Glandular tissue is the body’s manufacturing tissue: sheets of cells that make substances and release them for use elsewhere. Its products range from tears, saliva and sweat to digestive enzymes and the hormones that steer growth, stress and blood sugar. Every gland follows one of two delivery routes, piping its product onto a surface or handing it to the blood, and that choice shapes what the gland can do.
What Glandular Tissue Is Made Of
Glandular tissue belongs to a family called epithelium, the tissue that lines surfaces like the skin, the gut and the airways. Like other epithelium, it is one or more layers of cells resting on a thin sheet called the basement membrane.1Osmosis. Glandular Epithelium That sheet, made largely of collagen, holds the cells in place and separates them from the tissue underneath.2Osmosis. Glandular Epithelium Because the membrane separates lining cells from the tissue beneath, pathologists use whether cells stay above it as one way to judge how a growth is behaving, which is why biopsy reports comment on it. Most glands begin as lining cells that grow inward from a surface during development. Glands form when a patch of surface cells pushes down into the tissue below, like a finger pressed into a balloon, so many glands stay connected to their surface by a tube. Some lose that connection during development and become ductless. The thyroid is an example.
A gland has three working parts. The secreting cells form its working portion.3Compendium of Histology. Glandular Epithelium and Glands In many glands, ordinary lining cells form a system of tubes that carry the product away.4Compendium of Histology. Glandular Epithelium and Glands A frame of connective tissue holds everything together and brings in blood vessels and nerves.5Compendium of Histology. Glandular Epithelium and Glands
The scale varies enormously. Some glands are single cells, like the mucus-making goblet cells scattered through the gut and airways. Others are small coiled tubes in the skin, such as sweat glands. Large glands like the pancreas or the salivary glands contain millions of secreting cells.
You may meet the phrase “glandular tissue” on a report. Breast imaging reports often describe how much glandular tissue there is compared with fat. On a biopsy report, the words describe what kind of tissue a sample came from. On its own, the phrase describes normal tissue, not a disease. If a specific wording on your report is unclear, ask your doctor what it means for you.
How Gland Cells Make and Release Their Products
Cells that make large amounts of protein, like the insulin-making cells of the pancreas, are crowded with flat sheets of a protein-building network.6PubMed Central. Connecting the puzzle pieces between cytoskeleton and secretory pathway A packaging center inside the cell stretches and grows longer when the cell takes on more secretion work.7PubMed. Control of organelle size: the Golgi complex
The journey of a secreted protein follows a fixed order. The cell reads instructions in its genes to start building the protein, and it is assembled on the protein-building network. From there it moves to the packaging center to be finished and sorted. Then it is sealed in a small sac that waits for a release signal. When the signal comes, the sac fuses with the cell’s outer edge and spills its contents outside.
Gland cells make two broad kinds of product. Serous cells make a thin, protein-rich fluid that often contains digestive enzymes, and they store it in small sacs near the cell’s surface until release.8Indiana University School of Medicine. Human Structure Virtual Microscopy Mucous cells make mucus, a slippery, sugar-rich substance low in protein.9Indiana University School of Medicine. Human Structure Virtual Microscopy In airway glands, serous cells pump salts that draw water out, producing most of the fluid.10PubMed. Airway Gland Structure and Function The two often work together, one supplying water and protective proteins, the other the gel.11PubMed. Airway Gland Structure and Function
The product first collects in small rounded pockets lined with secreting cells, where it is released into the hollow center of each one. From each pocket the fluid drains into the smallest tubes, which merge into larger ones, much like streams joining a river. Duct cells downstream can add or remove salts and water on the way out, so what leaves the gland is not always what the secretory pockets first released.
Most gland cells release their products by emptying sacs at the surface while staying alive. In oil-making glands, though, cells fill with fat and then break apart, releasing their contents.12American Journal of Physiology-Cell Physiology. Rethinking holocrine secretion: functional logic in lipid-producing epithelia Skin oil glands near hair follicles work this way. The oil they release keeps skin and hair supple. Because cells are used up as part of the product, these glands must constantly make new ones.
Duct Glands Versus Hormone Glands
Exocrine glands, which this article will call duct glands, release their product onto a surface through tubes called ducts, lined with cells.13TeachMePhysiology. Structure of glands – Exocrine – Endocrine – Histology A duct can be a single tube or a branching tree.14TeachMePhysiology. Structure of glands – Exocrine – Endocrine – Histology Saliva, sweat, tears and digestive enzymes all reach their targets this way.
Endocrine glands, the ductless, hormone-making glands, have no ducts and release hormones straight into the bloodstream.15TeachMePhysiology. Structure of glands – Exocrine – Endocrine – Histology A hormone can therefore reach cells anywhere in the body. Examples include the thyroid, adrenal and pituitary glands.
Blood vessels help make this work. Those next to hormone cells are wider, thinner-walled and have about ten times more tiny pores than those next to digestive cells.16PubMed. A morphometric study of the endocrine and exocrine capillaries of the pancreas Hormones must cross a vessel wall to enter the blood, and thin walls with many pores make that crossing easy. Hormone glands therefore usually have a very rich blood supply for their size.
The route shapes the job. Duct glands act locally, where their product lands. Hormone glands send signals body-wide, and because hormones work at tiny amounts, they need tight control.
People often think all glands make hormones, but sweat and salivary glands make none. To tell which type a gland is, ask whether its product lands on a surface or in the blood, not what the product is, since the same chemical can sometimes act both ways.
The Pancreas, a Gland That Does Both
The pancreas works both as a digestive gland and as a hormone gland.17PubMed Central. Pancreas—Its Functions, Disorders, and Physiological Impact on the Mammals’ Organism Most of its tissue produces, stores and releases digestive enzymes into ducts.18PubMed Central. Interactions between the Exocrine and the Endocrine Pancreas Scattered among it are small islands of hormone cells, known as islets, which release insulin and glucagon into the blood to control blood sugar.19PubMed Central. Pancreatic endocrine and exocrine signaling and crosstalk in physiological and pathological status The two parts also signal to each other, and that crosstalk matters for overall health.20PubMed Central. Pancreatic endocrine and exocrine signaling and crosstalk in physiological and pathological status
After a meal, food reaching the gut triggers enzyme release down the ducts. The pancreas also releases a fluid that neutralizes stomach acid. Rising blood sugar prompts insulin release into the blood. The ducts from the digestive tissue join into a main duct that empties into the first part of the small intestine.
Because the two sides are separate, problems can strike one or the other. Pancreatitis involves the digestive side, while diabetes involves the islets.
How Nerves and Hormones Turn Glands On and Off
Automatic nerves, along with hormones in the blood and nearby, control gland secretion.21PubMed. Autonomic control of glands and secretion: a comparative view In the salivary glands, the “rest and digest” nerves release a chemical that makes cells pour out saliva.22PubMed. Regulation of salivary gland function by autonomic nerves The “fight or flight” nerves mainly trigger release of stored proteins.23PubMed. Regulation of salivary gland function by autonomic nerves That is why saliva can feel thin and plentiful at a meal but thick and sticky when you’re nervous. This nerve signal is also why many common medicines cause dry mouth. They block the chemical that nerves use to trigger saliva, so the salivary glands release less fluid. Sipping water or chewing sugar-free gum can help stimulate flow.
Nerve signals act within seconds and switch a gland on or off quickly, as when the smell of food makes your mouth water. Hormone signals travel in the blood, so they take longer to begin and tend to last longer. Many glands use both, with nerves handling the immediate response and hormones adjusting the longer-term level.
Hormone glands are often checked by negative feedback, where the hormone itself tells the brain to slow production.24PubMed Central. Endocannabinoid Signaling, Glucocorticoid-Mediated Negative Feedback and Regulation of the HPA Axis It works like a thermostat: low levels prompt the brain to signal for more, and rising levels switch the signal down, keeping levels in a steady range. The stress hormone cortisol feeds back on several brain areas and the pituitary to dampen its own release.25PubMed Central. Endocannabinoid Signaling, Glucocorticoid-Mediated Negative Feedback and Regulation of the HPA Axis Growth hormone has multiple overlapping feedback loops in the brain and pituitary, so the body has backups and one failure doesn’t throw hormones off.26PubMed. Negative Feedback Loops and Hormonal Factors that Regulate GH Secretion Disease or medicines that break the loop can still push levels too high or too low.
Some glands regulate themselves locally. In milk-making glands, stretching from full milk sacs and factors in the milk itself slow milk production.27PubMed. Autocrine-paracrine regulation of the mammary gland Serotonin made inside the breast also reduces milk-making when milk sits unremoved.28PubMed. Serotonin regulates mammary gland development via an autocrine-paracrine loop So regular milk removal tells the gland to keep producing.
What Can Go Wrong With Glandular Tissue
In Hashimoto’s thyroiditis and Graves’ disease, immune cells invade the thyroid.29PubMed Central. The Association of Sjögren Syndrome and Autoimmune Thyroid Disorders Hashimoto’s typically lowers thyroid hormone, while Graves’ raises it. In Hashimoto’s, immune cells gradually destroy thyroid tissue, so over time the gland can no longer make enough hormone, and many people then take daily replacement hormone. In Graves’ disease, the immune system makes antibodies that switch the thyroid on and keep it overproducing, ignoring the usual feedback signals. Blood tests that measure thyroid hormone and the pituitary’s signal to the thyroid find both. These conditions often occur alongside Sjögren syndrome, which targets tear and salivary glands.30PubMed Central. The Association of Sjögren Syndrome and Autoimmune Thyroid Disorders
In the pancreas, duct cells use a channel protein to release salt and water that keep enzymes dissolved.31PubMed Central. The Cystic Fibrosis of Exocrine Pancreas In cystic fibrosis this protein fails, so secretions turn thick and can block ducts.32PubMed Central. The Cystic Fibrosis of Exocrine Pancreas The enzymes stay concentrated and sticky inside the narrow ducts and can’t reach the intestine, so food, especially fat, is poorly absorbed. The same faulty channel affects glands elsewhere, such as in the airways, where thick mucus builds up.
An adenoma is a non-cancerous tumor of glandular tissue, and an adenocarcinoma is its cancerous form.33Wikipedia. Adenocarcinoma Some adenomas turn cancerous, though most never do.34Wikipedia. Adenocarcinoma That is why removing gut polyps that are adenomas is one way to prevent colon cancer.
Certain symptoms point toward particular glands. Persistent dry eyes and dry mouth can point to Sjögren syndrome. Unexplained weight change, fatigue or a racing heart can signal thyroid problems. Greasy stools and weight loss can reflect poor pancreatic enzyme output. These symptoms deserve a doctor’s evaluation, which often includes blood tests.
How Glands Change With Age
The thymus, a gland in the chest that trains infection-fighting T cells, shrinks and declines with age.35PubMed Central. Thymus and aging: morphological, radiological, and functional overview Its working tissue is replaced by fat.36WEHI. Can we turn back the clock on an ageing thymus? It then can’t perform the same immune work, which is one reason immunity weakens with age.37WEHI. Can we turn back the clock on an ageing thymus?38PubMed Central. Thymus and aging: morphological, radiological, and functional overview Older adults respond less strongly to some new infections and vaccines, so keeping up recommended vaccines matters more with age.
When it is working well, young T cells travel to the thymus to be trained, learning to recognize germs while ignoring the body’s own tissues. This training is the gland’s main job, and it is most active in childhood. The trained cells then leave and circulate through the blood and lymph system, ready to respond to infection.
Can Damaged Glands Be Regrown
Human salivary cells grown in a supportive gel can organize into ball-shaped clusters with hollow centers, like real secretory pockets.39PubMed Central. Concise Review: Salivary Gland Regeneration: Therapeutic Approaches from Stem Cells to Tissue Organoids Researchers start with stem cells or cells taken from salivary tissue, which can multiply and take on gland-cell roles. The soft gel mimics the support found in real tissue, and the cells arrange themselves into small gland-like clusters. Because they resemble real pockets, they also serve as models for studying how glands develop and function. Lab-grown human salivary mini-glands transplanted into mice survived long-term and connected to the host’s ducts.40PubMed Central. Functional human salivary gland organoids for tissue regeneration in chemically defined culture systems The treated mice made noticeably more saliva.41PubMed Central. Functional human salivary gland organoids for tissue regeneration in chemically defined culture systems But this has been shown in animals, not yet as a routine human therapy.
If it reaches people, those who could benefit include people whose salivary glands were damaged by head and neck radiation, and people with severe dry mouth from Sjögren syndrome. For now, ask about clinical trials rather than expecting an available treatment.