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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
Mouth
Esophagus
Two layers of cuboidal cells
Stratified columnar
o
Skin
Stratified cuboidal
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
o
Endocrine gland
Ductless
Secretions are hormones
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
Collagen fibers
Elastic fibers
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
Hyaline cartilage
o
Most common cartilage
o
Composed of:
o
Used to protect and support the body
Abundant collagen fibers
Rubbery matrix
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
Fibrosis
o
Replacement of destroyed tissue by the same kind of cells
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