In this lesson, we will explore what a gland is and the function that it performs. We'll also look at the many varied shapes that the tubular and alveolar structures take.
I'm sure you probably don't think of glands in your everyday life. In fact, some of you may even be thinking, 'Glands, what are those? Aren't those the things that swell when you get sick?' You would be right but those aren't the only type of glands in your body, and they do so much more than just swell when you get sick! They're responsible for everything from excreting sweat and tears to hormones and digestive enzymes. And, just to keep things interesting, they come in a few different shapes.
So, what's a gland? Glands are a collection of cells or an organ responsible for secretions and excretions. Secretion refers to the act of a substance moving internally from one part of your body to another, like when the lining of your stomach secretes digestive juices. Excretion describes how a substance leaves the body, such as when tears excrete from your tear ducts or sweat excretes from your sweat glands. Okay, so, now that we know what a gland is, let's explore some tubular and alveolar glands.
The glands in our bodies come in three overarching shapes. Acinar, meaning 'grape,' are ducts that have a large, bulbous collection of secretory and excretory cells within a small lumen, or interior space. They look something like a cluster of grapes in the body, hence their name. Tubular glands have cells of a consistent shape that form a uniform tubular lumen, while alveolar glands have cells of a similarly uniform size within a large, sac-like lumen. Tubular and alveolar glands can be further subdivided by their shape into simple, or non-branching glands, and compound, or branching glands.
Thankfully, the terminology for these glands is fairly self-explanatory, which should make them relatively easy to remember. Simple glands are exactly what you would think of in relation to shape: they have a simple straight duct, or opening, that connects the secretory and excretory cells, and where the exterior of the tissue is straight, without any complex branching systems. Tubular glands come in three simple shapes: simple tubular, simple coiled tubular, and simple branched tubular. Alveolar glands only have two simple shapes: simple alveolar and simple branched alveolar. Let's take a quick look at what these glands look like and where they might be found in the body.
Simple tubular glands are one of more uncommon shapes that, in a cross section, simply look like a straight test tube submerged in the tissue. These glands are found in the lining of the intestines, where they secrete mucous to help the byproducts of digestion pass through the intestinal tract.
Simple coiled tubular glands are like coiled tubes. They basically look like a garden hose tangled or coiled around itself at one end. The sweat glands in your skin are simple coiled tubular glands.
Simple branched tubular glands have a straight duct opening with branched clusters of secretory glands. They include the gastric glands of your stomach that produce acid, as well as the mucous secreting glands lining your esophagus, tongue, and duodenum of your small intestines.
Simple alveolar glands have a simple duct and a sac-like base. They are found in the paraurethral and periruethral glands of the urethra.
Simple branched alveolar glands have a simple duct and branched alveolar sacs. The oil-producing sebaceous glands in your skin, as well as the mucous secreting glands in your stomach that protect your stomach lining from the highly acidic gastric juices, are both examples of simple branched alveolar glands.
While simple glands have one straight duct that connects the secretory and excretory cells to the exterior tissue, compound glands have compound or branching ducts that join the branching network of glands to a single exterior opening. There are three types of compound glands: compound tubular glands, compound alveolar glands, and a hybrid of the two called a compound tubuloalveolar gland.
Compound tubular glands have a compound duct system with branching networks of tubular-shaped glands. These types of glands are found in the kidneys, the seminiferous tubules of the testes, and the mucous glands in the mouth.
Compound alveolar glands, like compound tubular glands, have a compound branching duct system; however, compound alveolar glands have a branching network of alveolar-shaped secretory and excretory cells. This is a widely occurring shape that can be found in certain salivary glands in the mouth, in the digestive-producing excretory portion of the pancreas, along with certain milk-producing mammary glands.
Compound tubuloalveolar glands are a combination of the alveolar and tubular glands and have a compound ductwork system, as well as both branching tubular and alveolar gland structures. These glands are found in the tear-producing lacrimal glands of the eye, in addition to certain salivary glands of the mouth, and mammary glands.
Glands are a collection of cells or an organ responsible for secretions, where a substance moves from a duct internally to another area, and excretions, where a substance leaves the body through a duct. There are three main shapes: acinar, a grape-like form with a small lumen, or interior space; tubular, which resemble a straight tube; and alveolar, or sac-like form with a large lumen. Tubular and alveolar glands display two main duct structures: simple, or straight ducts; and compound, or branching ducts.
Simple tubular glands include simple tubular, which are straight like a test tube; simple coiled tubular, which resemble a tangled garden hose; and simple branched tubular, which have a simple duct and branched tube-shaped glands. Simple alveolar glands include simple alveolar, which have a straight duct and a sac-like base, and simple branched alveolar, which have a series of branched sacs connected by a straight duct.
There are only three types of compound glands: the compound tubular, which have a branching duct system connected to branching tubular glands; compound alveolar, which have a branching duct system connected to branching alveolar shaped glands; and compound tubuloalveolar, which have a branching duct system connected to branching glands that are both tubular and alveolar in shape.