The Tissue Level of
Organization
Chapter 3
Tissue
• Definition – an aggregation of cells in
which each cooperates with all others in the
performance of a given function
• Examples of general functions
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Movement
Protection
Support
Production of chemicals
Principal Tissue Types
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Epithelial
Connective
Muscular
Nervous
Epithelial Tissue
• Functions
– Coverings and linings
– Forms glands
• Characteristics
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Closely packed cells
Basement membrane
Nerves
Avascular
Cell growth and
replacement by mitosis
• Classification
– Simple or stratified
– Squamous, cuboidal,
columnar, or
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Epithelia of Coverings and
Linings
Squamous Epithelium
• Simple Squamous
Epithelium
– Highly adapted to
diffusion, osmosis,
& filtration
• Stratified
Squamous
Epithelium
– Surface layer is flat
– Function protection
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Cuboidal Epithelium
• Simple cuboidal
epithelium
• Lines glands and
their ducts
• Function –
secretion and
absorption
• Stratified Cuboidal
epithelium
– Surface layer
cube-shaped
– Function –
protection
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Transitional Epithelium
• Can be stretched
• Lines hollow
structures that
expand
• Function – prevents
rupture of organ
http://www.mhhe.com/biosci/ap/histology_mh/stratepi.html
Columnar Epithelia
• Simple columnar
epithelium
– Functions –
protection,
absorption, secretion
• Stratified columnar
epithelium
– Surface layer is
column-shaped
– Function – protection
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Pseudostratified Columnar Epithelium
• Appear stratified
but all cells connect
to the basal lamina
• Functions –
protection,
secretion
http://bioweb.uwlax.edu/zoolab/Table_of_Contents/Lab-1b/Pseudostratified_Model_1/pseudostratified_model_1.htm
Glandular Epithelium
• Gland – 1 or more cells
– Unicellular gland – goblet cell
– Multicellular – secretory sheets or groups of
cells
• Serous
• Mucous
• Mixed
• Function – secretion
• Types
– Exocrine – to surface or ducts
– Endocrine – to blood
Mechanisms of Glandular Secretion
• Merocrine
– Secretion is released
by exocytosis
• Apocrine
– Secretion is released
by pinching off of
vesicles
• Holocrine
– Secretion is released
by entire cell
bursting
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Connective Tissue
• Most abundant tissue
• Functions are varied
• Characteristics
– Specialized cells, widely scattered
– Rich blood supply
– Much matrix
• Extracellular fibers
• Ground substance
Classification of Connective Tissues
• Embryonic
– Mesenchymal cells
• Adult connective tissues
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Embryonic Connective Tissues
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Cell Types Found in Connective Tissue
• Fibroblasts
– Secrete the molecules that form the matrix
– Fixed cells
• Fibrocytes
• Macrophages
– “Big eaters”
– May be fixed or wandering
Additional Connective Tissue Cells
• Adipocytes
– Fixed fat cells
• Mesenchymal cells
– Fixed cells that can divide (mitosis) to replace
damaged connective tissue
• Melanocytes
– Fixed cells that store melanin
• Lymphocytes
– Wandering immune system cells
• Mast cells
– Around blood vessels
– Wandering cells that produce histamine & heparin
Connective Tissue Fibers
• Collagen fibers
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Most common type
White
Strong, ropelike
Form ligaments, tendons
• Reticular fibers
– Thin
– Woven into rough, flexible network
• Elastic fibers
– Yellow
– Thin
– Stretch
• Contain elastin
Ground Substance
• Extracellular fluid in connective tissue
– Water
– Glycoproteins
Types of Connective Tissue
Loose (Areolar) Connective Tissue
• Fibers not abundant
• Contains all 3 types of fibers
• Examples of locations
– Between skin and muscles
– Around digestive tract
– Around blood vessels
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Adipose Tissue
• Most of the volume is adipocytes
• Provides padding, slows heat loss, food reserve
• Locations
– Wherever there is loose connective tissue
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Reticular Tissue
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Reticular fibers form a strong network
Provides strength and support
Forms the framework (stroma) of many organs
Binds together cells of smooth muscle
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Dense Connective Tissue
• Types
– Dense Regular Connective Tissue
– Dense Irregular Connective Tissue
– Elastic Connective Tissue
Dense Regular Connective Tissue
• Lots of collagen fibers in bundles
• Cells – fibroblasts in rows between bundles
• Examples
– Tendons, ligaments
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Dense Irregular Connective Tissue
• Tensions in various
directions
• Occurs in sheets
• Locations
– Periosteum
– Perichondrium
– Fibrous capsules of
some organs
– Fasciae
– Dermis
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Elastic Tissue
• Lots of elastic fibers
• Fibroblasts in spaces between fibers
• Provides stretch and strength
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Cartilage
• Dense network of collagenous fibers &
elastic fibers in a gel-like substance
• Cells – chondrocytes in lacunae
– Chondroblasts
• Perichondrium – surrounds surface of
cartilage
• Growth
– Interstitial growth
– Appositional growth
Growth of Cartilage
Types of Cartilage
• Hyaline cartilage
• Fibrocartilage
• Elastic cartilage
Hyaline Cartilage
• Most common
• Provides
flexibility and
support
• Locations
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Ends of bones
Trachea
Larynx
Embryonic
skeleton
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Fibrocartilage
• Visible collagenous fibers with scattered chondrocytes
• Provides strength and rigidity
• Locations
– Intervertebral discs
– Symphysis pubis
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Elastic Cartilage
• Threadlike network of elastic fibers with chondrocytes
• Provides strength and maintains shape
• Locations
– Pinna
– Eustacian tube
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Bone
• Solid matrix
• Cells
– Osteocytes in
lacunae
– Osteoblasts
– Osteoclasts
• Periosteum
surrounds surface
of bone
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Blood
• Functions
– Transport medium
– Regulation
– Protection
• Composition
– Plasma – fluid
– Formed elements –
cells & cell fragments
• Erythrocyte
• Leukocyte
• Thrombocyte
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A Red Blood Cell
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SEM of RBCs
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Membranes
• Epithelial layer +
underlying connective
tissue = epithelial
membrane
• Types
– Mucous membrane
– Serous membrane
– Cutaneous
membrane
– Synovial
membrane
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Fascia
• Fascia – collective term for sheets of
connective tissue
• Functions
– Provide strength and stability
– Maintain positions of internal organs
– Provide a route for the distribution of blood
vessels, lymphatics, and nerves
• 3 types
Types of Fascia
• Superficial Fascia
– Adipose tissue and
loose connective
tissue
– Immediately deep to
the skin
• Deep Fascia
– Dense connective
tissue
– Strong internal
framework
• Subserous Fascia
– Loose connective
tissue
– Between deep fascia
and serous
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Muscular Tissue
• Specialized cells
• Function - contraction
• 3 types
– Skeletal muscle
– Cardiac muscle
– Smooth muscle
Skeletal Muscle
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Connected to bones
Striated
Multinucleated
Voluntary
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Cardiac Muscle
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Found in the heart
Striations
Intercalated discs
Involuntary
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Smooth Muscle
• Found in walls of internal organs
• Nonstriated
• Involuntary
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Nervous Tissue
• Specialized cells
• Function – conduction of electrical impulses
• Cells
– Neurons
– Neuroglia
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