Download Tissues: The Living Fabric

Tissues: The Living Fabric
 To optimize functions, body cells are organized into tissues
 Four basic tissue types exist in humans
– Epithelial tissue
– Connective tissue
– Muscle tissue
– Nervous tissue
Tissues: The Living Fabric

Epithelial tissue
–
Cells that cover a body surface or line a body cavity


Lining and covering epithelium
–
Cover internal or external surfaces (all exposed body surfaces)
–
Located on the skin, GIT, respiratory tract
Glandular epithelium
–
–
Specialized secretory structures
Functions

Protection, absorption, filtration, excretion and secretion
Special Characteristics of Epithelium
 Specialized contacts
– Cells are held closely together forming continuous sheets
– Adjacent cells are tightly bound to each other via specialized contacts
(desmosomes and tight junctions)
Special Characteristics of Epithelium
 Polarity
– An apical surface and a basal surface is present in all epithelia
– The apical surface is exposed to the body exterior or cavity of an
internal organ
– The basal surface is attached to the underlying tissue
Special Characteristics of Epithelium

Supported by connective tissue
–
Epithelial tissue sheets rest on an underlying layer of connective tissue
that also provides support
–
The basal lamina of the epithelial tissue and the reticular lamina of the
connective tissue join together to form a basement membrane
–
The basement membrane is the interface between the epithelial tissue
and the connective tissue
Special Characteristics of Epithelium
 Avascularity
– Epithelia do not contain blood vessels
– Nutrients are obtained from the exposed or underlying surface
 Regeneration
– Epithelial cells are exposed to damage
– They have the ability to regenerate and replace the cells that slough off
the surface
Classification of Epithelia (Fig 4.1)
 Shape
– Squamous
– Cuboidal
– Columnar
 Degree of layering
– Simple
– Stratified
Classification of Epithelia
 Simple epithelia
– Consist of a single cell layer
– Line surfaces used for exchange
– Located in the GIT, respiratory tract, inner surface of blood vessels and
heart chambers
Classification of Epithelia
 Stratified epithelia
– Several layer of cells (additional protection)
– Different cell layers may have different cell types
– Epithelia is named with respect to the cells of the apical layer
– Found on the surface of the skin and lining of the mouth and vagina
Simple Squamous Epithelia (Fig. 4.2a)

Description
–

Flat thin cells with very little cytoplasm shaped like fried egg
Location
–
Found lining the alveoli and blood vessels (endothelium), lymph
vessels, and ventral body cavity

Function
–
Passage of materials by diffusion and filtration in areas where
protection is not a priority
–
Secretes lubricating substances in serosae
Simple Cuboidal Epithelium (Fig. 4.2b)
 Description
– Single layer of cubelike cells with large spherical centrally placed
nuclei
 Function
– Secretion and absorption
 Location
– Kidney tubules
– Surface of the ovary
– Ducts and secretory parts of small glands
Simple Columnar Epithelium (Fig. 4.2c)


Description
–
Single layer of tall cells with round nuclei
–
Apical surfaces may contain microvilli
–
Tissue may contain goblet cells (mucus- secreting cells)
Function
–

Absorption, secretion
Location
–
GIT (from stomach to anal canal)
Pseudostratified Columnar Epithelium (Fig. 4.2d)


Description
–
Single layer of cell with differing heights (false stratification)
–
May contain goblet cells and bear cilia
Function
–
Secretion (primarily mucus)
–

Mucus propulsion by ciliary action
Location
–
Nasal cavity, trachea and bronchi
Stratified Squamous Epithelia (Fig. 4.2e)

Description
–
Several call layers
–
Basal cells are cuboidal or columnar
–
Surface cells are squamous
–
Keratinized type has the protein keratin that helps in preventing water
loss

Function
–

Provides protection to underlying areas subject to abrasion
Location
–
Nonkeratinized
Esophageal lining, mouth, vagina
–
Keratinized

Epidermis of the skin
Transitional Epithelium (Fig. 4.2f)
 Description
– Basal cells are cuboidal or columnar
– Surface cells are dome-shaped or squamouslike depending on the
degree of stretch of the organ
 Function
– Allows distention (stretching) of urinary organs
 Location
– Ureters, bladder and parts of urethra
Glandular Epithelia
 Glands make and secrete watery substances referred to as secretions
 Two types exist
– Endocrine (ductless) glands

Release secretions directly into the blood stream or lymph
– Exocrine (ductal) glands

Release secretions onto body surface or into body cavities
Classification of Exocrine Glands (Fig. 4.4)
 Unicellular
– Goblet cell
 Multicellular
– Have a secretory portion (acinus) and duct
– Structurally classified as simple (straight duct) or compound (branched
duct)
– Classified based on secretory units as tubular (tube-shaped acinus),
alveolar (flasklike acinus), and tubuloalveolar if both are present.
Classification of Exocrine Glands
 Multicellular
– Classified based on secretory mode as:

Merocrine – secretes by exocytosis

Holocrine - secretory cells rupture to release secretion

Apocrine – apical portion of secretory cell ruptures to release
secretion
Connective Tissue (Fig. 4.6)
 Four main classes are: connective tissue proper, cartilage, bone, and blood
Connective Tissue
 Common characteristics
– Common origin

Develop from embryonic tissue called mesenchyme
– Degree of vascularity

May be avascular, mildly vascularized or richly vascularized
– Extracellular matrix

Major constituent of connective tissue surrounding cells

Has two main constituents, ground substance (IF, cell adhesion
molecules, and proteoglycans) and fibers
Connective tissue cells
 Adipocytes – Store fat
 Macrophages – Phagocytes
 Fibroblasts - Produce fiber
 WBCs – Immune cells
– Plasma cells – Produce antibodies
 Mast cells – Produce histamine and heparin
Connective Tissue
 Three types of fibers exist
– Collagen fibers

Long, flexible and tough

Found in tendons and ligaments
– Reticular fibers

Strong and flexible

Used to support organs
– Elastic fibers

Can stretch and return to original length
Types of Connective Tissue

Connective tissue proper excludes bone, cartilage and blood

Two subclasses exist

Lose connective tissue
–
Areolar tissue (Fig. 4.9a)

Found throughout the body acting as packing material between
tissues
–
Adipose tissue (Fig. 4.9b)

–
Stores fat
Reticular tissue (Fig. 4.9c)

Found in the lymphatic system where it provides support to the cells
of the immune system
Types of Connective Tissue
– Dense connective tissue (dense regular connective)
 Dense connective tissue
– Dense regular (Fig. 4.9d)

Includes tendons and ligaments
– Dense irregular (Fig. 4.9e)

Found in skin, joint capsule and surrounding various organs
Types of Connective Tissue


Cartilage
–
Properties are intermediate between dense connective tissue and bone
–
Primary cells are chondrocytes
Hyaline cartilage (Fig. 4.9f)
–
Most common
–
Matrix has closely packed collagen fibers for strength and flexibility
–
Found between ribs and the sternum, trachea and articular surfaces of
most joints
Types of Connective Tissue


Elastic cartilage (Fig. 4.9g)
–
Contains lots of elastic fibers
–
Found in the outer ear, epiglottis and larynx
Fibrocartilage (Fig. 4.9h)
–
Densely packed with collagen
–
Very tough
–
Found between the vertebrae (intervertebral disks) and between the
pubic bones (pubic symphysis)
Covering and Lining Membranes (Fig. 4.12)

Membranes are formed by epithelial and connective tissues
–
Cutaneous membranes (Dry membrane)

–
Mucous membranes (mucosae) (Moist)

–
Skin
GIT, respiratory, reproductive, urinary tracts
Serous membranes (moist)

–
Pleura, peritoneum and pericardium
Synovial membranes

Joints
–
Note that synovial membranes are NOT epithelial membranes
and are solely made up of connective tissue
Tissue Repair (Fig. 4.13)
 Tissue injury results in body damage and increased susceptibility to
pathogenic invasion
 Tissue repair stimulates two major body responses
– Inflammatory response
– Immune response
Tissue Response
 Inflammatory response
– Remove harmful agents
– Prevent further injury
– Restore tissue health
 Immune response
– Specific and deadly attacks against invading pathogens
Tissue Repair
 Steps of tissue repair
– Inflammation

Chemicals (histamines) are released from damaged tissue and they
cause capillaries to dilate and leak

Fluid enters injury site with more chemicals (clotting factors and
antibodies)

WBCs enter site of injury
– Organization

New capillaries proliferate and restore proper blood flow to injured
tissue

Fibroblasts produce collagen fibers to help strengthen injured tissue
Tissue Repair

Regeneration and fibrosis
–
Regeneration is replacement of damaged tissue with new tissue
–
Fibrosis is the proliferation of connective tissue to form scar

Fibrosis may occur depending on the type and severity of the injury

Epithelial tissue and bone tissue are good at regenerating without
fibrosis

Dense regular connective tissue and cartilage have considerably less
regenerative properties

Cardiac tissue and nervous tissue have essentially no functional
regenerative capacity