Glandular Epithelium
Emma Cunningham
What are Glandular Epithelium tissues?
Specialized epithelial cells that secrete bodily products that include two types known as endocrine and exocrine.
Secretory Components
Glandular epithelium cells can be unicellular or multicellular.
Exocrine glands have ducts (circumscribed channel leading from an exocrine gland or channel)
Endocrine glands do not have ducts
Mode of Secretion
Merocrine
This mode is used in exocytosis only, some examples of where it is used is in the pancreas and salivary glands. This mode of secretion is when secretions are excreted into an epithelial-walled duct then onto a bodily surface or a lumen.
Example - Sweat Glands located all over the body
Apocrine
This mode is known as decaptitation secretion, and some examples are apocrine sweat glands and mammary glands. This is when the cells close off their secretion by the plasma membrane which produces membrane bound vesicles in the lumen.
Example - mammary glands that secret breast milk
Holocrine
This mode can be defined as secretion of whole disintegrated cells. These secretions are produced in the cytoplasm and released when the plasma membrane ruptures, this destroys the cell and the secretion ends up in the lumen.
Example - meibomian glands found in the inside of the eyelid.
Types of Secretion
Serous
thin, watery protein-rich secretion, typically yellow and transparent
Example - sublingual glands, these are specific salivary glands in the mouth.
Mucous
Viscous secretion with a lubricating/protective function
Example - Salivary Glands in the mouth
Mixed Serous-mucous
Serous demilunes (cells) secret into the space between mucous cells
Examples - Glands on the tongue.
Glandular Structure
Simple Tubular
This gland appears as a tube with an opening on one end, I would describe it as looking like a very deep ditch
Example - Large intestines or uterine glands
Simple Coiled Tubular
This is when the gland is coiled but does not lose its tubular shape
Example - Sweat Glands
Simple Branched Tubular
This is when the gland has a tubular shape but there is more than one branching off of the original area, there are no branches branching off of the other branches.
Example - pyloric glands of the stomach
Compound Tubular
This gland appears almost like a tree, there is one specific branch, like the trunk from which all of the other branches originate and from these other branches come more branches.
Example - pyloric glands of the stomach
Simple alveolar
This is one long tube, and at the end of it is a small circular pouch.
Example - Salivary glands, esophagus, and mammary glands
Simple Branched Alveolar
There is one trunk from which the rest of the branches originate, however, instead of having branches, the glands appear more as pouches.
Example - Salivary glands, esophagus, and mammary glands
Compound branched alveolar
These again look like trees which branches branching from both the trunk as well as other branches. However, at the end of each branch, there is more of a pouch than a branch.
Example - Salivary glands, esophagus, and mammary glands
Function of Glands
Serous
This type of secretion aids in digestion, secretion as well as respiration. It also helps to lubricate between cells to avoid friction, especially in the lungs.
mucous
mucous is used as a protective secretion in the mucous membranes. In the stomach it lubricates the passage of food and protects the epithelial cells; in the nose and throat and lungs it can make it difficult for bacteria to penetrate the body through the epithelium.
Mixed Serous-mucous
Not only is this secretion used for lubrication between cells but it can also typically be found in the mouth and is an important part of digesting carbohydrates.
Differences between exocrine and endocrine glands
The secretion from endocrine glands are known as hormones and are collected by blood and transported through the circulatory system to each of the different kinds of tissues. These glands do not have ducts and therefore they secrete their products in between the cells into the spaces called intersitial spaces. Three examples of endocrine glands are the pituitary glands and the adrenal glands above the kidneys as well as the islet cells in the pancreas. Exocrine glands however secrete their products through ducts and into the skin, the intestinal lumen and the mouth. Two examples of exocrine glands are the sebaceous and salivary glands. Structures of the exocrine glands include all tubular as well as alveolar structures.
References
"The Endocrine SystemComplete Review." Biology Questions and Answers. N.p., n.d. Web. 10 Apr. 2013.
"Epithelial Cells." Glandular Epithelium. N.p., n.d. Web. 10 Apr. 2013.
"Glands." Glands. N.p., n.d. Web. 10 Apr. 2013
"SIU SOM Histology GI." SIU SOM Histology GI. N.p., n.d. Web. 10 Apr. 2013.