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Chapter 4
The Tissue Level of
Organization
Copyright 2009, John Wiley & Sons, Inc.
What is a Tissue?

A tissue is a group of cells
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Common embryonic origin
Function together to carry out specialized
activities
Hard (bone), semisolid (fat), or liquid (blood)
Histology is the science that deals with the
study of tissues.
Pathologist specialized in laboratory studies
of cells and tissue for diagnoses
Copyright 2009, John Wiley & Sons, Inc.
4 Types of Tissues
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Epithelial
 Covers body surfaces and lines hollow organs,
body cavities, duct, and forms glands
Connective
 Protects, supports, and binds organs.
 Stores energy as fat, provides immunity
Muscular
 Generates the physical force needed to make body
structures move and generate body heat
Nervous
 Detect changes in body and responds by
generating nerve impulses
Copyright 2009, John Wiley & Sons, Inc.
Development of Tissues

Tissues of the body develop from three primary
germ layers:
 Ectoderm, Endoderm, and Mesoderm
 Epithelial tissues develop from all three germ
layers
 All connective tissue and most muscle tissues
drive from mesoderm
 Nervous tissue develops from ectoderm
Copyright 2009, John Wiley & Sons, Inc.
Cell Junctions
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Contact points between the
plasma membranes of
tissue cells
 5 most common types:
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Tight junctions
Adherens junctions
Desmosomes
Hemidesmosomes
Gap junctions
Copyright 2009, John Wiley & Sons, Inc.
Tight Junctions
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Web-like strands of
transmembrane proteins
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Fuse cells together
Seal off passageways
between adjacent cells
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Common in epithelial
tissues of the stomach,
intestines, and urinary
bladder
Help to retard the passage
of substances between
cells and leaking into the
blood or surrounding
tissues
Copyright 2009, John Wiley & Sons, Inc.
Adherens Junctions
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Dense layer of proteins called
plaque
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Resist separation of cells
during contractile activities
Located inside of the plasma
membrane attached to both
membrane proteins and
microfilaments of the
cytoskeleton
Transmembrane glycoproteins
called cadherins insert into the
plaque and join cells
In epithelial cells, adhesion
belts encircle the cell
Copyright 2009, John Wiley & Sons, Inc.
Desmosomes
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Contain plaque and
cadherins that extends into
the intercellular space to
attach adjacent cells
together
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Desmosome plaque
attaches to intermediate
filaments that contain
protein keratin
Prevent epidermal cells
from separating under
tension and cardiac
muscles cells from pulling
apart during contraction
Copyright 2009, John Wiley & Sons, Inc.
Hemidesmosomes
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Resemble half of a
desmosome
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Do not link adjacent cells
but anchor cells to the
basement membrane
Contains transmembrane
glycoprotein integrin
Integrins attach to
intermediate filaments
and the protein laminin
present in the basement
membrane
Copyright 2009, John Wiley & Sons, Inc.
Gap Junctions
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Connect neighboring cells
via tiny fluid-filled tunnels
called connexons
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Contain membrane proteins
called connexins
Plasma membranes of gap
junctions are separated by
a very narrow intercellular
gap (space)
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Communication of cells
within a tissue
Ions, nutrients, waste,
chemical and electrical
signals travel through the
connexons from one cell to
another
Copyright 2009, John Wiley & Sons, Inc.
Epithelial Tissues
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Epithelial tissue consists of cells arranged in
continuous sheets, in either single or multiple layers
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Closely packed and held tightly together
Covering and lining of the body
Free surface
3 major functions:
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Selective barrier that regulates the movement of materials
in and out of the body
Secretory surfaces that release products onto the free
surface
Protective surfaces against the environment
Copyright 2009, John Wiley & Sons, Inc.
General Features of Epithelial Cells
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Surfaces of epithelial cells differ in structure and
have specialized functions
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Apical (free) surface
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Lateral surfaces
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Faces the body surface, body cavity, lumen, or duct
Faces adjacent cells
Basal surface
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Opposite of apical layer and adhere to extracellular
materials
Copyright 2009, John Wiley & Sons, Inc.
General Features of Epithelial Cells
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Basement membrane
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Thin double extracellular layer that serves as the point of
attachment and support for overlying epithelial tissue
Basal lamina
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Closer to and secreted by the epithelial cells
Contains laminin, collagen, glycoproteins, and proteoglycans
Reticular lamina
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Closer to the underlying connective tissue
Contains collagen secreted by the connective tissue cells
Copyright 2009, John Wiley & Sons, Inc.
Epithelial Cells
Copyright 2009, John Wiley & Sons, Inc.
Epithelial Tissues
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Own nerve supply
Avascular or lacks its own blood supply
Blood vessels in the connective tissue bring in
nutrients and eliminate waste
High rate of cell division for renew and repair
Numerous roles in the body (i.e. protection and
filtration)
Covering and lining epithelium
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Outer covering of skin and some internal organs
Glandular epithelium
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Secreting portion of glands (thyroid, adrenal, and sweat
glands)
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Covering and Lining Epithelium
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Normally classified according to:
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Arrangement of cells into layers
Shapes of cells
Copyright 2009, John Wiley & Sons, Inc.
Covering and Lining Epithelium
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Arrangement of cells in layers
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Consist of one or more layers depending on function
Simple epithelium
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Pseudostratified epithelium
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Single layer of cells that function in diffusion, osmosis,
filtration, secretion, or absorption
Appear to have multiple layers because cell nuclei at different
levels
All cells do not reach the apical surface
Stratified epithelium
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Two or more layers of cells that protect underlying tissues in
areas of wear and tear
Copyright 2009, John Wiley & Sons, Inc.
Different Types of Covering and Lining
Epithelium
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Cells vary in shape depending on their
function
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Squamous
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Thin cells, arranged like floor tiles
Allows for rapid passage of substances
Cuboidal
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As tall as they are wide, shaped like cubes or hexagons
May have microvilli
Function in secretion or absorption
Copyright 2009, John Wiley & Sons, Inc.
Different Types of Covering and Lining
Epithelium
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Columnar
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Much taller than they are wide, like columns
May have cilia or microvilli
Specialized function for secretion and absorption
Transitional
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Cells change shape, transition for flat to cuboidal
Organs such as urinary bladder stretch to larger size
and collapse to a smaller size
Copyright 2009, John Wiley & Sons, Inc.
Simple Epithelium
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Simple squamous epithelium
Simple cuboidal epithelium
Simple columnar epithelium (nonciliated and
ciliated)
Pseudostratified columnar epithelium (nonciliated
and cilated)
Copyright 2009, John Wiley & Sons, Inc.
Simple squamous epithelium
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Single layer of cells that resembles a tiled floor on the
surface
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Nucleus is centrally located and appears flattened oval or
sphere
Found at sites for filtration or diffusion
Copyright 2009, John Wiley & Sons, Inc.
Covering and Lining Epithelium
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Endothelium
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Mesothelium
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The type of simple squamous that lines the heart,
blood vessels, and lymphatic vessels
The type of epithelial layer of serous membranes
such as the pericardium, pleura, or peritoneum
Unlike other epithelial tissue, Both are
derived from embryonic mesoderm
Copyright 2009, John Wiley & Sons, Inc.
Simple cuboidal epithelium
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Cuboidal shaped cells
Cell nuclei round and centrally located
Found in thyroid gland and kidneys
Functions in secretion and absorption
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Simple columnar epithelium
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Column shaped cells
Oval nuclei at near base
Nonciliated and ciliated
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Nonciliated simple columnar epithelium
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Contains columnar cells
with microvilli at their
apical surface and goblet
cells
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Secreted mucus serves
as lubricant for the lining
of digestive, respiratory,
reproductive and urinary
tracts
Also prevents the
destruction of the
stomach lining by acidic
gastric juices
Copyright 2009, John Wiley & Sons, Inc.
Ciliated simple columnar epithelium
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Columnar epithelial cells
with cilia at the apical
surface
 In respiratory tract,
goblet cells are
interspersed among
ciliated columnar
epithelia
 Secreted mucus on the
surface traps inhaled
foreign particles.
Beating cilia moves
particles to the throat for
removal by coughing,
swallowing, or sneezing
 Cilia also moves oocytes
to the uterine tubes
Copyright 2009, John Wiley & Sons, Inc.
Covering and Lining Epithelium
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Pseudostratified columnar epithelium
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Appears to have several layers due to nuclei are
various depths
All cells are attached to the basement membrane
in a single layer but some do not extend to the
apical surface
Ciliated cells secrete mucus and bear cilia
Nonciliated cells lack cilia and goblet cells
Copyright 2009, John Wiley & Sons, Inc.
Covering and Lining Epithelium
Copyright 2009, John Wiley & Sons, Inc.
Stratified Epithelium
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Two or more layers of cells
Specific kind of stratified epithelium depends
on the shape of cells in the apical layer
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Stratified squamous epithelium
Stratified cuboidal epithelium
Stratified columunar epithelium
Transitional epithelium
Copyright 2009, John Wiley & Sons, Inc.
Stratified Squamous Epithelium
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Several layers of cells that are flat in the apical layer
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Keratinized form contain the fibrous protein keratin
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New cells are pushed up toward apical layer
As cells move further from the blood supply they dehydrate, harden,
and die
Found in superficial layers of the skin
Nonkeratinized form does not contain keratin

Found in mouth and esophagus
Copyright 2009, John Wiley & Sons, Inc.
Stratified Cuboidal Epithelium
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Fairly rare type of epithelium
Apical layers are cuboidal
Functions in protection
Copyright 2009, John Wiley & Sons, Inc.
Stratified columnar epithelium
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Also very uncommon
Columnar cells in apical layer only
Basal layers has shorten, irregular shaped cells
Functions in protection and secretion
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Transitional Epithelium
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Found only in the urinary system
Variable appearance
In relaxed state, cells appear cuboidal
Upon stretching, cells become flattened and appear
squamous
Ideal for hollow structure subjected to expansion
Copyright 2009, John Wiley & Sons, Inc.
Glandular Epithelium: Endocrine
Glands
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Secretions, called hormones, diffuse directly into the
bloodstream
Function in maintaining homeostasis
Copyright 2009, John Wiley & Sons, Inc.
Glandular Epithelium: Exocrine Glands
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Secrete products into ducts that empty onto the surfaces of
epithelium
Skin surface or lumen of a hollow organ
Secretions of the exocrine gland include mucus, sweat, oil,
earwax, saliva, and digestive enzymes
Examples of glands include sudoriferous (sweat) glands
Copyright 2009, John Wiley & Sons, Inc.
Structural Classification of Exocrine
Glands
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Multicellular glands are categorized
according to two criteria:
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Ducts are branched or unbranched
Shape of the secretory portion of the gland
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Simple gland duct does not branch
Compound gland duct branches
Tubular glands have tubular secretory parts
Acinar glands have rounded secretory parts
Tubuloacinar glands have both tubular and rounded
secretory parts
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Structural Classification of Exocrine
Glands
Copyright 2009, John Wiley & Sons, Inc.
Functional Classification of Exocrine
Glands
SWEAT GLAND
MAMMARY GLAND
ZIT
Copyright 2009, John Wiley & Sons, Inc.
Connective Tissue
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Most abundant and widely distributed tissues
in the body
Numerous functions
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Binds tissues together
Supports and strengthen tissue
Protects and insulates internal organs
Compartmentalize and transport
Energy reserves and immune responses
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Extracellular matrix of Connective
Tissue
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Extracellular matrix is the material located
between the cells
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Consist of protein fibers and ground substance
Connective tissue is highly vascular
Supplied with nerves
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Exception is cartilage and tendon. Both have little
or no blood supply and no nerves
Copyright 2009, John Wiley & Sons, Inc.
Cells and Fibers in Connective Tissue
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Connective Tissue Cells
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Fibroblasts
 Secrete fibers and components of ground substance
Adipocytes (fat cells)
 Store triglycerides (fat)
Mast cells
 Produce histamine
White blood cells
 Immune response
 Neutrophil and Eosinophils
Macrophages
 Engulf bacteria and cellular debris by phagocytosis
Plasma cells
 Secrete antibodies
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Connective Tissue Extracellular Matrix
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Ground substance
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Between cells and fibers
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Fluid, semifluid, gelatinous, or calcified
Functions to support and bind cells, store water, and allow
exchange between blood and cells
Complex combination of proteins and polysaccharides
Fibers
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Collagen fibers
Elastic fibers
Reticular fibers
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Classification of Connective Tissues
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Embryonic connective tissue
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Mesenchyme and mucous connective tissue
Mature connective tissue
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Loose connective tissue
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Dense connective tissue
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Dense regular, dense irregular, and elastic
Cartilage
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Areolar, adipose, and reticular
Hyaline, fibrocartilage, and elastic cartilage
Bone tissue
Liquid connective tissue
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Blood and lymph
Copyright 2009, John Wiley & Sons, Inc.
Embryonic Connective Tissue
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Mesenchyme
 Gives rise to all other connective tissues
Mucous (Wharton’s Jelly)
 Found in umbilical cord of the fetus
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Loose Connective Tissue: Areolar
Connective Tissue
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Most widely distributed in the body
Contains several types of cells and all three fibers
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Loose Connective Tissue: Adipose Tissue
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Contains adipocytes
Good for insulation and energy reserves
White (common) and brown adipose tissue
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Loose Connective Tissue: Reticular
Connective Tissue
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Fine interlacing reticular fibers and cells
Forms the stroma of liver, spleen, and lymph nodes
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Dense Connective Tissue
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Dense connective tissue
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Contains numerous, thicker, and denser fibers
Packed closely with fewer cells than loose connective tissue
Dense regular connective tissue
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Bundles of collagen fibers are regularly arranged in parallel
patterns for strength
Tendons and most ligaments
Copyright 2009, John Wiley & Sons, Inc.
Types of Mature Connective Tissue:
Dense Irregular Connective Tissue
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Collagen fibers are usually irregularly arranged
Found where pulling forces are exerted in many directions
Dermis of skin and heart
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Dense Connective Tissue: Elastic
Connective Tissue
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Contain branching elastic fibers
Strong and can recoil to original shape after stretching
Lung tissue and arteries
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Types of Mature Connective Tissue:
Cartilage
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Cartilage is a dense network of collagen
fibers and elastic fibers firmly embedded in
chondroitin sulfate
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Chrondrocytes
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Pericondrium
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Cartilage cells found in the spaces called lucunae
Covering of dense irregular connective tissue that
surrounds the cartilage
Two layers: outer fibrous layer and inner cellular layer
No blood vessels or nerves, except
pericondrium
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Hyaline cartilage
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Most abundant cartilage in the body
Surrounding by perichondrium (some exceptions like
articular cartilage)
Provide flexibility and support. Reduces friction
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Fibrocartilage
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Chondrocytes are scattered among bundles of collagen
fibers within the extracellular matrix
Lack a perchondrium
Strongest type of cartilage
Found in intervertebral disc (between vertebrae)
Copyright 2009, John Wiley & Sons, Inc.
Elastic Cartilage
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Chrondrocytes are located within a threadlike network of
elastic fibers
Pericondrium is present
Provides strength and elasticity
Copyright 2009, John Wiley & Sons, Inc.
Repair and Growth of Cartilage
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Cartilage grows slowly
When injured or inflamed, repairs is slow due
to its avascular nature.
Two patterns of cartilage growth:
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Interstitial growth
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Growth from within the tissue
Appositional growth
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Growth at the outer surface of the tissue
Copyright 2009, John Wiley & Sons, Inc.
Bone tissue
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Bones are organs composed of several different
connective tissues: bone (osseous) tissue,
periosteum, and endosteum.
Compact or spongy
Osteon or haversian system

Spongy bone lacks osteons. They have columns called
trabeculae
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Liquid Connective Tissue
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Blood tissue
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Connective tissue with liquid extracellular matrix called blood
plasma
Lymph
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Membranes
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Epithelial Membranes
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Mucous membranes (GOBLET CELLS)
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Lines a body cavity that opens Directly to the
exterior
Epithelial layer is important for the body’s defense
against pathogens
Connective tissue layer is areolar connective
tissue and is called lamina propria
Copyright 2009, John Wiley & Sons, Inc.
Epithelial Membranes

Serous membranes or serosa
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Lines a body cavity that does not open directly to
the exterior. Also covers the organs that lie within
the cavity
Consist of areolar connective tissue covered by
mesothelium (simple squamous epithelium) that
secrete a serous fluid for lubrication
Copyright 2009, John Wiley & Sons, Inc.
Epithelial membranes: Mucous
Membranes
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Membranes are flat sheets of pliable tissue
that cover or line a part of the body
Epithelial membranes are a combination of
an epithelial layer and an underlying
connective tissue layer
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Mucous, Serous, and Cutaneous membranes
Synovial membranes
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Lines joints and contains connective tissue but not
epithelium
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Muscular Tissue
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Consists of elongated cells called muscle
fibers or myocytes
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Cells use ATP to generate force
Several functions of muscle tissue
Classified into 3 types: skeletal, cardiac, and
smooth muscular tissue
Copyright 2009, John Wiley & Sons, Inc.
Skeletal Muscle Tissue
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Attached to bones of the skeleton
Have striations
Voluntary movement or contractions by conscious control
Vary in length (up to 40 cm) and are roughly cylindrical in
shape
Copyright 2009, John Wiley & Sons, Inc.
Muscular Tissue

Cardiac muscle tissue
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Have striations
Involuntary movement or contraction is not consciously
controlled
Intercalated disc unique to cardiac muscle tissue
Copyright 2009, John Wiley & Sons, Inc.
Smooth Muscle Tissue
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Walls of hollow internal structures
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Blood vessels, airways of lungs, stomach, and intestines
Nonstriated
Usually involuntary control
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Nervous Tissue

Consists of two principle types of cells
 Neurons or nerve cells
 Neuroglia
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Excitable Cells
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Neurons and muscle fibers
Exhibit electrical excitability
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The ability to respond to certain stimuli by
producing electrical signals such as action
potentials
Actions potentials propagate along a nerve or
muscle plasma membrane to cause a response
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Release of neurotransmitters
Muscle contraction
Copyright 2009, John Wiley & Sons, Inc.
Tissue Repair: Restoring Homeostasis

When tissue damage is extensive both
stroma and parenchymal cells are active in
repair
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Fibroblast divide rapidly
New collagen fibers are manufactured
New blood capillaries supply materials for healing
All of these process create an actively
growing connective tissue called granulation
tissue
Copyright 2009, John Wiley & Sons, Inc.
Aging and Tissues
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Tissue heal faster in young adults
Surgery of a fetus normally leaves no scars
Young tissues have a better nutritional state,
blood supply, and higher metabolic rate
Extracellular components also changes with
age
Changes in the body’s use of glucose,
collagen, and elastic fibers contribute to the
aging process
Copyright 2009, John Wiley & Sons, Inc.
End of Chapter 4
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