Chapter 4 Tissue The Living Fabric part 1 PDF

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Chapter 4 Tissue: The Living Fabric Tissues – Introduction • Tissues are groups of cells that are similar in structure and perform a related function • Four primary types of tissue in the body 1. Epithelial tissue 2. Connective tissue 3. Muscle tissue 4. Nerve tissue

Epithelial Tissue (Epithelium) • Found on every internal and external body surface • Two main types (by location): 1.

Covering and lining epithelia • On external and internal surfaces of body

2.

Glandular epithelia

Secretory tissue in glands

Shared Characteristics of Epithelial Tissue 1. Cells have polarity—apical (upper, free), lateral, and basal (lower, attached) surfaces are different -Cell membrane of apical surface may be modified depending on specific function of epithelia cell -microvilli - increase membrane surface area to border of epithelia lining small intestine and kidney tubules)

augment absorption (form brush

-cilia - actively mobile projections of cell membrane that sweep materials across the surface of the cell (e.g., lining of trachea and bronchi, uterine tubes)

Characteristics of Epithelial Tissue (continued)

2. Specialized contacts (membrane junctions) on lateral surfaces of cells that hold cells together

-tight junctions and/or desmosomes allow cells to fit

closely together to form continuous

sheets 3. Supported by a basement membrane (noncellular layer of connective tissue) -2 layers: -basal lamina located right underneath basal

surface of epithelial cells

-reticular lamina located beneath basal lamina 3. Avascular (lack blood vessels) but innervated 4. High rate of cell turnover/regeneration 5. Membrane Junctions Commonly Found on Epithelial Cells Three types: • Tight junction • Desmosome • Gap junction • •

Tight junctions: Impermeable junctions prevent molecules from passing through the intercellular space.

• Desmosomes: Anchoring junctions bind adjacent cells together • and help form an internal tension-reducing network of fibers • Gap junctions: Allow ions and small molecules to pass from one cell • to the next for intercellular communication. Classification of Epithelia

• Two criteria for naming and classifying epithelia: 1. How many layers of cells? 1 layer = simple epithelium >1 layer = stratified epithelium 1. What is the shape of cell? • Squamous (flat)

• Cuboidal • Columnar (If stratified, epithelia is named according to shape of cells in apical layer) • Most epithelial tissues have names that consist of two parts: the first name indicates the number cell layers present and the second name indicates the shape of its cells Overview and Classification of Epithelial Tissues For each specific type of epithelium presented in the following slides, you will need to learn: • Description • Function Location

Epithelia: Simple Squamous Given special names in two locations • Endothelium -

The lining of lymphatic vessels, blood vessels, and heart

• Mesothelium -

The epithelium of serous membranes in the ventral body cavity

Stratified Epithelia • Stratified Squamous -

Most common type of stratified epithelia (see next slide)

• Stratified Cuboidal -

Quite rare in body; typically two cell layers thick

-

Found in some sweat and mammary glands

• Stratified Columnar -

Limited distribution in body

-

Small amounts in pharynx, male urethra, and lining some glandular ducts

• Transitional (see slide following stratified squamous epithelium) Glandular Epithelia • A gland is one or more cells that makes and secretes an aqueous fluid

• Classified by: • Site of product release—endocrine or exocrine • Relative number of cells forming the gland—unicellular (e.g., goblet cells) or multicellular Endocrine Glands • Ductless glands • Secrete hormones that travel through lymph or blood to target organs Exocrine Glands • More numerous than endocrine glands • Secrete products into ducts • Secretions released onto body surfaces (skin) or into body cavities • Examples include mucous, sweat, oil, and salivary glands Unicellular Exocrine Glands • The only important unicellular exocrine glands are goblet cells and mucous cells • Abundant in digestive system and air passageways of respiratory system • Both cell types produce and secrete mucin • Complex glycoprotein that dissolves in water when secreted Multicellular Exocrine Glands • Multicellular exocrine glands are composed of a duct and a secretory unit • Classified according to: • Duct type (simple or compound) • Shape/structure of their secretory units (tubular, alveolar, or tubuloalveolar)...