Acinar cells are specialized cells within the body’s exocrine glands responsible for producing and secreting various substances. Exocrine glands release their products through ducts to a particular location. The primary role of acinar cells is to synthesize and store compounds, releasing them on demand for functions ranging from digestion to protecting the surface of our eyes.
Where Acinar Cells Are Found
Acinar cells are organized into functional units called acini (singular: acinus). The name comes from the Latin for “berry in a cluster,” as the cells form a circular cluster connected to a small duct. This structure allows the substances they produce to be collected and channeled into the ductal system for transport.
These cellular clusters are found in several glands:
- The pancreas, where they form the bulk of the gland’s tissue.
- The salivary glands, including the parotid, submandibular, and sublingual glands.
- The lacrimal glands, located above each eyeball, which produce tears.
- The mammary glands, which contain acinar structures for milk production.
The Functions of Acinar Cells
The function of acinar cells is directly related to their location. In the exocrine pancreas, acinar cells synthesize digestive enzymes like amylase for carbohydrates, lipase for fats, and proteases for proteins. These enzymes are necessary to break down food into absorbable nutrients. The cells release these enzymes into the pancreatic duct system, which leads to the small intestine.
In the salivary glands, acinar cells produce saliva. Saliva lubricates food to aid in swallowing, begins digestion with enzymes like salivary amylase, and protects the mouth and throat. The composition can vary between glands, with some producing a watery serous fluid and others a thicker mucous secretion.
Lacrimal glands have acinar cells that secrete the aqueous layer of the tear film. This fluid lubricates the eye’s surface, washes away debris, and provides antimicrobial defense. In mammary glands, acinar cells respond to hormonal signals to produce and secrete milk to nourish an infant.
The Secretion Process
The secretion process begins with the synthesis of proteins, such as digestive enzymes, on the rough endoplasmic reticulum. From there, these newly made proteins are transported to the Golgi apparatus, which modifies, sorts, and packages them for their final destination.
This packaging results in small, membrane-bound sacs called secretory vesicles. In pancreatic acinar cells, these are known as zymogen granules, which store enzymes in an inactive form to prevent them from damaging the cell. Upon receiving a signal, like a hormone or nerve impulse, these granules move toward the side of the cell facing the duct.
The final step is exocytosis. During this process, the membrane of the secretory vesicle fuses with the cell’s outer membrane. This fusion creates an opening through which the contents of the vesicle are released into the lumen of the acinus. From there, the secreted substance is transported through the network of ducts to its target location.
Conditions Involving Acinar Cells
Several medical conditions arise when acinar cells do not function correctly. Pancreatitis is an inflammation of the pancreas caused by the premature activation of digestive enzymes within the acinar cells. Instead of being released into the small intestine, these enzymes begin to digest the pancreatic tissue, leading to severe pain and damage.
Sjögren’s syndrome is an autoimmune disorder where the immune system attacks the body’s moisture-producing glands. The primary targets are acinar cells within the lacrimal and salivary glands. This damage impairs their ability to produce tears and saliva, resulting in the symptoms of dry eyes and dry mouth.
Cystic fibrosis also impacts acinar cells, particularly in the pancreas. This genetic disorder disrupts the normal movement of salt and water across cell membranes, causing secretions from exocrine glands to become thick and sticky. In the pancreas, this fluid can block the ducts, preventing the acinar cells’ digestive enzymes from reaching the intestines and leading to problems with nutrient absorption.