tissue: the living fabric chapter 4. chapter outline epithelial tissue connective tissue epithelial...

Tissue: The Living Fabric

Chapter 4

Chapter Outline

Epithelial Tissue Connective Tissue Epithelial Membranes Nervous Tissue Muscle Tissue Tissue Repair Developmental Aspects of Tissue

Introduction to Tissue The human body is a multicellular

organism– Its cells form tight communities that have

similar functions– Cell specialization allows for division of

labor – However, the risk is that loss of specialized

cells means the loss of that function and potentially the individual

Introduction to Tissue A tissue is defined as a group of closely

associated cells that perform related functions are similar in structure

Tissue do not consist entirely of cells as between the living cells is nonliving extracellular material

Tissue Groups of closely associated cells that are

similar in structure and function are called tissues

Four primary tissues interweave to form the “fabric” of the body– Epithelial (covering)– Connective (support)– Muscle (movement)– Nervous (control)

Organs

Tissues are organized into organs – Most organs contain all four tissue types– However, most organs will have one

predominant tissue type present– The arrangement and proportion of tissues

present determines the function of the organ

SECTION I

EPITHELIAL TISSUE

Epithelial Tissue Epithelial tissue is a sheet of cells that

covers a body surface, a body cavity, or has a glandular function

Epithelia form the boundaries between environments

Epithelial has many functions including; protection, absorption, filtration, excretion, secretion, and sensory reception

Epithelial Tissue Epithelial tissue constitutes all the inner and

outer surfaces of the body including;– Skin– Viscera of the digestive and respiratory system– The lining of body cavities– Linings of blood vessels– Most glandular tissue

Special Characteristics of Epithelium Cellularity Epithelial tissue is composed

almost entirely of close packed cells with little extracellular material lying in the space between them

Specialized Cells form continuous sheets. contacts Adjacent cells are bound

together at many points by lateral contacts including, tight junctions and desmosomes

Special Characteristics of Epithelium

Junctions & Desmosomes

Tight junctions occur where protein molecules in adjacent cells fuse together to form an impermeable junction

Desmosomes are anchoring junctions that bind adjoining cells and prevent their separation

Gap Junctions

Gap junctions allow chemical substances to pass to adjacent cells

Cells connected by hollow connexons

Found in electrically excitable tissues (heart and smooth muscle)

Ion passage from one cell to another helps to synchronize electrical activity

Special Characteristics of Epithelium Polarity

– All epithelial tissue has an upper (apical) surface exposed to the body exterior or an internal cavity

– All epithelia exhibit polarity where the cells near the apical surface differ from those at the basal surface

– Apical surfaces can be smooth, most have microvilli, and some have cilia

– The basal surface of epithelium is called the basal lamina, which acts as a selective filter that determines which molecules are allowed to enter the epithelium

Special Characteristics of Epithelium

Special Characteristics of Epithelium The basal surface of epithelium lies on a thin

sheet called a basal lamina, which is part of the basement membrane

Deep to the basal lamina is a layer of reticular fibers belonging to the underlying connective tissue

Together the reticular fibers and the basal lamina form the basement membrane

Special Characteristics of Epithelium Supported by connective tissue

– All epithelial tissue sheets rest upon and are supported by connective tissue

– Deep to the basal lamina is the reticular lamina, a layer of extracellular material containing a fine network of collagen fibers from the underlying connective tissue

– The basement membrane reinforces the epithelial sheet enabling it to resist stretching and tearing

– It also defines the epithelial boundary

Special Characteristics of Epithelium

Innervated but avascular– Epithelial tissues are supplied with nerve

cells• Thus they can contribute to sensory function

– Epithelial tissues contain no blood vessels• Epithelial tissue receive nutrients by substances

diffusing from blood vessels in the underlying connective tissue layers

Special Characteristics of Epithelium

Regeneration– Epithelial cells have a high regenerative

capacity– Epithelial cells are exposed to friction, others

are damaged by hostile substances in their environment

– If nourished adequately, epithelial tissue can replace lost cells rapidly by cell division

Classification of Epithelia

Each epithelium is given two names:– The first name references the number of

epithelial cell layers present• Simple

• Stratified

– The second name describes the shape of the cells present in the epithelial cell layer

• Squamous

• Cuboidal

• Columnar

Simple and Stratified Epithelium

Simple epithelium is composed of a single tissue layer– It is usually found where absorption and

filtration occur, thus a thin layer facilitates these processes

Stratified epithelium consists of two or more layers stacked one upon the other– It is usually found in areas of high abrasion

and functions to protect underlying cell layers

Epithelial cells All epithelial cells are hexagon shaped This shape allows the cells to be tightly

packed with little wasted space Epithelial cells look like a honeycomb Epithelial cells vary in height and are

named on the basis of shape– Squamous cells are flattened and scalelike– Cuboidal cells are boxlike in appearance– Columnar cells are tall and column shaped

Epithelial shape

Squamous - flat and scale-like

Cuboidal - boxlike Columnar - tall

and column shaped

Simple Epithelia All the cells in the layer have the same

shape There are four major classes of simple

epithelia– Simple squamous– Simple cuboidal– Simple columnar– Pseudostratified columnar (Highly modified

simple epithelium)

Stratified Epithelia There are also four major classes of

stratified epithelia– Stratified squamous– Stratified cuboidal– Stratified columnar– Transitional epithelium (a modified

stratified squamous epithelium)

Simple Squamous Epithelium The simplest form of epithelium A single layer of flattened cells Thin and permeable, this type is often

found where filtration or diffusion is a priority

Two simple squamous epithelium have special names related to their location– Endothelium (lining blood vessels)– Mesothelium (found in serous membranes)

Simple EpitheliaSimple Squamous Epithelium

Simple squamous epithelium forming walls of alveoli (air sacs) of the lung

Simple Epithelium:Simple Cuboidal Epithelium

Single layer of cube like cells Important functions are secretion and

absorption It forms ducts and secretary portions of

small glands and tubules in the kidneys

Simple Epithelium:Simple Cuboidal Epithelium

Simple cuboidal epithelium in kidney tubules

Simple Epithelium:Simple Columnar Epithelium

Consists of a single layer of tall, closely packed cells

It lines the digestive tube from stomach to anal canal

Important functions are secretion and absorption and it forms a layer thin enough for ion transport yet thick enough to house the cellular structures of ion transport

Simple Epithelia:Simple Columnar Epithelium

Consists of a single layer of tall cells– unciliated in the digestive tract

• associated with absorption and secretion

• mircovilli add surface area and aid absorption

• globlet cells secret protective lubricants

– ciliated in the respiratory passages• cilia “sweep” or propel mucus by ciliary action

Simple Epithelium:Simple columnar epithelium

Simple columnar epithelium of the stomach mucosa

Simple Epithelium:Pseudostratified Columnar

Epithelium Single layer of cells of differing heights The cell nuclei are located at differing

levels above the basement membrane giving the false (pseudo) impression of multiple cell layers

Ciliated in the upper respiratory tracts Nonciliated in large body ducts

Simple Epithelium:Pseudostratified Epithelium

Pseudostratified ciliated epithelium lining the human trachea

Stratified Epithelium:Stratified Squamous Epithelium Tissue is composed of several cell layers Surface cells are flattened (squamous)

while deeper cell layers are cuboidal or columnar

Surface cells are full of keratin and dead, while basal cells are alive and active in cell mitosis

Protective in function, these cells are found in areas subjected to abrasion

Stratified Epithelium:Stratified Squamous Epithelium

Stratified squamous epithelium lining the esophagus

Stratified Epithelium:Stratified Cuboidal Epithelium Generally two layers of cube-shaped cells Form large ducts of some glands Function to protect Relatively rare tissue type

Stratified Epithelium:Stratified Cuboidal Epithelium Location

– Largest ducts of sweat glands, mammary glands and salivary glands

– No table provided in Marieb A & P, 5th edition

– Table 4.3f in 3th edition Marieb and Mallatt

Stratified Epithelium:Stratified Cuboidal Epithelium

Stratified cuboidal forming a salivary duct

Stratified Epithelium:Stratified Columnar Epithelia

Several Cell layers present Basal cells are cuboidal while superficial

cells are columnar Rare in the body; found in the large ducts

of some glands and in the male urethra Functions include protection and secretion

Stratified Epithelium:Stratified Columnar Epithelium

Stratified columnar epithelium lining the male urethra

Stratified Epithelium:Transitional Epithelium

Forms the lining of hollow urinary organs Resembles both stratified squamous and

cuboidal The cells vary in appearance depending on

the degree of distension of the organ The ability of the epithelium to thin under

pressure allows for a greater volume of urine to pass through these organs

Transitional Epithelium

Transitional epithelium lining of the bladder, relaxed state

Epithelial Surface Features The apical, lateral and basal cell surfaces

of epithelia have special features Apical surfaces have microvilli and cilia Lateral surfaces have cell junctions Basal surface has a basal lamina

Apical Surface Features Microvilli are fingerlike extension of the

plasma membrane of apical epithelial cells They occur on almost very moist

epithelium in the body Most abundant on epithelia that absorb

nutrients (small intestine) or transport ions (kidney)

Microvilli maximize the surface area across which small molecules enter or leave cells

Apical Surface Features Microvilli are abundant on epithelia that

secrete mucus, where they help anchor the mucus sheets to the epithelial surface

Finally, microvilli may act as “stiff knobs” to resist abrasion

Apical Surface Features Cilia are whip-like,

highly motile extensions of the apical surface membranes of certain epithelia cells

Each cilium contains a core of micro- tubules, nine pairs which encircle one pair

Apical Surface Features The center set of

microtubules is an axonene and each pair is called a doublet

Ciliary movement is generated when adjacent doublets grip one another with side arms made of the protein dynein causing ocillation

Apical Surface Features When the side arms

start to oscillate the doublets slide against one another causing the cilium to bend

The cilia on an epithelium bend and move in coordinated waves

The waves push mucus over its surface

Apical Surface Features

Each cilium executes a propulsive power stroke, followed by a recovery stroke

This sequence ensures that fluid is moved in one direction only

Apical Surface Features An extremely long, isolated cilium is

called a flagellum The only flagellated cells in the human

body are male sperm Sperm use their flagella to swim through

the female reproductive tract

Lateral Surface Features Three factors act to hold epithelial cells

to one another– Immunoglobulin-like proteins in the plasma

membranes are linked together– The wavy contours of the membranes of

adjacent cells join in a tongue and groove fashion

– There are special cell junctions seal off the extracellular space

Cells junctions are characteristic of epithelia cells but can be found in other tissue types as well

Lateral Surface Features

Desmosomes are the main junctions for binding cells together and are scattered along cell margins

Lateral Surface Features

The surface of each plasma membrane has an area called the circular plaque

Lateral Surface Features

The plaques of adjacent cells are joined by linker proteins called cadherins

Lateral Surface Features

Cadherins project from the cell membranes of both cells and interdigitate like the teeth of a zipper in the extracellular space

Lateral Surface Features

Intermediate filaments which are cytoskeletal elements that resist tension insert into each plaque from the inner cytoplasmic side

Lateral Surface Features

Cadherins project from the cell membranes of both cells and interdigitate like the teeth of a zipper in the extracellular space

Lateral Surface Features Bundles of intermediate filaments extend

across the cytoplasm and anchor at other desmosomes on the opposite side of the same cell

This arrangement holds not only adjacent cells together but also interconnects all the intermediate filaments of the entire epithelium into one continuous network of strong “guy wires”

This distributes tension forces evenly across the entire epithelial sheet

Lateral Surface Features

Tight junctions seal off the extracellular space

Lateral Surface Features

Tight junctions are typically located in the apical region of most epithelial cells

Lateral Surface Features At tight junctions the adjacent cells are

so close that some proteins in their plasma membranes are fuse

Fusion forms a seal that closes off the extracellular space

This prevents molecules from passing between the cells of epithelial tissue

Lateral Surface Features

Gap junctions or nexus is a spot-like junction that can occur anywhere along the lateral membranes of adjacent cells

Lateral Surface Features Gap junctions let small molecules move

directly between neighboring cells At gap junctions the adjacent plasma

membranes are very close and the cells are connected by hollow cylinders of protein (connexons)

Ions, simple sugars, and other small molecules pass through these cylinders from one cell to the next

Basal Lamina Features

At the border between the epithelium and the connective tissue is a supporting sheet called the basal lamina

Basal Lamina Features The basal lamina is a thin, noncellular

sheet consisting of proteins secreted by the epithelial cells in the overlying layer

Functionally, the basal lamina acts as a selective filter

It determines which molecules from capillaries in the underlying connective tissue will be allowed to enter the epithelium

Basal Lamina Features The basal lamina also acts as scaffolding

along which regenerating epithelial cells can migrate

Regeneration can typically occur because infections and mechanisms that destroy the epithelial cells usually leave the basal lamina intact

Without a basal lamina, regeneration of the epithelial tissue is more difficult

Basal Lamina Features

Directly deep to the basal lamina is a layer of reticular fibers belonging to the underlying connective tissue

Basal Lamina Features Combined the reticular fibers and the

basal lamina form the basement membrane

While the basal lamina and the basement membrane are different structures the terms are sometimes used interchangeably which is incorrect

Glandular Epithelia A gland consists of one or more cells that

make a secretion Many epithelial cells make secretions Secretions are usually water based fluids

containing proteins Secretion is a process whereby gland cells

obtain needed substances from the blood and transform them chemically into a product that is discharged from the cell

Glandular Epithelia Glands are classified on where they release

their secretion:– endocrine (internal secretion)– exocrine (external secretion)

Glands are classified by number of cells: – unicellular exocrine glands– multicellular exocrine glands

Unicellular glands are scattered within epithelial sheets

Multicellular glands develop by invaginating into an epithelial sheet and connective tissue

Endocrine Glands All endocrine glands eventually lose their

ducts and are considered to be ductless Endocrine glands produce hormones that

regulate body functions These glands secrete directly into the

extracellular space The hormones then enter the blood or

lymphatic fluid– Pituitary, Thyroid, Parathyroid, Adrenal,

Thymus,, and others

Exocrine Glands Exocrine glands are far more numerous

than endocrine These glands secrete their products

through a duct onto a body surface or into a body cavity

These glands secrete mucous, sweat, oil, saliva, bile, digestive enzymes, and many other substances

Unicellular Exocrine Glands

The only important example of a unicellular gland is the goblet cell

Shaped liked a goblet Distributed in the epithelial linings of the

intestinal and respiratory tract amid columnar cells with other functions

Produces mucin which when dissolved in water forms mucus, a slimy coating that protects and lubricates surfaces

Goblet cells

Found in columnar epithelium cells lining the intestinal and respiratory tract

Multicellular Exocrine Glands Multicellular exocrince glands have two

common structural elements– An epithelium derived duct – A secretory unit consisting of secreting cells

In all but the simplest glands connective tissue surrounds the secretory unit supplying it with blood an nerve fibers

Often the connective tissue forms a fibrous capsule and may subdivide the gland into lobes

Multicellular Exocrine GlandsStructural Classification

On the basis of their duct structures, multicellular exocrine glands are either simple or compound– Simple glands have a single unbranched duct– Compound glands have a branched duct

The glands are further categorized by their secretory units– Tubular (forms tubes)– Alveolar (forms sacs)– Tubuloalveolar (contains both types)

Simple Duct Structure

Compound Duct Structure

Multicellular Exocrine GlandsModes of Secretion

Merocrine glands (salivary, sweat, pancreas)– Secret their products by exocytosis and gland is

not altered Holocrine glands (sebaceous oil glands)

– The entire cell ruptures releasing the secretions Apocrine glands (mammary?)

– The apex of the secretory cell pinches off and release its secretion

Chief Modes of Secretion

Merocrine glands– Secrete products

by exocytosis

– Secretions do not alter gland

– Secretions leave gland via duct

Chief Modes of Secretion

Holocrine glands– Accumulate their

products within the gland until they rupture

– They are replaced by the division of underlying cells

– Sebaceous oil glands are the only true example in humans

Chief Modes of Secretion Apocrine glands

– Accumulate products just beneath free surface

– Apex of the cell pinches off releasing its contents

– Cell repairs the damage and the process is repeated

– Some controversy as to its presence in humans

CONNECTIVE TISSUE

SECTION II

Connective Tissue:An Introduction

Connective tissue is found everywhere in the body but the proportion present in a tissue varies

Its major functions are:– support and binding– holding body fluids– defending the body against infection– Storing nutrients as fat

Common Characteristics Common origin

– All tissue arise from mesenchyme layer Varying degrees of vascularity

– Tissue vary from rich vascular supply to avascular

Extracellular matrix– The living cells are widely distributed within

a matrix of nonliving extracellular substances

– The matrix creates the ability to bear weight, withstand tension, and abrasion

Connective Tissue: Cells in a Matrix

Structural Elements Any connective tissue is made up of three

elements; ground substance, fibers, and cells

Ground substance and fibers make up the extracellular matrix

The composition and arrangement of extracellular elements yields the diversity of connective tissues

It can be delicate and fragile, or thick, dense and strong

Ground Substance Ground substance is an unstructured material

that fills the space between cells and contain the fiber that support the tissue

It is composed of interstitial fluid, cell adhesion proteins, and proteoglycans

The ground substance holds fluid and functions as a medium through which nutrients and substances can diffuse between blood vessels and cells

Ground Substance Nutrients and oxygen diffuse out of the

capillaries and travel through a watery fluid in the extracellular matrix to reach the surrounding cells

Waste molecules from cells diffuse back through this fluid into the capillaries to be taken away by the bloodstream

The fluid through which these substances move is interstitial fluid (tissue fluid) and it derives from the blood itself

Ground Substance Ground substance is a jelly-like material

consisting of large sugar and sugar-protein molecules that soak up fluid

The molecules are called glycosaminoglygens and proteogylcans

Adhesion Proteins

Adhesion proteins serve as the “glue” that allows connective tissue cells to attach to matrix elements

Adhesion proteins include:– Fibronectin– Laminin

Proteoglycans

Proteoglycans consist of a protein core to which (GAGs) attach

GAG’s (glycoaminoglycans) are large, negatively charged polysaccharides that stick out from the core protein like fibers of a bottle brush

The polysaccharides trap water and determine the properties of the matrix

The matrix may vary from fluid to a semi stiff gel

Connective Tissue: Fibers

The fibers within connective tissue provide support

Three type of fibers are found in connective tissue matrix– Collagen– Elastic – Reticular

Collagen Fibers

Collagen fibers are extremely tough and have a high tensile strength

Fibers are able to withstand great longitudinal stresses

Collagen fibers align along lines of stress Collagen fibers are located wherever

support is needed to reinforce an organ or joint

Elastic Fibers Elastin has a randomly coiled structure

that allows it to stretch and recoil Elastin in the matrix gives it a resilient

quality Collagen fibers limit distension of the

tissue and elastin fibers return the tissue to its normal length and shape

Found where elasticity is needed– Skin, lungs, walls of blood vessels

Reticular Fibers Fine collagen fibers with a special type of

collagen unit fibril Form branching networks of delicate

fibers that surround blood vessels and support soft tissue of organs

Very apparent where connective tissue abuts other tissue types– Basement membranes of epithelial cells

Connective Tissue: Cells Each major class of connective tissue has

a fundamental cell type Actively mitotic cells are called “blast”

which implies a forming cell The primary cells types of connective

tissue are:– fibroblast - connective tissue– chondroblast - cartilage– osteoblast - bone– hemocytoblast (hematopiotetic stem cell)-

blood

Cells (con’t) Once the blast cells have synthesized the

matrix they become less active and are referred to (chrondocyte)

Mature cells maintain the health of the matrix

If the tissue is damaged they become active to repair and regenerate the matrix

Cells (con’t)

Connective tissue also harbor an assortment of other cell types– white blood cells - infection

• Neutrophils, eosinophils, lymphocytes

– mast cells - detect foreign substances and initiate a local inflammatory response

– macrophages - phagocytize a broad variety of foreign molecules and bacteria

Defense Cells Fight Infection

Areolar connective tissue is the main battlefield in the body’s war against infectious microorganisms such as bacteria, viruses, fungi and parasites

Every effort is made by the body to destroy infection at the entry site to prevent entry into the circulatory system and the potential spread throughout the body

Defense Cells Fight Infection

Areolar connective tissue contains a variety of defense cells that originate as blood cells and migrate to the connective tissues by leaving the capillaries

These defensive cells gather at infection sites in large numbers

These cells fights infection using a variety of mechanisms

Defense Cells Fight Infection Macrophages are

cells ruffled by pseudopods

These cells are non-specific phagocytic cells that devour a variety of foreign materials

Marcophages will also dispose of dead tissue cells

Defense Cells Fight Infection Plasma cells secrete protein molecules called

antibodies Antibodies bind to foreign micro organisms

and mark them for destruction Once marked a greater amount are destroyed

Defense Cells Fight Infection Mast cells lie near

small blood vessels Mast cells possess

many small granules containing chemicals that mediate inflammation especially in severe allergies

Defense Cells Fight Infection Chemical mediators include histamine,

heparin and proteases (protein degrading enzymes) and are secreted in response to infections– Histamine increases the permeability of the

nearby capillaries, causing more tissue fluid to leave the bloodstream with the subsequent swelling of the areolar tissue with fluid is a major symptom of infection

Defense Cells Fight Infection Chemicals (continued)

– Heparin in mast cells binds and stores the other mast cell molecules and regulate their action

Mast cells also play a role in defense against parasitic worms, our natural immunity against bacteria, and the normal repair of fibers, ground substance, and blood vessels in connective tissue

Defense Cells Fight Infection Neutrophils,

lymphocytes, and eosinophils are white blood cells that leave the bloodstream to fight infection

Neutrophils quickly enter infected areas and phagocytize bacteria

Defense Cells Fight Infection Additional defenses to infection comes

from both the ground substances and the collagen fibers which slow the progress of invading microorganisms

However, some bacteria secrete enzymes that rapidly break down ground substances or collagen

Connective Tissue: Mesenchyme Mesenchyme tissue is the first tissue

formed from the mesodermal germ layer It is made up of star shaped

mesenchymal cells It is a gel-like ground substance

containing fine fibers During embryonic development other

tissues differentiate from it

Mesenchyme

Connective Tissue:Connective Tissue Proper

Loose Connective Tissue– Areolar

– Adipose

– Reticular

Dense Connective Tissue– Dense Regular

– Dense Irregular

– Elastic

Areolar Connective Tissue A gel-like matrix with a loose arrange-

ment of all three fiber types Contains cells, fibroblasts, macrophages,

mast cells, and some white blood cells Because of the loose nature of the tissue it

serves as a reservoir for water and salts for the surrounding tissues

Areolar: Location

Most widely distributed type of connective tissue

Serves as the universal packing material between tissues

Packages organs Surrounds capillaries Forms subcutaneous tissue Present in all mucus membranes

Areolar Tissue: Function Wraps and cushions organs Macrophages phagocytize bacteria Plays important role in inflammation Holds and conveys fluid

Areolar Tissue

Adipose (fat) Tissue Adipose tissue is basically areolar

connective tissue in which the nutrient storing functioning is greatly increased

Adipocytes predominate tissue as little matrix is present

Oil (fat) occupies most of cell volume Compression of the cell nucleus to one side

gives it a name of “signet” cells Tissue is richly vascular owing to high

metabolic activity

Adipose Tissue: Location

Under skin Around kidneys and eyeballs In bones Within abdomen Within breasts

Adipose Tissue: Function

Provides reserve food source for fuel Insulates against heat loss Supports and protects organs

Adipose Tissue

Reticular connective tissue Reticular connective tissue resembles

areolar tissue, but the only fibers in the matrix are reticular

Fibers form a delicate internal network along which fibroblasts are distributed

Widely distributed in the body, the tissue provides internal support for many lymphocytes within lymphatic tissues such as lymph nodes, the spleen, and bone marrow

Reticular Connective Tissue:Location

Lymphoid organs– Lymph nodes– Bone marrow– Spleen

Reticular Connective Tissue:Function

Fibers form the soft internal skeleton (stroma) that supports other cell types

Supports many free blood cells in lymphatic tissue

Reticular Connective Tissue

Dense Regular Connective Tissue

A type of connective tissue consisting of dense bundles of collagen fibers

Collagen fibers are arranged in parallel that lie in the direction of pull or stress

Great resistance to tension Slightly wavy alignment allows for some

degree of stretch Has few other cells and is poorly

vascularized

Dense Regular Connective Tissue: Location

Dense regular connective tissue forms:– Tendons Muscle to bone – Aponeuroses Muscle to muscle or

bone– Ligaments Bone to bone

Ligaments have a little stretch, tendons very little

Dense Regular Connective Tissue:Function

Attaches muscle to bones or to muscles Attaches bones to bones Withstands great tensile stress when

pulling force is applied in one direction

Dense Regular Connective Tissue

Dense Irregular Connective Tissue Same structural components as regular

variety Dense bundles of collagen fibers are

thicker and arranged with fibers flowing in more than one plane

Fibers form sheets of tissue that cope with tension from a variety of directions

Dense Irregular Connective Tissue:Location

Dermis of the skin Submucosa of digestive tract Fibrous capsules of organs and joints

Dense Irregular Connective Tissue:Function

Able to withstand tension exerted in many directions

Provides structural strength to many diverse tissues and organs

Dense Irregular Connective Tissue

Cartilage Has qualities that intermediate between

dense connective tissue and bone It is tough but flexible, providing a

resilient rigidity to the structure it supports

Cartilage is avascular and devoid of nerve fibers

Ground substance contains large amounts of GAG, a major adhesion protein

Cartilage continued Ground substance contain many collagen

fibers and in some cases elastic fibers to yield a substance that is quite firm

Cartilage matrix is approximately 80%water Movement of tissue fluid in its matrix

enables cartilage to rebound after being compressed

Movement of tissue fluid helps to nourish cartilage cells

Cartilage continued

The surfaces of most cartilage structures are surrounded by a well vascularized dense irregular tissue membrane called a perichondrium

Nutrients diffuse from the perichondrium to the matrix and then to the chondrocytes

Cartilage continued

Chondroblasts in growing cartilage produce new matrix that becomes bone– During interstitial growth chondroblasts

secrete new matrix to form the cartilage piece from which a bone will develop

– During appositional growth chondroblasts secrete new matrix on the superficial surface of the cartilage structure

The firm cartilage matrix prevents the cells from becoming widely separated

Hyaline Cartilage Hyaline cartilage contains large amounts of

collagen fibers formed in an imperceptible network

Hyaline cartilage provides firm support with some pliability

It has resilient properties that resist compression

Matrix appears blue-white with a smooth almost slick surface

Hyaline Cartilage: Location

Forms most of the embryonic skeleton Covers the ends of long bones in joint

cavities Forms costal cartilages of the ribs Cartilages of the nose, trachea, and

larynx

Hyaline Cartilage: Function

Supports and reinforces with some pliability

Has resilient cushioning properties Resists compressive stress

Hyaline Cartilage

Elastic Cartilage

Similar to hyaline cartilage but with more elastic fibers in the matrix

Elastic fibers gives this tissue greater resilience to repeated bending

Found where the tissue supports the shape of the structure while allowing great flexibility

Elastic Cartilage: Location

Supports the external ear Epiglottis

Elastic Cartilage: Function

Maintain shape of structure while allowing great flexibility

Elastic cartilage

Fibrocartilage

Consists of alternating rows of thick collagen fibers

Matrix is similar to hyaline cartilage but less firm

It is compressible and resists tension well Located where strong support and the

ability to withstand heavy pressure is required

Fibrocartilage: Location

Intervertebral disks of the vertebral column

Pubic symphysis Disks of knee joint

Fibrocartilage: Function

Tensile strength with the ability to absorb compressive shock

Fibrocartilage

Bone Bone matrix is similar to that of cartilage

but is harder and more rigid Differs from cartilage in that it contains

more collagen fibers and an added matrix element of inorganic calcium salts

Osteoblasts produce the matrix then bone salts are deposited on and between fibers

Well supplied with blood vessels

Bone: Location

All structural elements of the skeletal system

Appears as long, flat, short, and irregular bones

Includes compact and spongy bone

Bone: Function

Supports the weight of the body Protects vital organs and structures Provides levels for muscles to act upon Stores calcium, other minerals, and fat Bone marrow is the site for blood cell

formation

Bone

Blood Classified as a connective tissue because

it consists of blood cells surrounded by a nonliving matrix

The fibers of blood are soluble protein molecules that become visible only during blood clotting

Blood: Location

Contained within blood vessels of the circulatory system

Blood

Blood: Function

Transport vehicle of the circulatory system

Carries nutrients, wastes, respiratory gases, and many other substances throughout the body

Blood

EPITHELIAL MEMBRANES

SECTION III

Epithelial Membranes: Epithelial membranes incorporate both

connective and epithelial tissues Epithelial membranes are a continuous

multicellular sheet composed of at least two primary tissues

Can be considered a simple organ The three common forms of epithelial

membranes are cutaneous, mucous, and serous

Cutaneous membrane

It is an organ system consisting of ketatinized stratified squamous epithelium attached to a layer of dense irregular connective tissue

A dry membrane

Mucous membranes Mucosae line body

cavities that are open to the exterior

These are moist membranes bathed by secretions

Often adapted for absorption and secretion

Serous membranes Moist membranes

found in the central body cavities

Each consists of a parietal and visceral layer

Serous fluid lubricates the two layers

NERVOUS TISSUE

SECTION IV

Nervous Tissue Nervous tissue makes regulates and

controls body functions Neurons are highly specialized cells that

generate and conduct nerve impulses Support cells are nonconducting tissue

that support, insulate and protect the delicate neurons

Nervous Tissue: Location

Brain and spinal cord of the central nervous system (CNS)

All cranial and spinal nerves of the peripheral nervous system (PNS)

Nervous Tissue: Function

Transmit electrical signals from sensory receptors to the brain

Brain interprets impulse for potential response

Signals from brain to effectors (muscles and glands) control response

Nervous Tissue

MUSCLE TISSUE

SECTION V

Muscle Tissue: Muscle tissues are highly cellular, well-

vascularized tissue responsible for most types of body movement

Muscle provides contractile force by shortening their elongated shape

Muscle cells possess myofilaments The three kinds of muscle tissue are

skeletal, cardiac and smooth

Skeletal muscle

Skeletal muscle is wrapped by connective tissue into organs called muscles which attach to bones

As skeletal muscle contracts it causes gross body movements

Skeletal muscle is identified by its long cylindrical form and obvious striations

Voluntary control

Skeletal muscle: Location

Skeletal muscle attach to bones of the skeletal system

Occasionally muscle will attach to skin

Skeletal Muscle: Function

Produces movement– Locomotion– Manipulation of the environment– Facial expression

Maintains posture Stabilizes joints Generates heat

Skeletal Muscle

Cardiac muscle

Occurs in the walls of the heart and no where else in the body

Muscle cells are striated Uninucleate cells fit together at unique

junctions called intercalated discs

Cardiac muscle: Location

Found only in the myocardium of the heart

Cardiac Muscle

Smooth muscle

Smooth muscle is so named because its fibers have no visible striations

Spindle shaped muscle cells contain one centrally located nuclei

Closely arranged to form sheets

Smooth muscle: Location

Occurs mainly in the walls of hollow organs– digestive tract– blood vessels

Smooth muscle: Function

Act to propel substances or objects along internal passageways– Food– Urine– Baby

Involuntary control Long, sustained contractions

Smooth Muscle

TISSUE REPAIR

SECTION VI

Tissue Repair Tissue repairs requires cells to divide and

migrate in response to hormones released by damaged cells

Tissue repair occurs in two major ways: by regeneration and by fibrosis

Which healing process to occur depends upon:– The type of tissue damaged – The extent of the injury

Tissue Repair

Regeneration is the replacement of destroyed tissue with the same kind of tissue

Fibrosis involves the proliferation of fibrous connective tissue called scar tissue

Tissue Repair: Inflammation Inflammation of

injury site due to release of histamine

Capillaries dilate, become permeable

White blood cells, antibodies, clotting proteins arrive

Clotting isolates injured area

Tissue Repair: Organization Blood clot replaced

by granulation tissue

Capillary buds invade area

Fibroblasts secret collagen fibers

Macrophages digest and remove dead cells

Tissue Repair: Regeneration Surface epithelium

begins to regenerate

Granulation tissue is replaced by epithelium

Fibrosed area is found deep to epithelium

Scar may not be evident

Factors Affecting Tissue Repair

The type of tissue injured Type of injury and the immediate care

received Nutrition Adequacy of blood supply State of health of the individual Age of the individual

Tissue Repair: Tissue Type Epithelial tissues regenerate very well Bone and fibrous tissue heal quite well Smooth muscle and dense regular

connective tissue have very limited capacity for regeneration

Skeletal muscle and cartilage regenerate poorly

Cardiac and nerve tissue have no regenerative capacity and are replaced by scar tissue

DEVELOPMENTAL ASPECTS OF TISSUES

SECTION VII

Developmental Aspects of Tissue

One of the first events of embryonic development is the formation of the three primary germ layers

These three germ layers are the ectoderm, mesoderm and endoderm

These primary germ layers begin to form the four primary tissues from which all body organs are derived

Tissue Origins Epithelial tissue are formed from all

three tissue layers Muscle and connective tissue form from

the mesoderm Nervous tissue forms from the ectoderm

Embryonic Germ Layers

Cell Development By the end of the second month of

development, the primary tissues have appeared, and all major organs have been laid down

Tissue growth continues on at a rapid rate throughout the embryonic and fetal periods

Most tissues cells except neurons continue to undergo cell mitosis until adulthood

Adulthood In adulthood only epithelia and blood

forming tissue are highly mitotic With increasing age the amount of

collagen generated decreases making tissue repair less efficient

Declining circulatory efficiency results in less nutrients delivered to tissue

Dietary choices also influences tissue repair

TISSUE: THE LIVING FABRIC

END OF CHAPTER 4