams.
Epithelium Study Guide
The cells in epithelia have different shapes, and different types of epithelia have different numbers of There are three main criteria for classifying epithelia. The three basic types of cell-to-cell junctions are tight junctions, gap junctions, they include additional types of cells interspersed among the epithelial cells. Epithelial cells (EC) are the first cell types to come into contact with external stimuli, cells are classified into three main cell groups according to their shape.