cells are specialized for particular...
TRANSCRIPT
Cells and Tissues Cell Diversity
§ Cells are specialized for particular functions
Body Tissues
• Tissues
o Groups of cells with similar structure and function
o Four primary types
§ Epithelium
§ Connective tissue
§ Nervous tissue
§ Muscle
Epithelial Tissues
• Found in different areas
o Body coverings
o Body linings
o Glandular tissue
• Functions
o Protection
o Absorption
o Filtration
o Secretion
Epithelium Characteristics
• Cells fit closely together
• Tissue layer always has one free surface
• The lower surface is bound by a basement membrane
• Avascular (have no blood supply)
• Regenerate easily if well nourished
Classification of Epithelium
• Number of cell layers
o Simple – one layer
o Stratified – more than one layer
• Shape of cells
o Squamous – flattened
o Cuboidal – cube-shaped
o Columnar – column-like
Simple Epithelium
• Simple squamous
o Single layer of flat cells
o Usually forms membranes
§ Lines body cavities
§ Lines lungs and capillaries
• Simple cuboidal
o Single layer of cube-like cells
o Common in glands and their ducts
o Forms walls of kidney tubules
o Covers the ovaries
• Simple columnar
o Single layer of tall cells
o Often includes goblet cells, which produce mucus
o Lines digestive tract
• Pseudostratified
o Single layer, but some cells are shorter than others
o Often looks like a double cell layer
o Sometimes ciliated, such as in the respiratory tract
o May function in absorption or secretion
Stratified Epithelium
• Stratified squamous
o Cells at the free edge are flattened
o Found as a protective covering where friction is common
o Locations
§ Skin
§ Mouth
§ Esophagus
• Stratified cuboidal
o Two layers of cuboidal cells
• Stratified columnar
o Surface cells are columnar, cells underneath vary in size and shape
• Stratified cuboidal and columnar
o Rare in human body
o Found mainly in ducts of large glands
• Transitional epithelium
o Shape of cells depends upon the amount of stretching
o Lines organs of the urinary system
Glandular Epithelium
• Gland – one or more cells that secretes a particular product
• Two major gland types
o Endocrine gland
§ Ductless
§ Secretions are hormones
o Exocrine gland
§ Empty through ducts to the epithelial surface
§ Include sweat and oil glands
Connective Tissue
• Found everywhere in the body
• Includes the most abundant and widely distributed tissues
• Functions
o Binds body tissues together
o Supports the body
o Provides protection
Connective Tissue Characteristics
• Variations in blood supply
o Some tissue types are well vascularized
o Some have poor blood supply or are avascular
• Extracellular matrix
o Non-living material that surrounds living cells
Extracellular Matrix
• Two main elements
o Ground substance – mostly water along with adhesion proteins and
polysaccharide molecules
o Fibers
§ Produced by the cells
§ Three types
Ø Collagen fibers
Ø Elastic fibers
Ø Reticular fibers
Connective Tissue Types
• Bone (osseous tissue)
o Composed of:
§ Bone cells in lacunae (cavities)
§ Hard matrix of calcium salts
§ Large numbers of collagen fibers
o Used to protect and support the body
• Hyaline cartilage
o Most common cartilage
o Composed of:
§ Abundant collagen fibers
§ Rubbery matrix
o Entire fetal skeleton is hyaline cartilage
• Elastic cartilage
o Provides elasticity
o Example: supports the external ear
• Fibrocartilage
o Highly compressible
o Example: forms cushion-like discs between vertebrae
• Dense connective tissue
o Main matrix element is collagen fibers
o Cells are fibroblasts
o Examples
§ Tendon – attach muscle to bone
§ Ligaments – attach bone to bone
• Areolar connective tissue
o Most widely distributed connective tissue
o Soft, pliable tissue
o Contains all fiber types
o Can soak up excess fluid
• Adipose tissue
o Matrix is an areolar tissue in which fat globules predominate
o Many cells contain large lipid deposits
o Functions
§ Insulates the body
§ Protects some organs
§ Serves as a site of fuel storage
• Reticular connective tissue
o Delicate network of interwoven fibers
o Forms stroma (internal supporting network) of lymphoid organs
§ Lymph nodes
§ Spleen
§ Bone marrow
• Blood o Blood cells surrounded by fluid matrix
o Fibers are visible during clotting
o Functions as the transport vehicle for materials
Muscle Tissue
• Function is to produce movement
• Three types
o Skeletal muscle
o Cardiac muscle
o Smooth muscle
Muscle Tissue Types
• Skeletal muscle
o Can be controlled voluntarily
o Cells attach to connective tissue
o Cells are striated
o Cells have more than one nucleus
• Cardiac muscle
o Found only in the heart
o Function is to pump blood
(involuntary)
o Cells attached to other cardiac muscle
cells at intercalated disks
o Cells are
striated
o One
nucleus
per cell
• Smooth muscle
o Involuntary muscle
o Surrounds hollow
organs
o Attached to other
smooth muscle cells
o No visible striations
o One nucleus per cell
Nervous Tissue
• Neurons and nerve support cells
• Function is to send impulses to other areas of the body
o Irritability
o Conductivity
Plasma Membrane Specializations
• Microvilli
o Finger-like projections that increase surface
area for absorption
• Membrane junctions
o Tight junctions
o Desmosomes
o Gap junctions
Tissue Repair
• Regeneration
o Replacement of destroyed tissue by the same kind of cells
• Fibrosis
o Repair by dense fibrous connective tissue (scar tissue)
• Determination of method
o Type of tissue damaged
o Severity of the injury
Events in Tissue Repair
• Capillaries become very permeable
o Introduce clotting proteins
o Wall off injured area
• Formation of granulation tissue
• Regeneration of surface epithelium
Regeneration of Tissues
• Tissues that regenerate easily
o Epithelial tissue
o Fibrous connective tissue and bone
• Tissues that regenerate poorly
o Skeletal muscle
• Tissues that are replaced largely with scar tissue
o Cardiac muscle
o Nervous tissue within the brain and spinal cord
Developmental Aspects of Tissue
• Epithelial tissue arises from all three primary germ layers
• Muscle and connective tissue arise from the mesoderm
• Nervous tissue arises from the ectoderm
• With old age there is a decrease in mass and viabililty in most tissues