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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