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TISSUES
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Tissues are communities of cells working together
to perform a function for the organism.
Remember at all times that we are still talking
about CELLS!
Even though commonly we think of organs as
heart, lungs, kidney etc. that other tissues are
also called organs such as muscles, bones etc.
Four Basic Tissue Types and Basic Functions
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Epithelial tissue – covering - ectoderm
Connective tissue – support –
mesoderm/endoderm
Muscle tissue – movement - mesoderm
Nervous tissue – control - ectoderm
Epithelial Tissue
 Covers the body surface and lines body cavities
 Forms parts of most glands (organs are mainly epithial
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and connective tissues with nerves and blood vessels
serving the cells)
Functions of epithelium
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Protection – part of immune system
Absorption (intestine), secretion (glands), and ion transport
(nephron tubules)
Filtration (capillaries)
Forms slippery surfaces (mucus membranes)
Glandular Epithelium (sweat, oil, wax, hormones, mucus)
Greatest capacity for regeneration (therefore is the origin of
most cancers)
Classifications of Epithelia
 First name of tissue indicates number of cell layers
 Simple – one layer of cells
 Stratified – more than one layer of cells
 Last name of tissue
describes shape of
cells
 Squamous –
cells are wider
than tall (platelike)
 Cuboidal –
cells are as
wide as tall,
like cubes
 Columnar –
cells are taller
than they are
wide, like
columns
EPITHELIUM AS GLANDS
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EXOCRINE GLANDS –with ducts
ENDOCRINE GLANDS – without ducts
Exocrine Glands
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Ducts carry products of exocrine glands to
epithelial surface
Include the following diverse glands
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Goblet cells produce mucin
 Mucus-secreting glands
 Sweat and oil glands
 Salivary glands
 Liver and pancreas
 Mucin + water  mucus
 Protects and lubricates many internal body surfaces
 Goblet cells are a unicellular exocrine gland and
are epithelial
Goblet Cells – a type of epithelial cell (Unicellular gland)
Figure 4.5
Multicellular Exocrine Glands
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Have two basic parts
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Classified by structure of duct
 Epithelium-walled duct
 Secretory unit
 Simple
 Compound
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Categorized by secretory unit
 Tubular
 Alveolar
 Tubuloalveolar
Types of Multicellular Exocrine Glands
For information only!
Figure 4.6
Endocrine Glands
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Endocrine glands are ductless glands
 Secrete substances directly into extracellular space
to be picked up by the bloodstream by diffusion
 Produce molecules called hormones
Special Characteristics of Epithelia
1) Cellularity - cells separated by minimal extra cellular material
2) Specialized contacts - cells joined by specialized cell junctions
3) Polarity - cell regions of the apical surface differ from the basal
surface
Special Contacts (Lateral Surface Features) – Cell Junctions
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Think about the function of epithelial tissues and what
characteristics it would have to have to perform that
function.
Since exposure to digested food would be very dangerous
if exposed to the contents of the abdominal cavity, the
intestinal tissue needs to be a barrier.
Therefore, cells need to be tightly held together
Factors holding epithelial cells together
 Adhesion proteins link plasma membranes of adjacent cells
 Contours of adjacent cell membranes
 (Like puzzle pieces)
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Special cell junctions
A) Tight Junction
Tight junctions (zona occludens) – close off intercellular space
Figure 4.7a
B) Desmosome
Desmosomes – two disclike plaques connected across
intercellular space
Figure 4.7b
C) Gap Junction
Gap junctions – passageway between two adjacent cells
Figure 4.7c
D) Adherens Junctions
Has linker
proteins;
Important for
the skin
Zonula adherens
Special Characteristics of Epithelia
4) Support by connective tissue
5) Avascular but innervated - Epithelia receive nutrients from underlying
connective tissue
6) Regeneration - Lost cells are quickly replaced by cell division
Basal Feature: The Basal Lamina
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Noncellular supporting sheet between the ET and the CT
deep to it
Consists of proteins secreted by ET cells
Basal Lamina
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Damage to the basal lamina due to untreated
diabetes may lead to kidney failure and blindness.
Basal Feature: The Basal Lamina
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Functions
 Acts as a selective filter, determining which
molecules from capillaries enter the epithelium
 Acts as scaffolding along which regenerating ET
cells can migrate
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Basal lamina and reticular layers of the
underlying CT deep to it form the basement
membrane
Epithelial Apical Surface Features
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Apical surface features
1) Microvilli – fingerlike extensions of plasma membrane
 Abundant in ET of small intestine and kidney
 Maximize surface area across which small
molecules enter or leave
 Act as stiff knobs that resist abrasion
2) Cilia – whiplike, highly motile extensions of apical
surface membranes
 Contains a core of nine pairs of microtubules
encircling one middle pair
 Each pair of microtubules – arranged in a
doublet
 Movement of cilia – in coordinated waves
Cilia – found in upper respiratory passageways
For information only
Figure 4.8
Simple Squamous Epithelium
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Description – single layer – flat cells with discshaped nuclei
Specialized types
 Endothelium (inner covering) – slick lining of
hollow organs
 Mesothelium (middle covering)
 Lines peritoneal, pleural, pericardial cavities
 Covers visceral organs of those cavities
Simple Squamous Epithelium
Figure 4.3a
Simple Cuboidal Epithelium
Figure 4.3b
Simple Columnar Epithelium
Figure 4.3c
Pseudostratified Ciliated Columnar Epithelium
Figure 4.3d
Stratified Epithelia
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Properties
 Contain two or more layers of cells
 Regenerate from below (basal layer)
 Major role is protection
 Named according to shape of cells at apical layer
Stratified Squamous Epithelium
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Description
 Many layers of cells – squamous in shape
 Deeper layers of cells appear cuboidal or columnar
 Thickest epithelial tissue
 Adapted for protection from abrasion
Stratified Squamous Epithelium
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Two types
 Keratinized and nonkeratinized
 Keratinized
 Location – epidermis
 Contains the protective protein keratin
 Waterproof
 Surface cells are dead and full of keratin
 Nonkeratinized
 Forms moist lining of body openings
Stratified Squamous Epithelium
Figure 4.3e
Stratified Cuboidal Epithelium
Figure 4.3f
Stratified Columnar Epithelium
Figure 4.3g
Transitional Epithelium
Figure 4.3h
Classes of Connective Tissue
 Most diverse and abundant tissue
 Main classes
 Connective tissue proper
 Cartilage
 Bone tissue
 Blood and fat!
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Cells separated by large amount of extracellular matrix
Common embryonic origin – mesenchyme
Extracellular matrix is composed of ground substance
Classes of Connective Tissue
Figure 4.9
Connective Tissue Proper
This cell type is the most divers and abundant type of tissue
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Has two subclasses
 Loose connective tissue
 Areolar, adipose, and reticular
 Dense connective tissue
 Dense irregular, dense regular, and elastic
Areolar Connective Tissue – A Model Connective Tissue
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Areolar connective tissue
 Underlies epithelial tissue
 Surrounds small nerves and blood vessels
 Has structures and functions shared by other CT
 Borders all other tissues in the body
 Is a “model” connective tissue – why?
 It has all 3 fiber types: Reticular, elastic and
collagen fibers
Major Functions of Connective Tissue
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Structures within areolar CT and function
 Support and binding of other tissues
 Holding body fluids (interstitial fluid  lymph)
 Defending body against infection
 Storing nutrients as fat
Areolar Connective Tissue
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Fibers provide support
 Three types of protein fibers in extracellular matrix
 Collagen fibers
 Reticular fibers
 Elastic fibers
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Fibroblasts produce these fibers
Areolar Connective Tissue
Figure 4.12b
Areolar Connective Tissue
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Tissue fluid (interstitial fluid)
 Watery fluid occupying extracellular matrix
 Tissue fluid derives from blood
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Ground substance
 Viscous, spongy part of extracellular matrix
 Consists of sugar and protein molecules
 Made and secreted by fibroblasts
Areolar Connective Tissue
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Main battlefield in fight against infection
Defenders gather at infection sites
 Macrophages
 Plasma cells
 Mast cells
 White blood cells
 Neutrophils, lymphocytes, and eosinophils
Adipose Tissue
Figure 4.12c
Reticular Connective Tissue
Figure 4.12d
Dense Connective Tissue
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Dense irregular connective tissue
Dense regular connective tissue
Elastic connective tissue
Dense Irregular Connective Tissue
Figure 4.12e
Dense Regular Connective Tissue
Figure 4.12f
Elastic Connective Tissue
Figure 4.12g
Other Connective Tissues
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Cartilage
Bone
Blood
Cartilage
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Firm, flexible tissue
Contains no blood vessels or nerves
Matrix contains up to 80% water
Cell type – chondrocyte
Types of Cartilage
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Hyaline cartilage
Elastic cartilage
Fibrocartilage
Hyaline Cartilage
collagen fibers (hyaline = glassy); Chodroblasts produce matrix; Chondrocytes lie in lacunae
Figure 4.12h
Elastic Cartilage
Figure 4.12i
Fibrocartilage
Figure 4.12j
Bone Tissue
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Description
 Calcified matrix containing many collagen fibers
 Osteoblasts – secrete collagen fibers and matrix
 Osteocytes – mature bone cells in lacunae
 Well vascularized
Bone Tissue
Figure 4.12k
Blood Tissue
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An atypical connective tissue
Develops from mesenchyme
Consists of cells surrounded by nonliving matrix
Blood Tissue
Figure 4.12l
Muscle Tissue
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Skeletal muscle tissue
Cardiac muscle tissue
Smooth muscle tissue
Skeletal Muscle Tissue
Figure 4.14a
Cardiac Muscle Tissue
Figure 4.14b
Smooth Muscle Tissue
Figure 4.14c
Nervous Tissue
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Description
 Main components are brain, spinal cord, and
nerves
 Contains two types of cells
 Neurons – excitatory cells
 Supporting cells (neuroglial cells)
Nervous Tissue
Figure 4.15
The Tissues Throughout Life
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With increasing age
 Epithelia thin
 Collagen decreases
 Bones, muscles, and nervous tissue begin to
atrophy
 Poor nutrition and poor circulation – poor health
of tissues
Covering and Lining Membranes
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Combine epithelial tissues and connective tissues
Cover broad areas within body
Consist of epithelial sheet plus underlying
connective tissue
Three Types of Membranes
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Cutaneous membrane – skin
Mucous membrane
 Lines hollow organs that open to surface of body
 An epithelial sheet underlain with layer of lamina
propria
Three Types of Membranes
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Serous membrane – slippery membranes
 Simple squamous epithelium lying on areolar
connective tissue
 Line closed cavities
 Pleural, peritoneal, and pericardial cavities
Covering and Lining Membranes
Figure 4.13a, b
Covering and Lining Membranes
Figure 4.13c
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HOMEWORK
What are the four tissue types, where are they found in the
body and what are their general functions?
Name the 3 shapes of epithelial tissue and their subtypes
and where they would be found on the body
What are the features of the basal surface, the apical
surface and the lateral surfaces of epithelial tissues?
What are the various cell junctions and in which tissues
(specifically, where in the body) would they be found?
What is a gland? How many types of glands are there and
what do they secrete?
What type of tissue is bone, tendon, ligaments, blood, fat,
nerves, muscles?
What is the simple squamous layer that lines blood vessels
called?
HOMEWORK
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What are the types of connective tissues, where would
they be found in the body and what are their functions?
What are the filaments (fibers) which are secreted by CT?
What are the contents of loose areolar tissue?
What is the difference between DICT and DRCT?
What type of tissue is a tendon made of?
What are the three types of muscle tissue?
How do you distinguish cardiac from skeletal muscle?
How do you distinguish smooth muscle from skeletal
muscle?
What is the last tissue type? What is it’s function?
Elastic fibers are composed of?
IVD are made of? (intervertebral discs)
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Name all cell junction types and what are their
distinguishing features?
How many layers is pseudostratified epithelium?