1 chapter 5 tissues – epithelial. 2 introduction similar cells with a common function are called...
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1
Chapter 5
Tissues – Epithelial
2
Introduction
• Similar cells with a common function are called tissues.
• The study of tissues is called histology.
• There are four (4) primary or major tissue types:
1. Epithelial Tissue (covering/lining; ET)2. Connective Tissue (support; CT)3. Muscle Tissue (movement; MT)4. Nervous Tissue (control; NT)
Figure 4.1
Nervous tissue: Internal communication• Brain, spinal cord, and nerves
Muscle tissue: Contracts to cause movement• Muscles attached to bones (skeletal)• Muscles of heart (cardiac)• Muscles of walls of hollow organs (smooth)
Epithelial tissue: Forms boundaries between different environments, protects, secretes, absorbs, filters• Skin surface (epidermis)• Lining of GI tract organs and other hollow organs
Connective tissue: Supports, protects, bindsother tissues together• Bones• Tendons• Fat and other soft padding tissue
Epithelial Tissue (Epithelium)
Two main types (by location):1. Covering and lining epithelia
• On external and internal surfaces o body (i.e. epidermis) and
o ventral cavity organs (i.e. visceral serous membranes)
2. Glandular epithelia• Secretory tissue in glands
o internal spaces (i.e. lumen of the intestine), o line body cavities (i.e. parietal membranes),o line ducts of exocrine glands (i.e. sweat glands).
Epithelial Tissue
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Functions of Epithelial Tissue
• Protection• Absorption• Filtration• Secretion
1. Cells exibit polarity—apical (upper, free) and basal (lower, attached) surfaces
– Apical surfaces may bear microvilli (e.g., brush border of intestinal lining) or cilia (e.g., lining of trachea).
– Apical surfaces always have a free space, which opens to the outside or to an internal space (lumen)
– Noncellular basal lamina of glycoprotein and collagen lies adjacent to basal surface
Characteristics of Epithelial Tissue
2. Cellularity - cells are in close contact with each other with little or no intercellular space between them.
3. Supported by a connective tissue - reticular lamina (under the basal lamina) at the basal surface, both the epithelial tissue and the connective tissue contribute to the basement membrane
4. Avascular (no blood supply).
5. Innervated (supplied with nerves)
6. Rely on diffusion and underlying connective tissue for nutrients and O2
7. High rate of regeneration
Characteristics of Epithelial Tissue
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Cellularity - Intercellular Junctions
Gap junctions• Tubular channels between cells• Located in cardiac muscle cells
• cardiac muscle cells• digestive smooth muscle cells
Tight junction
Cell membrane
Cell membrane
Cell membrane
Desmosome
Gap junction
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Tight junctions• Close space between cells• Located among cells that form linings
• lining cells in small intestine• kidney tubules• blood-brain barrier
Desmosomes• Form “spot welds” between cells• Found in tissues that undergo repeated episodes of tension and stretching
• skin, heart, uterus
Basement Membrane: The Basal Lamina
• Noncellular supporting sheet between the epithelium and the connective tissue deep to it
• Consists of proteins secreted by the epithelial cells • Functions:
– Acts as a selective filter, determining which molecules from capillaries enter the epithelium
– Acts as scaffolding along which regenerating epithelial cells can migrate
• Basal lamina and reticular layers of the underlying connective tissue form the basement membrane
• First name of tissue indicates number of layers
– Simple – one layer of cells
– Stratified – more than one layer of cells
Classifications of Epithelia
- Pseudostratified- tissue appears to be stratified, but all cells contact basement membrane so it is in fact simple
• Last name of tissue describes shape of cells– Squamous – cells wider than
tall (plate or “scale” like)
– Cuboidal – cells are as wide as tall, as in cubes
- Columnar – cells are taller than they are wide, like columns
Classifications of Epithelia
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Epithelial Tissue
• Simple squamous:• Single layer of flat cells• Substances pass easily through• Line air sacs• Line blood vessels• Line lymphatic vessels
• Simple cuboidal:• Single layer of cube-shaped cells• Line kidney tubules• Cover ovaries• Line ducts of some glands
(b)(a)
Free surfaceof tissue
Simplesquamousepithelium
Basement
Nucleus
Connectivetissue
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b,d: © Ed Reschke
Nucleus
Basementmembrane
Free surfaceof tissue
Simplecuboidalepithelium
Connectivetissue
Lumen
(a) (b)
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b: © The McGraw-Hill Companies, Inc./Al Telser, photographer
Simple Squamous Epithelium
Figure 4.3a
Simple Cuboidal Epithelium
Figure 4.3b
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• Simple columnar:• Single layer of elongated cells• Nuclei usually near the basement• Membrane at same level• Sometimes possess cilia• Sometimes possess microvilli• Often have goblet cells• Line uterus, stomach, intestines
• Pseudostratified columnar:• Single layer of elongated cells• Nuclei at two or more levels• Appear striated• Often have cilia• Often have goblet cells• Line respiratory passageways
Nucleus
Basementmembrane
Microvilli(free surfaceof tissue)
Connectivetissue
Mucus
Cytoplasm
Goblet cell
(a) (b)
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b: © The McGraw-Hill Companies, Inc./Al Telser, photographer.
(a) (b)
Cilia(free surfaceof tissue)
Goblet cell
Basementmembrane
Nucleus
Connectivetissue
Cytoplasm
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b: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer
Epithelial Tissue
Simple Columnar Epithelium
Figure 4.3c
Pseudostratified Ciliated Columnar Epithelium
Figure 4.3d
• Contain two or more layers of cells
• Regenerate from below
• Major role is protection
• Are named according to the shape of cells at apical layer
Stratified Epithelial Tissue
• Specific types – Keratinized – contain the protective protein keratin
• Surface cells are dead and full of keratin
– Non-keratinized – forms moist lining of body openings
• Function– Protects underlying tissues in areas subject to abrasion
• Location – Keratinized – forms epidermis
– Non-keratinized – forms lining of esophagus, mouth, and vagina
Stratified Squamous Epithelium
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• Stratified squamous: • Many cell layers• Top cells are flat• Can accumulate keratin• Outer layer of skin• Line oral cavity, vagina, and anal canal
• Stratified cuboidal: • 2-3 layers• Cube-shaped cells• Line ducts of mammary glands, sweat glands, salivary glands, and the pancreas
Basementmembrane
Layer ofdividingcells
Connectivetissue
Free surfaceof tissue
Squamouscells
(b)(a)
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b: © The McGraw-Hill Companies, Inc./Al Telser, photographer
(a) (b)
Stratifiedcuboidalepithelium
Free surfaceof tissue
Lumen
Basementmembrane
Connectivetissue
Nucleus
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
b: © The McGraw-Hill Companies, Inc./Al Telser, photographer.
Epithelial Tissue
Stratified Squamous Epithelium
Figure 4.3e
Stratified Cuboidal Epithelium
• Description– generally two layers
of cube-shaped cells
• Function– protection
• Location– Forms largest ducts
of sweat glands– Forms ducts of
mammary glands and salivary glands
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• Stratified columnar:• Top layer of elongated cells• Cube-shaped cells in deeper layers• Line part of male urethra and part of pharynx
• Transitional:• Many cell layers• Cube-shaped and elongated cells• Line urinary bladder, ureters, and part of urethra
(b)(a)
Lumen
Stratifiedcolumnarepithelium
Connectivetissue
Basementmembrane
Free surfaceof tissue
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b: © The McGraw-Hill Companies, Inc./Al Telser, photographer
Stretchedtransitionalepithelium
Basementmembrane
Underlyingconnective tissue
Basementmembrane
Underlyingconnective tissue
Unstretchedtransitionalepithelium
(b)(a)
(d)(c)
Free surfaceof tissue
Free surfaceof tissue
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
b,d: © Ed Reschke
Epithelial Tissue
Stratified Columnar Epithelium
• Description– several layers; basal
cells usually cuboidal; superficial cells elongated
• Function– protection and secretion
• Location – Rare tissue type– Found in male urethra
and vas deferens, largest ducts of salivary glands, nasopharynx
Figure 4.3h
Transitional Epithelium
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Glandular Epithelium
• Composed of cells that are specialized to produce and secrete substances
• There are two (2) types:• Endocrine glands are ductless (key word: hormone)• Exocrine glands have ducts
• Unicellular exocrine gland: • Composed of one cell • Goblet cell
• Multicellular exocrine gland: • Composed of many cells• Sweat glands, salivary glands, etc.• Simple and compound
Endocrine Glands
• Glands that do not have ducts or tubules and whose secretions are distributed throughout the body• Produce and secrete hormones into the bloodstream or the lymphatic system• Part of a complex, biochemical network known as the endocrine system
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Unicellular Exocrine Glands (The Goblet Cell)
• Goblet cells produce mucin
• Mucin + water mucus
• Protects and lubricates many internal body surfaces
Multicellular Exocrine Glands
• Have two basic parts– Epithelium-walled duct
– Secretory unit
• Classified by structure of duct– Simple
– Compound
• Categorized by secretory unit– Tubular
– Alveolar
– Tubuloalveolar
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Types of Glandular Secretions
• Merocrine Glands • Fluid product• Salivary glands• Pancreas gland • Sweat glands
• Apocrine Glands • Cellular product• Portions of cells• Mammary glands• Ceruminous glands
• Holocrine Glands• Secretory products• Whole cells• Sebaceous glands
(a) Merocrine gland (b) Apocrine gland (c) Holocrine gland
Secretion
Pinched offportion of cell(secretion)
Intactcell
Disintegrating celland its contents(secretion)
New cellforming bymitosis andcytokinesis
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Multicellular Exocrine Glands
• Classified by structure (branching & shape) of duct
• Can also be classified by mode or type of secretion– Merocrine secretion – secretory vesicles
released via exocytosis (saliviary glands)– Apocrine secretion – apical portion of the
cell is lost, cytoplasm + secretory product (mammary glands)
– Holocrine secretion – entire cell is destroyed during secretion (sebaceous gland)
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Structural Types of Exocrine Glands
Duct
Secretory portion
Tissue surface
Simple tubular Simple branchedtubular
Simple branchedalveolar
Simple coiledtubular
Compound tubular Compound alveolar
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May also be classified by types of secretions from exocrine glands
• Serous– mostly water but also contains some enzymes– Ex. parotid glands, pancreas
• Mucous– mucus secretions– Ex. sublingual glands, goblet cells
• Mixes– serous & mucus combined– Ex. submandibular gland
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