Tissue
Terms
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- TISSUES -
- group of similar cells with a common function
- Histology
- - study of tissues
- 3 primary germ layers - first tissues of embryo
- ectoderm, mesoderm, endoderm
- ectoderm
- dorsal layer
- mesoderm
- middle layer
- endoderm
- ventral layer
- 4 Basic Tissue Types
- Epithelial, Muscular, Connective, Nervous
- Epithelial Tissue is from what germ layer
- from all 3 layers depending on location, (ectoderm, mesoderm, and endoderm)
- Nervous Tissue is from what germ layer
- ectoderm
- Muscle Tissue is from what germ layer
- mesoderm
- Connective Tissue is from what germ layer
- mesoderm
- Cell Junctions
- - contact points between cells that bind them together into a functional unit, form seals between cells, anchor cells in place, provide channels for communication between cells
- Tight junctions
- - web of membrane proteins on adjacent cells fuse together forming a watertight seal (eg. cells lining digestive tract)
- Desmosomes
- plaque (dense area of proteins) on membrane with cell adhesion molecules. desmosones of adjacent cells attach cell to each other like velcro intermediate filaments link desmosomes to cytoskeleton of contributes strength and stability to tissues basement membrane
- Hemidesmosomes
- similar to desmosomes, but attach epithelial cells to a basement membrane
- Gap junctions
- membrane proteins of adjacent cells bind together forming channels between cells certain particles can diffuse from one cell to the other, allowing intercellular communication
- Neural Tissue
- - (found in brain and spinal cord) detects changes in internal and external environment and responds by transmitting signals to other tissues to maintain homeostasis or cause a response
- neurons
- cell in the neural tissue that detects stimuli, creates nerve impulses; composed of a cell body, with fibrous processes
- neuroglia
- Neural Tissue that supports neurons
- Muscle Tissue
- use ATP to contract; cause body movements
- 3 muscle types:
- Skeletal, Cardiac, Smooth
- Skeletal muscle
- usually attaches to bone striated (striped) appearance under microscope, very long, multinucleate cells contractions are voluntary
- Cardiac muscle
- heart muscle, branched, striated cells with 1 nucleus. Intercalated discs -junctions between cells with gap junctions. Contracts are involuntary.
- Smooth Muscle
- walls of hollow organs and vessels, spindle-shaped with 1 central nucleus and no striations. Contractions are involuntary.
- What is Epithelial Tissue?
- sheets of epithelial cells held together by cell junctions and anchored to a basement membrane
- basement membrane
- fibrous layer which anchors epithelium to underlying connective tissue. Composed of protein fibers and adhesion proteins secreted by the epithelium and underlying connective tissue.
- 2 functions of the Epithelial Tissue
- to cover and line surfaces and to form glands
- Polarity of Epithelial Cells
- they have directionality
- basal surface
- cell surface which adheres to basement membrane via hemidesmosomes (basal layer = deepest layer)
- apical surface
- cell surface opposite basal surface; faces body surface, body cavity, or lumen of organ or duct (apical layer = most superficial layer)
- lateral surfaces
- face adjacent cells and are attached by various cell junctions
- epithelium is avascular
- (no blood vessels) so nutrients and wastes diffuse to and from epithelium from blood vessels in connective tissue beneath
- CLASSIFICATION OF EPITHELIUM
- by number of cell layers and classification by cell shapes:
- simple epithelium
- single layer of cells
- stratified epithelium
- 2 or more layers of cells
- pseudostratified epithelium
- 1 layer that appears multilayered
- Squamous
- flat; nucleus in center
- Cuboidal
- cubes or hexagons; nucleus in center
- Columnar
- height greater than width; nucleus at base
- Transitional
- shape varies due to tissue stretching (flat to cuboidal)
- cilia
- hair-like microtubule structures on apical surface, function in sweeping mucus and other materials on surface (eg. upper respiratory tract, uterine tubes)
- microvilli
- finger-like extensions of cell membrane on apical surface, increase surface area for absorption or secretion (eg. small intestine, kidney tubules)
- simple squamous
- simple squamous - smooth, single, flat layer gas exchange surfaces of lungs 2 types
- -mesothelium
- lines body cavities and viscera
- -endothelium
- lines inside of blood vessels
- stratified squamous
- many layers, apical layer is flat, lines surfaces exposed to damaging environement especially abrasion (skin, mouth, esophagus, vagina and anus)
- simple cuboidal
- single cuboidal layer, sites of secretion and absorption, many glands, kidney tubules, may have cilia or microvilli
- stratified cuboidal
- 2 or more cuboidal layers, lining large ducts of glands (not very common)
- simple columnar
- single columnar layer, thickness provides some protection, capable of secretion and absorption. (lining digestive tract, uterine tubes. may have cilia or microvilli
- stratified columnar
- multiple layers, apical layer is columnar, protective and secretory, rare (male urethra)
- pseudostratified ciliated columnar
- lines most of respiratory airways, has goblet cells which produce mucus, traps and sweeps debris out of airways. (really rare)
- transitional
- found in urinary bladder and ureters, variable number of layers and shape of apical layer depending on fullness of organ. full stretches out appears squamous with fewer layers; empty-not stretched; appears cuboidal to round with more layers
- GLANDS
- epithelia that produce secretions; most invaginate to form clusters of cells beneath the covering layers of epithelium
- exocrine glands
- secrete into ducts that empty onto covering or lining epithelium (eg. mucus, sweat, saliva)
- endocrine glands
- ductless glands which secrete (hormones) into interstitial fluid, from which it diffuses into bloodstream
- multicellular glands
- multiple cells, simple, branched, compound; tubular-tube shaped acinar-sac like
- unicellular glands
- 1 cell; goblet cells - modified columnar epithelial cells secrete mucus for lubrication and protection (eg. upper respiratory tract, digestive tract)
- Functional classification of glands
- how secretion is released
- merocrine glands
- most common type; secretory vesicles containing product empty via exocytosis (eg. salivary glands)
- holocrine glands
- product accumulates in cytoplasm and is released as cell ruptures (eg. sebaceous glands)
- apocrine glands
- product accumulates in apical region of cell and cell pinches of apex to release (mammary glands)