Glands are fascinating and essential parts of our bodies, each with unique roles and features. They can be classified based on their structure, similar to the epithelia, but also the type of secretion they produce, and how they release it. Understanding these differences helps us appreciate how our bodies function and stay healthy. Let’s dive into the world of glands and explore their classification and characteristics!

Types of glands and characteristic features of glands vary, depending on

• The form and arrangement of the component parts
• the nature of the secretion
• the mechanism of secretion

Structural variations of glands

Structural variations of glands are according to

• The shape of the secretary units
• The secretory units are elongated in shape – tubular.
• They or grape like or ovoid shaped – alveolar
• The secretory units are rounded – acinar

• The pattern of branching of the ducts
  • unbranched one duct system – simple
  • branched multiple duct system – compound

Therefore the glands will be of the following types

Nature of secretion

Glands may be serous, mucous, or mixed types. Glands that secrete a watery or serous fluid are the serous glands. Glands that secrete a thick mucus like secretion are mucous glands. Mixed glands have serous, mucous, and mixed secretory units.

Serous glands

The pyramidal shaped secretory cells are arranged in the form of secretory acini. Cells have a deeply stained bluish granular cytoplasm due to the presence of ribosomes and secretory granules. The nuclei are rounded and located at the base of the cell. stained with H&E. The secretions are protein in nature. Cells are basophilic.

Examples

• Parotid salivary gland,
• Exocrine pancreas

Mucous gland

The cells of a mucous secretory acinus have droplets of mucous in their cytoplasm. With hematoxylin and eosin stain mucous gives a pale color and cells show a positive reaction with Periodic Schiff Reagent (PAS positive). The nuclei are pushed to the base of the cell by the mucous droplets. Depending on the amount of mucous droplets nucleus becomes flattened and lies against the base of the cell.

Example: Sublingual salivary gland

Mixed glands

These glands are made up of mucous secretory acini capped by a crescentic mass of serous cells they are called serous demilunes. In the mixed secretory unit, secretions from the serous cells pass through canals between the mucous cells to open into the lumen of a mucous unit. There may be separate serous and mucous units in a mixed gland in addition to serous demilunes.

Surrounding the secretory units are myoepithelial cells or basket cells. They have numerous cytoplasmic processes and contractile functions. They help to expel the secretions into the lumen.

Example: Submandibular salivary gland

* Major past of the gland is filled with fat cells

* There are many sections of duct’s surrounded by connective tissue therefore it is a compound gland

Mechanism of secretion

• 3 types
• Merocrine type
• Holocrine type
• Apocrine type

Merocrine type of secretion

Merocrine glands are a type of exocrine gland that release secretions directly onto the skin or into ducts. This process does not damage the gland cells. These glands produce secretions through exocytosis. In this process, vesicles containing the secretion fuse with the cell membrane and release their contents. Many sweat glands, including those in the skin, use this method of secretion. Some salivary glands and the pancreas also follow this process. The merocrine mode of secretion is efficient, allowing the gland cells to continue functioning without any structural changes.

Holocrine type of secretion

Holocrine glands are a type of exocrine gland that release secretions by rupturing and disintegrating the entire gland cell. This process, known as holocrine secretion, differs from other glands where cells remain intact. Holocrine glands accumulate secretions within the cell until it becomes full and bursts, releasing the contents into the duct. This results in the destruction of the cell, which is then replaced by new cells formed through mitosis. The sebaceous glands in the skin, which produce oily sebum to lubricate and protect the skin and hair, are a prime example of holocrine glands. Due to the nature of holocrine secretion, these glands produce a thicker, more lipid-rich secretion compared to other exocrine glands.

Apocrine glands are a type of exocrine gland that secrete a thick, milky fluid often linked to body odor. Unlike merocrine glands, apocrine glands release secretions by pinching off a portion of the cell’s cytoplasm, which then enters the gland’s duct. These glands are mainly located in the armpits, groin, and around the nipples. Apocrine glands become active during puberty and are influenced by hormonal changes, especially those related to stress or sexual arousal. The secretions of apocrine glands are initially odorless. However, when they come into contact with bacteria on the skin, they can produce a distinct scent.