Anatomy & Physiology

Anatomy & Physiology Study Guide type lines the digestive tract and gallbladder, and the ciliated type line small bronchi, uterine tubes, and some regions of the uterus. Epithelia: Stratified Columnar Stratified columnar tissue consists of a single layer of cells with different heights of which some do not reach the free surface. Nuclei are visible at different layers. This epithelia functions in secretion and propulsion of mucus and is present in the sperm-carrying ducts (non-ciliated) and trachea (ciliated). Epithelia: Stratified Squamous Stratified squamous tissue is a thick membrane composed of several layers of cells. It functions in the protection of underlying areas subjected to abrasion. It forms the external epidermis of the skin (keratinized cells) and linings of the esophagus, mouth, and vagina (non-keratinized cells). Epithelia: Transitional Transitional epithelial tissue consists of several cell layers. The basal cells are cuboidal, and the surface cells are dome-shaped. It lines the urinary bladder, ureters, and part of the urethra. The tissue stretches to permit the distension of the urinary bladder. Glandular Epithelia Many epithelia contain gland cells that are specialized for secretion. Collections of epithelial cells (or structures derived from epithelial cells) that produce secretions are called glands . Some of these glands release their secretions into the interstitial fluid and are called endocrine glands. Others, known as exocrine glands, release their secretions into passageways called ducts that open onto an epithelial surface. Endocr ne Glands An endocrine gland produces secretions that are released directly into the surrounding interstitial fluid. These secretions, also called hormones, enter the bloodstream for distribution throughout the body. Examples of endocrine glands include the thyroid and the pituitary gland. Because their secretions are not released into ducts, endocrine glands are often called ductless glands. Exocrine Gl nds Exocrine glands produce secretions that are discharged onto an epithelial surface. Most exocrine secretions reach the surface through tubular ducts. They empty onto the skin surface or onto epithelial-lined internal passageways that communicate with the exterior. Examples of exocrine secretions delivered to epithelial surfaces by ducts are enzymes entering the digestive tract, perspiration on the skin, tears in the eyes, and milk produced by mammary glands. Modes of Secretion A glandular epithelial cell releases its secretions by either merocrine secretion, apocrine secretion, or holocrine secretion. In merocrine secretion, the product is released from secretory vesicles by exocytosis. Apocrine secretion involves the loss of cytoplasm as well as the secretory product. Holocrine secretion destroys the gland cell.

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