Surface and Glandular Epithelium (Nursing)

00:00 So first, let's start with surface epithelia. Surface epithelia, again, form the outer coverings and the inner linings of the body's organs. In covering and lining epithelia or surface epithelia, there are 3 surfaces. The most superficial or the top or the part that is facing a cavity or the free surface is referred to as the apical surface. The 2nd part is the basal surface. This is located at the bottom of the cell or the deepest portion of the cell. This is usually attached to some type of basement membrane usually by hemidesmosomes. The 3rd surface is going to be the lateral surfaces. These are the surfaces on each side of the cell that are going to interact or face the adjacent cells. This surface often contains multiple cell junctions as this is the way the cells are held together. The other type of epithelium that we find in the body is going to be glandular epithelium. Again, a gland is a single cell or massive epithelial cells that are adapted for secretion. There are 2 types of glandular epithelia. We have endocrine glands and we have exocrine glands. In endocrine glands, the secretions are going to enter either the interstitial fluid or they're going to be diffused into the bloodstream. In exocrine glands, the secretions are going to enter into ducts that then empty on to the surface of covering and lining epithelia such as the skin surface or the lumen of the stomach. So first, let's start with endocrine glands. Endocrine glands are glands that are going to secrete a substance that is likely going to be used in another part of the body. This works very closely with our blood vessels as our cardiovascular system and also the lymphatic system are going to carry these secretions also referred to as hormones from one part of the body to the other. Unlike endocrine glands where the secretory product is secreted into the bloodstream where then it is then taken to other parts of the body, with exocrine glands the secretory product is going to be released into ducts that are going to empty on to a surface of a covering or lining epithelium. There are multiple types of exocrine glands. You have unicellular exocrine glands and multicellular exocrine glands. An example of unicellular exocrine glands are the goblet cells that are found in the respiratory tract that release the mucous that we often cough up when we have a cold. With multicellular, we're going to actually have larger glands that are made up of multiple cells. Examples of multicellular epithelial glands include sweat glands, oil or sebaceous glands, and the salivary glands. When we categorize our multicellular exocrine glands, we do so structurally and functionally. When categorizing them structurally, we look at the shape of the duct as well as the shape of the gland. A simple exocrine gland has no branches whereas a compound exocrine gland has a branched duct. When we talk about the shape of the gland, there are 3 different shapes; acinar or alveolar which is a rounded shape, tubular which is a more elongated shape and also we can't really decide tubuloacinar and where the gland has an elongated shape but a round bulb at the end. So there are 3 functional classifications of glandular epithelia as well. There are merocrine glands, apocrine glands, and holocrine glands. Merocrine glands are made when the secretions are produced by the rough ER, process sorted and packaged by the Golgi, and then secreted by exocytosis and secretory vesicles to the extracellular space. In an apocrine gland, instead of exocytosis through secretory vesicles, the entire secretory product accumulates at the apical surface of the cell and then that entire portion of the cell pinches off. Lastly, in holocrine glands, the secretory product is going to accumulate in the entire cell then as a whole the entire cell ruptures and then it's replaced with a new cell. Now because the entire cell is rupturing, the secretions of holocrine glands often contain lots of lipids. So when you think about it, the reason why you have oily skin is because the sebaceous glands of the skin are a type of holocrine gland.