Histology Lecture Flashcards
Specializations of Epithelial Cells
Epithelial cells have several structural specializations. For the epithelium as a whole to perform its functions, individual epithelial cells may be specialized for,
1. Move fluids over the epithelium (protection)
2. Move fluids through the epithelium (permeability)
3. Produce secretions (protection and messengers)
Polarity (characteristic of epithelia)
The specialized epithelial cell is often divided into two functional regions, which means the cell has strong polarity.
1. Apical surfaces - Microvilli increase absorption or secretion; Cilia (ciliated epithelium) move fluid
2. Basolateral surfaces - include both the base (basal surface), where the cell attached to underlying epithelial cells or deeper tissues, and the sides (lateral surfaces), where the cell contacts its neighbors
Glandular Epithelia
gland cells that are specialized for secretions
Clear Layer (lamina lucida)
-Thin layer
-Secreted by epithelia
-Barrier to proteins
Dense layer (lamina densa)
-Thick fibers
-Produced by connective tissue
-Strength and filtration
Epithelial Maintenance and Repair
-Epithelia are replaced by division of germinative cells (stem cells)
-Near basement membrane
Simple Squamous Epithelium
This type of epithelium is located in protected regions where absorption and diffusion takes place. Examples are the respiratory exchange surfaces of the lungs, the lining of the thoracic and the lining of the heart and blood vessels
Mesothelium
Lines body cavities
Endothelium
Lines heart and blood vessels
Stratified Squamous Epithlium
generally located where mechanical stresses are severe. The surface of the skin and the lining of the mouth. esophagus, and anus are areas where this type of epithelium protects against physical and chemical attacks
Simple Cuboidal Epithelium
provides limited protection and occurs where secretion or absorption takes place.
Stratified Cuboidal Epithelia
Sweat ducts and mammary glands
Simple Columnar Epithelium
Absorption or secretion takes place, such as in the small intestine. In the stomach and large intestine, the secretions of simple columnar epithelia protect against chemical stresses.
Pseudostratified Columnar Epithelium
Cilia movement. Epithelia of this type line most of the nasal cavity, the trachea (windpipe), the bronchi (branches of the trachea leading to the lungs), and portions of the male reproductive tract.
Transitional Epithelium
permits repeated cycles of stretching without damage. A transitional epithelium is found in regions of the urinary system, such as the urinary bladder
Stratified Columnar Epithelium
Protection along portions of the pharynx, epiglottis, anus, and urethra, as well as along a few large excretory ducts.
Endocrine Glands
Produce endocrine secretions called hormones. These hormones enter the bloodstream for distribution throughout the body. Hormones regulate or coordinate the activities of various tissues, organs, and organ systems. Because their secretions are not released into ducts, endocrine glands are often called ductless glands..
Exocrine Glands
Produce exocrine secretions onto the epithelial surface through ducts
Merocrine Secretion (Exocrine method of secretion)
-Produce in Golgi apparatus
-Release by vesicles (exocytosis)
-For example, sweat glands
Apocrine Secretion (Exocrine method of secretion)
-Produced in Golgi apparatus
-Released by shedding cytoplasm
-For example, mammary glands
Holocrine Secretion (Exocrine method of secretion)
-Released by cells bursting, killing gland cells
-Gland cells replaced by stem cells
-For example, sebaceous glands
Serous Glands ( Exocrine type of secretion)
Watery secretions
Mucous Glands (Exocrine type of secretion)
Secrete mucins
Mixed Exocrine Glands (Exocrine type of secretion)
Both serous and mucous
Unicellular Glands (Gland Structure)
-Mucous (goblet) cells are the only unicellular exocrine glands
->Scattered among epithelia
->For example, in intestinal lining
Epithelial Tissue
covers exposed surfaces, lines internal passageways and chambers, and forms glands
Connective tissue
fills internal spaces, provides structural support for other tissues, transports materials within the body, and stores energy
Muscle Tissue
specialized for contraction and includes the skeletal muscles of the body, the muscle of the heart, and the muscular walls of hollow organs
Nervous Tissue
carries information from one part of the body to another in the form of electrical impulses
Cellularity (characteristic of epithelia)
epithelia are made almost entirely of cells bound closely together by interconnections known as cell junction
Attachment (characteristic of epithelia)
Epithelia cells display attachment which means that the basal surfaces of the cells are attached to a special layer called the basal lamina or basement membrane. The basal lamina or membrane supports the epithelium and anchors it firmly to the underlying connective tissue.
Avascularity (characteristic of epithelia)
Epithelia are avascular which means that they lack blood vessels. Epithelia cells get nutrients by diffusion or absorption across either the exposed or the attached epithelial surface
Regeneration (characteristic of epithelia)
Epithelial cells that are damaged or lost at the exposed surface are continuously replaced through stem cell division in the epithelium. The rate of cell division in epithelia is much higher than in other tissues.
Intracellular Connections
Large areas of opposing plasma membranes are interconnected by transmembrane proteins called cell adhesion molecules (CAMs), which bind to each other and to extracellular materials. The membranes of adjacent cells may also be bonded by a thin later of proteoglycans that contain polysaccharide derivatives known as glycosaminoglycans (GAGs), most notably, hyaluronan (hyaluronic acid)
Cell Junctions
specialized areas of the plasma membrane that attach a cell to another cell or to extracellular materials.
Tight Junctions
formed by the fusion of the outer layers of two plasma membranes. Tight junctions prevent the diffusion of fluids and solutes between the cells. A continuous adhesion belt lies deep to the tight junction. This belt is tied to the microfilaments of the terminal web.
Gap Junction
two cells are held together by channel proteins called connexons. Two aligned connexons form a narrow passageway that lets small molecules and ions pass from cell to cell. Gap junctions in cardiac muscle tissue and smooth muscle tissue are essential in coordinating muscle cell contractions.
Spot Demosomes
-Ties adjacent cells together
-Allow bending and twisting
Hemidesmosomes
Attach a cell to extracellular structures, such as the protein fibers in the basement membrane
Functions of Epithelial Tissue
-Provide Physical Protection
-Control Permeability
-Provide Sensation
-Produce Specialized Secretions (glandular epithelium)