Learn the definition and classification of glands. Know the difference between tubular and alveolar glands. Learn about simple and compound glands as well as acinar glands and the secretory process.
Updated: 03/05/2022
Glands: Classification of Tubular, Alveolar & Acinar Glands
Simple Glands vs. Compound Glands
A gland consists of epithelial tissue arranged in a manner to secrete substances. Glands can be divided into exocrine and endocrine glands. An exocrine gland's secretions pass through a duct to the tissue surface. Endocrine glands release their secretory contents directly into the bloodstream without passing through a duct. This lesson will overview exocrine glands.
Exocrine glands can be classified based on different characteristics of the gland:
- Shape of the duct
- Branching of the duct
- Gland function
- Type of secretion
Secretion is a term that means the internal movement of a substance through a duct from one area to another. This differs from excretion which moves substances through a duct to the exterior of the body.
One aspect of classifying glands depends on how the duct system is designed. A simple gland contains an unbranched duct. Examples of simple glands include sweat glands or those within the large intestine. A compound gland contains a branched duct system. Salivary glands and the pancreas are compound glands.
Understanding Glands
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.
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Tubular Glands
Glands are also classified by the shape of their duct. Tubular glands have a tube shape to their secretory duct with an interior lumen to transport secretions. Tubular glands have an oblong tubular structure and gland shape. Examples of tubular glands are seen in the sweat glands as well as in the stomach and uterus.
Tubular glands are exocrine glands and can be further subcategorized based on their shape and the branching of the ducts. These will be discussed below.
Simple Tubular Gland
A simple tubular gland consists of a single straight duct with an elongated or tubular shape to the gland.
Simple tubular glands are found in the large intestine in the epithelial lining of the wall. The straight and non-branching glands in the intestinal wall contain goblet cells and absorptive cells. These glands secrete mucus to assist in intestinal motility.
Simple Coiled Tubular Gland
A simple coiled tubular gland consists of a long unbranched duct that is coiled in a continuous loop. Simple coiled tubular glands are present in eccrine and apocrine glands.
Eccrine sweat glands occur on the skin. Apocrine glands have a wider lumen than eccrine glands and are present in the anus, axillary, and areolar regions. The coiled tubular apocrine glands will secrete substances at the base of hair follicles near a sebaceous gland. When this secretory substance mixes with bacteria on the skin it causes body odor.
Compound Tubular Gland
A compound tubular gland has branched secretory ducts. The pancreas and salivary glands provide an example of compound tubular glands.
Salivary glands are exocrine glands with branching ducts. The secretory components will release to the surface to provide salivation and mucus to assist with mastication and digestion. The pancreas is an organ in the body that is made up of multiple glands including compound tubular glands with branching ducts.
Simple Branched Tubular
Simple branched tubular glands occur in the stomach. They consist of one single duct that branches into smaller ducts. The simple branched tubular glands of the stomach secrete stomach acid and enzymes to aid with food breakdown and digestion.
Alveolar Gland
An alveolar gland is an exocrine gland that is spherical in shape. An alveolar gland has a bulbous and rounded base with a large ductal lumen.
An example of an alveolar gland is seen in salivary glands. Alveolar glands can also be classified depending on the duct branching system as either compound or simple. They also can be considered secretory or excretory.
Sebaceous glands are an example of alveolar glands. Alveolar glands will be discussed further and categorized in more detail below based on their lumen size and branch system.
Simple Branched Alveolar
A sebaceous gland in the skin is an example of a simple branched alveolar gland. It is a rounded or spherical gland with one duct to the surface but the single duct branches in the deep tissues. A sebaceous gland secretes sebum which is an oily substance into the base of hair follicles. It keeps skin flexible and prevents excessive water loss.
Compound Alveolar
A compound alveolar gland duct system has multiple branches in the duct system. An example of a compound alveolar gland is seen in mammary glands.
Compound Tubuloalveolar
A compound tubuloalveolar gland combines the characteristics of the other subtypes. It will contain multiple branching ducts but each duct could include both the spherical alveolar glands or conical tubular glands.
This compound gland system is seen in the respiratory system of the lungs as well as in the pancreas.
The pancreas contains multiple gland types in one system that are responsible for secreting enzymes to assist with digestion. The pancreas is an organ that has glands to perform both endocrine and exocrine functions.
Acinar Gland
An acinar gland is another exocrine gland structure that has spherical glands similar to an alveolar gland. The difference between acinar and alveolar glands lies in the size of the lumen. An acinar gland has a bulbous base with a small lumen, while an alveolar gland contains a large lumen.
Acinar glands are found in the mammary glands of breast tissue.
Lesson Summary
Glands are a collection of epithelial tissue arranged into secretory structures. Glands can be considered exocrine glands with secretions that flow through a duct to the surface. An endocrine gland secretes directly into the bloodstream. Exocrine glands are classified based on their duct structure, duct branching, gland function, or type of secretion. Secretion is the internal movement of substances via a duct through internal structures. Excretion moves substances through a duct to be released onto the surface of the body.
Simple glands pertain to glands with straight ducts. Compound glands contain branching ducts. Exocrine glands can be classified based on the shape of the gland. A tubular gland has a tubular shape of the gland and the ducts have a tubular lumen. Alveolar and acinar glands have a spherical gland shape with a bulbous base. An alveolar gland has a large lumen while the acinar gland has a small lumen. Alveolar glands can be simple or compound and also be excretory or secretory. Tubuloalveolar glands contain a combination of tubular and spherical glands.
Gland Shapes
 |
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.
Simple 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.
Compound 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.
Lesson Summary
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.
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Video Transcript
Understanding Glands
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.
Gland Shapes
|
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.
Simple 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.
Compound 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.
Lesson Summary
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.
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Frequently Asked Questions
Are alveolar and acinar the same?
Alveolar and acinar glands are both spherical-shaped exocrine glands. They differ in the size of the lumen of the secretory duct. An acinar gland duct has a small lumen while the alveolar gland duct has a large lumen.
What is the difference between alveolar and tubular glands?
Alveolar and tubular glands differ based on the shape of the gland. They are both exocrine glands and the tubular gland is in the shape of a tube, while alveolar glands are spherical in shape.
What is acinar gland?
An acinar gland is a secretory collection of epithelial tissue considered an exocrine gland. An acinar gland has a spherical structure and the secretory duct has a small lumen. Salivary glands are an example of an acinar gland.
What is a compound alveolar gland?
An alveolar gland is an exocrine gland that has a spherical shape. A compound alveolar gland contains multiple branching ducts.
Where are compound branched tubular glands found?
A compound tubular gland is an exocrine gland that contains tube-shaped secretory ducts. Compound tubular glands can be found in the testis.
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