Bio 2311 Chapter 4 -6 Notes

Fundamentals of Anatomy & Physiology Study Guide CH 4 – 6
Chapter 4: The Tissue Level of Organization
An Introduction to Tissues
 Tissues
o Collections of specialized cells and cell products that perform specific functions
o Tissues in combination form organs, such as the heart or liver
o Histology is the study of tissues
4 – 1 Four Types of Tissues
 Four types of tissue
1. Epithelial
2. Connective
3. Muscle
4. Nervous
 Epithelial tissue
o Covers exposed surfaces
o Lines internal passageways
o Forms glands
 Connective tissue
o Fills internal spaces
o Supports other tissues
o Transport materials
o Stores energy
 Muscle tissue
o Specialized for contraction
o Skeletal muscle, heart muscle, and muscular walls of hollow organs
 Nervous tissue
o Carries electrical signals from one part of the body to another
4 – 2 Epithelial Tissue
 Epithelial tissue includes epithelia and glands
o Epithelia (singular, epithelium)
 Layers of cells covering internal or external surfaces
o Glands
 Structures that produce fluid secretions
 Functions of epithelial tissue
1. Provides physical protection
2. Controls permeability
3. Provide sensation
4. Produce specialized secretions
 Characteristics of epithelia

, o Polarity (apical and basal surfaces)
o Cellularity (cell junctions)
o Attachment (basement membrane)
o Avascularity (avascular)
o Regeneration
 Specialization of epithelial cells
1. Move fluids over the epithelium (protection)
2. Move fluids through the epithelium (permeability)
3. Produce secretions (protection and messaging)
 Polarity
o Apical surface
 Microvilli increase absorption or secretion
 Cilia on a ciliated epithelium move fluids
o Basolateral surface
 Integrity of epithelia is maintained by
1. Intercellular connections
2. Attachment to the basement membrane
3. Epithelial maintenance and repair
 Intercellular connections
o Support and communication
 Cell adhesion molecules (CAMs)
 Transmembrane proteins
 Proteoglycans act as intercellular cement
 Contain glycosaminoglycans such as hyaluronan (hyaluronic acid)
o Cell junctions
 Form bonds with other cells or extracellular material
1. Gap junctions
2. Tight junctions
3. Desmosomes
 Gap junctions
o Allows rapid communication
o Cells held together by interlocking transmembrane proteins (connexons)
o Allows small molecules and ions to pass
o Coordinate contractions in heart muscle
 Tight junctions
o Between two plasma membranes
o Adhesion belt attaches to terminal web
o Prevent passage of water and solutes
o Keep enzymes, acids, and wastes in the lumen of the digestive tract
 Desmosomes
o CAMs and proteoglycans link opposing plasma membranes
o Spot desmosomes
 Tie cells together

,  Allow bending and twisting
o Hemidesmosomes
 Attach cells to the basement membrane
 Attachment to the basement membrane
o Basal lamina
 Closest to the epithelium
o Reticular lamina
 Deeper portion of basement membrane
 Provides strength
 Epithelial maintenance and repair
o Epithelial cells are replaced by continual division of stem cells
 Located near basement membrane
4 – 3 Classification of Epithelia
 Classification of epithelia
1. Based on shape
o Squamous – thin and flat
o Cuboidal – square shaped
o Columnar – tall, slender rectangles
2. Based on layers
o Simple epithelium – single layer of cells
o Stratified epithelium – several layers of cells
 Squamous epithelia
o Simple squamous epithelia
 Absorption and diffusion
 Mesothelium
 Lines body cavities
 Endothelium
 Forms inner lining of heart and blood vessels
o Stratified squamous epithelia
 Protects against mechanical stresses
 Keratin adds strength and water resistance
 Cuboidal epithelia
o Simple cuboidal epithelia
 Secretion and absorption
 Glands and portions of kidney tubules
o Stratified cuboidal epithelia
 Relatively rare
 Ducts of sweat glands and mammary glands
 Transitional epithelia
o Tolerate repeated cycles of stretching without damage
o Appearance changes as stretching occurs
o Found in urinary bladder

,  Columnar epithelia
o Simple columnar epithelia
 Absorption and secretion
 Found in stomach, small intestine, large intestine
o Pseudostratified columnar epithelia
 Typically have cilia
 Found in nasal cavity, trachea, bronchi
o Stratified columnar epithelia
 Relatively rare
 Provide protection in pharynx, anus, urethra
 Glandular epithelia
o Glands are collection of epithelial cells that produce secretions
o Endocrine glands
 Releases hormones that enter bloodstream
 No ducts
o Exocrine glands
 Produces exocrine secretions
 Discharge secretions through ducts onto epithelial surfaces
 Gland structure
o Unicellular glands
o Multicellular glands
 Unicellular glands
o Goblet cells are unicellular exocrine glands
 In epithelia of intestines
 Secret mucin, which mixes with water to form mucus
 Multicellular exocrine glands are classified by
1. Structure of the duct
o Simple (undivided)
o Compound (divided)
2. Shape of secretory portion of the gland
o Tubular (tube shaped)
o Alveolar or acinar (blind pockets)
3. Relationship between ducts and glandular areas
o Branched (several secretory areas sharing one duct)
 Methods of secretion
1. Merocrine
2. Apocrine
3. Holocrine
 Merocrine secretion
o Released by secretory vesicles (exocytosis)
o Example: merocrine sweat glands
 Apocrine secretion
o Released by shedding cytoplasm