Lecture 8(unit2)- Epithelia & Membranes Flashcards
Principal functions of epithelial tissues
-Control permeability
-Protection
-Specialized secretions
-Sensation
•Neuroepithelia (special senses)
Characteristics of epithelial tissues (SPARCS)
- Specialized connections
- Polarity
- Avascular
- Regeneration
- Cellularity
- Supported (by a Connective Tissue)
Specialized attachments
- Tight junction
- Desmosome
- Hemidesmosome
What forms a membrane?
- Epithelia
- Connective Tissue
Each membrane consists of ?
- Sheet of epithelial cells
- An underlying Areolar connective tissue (other Connective tissues layers may be present but deeper)
Serous membranes
-line the ventral body cavities (the peritoneal, pleural, and pericardial cavities)
Mucous membranes
- are coated with the secretions of mucous glands
- line most of the digestive and respiratory tracts and portions of the urinary and reproductive tracts
Synovial membranes
- line joint cavities and produce the fluid within the joint
Cutaneous membrane
- the skin
- covers the outer surface of the body
Myoepithelial cells
- Its contractile function helps to expel secretions from the Lumina of the secretory units and ducts. Supporting functions are: The structure of myoepithelial cell is similar to that of smooth muscle.
- usually found in glandular epithelium as a thin layer above the basement membrane but generally beneath the luminal cells.
Neuroepithelia
-Neuroepithelial cells are the stem cells of the central nervous system, known as neural stem cells, and generate the intermediate progenitor cells known as radial glial cells, that differentiate into neurons and glia in the process of neurogenesis.
Exocrine glands
- Discharge their secretions onto the surface of the skin onto an epithelial surface lining.
- Ex: Enzymes entering the digestive tract, perspiration on the skin, and the milk produced by mammary glands.
Serous glands
-Secrete a watery solution that usually contains enzymes, such as the salivary amylase in saliva.
Mucous Glands
-Secrete glycoproteins called mucins that absorb water to form a slippery mucus, such as the mucus in saliva.
Mixed exocrine glands
-Contain more than one type of gland cell and may produce two different exocrine secretions, one serous and the other mucous.
Two types of unicellular glands and where are they found?
- Goblet cells, found in Columnar Epithelium of the small and large intestine
- Mucous cells, found in pseudostratified ciliated Columnar Epithelium that lines the trachea
Merocrine secretion
-The secretory product, packaged into secretory vesicles, is released through exocytosis onto the surface of the cell.
-Most common mode of secretion.
•Ex: Release of saliva from serous cells in the salivary gland, or mucins from goblet cells in the intestine.
Apocrine secretion
-the secretory product is released during the shedding of the apical portion of the cell’s cytoplasm, which has become packed with secretory vesicles.
-The cells then undergo regrowth and produce additional secretory vesicles.
•Ex: Lactiferous cells of the mammary glands.
Holocrine secretion
-Holocrine secretion destroys the gland cell.
-During the secretion m, the entire cell becomes packed with secretory products and then bursts apart. The secretion is released and the cell dies.
-Further secretion depends on gland cells being replaced by the division of the stem cells found deeper within the Epithelium.
•Ex: Sebaceous gland cells
Endocrine glands
- release their secretion by exocytosis from the gland cells into the fluid surrounding cell.
- These secretions, called hormones, diffuse into the blood for distribution to other regions of the body, where they regulate or coordinate the activities of various tissues, organs, and organ systems.
