Glandular Epithelial Tissue
1. Introduction
Glandular epithelial tissues are specialized types of epithelial cells that are responsible for producing and releasing secretions such as enzymes, hormones, mucus, and sweat. These secretions play vital roles in protection, digestion, lubrication, and regulation of body functions.
While membranous epithelium mainly covers and lines body surfaces, glandular epithelium forms the secretory part of glands.
2. Meaning and Characteristics of Glandular Epithelium
Glandular epithelium consists of cells adapted for secretion. The secreted substances may be released onto body surfaces (like the skin), into cavities, or directly into the blood.
Main characteristics:
– Composed of specialized secretory cells.
– Rich in organelles such as rough endoplasmic reticulum and Golgi apparatus.
– May exist as single cells or large groups forming glands.
– Often supported by connective tissue and blood vessels that supply nutrients.
3. Classification of Gland
Glands can be classified based on several criteria:
A. Based on the Number of Cells
– Unicellular glands: Made up of a single cell (e.g., goblet cell in the intestinal lining secreting mucus).
– Multicellular glands: Made up of many secretory cells organized into larger structures (e.g., sweat glands, salivary glands).
B. Based on the Presence or Absence of Ducts
– Exocrine glands: Have ducts through which their secretions are carried to a surface or cavity. Examples include sweat glands, salivary glands, and mammary glands.
– Endocrine glands: Do not have ducts. They release hormones directly into the bloodstream. Examples include the thyroid gland, pituitary gland, and adrenal glands.
C. Based on Mode of Secretion
– Merocrine glands: Secrete their products by exocytosis without losing any part of the cell. Example: salivary glands, pancreas.
– Apocrine glands: Release secretions along with small portions of the cell’s cytoplasm. Example: mammary glands.
– Holocrine glands: The entire cell disintegrates to release its contents. Example: sebaceous (oil) glands of the skin.
D. Based on the Nature of Secretion
– Serous glands: Produce watery, enzyme-rich secretions (e.g., parotid gland).
– Mucous glands: Produce thick, sticky mucus (e.g., goblet cells).
– Mixed glands: Contain both serous and mucous cells (e.g., submandibular gland).
4. Structure of Exocrine Glands
Exocrine glands vary in shape and complexity:
– Simple glands: Have a single unbranched duct (e.g., sweat glands).
– Compound glands: Have branched ducts (e.g., salivary glands, pancreas).
They can also be classified based on the shape of their secretory portions:
– Tubular glands: Tube-shaped secretory units (e.g., intestinal glands).
– Alveolar or acinar glands: Flask-shaped secretory units (e.g., sebaceous glands).
– Tubuloalveolar glands: Have both tubular and alveolar features (e.g., salivary glands).
5. Functional Importance of Glandular Epithelium
– Maintains internal body balance by secreting hormones and enzymes.
– Produces mucus for lubrication and protection of surfaces.
– Assists in digestion through enzyme production.
– Regulates metabolism through hormonal secretion.
6. Microscopic Appearance
Under the microscope, glandular epithelium appears as clusters or cords of cells arranged around ducts or blood vessels. The cells usually have prominent nuclei and cytoplasm filled with secretory granules.
7. Examples of Major Glands and Their Secretions
– Sweat glands: Secrete sweat for temperature regulation.
– Sebaceous glands: Secrete sebum (oil) for skin lubrication.
– Salivary glands: Produce saliva containing enzymes.
– Thyroid gland: Secretes thyroxine hormone for metabolism.
– Pancreas: Produces digestive enzymes and insulin.
8. Clinical Relevance
– Overactivity or underactivity of glands can cause diseases such as hyperthyroidism, hypothyroidism, or diabetes.
– Blockage of ducts can lead to swelling and infections (e.g., acne, salivary gland stones).
In Complementary and Alternative Medicine, gland health is important for maintaining hormonal balance and supporting detoxification through natural therapies.
9. Summary
– Glandular epithelial tissues are specialized for secretion.
– Glands are classified as exocrine or endocrine depending on whether they have ducts.
– Modes of secretion include merocrine, apocrine, and holocrine types.
– Their secretions serve essential functions in protection, digestion, and regulation.
– Understanding glandular epithelium helps CAM practitioners relate natural therapies to hormonal and metabolic balance.
Video Credits
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