Duct Gland: What Is It and How Does It Work?
A duct gland is a type of exocrine gland that consists of a duct and an acinus. A duct is a passage that transports the secretions of the gland to the target organ or tissue. An acinus is a cluster of cells that produces the secretion. Duct glands are involved in the production and secretion of various chemical substances, such as enzymes, hormones, saliva, milk, bile, and semen.
Duct glands can be classified into two main types: simple and compound. Simple duct glands have a single duct and a single acinus. Compound duct glands have multiple ducts and multiple acini. The ducts can be further divided into intralobular, interlobular, and interlobar ducts based on their size and location. The epithelium of the ducts can vary from simple cuboidal to stratified columnar depending on the type of duct.
The secretions of the duct glands are regulated by various factors, such as hormones, nerves, and feedback mechanisms. The secretions can have different functions depending on the type of gland and the target organ or tissue. For example, salivary glands secrete saliva that helps in digestion and lubrication of the mouth; mammary glands secrete milk that nourishes the offspring; liver secretes bile that aids in fat digestion; pancreas secretes digestive enzymes and hormones that regulate blood glucose levels; and reproductive glands secrete semen that carries sperm cells.
References
- Difference Between Duct and Gland | Definition, Types, Secretions …
- Duct (anatomy) – Wikipedia
Examples of Duct Glands
There are many examples of duct glands in the human body, each with a specific function and location. Some of the most common duct glands are:
- Sweat glands: These are tubular glands that secrete sweat onto the skin surface. Sweat helps regulate body temperature and eliminate waste products. There are two types of sweat glands: eccrine and apocrine. Eccrine sweat glands are found all over the body and produce clear, watery sweat. Apocrine sweat glands are found in the armpits, groin, and nipples and produce thicker, milky sweat that contains fatty acids and proteins.
- Salivary glands: These are compound tubuloalveolar glands that secrete saliva into the oral cavity. Saliva helps moisten and lubricate the mouth, initiate digestion, and protect against infections. There are three pairs of major salivary glands: parotid, submandibular, and sublingual. Parotid glands are located near the ears and produce mostly serous saliva. Submandibular glands are located under the jaw and produce both serous and mucous saliva. Sublingual glands are located under the tongue and produce mostly mucous saliva.
- Lacrimal glands: These are compound alveolar glands that secrete tears into the eyes. Tears help lubricate and protect the eyes from drying out and foreign particles. Tears also contain lysozyme, an enzyme that kills bacteria. Lacrimal glands are located above the upper eyelids and drain into small ducts that open near the inner corners of the eyes.
- Mammary glands: These are compound alveolar glands that secrete milk into the nipples. Milk provides nourishment and immunity to the newborns. Mammary glands are modified sweat glands that develop during pregnancy and lactation. Mammary glands consist of lobes that contain clusters of alveoli. Alveoli produce milk that is stored in lactiferous ducts and sinuses.
- Sebaceous glands: These are simple alveolar glands that secrete sebum into the hair follicles. Sebum is an oily substance that lubricates and protects the hair and skin from drying out and infection. Sebaceous glands are found all over the body except for the palms and soles. Sebaceous glands are usually associated with hair follicles but can also open directly onto the skin surface.
- Mucous glands: These are simple tubular or branched tubular glands that secrete mucus onto various mucous membranes. Mucus is a sticky substance that traps dust, bacteria, and other foreign particles and helps move them out of the body. Mucous glands are found in many organs, such as the respiratory tract, digestive tract, urinary tract, and reproductive tract.
References
- Difference Between Duct and Gland | Definition, Types, Secretions …
- Duct (anatomy) – Wikipedia
- Glands: Anatomy and clinical notes | Kenhub
- Exocrine Glands: Function, Examples & Types – Cleveland Clinic