Chapter 4

Chapter 4Chapter 4

The Tissue Level The Tissue Level

of Organizationof Organization

Tissues are a group of cells with a common Tissues are a group of cells with a common embryonic origin that function together to embryonic origin that function together to carry out specialized activities.carry out specialized activities.

TissuesTissues

Histology is the study of the Histology is the study of the microscopic anatomy of cells and microscopic anatomy of cells and tissues – it is a branch of pathology.tissues – it is a branch of pathology.

TissuesTissues

Tissues are formed Tissues are formed

by grouping cells by grouping cells

together using a together using a

variety of variety of

Intercellular Intercellular

Junctions .Junctions .

Intracellular JunctionsIntracellular Junctions

Tight JunctionsTight Junctions are found where a are found where a

leakproof seal is needed between leakproof seal is needed between

cells.cells.

Intracellular Intracellular JunctionsJunctions

Adherens JunctionsAdherens Junctions make an adhesion belt (like make an adhesion belt (like

the belt on your pants) that keeps tissues from the belt on your pants) that keeps tissues from

separating as they stretch and contract.separating as they stretch and contract.

Cadherin is a glycoprotein Cadherin is a glycoprotein

that forms the belt-like that forms the belt-like

““plaque”.plaque”.


DesmosomesDesmosomes act as “spot welds”. act as “spot welds”. They also use cadherin glycoprotein They also use cadherin glycoprotein (plus intermediate filaments) to hook (plus intermediate filaments) to hook into the cytoplasm.into the cytoplasm.


HemidesmosomesHemidesmosomes are half-welds that join are half-welds that join cells to the basement membrane.cells to the basement membrane.

Intracellular Intracellular JunctionsJunctions

Gap JunctionsGap Junctions are are pores (connexons) that pores (connexons) that allow small substances allow small substances like ions to pass like ions to pass between cells. If one between cells. If one of the cells gets sick or of the cells gets sick or dies, these seal like a dies, these seal like a hatch to prevent hatch to prevent damage to other cells.damage to other cells.


Of all the cells in the body, they combine Of all the cells in the body, they combine to make only 4 basic tissue types:to make only 4 basic tissue types: Epithelial tissuesEpithelial tissues Connective tissuesConnective tissues Muscular tissuesMuscular tissues Nervous tissuesNervous tissues

The 4 Basic TissuesThe 4 Basic Tissues

Epithelial tissuesEpithelial tissues cover body surfaces and form cover body surfaces and form

glands and line hollow organs, body cavities, and glands and line hollow organs, body cavities, and

ducts.ducts.


Connective tissues (C.T.)Connective tissues (C.T.) protect, protect, support, and bind organs.support, and bind organs. Fat is a type of C.T. that stores energy.Fat is a type of C.T. that stores energy. Red blood cells, white blood cells, and Red blood cells, white blood cells, and

platelets are all C.T.platelets are all C.T.


Muscular tissuesMuscular tissues generate the generate the physical force needed to make body physical force needed to make body structures move. They also generate structures move. They also generate heat used by the body.heat used by the body.

Nervous tissuesNervous tissues detect changes in detect changes in the body and respond by generating the body and respond by generating nerve impulses.nerve impulses.


Tissues of the body develop from three primary germ Tissues of the body develop from three primary germ

layers: layers: Endoderm, Mesoderm, and EctodermEndoderm, Mesoderm, and Ectoderm

Epithelial tissues from Epithelial tissues from

all three germ layersall three germ layers

C.T. and muscle are C.T. and muscle are

derived from mesoderm.derived from mesoderm.

Nervous tissue Nervous tissue

develops from develops from

ectoderm.ectoderm.


EpitheliuEpitheliumm Epithelium is used to line surfaces Epithelium is used to line surfaces

and form protective barriers. and form protective barriers. Epithelium is also good at secreting Epithelium is also good at secreting things like mucous, hormones, andthings like mucous, hormones, and

other substances .other substances . All epithelia have a All epithelia have a

free apical surface free apical surface

and an attached and an attached

basal surface.basal surface.

The basal layer of the epithelium The basal layer of the epithelium secretes a basal lamina; the secretes a basal lamina; the underlying C.T. secretes a reticular underlying C.T. secretes a reticular lamina.lamina. Together the basal Together the basal

lamina and the reticular lamina and the reticular

lamina form a non-lamina form a non-

cellular basement cellular basement

membrane on which membrane on which

the epithelium sits.the epithelium sits.

EpitheliumEpithelium

Epithelia are Epithelia are namednamed according to the according to the shape of their cells, and the thickness or shape of their cells, and the thickness or arrangement of their layers (of cells).arrangement of their layers (of cells).

EpitheliuEpitheliumm


Naming epithelia according to Naming epithelia according to shapeshapeEpitheliumEpithelium

Flat, wide “paving stone” cells

Cells as tall as they are wide

Cells taller than they are wide

One layer. All cells in contact with

basement membrane

Appears to have layers, but in reality all cells go

from the apex to the base

Two or more layers. Only basal layer in

contact with basement membrane

Naming epithelia according to Naming epithelia according to arrangementarrangementEpitheliumEpithelium

Naming epithelia Naming epithelia Three different cell shapes Three different cell shapes xx three different three different

cell arrangements = nine possibilities. Two cell arrangements = nine possibilities. Two of these are not used. Add transitional (cells of these are not used. Add transitional (cells that change shape), and we’re back up to that change shape), and we’re back up to eight possible combinations.eight possible combinations.

If different shapes are present in layers of If different shapes are present in layers of cells, the epithelium is always named by the cells, the epithelium is always named by the shape of cells in the apical (outermost) layer.shape of cells in the apical (outermost) layer.


simple squamous

pseudostratified squamous

stratified squamous

simple cuboidalpseudostratified

cuboidalstratified cuboidal

simple columnarpseudostratified

columnarstratified columnar

transitional

Simple Squamous EpitheliumSimple Squamous Epithelium is is composed of a single layer of flat cells composed of a single layer of flat cells found:found: In the air sacs of lungsIn the air sacs of lungs In the lining of blood In the lining of blood

vessels, the heart, and lymphatic vesselsvessels, the heart, and lymphatic vessels In all capillaries, including those of the kidneyIn all capillaries, including those of the kidney As the major part of a As the major part of a

serous membraneserous membrane


Simple Cuboidal EpitheliumSimple Cuboidal Epithelium is is composed of a single layer of cube composed of a single layer of cube shaped cells.shaped cells. It is often found liningIt is often found lining

the tubules of the the tubules of the

kidneys and manykidneys and many

other glands.other glands.


simple squamouspseudostratified

squamousstratified squamous

simple cuboidal

pseudostratified cuboidal

stratified cuboidal



transitional

Simple Columnar EpitheliumSimple Columnar Epithelium forms forms a single layer of column-like cells, ± a single layer of column-like cells, ± cilia, ± microvilli, ± mucous (goblet cilia, ± microvilli, ± mucous (goblet cells).cells). Goblet cells are simple Goblet cells are simple

columnar cells that columnar cells that

have differentiated to have differentiated to

acquire the ability to acquire the ability to

secrete mucous.secrete mucous.




simple cuboidal pseudostratified cuboidal

stratified cuboidal

simple columnar

pseudostratified columnar

stratified columnar

transitional

Pseudostratified Columnar EpitheliumPseudostratified Columnar Epithelium appears appears

to have layers, due to nuclei which are at various to have layers, due to nuclei which are at various

depths. In reality, all cells are attached to the depths. In reality, all cells are attached to the

basement basement

membrane in a single membrane in a single

layer, but some do not layer, but some do not

extend to the apical surface.extend to the apical surface.



simple cuboidal pseudostratified cuboidal stratified cuboidal



transitional


Stratified Squamous EpitheliumStratified Squamous Epithelium has an apical has an apical

surface that is made up of squamous (flat) cells.surface that is made up of squamous (flat) cells.

The other layers have different The other layers have different

shapes, but the name is based shapes, but the name is based

on the apical layer.on the apical layer.

The many layers are ideal forThe many layers are ideal for

protection againstprotection against

strong frictionstrong friction

forces.forces.


squamousstratified

squamous





transitional

EpitheliuEpitheliumm

Stratified Cuboidal EpitheliumStratified Cuboidal Epithelium has has an apical surface made up of two or an apical surface made up of two or more layers of cube-shaped cells.more layers of cube-shaped cells. Locations include the sweatLocations include the sweat

glands and part of the glands and part of the

♂ ♂ urethraurethra Stratified Columnar EpitheliumStratified Columnar Epithelium is is

very rare, and for very rare, and for ourour

purposes, hardly purposes, hardly

worth mentioning.worth mentioning.








transitional







transitional

The cells of The cells of Transitional EpitheliumTransitional Epithelium change change shape depending on the state of stretch in the shape depending on the state of stretch in the tissue.tissue.


Simple squamous makes up epithelial membranes and Simple squamous makes up epithelial membranes and

lines the blood vessels.lines the blood vessels.

Columnar is common in the digestive tract.Columnar is common in the digestive tract.

Pseudostratified ciliated Pseudostratified ciliated

columnar is characteristic columnar is characteristic

of the upper respiratory tract.of the upper respiratory tract.

Transitional is found in Transitional is found in

the bladder.the bladder.

Cuboidal lines ducts and Cuboidal lines ducts and

sweat glands.sweat glands.


Connective Tissues are the most abundant Connective Tissues are the most abundant

and widely distributed tissues in the body. and widely distributed tissues in the body.

They perform numerous functions:They perform numerous functions:• Bind tissues togetherBind tissues together

• Support and strengthen tissueSupport and strengthen tissue

• Protect and insulate internal organsProtect and insulate internal organs

• Compartmentalize and transportCompartmentalize and transport

• Energy reserves and immune responsesEnergy reserves and immune responses

Connective TissueConnective Tissue

Collagen is the main protein of C.T. and the Collagen is the main protein of C.T. and the

most abundant protein in the body, making most abundant protein in the body, making

up about 25% of total protein content.up about 25% of total protein content.

Connective tissue is usuallyConnective tissue is usually

highly vascular and suppliedhighly vascular and supplied

with many nerves.with many nerves.

The exception is cartilage and The exception is cartilage and

tendon - both have little or no tendon - both have little or no

blood supply and no nerves.blood supply and no nerves.

Connective TissuesConnective Tissues

Although they are a varied group, all C.T. Although they are a varied group, all C.T.

share a common “theme”:share a common “theme”: Sparse cellsSparse cells

Surrounded by an Surrounded by an extracellular matrixextracellular matrix

The extracellular matrix is a non-cellular The extracellular matrix is a non-cellular

material located between and around the material located between and around the

cells.cells. It consists of It consists of protein fibers protein fibers and and ground ground

substance substance (the ground substance may be fluid, (the ground substance may be fluid,

semifluid, gelatinous, or calcified.)semifluid, gelatinous, or calcified.)


Common C.T. cellsCommon C.T. cells FibroblastsFibroblasts are the most numerous are the most numerous

cell of connective tissues. These cells cell of connective tissues. These cells secrete protein fibers (collagen, secrete protein fibers (collagen, elastin, & reticular elastin, & reticular

fibers) and afibers) and a

““ground substance”ground substance”

which varies from which varies from

one C.T. to another.one C.T. to another.

Cells Of Connective TissuesCells Of Connective Tissues

Of the other common C.T. cells:Of the other common C.T. cells: Chondrocytes Chondrocytes make the various cartilaginous C.T.make the various cartilaginous C.T.

AdipocytesAdipocytes store triglycerides. store triglycerides.

OsteocytesOsteocytes make bone. make bone.

White blood cells White blood cells are part of the blood.are part of the blood.

Cells of Connective TissuesCells of Connective Tissues

C.T. cells secrete 3 common fibers:C.T. cells secrete 3 common fibers: Collagen fibersCollagen fibers

Elastin fibersElastin fibers

Reticular fibersReticular fibers


This graphic represents a collage of This graphic represents a collage of different C.T. elements (cells and different C.T. elements (cells and fibers) and not a specific C.T.fibers) and not a specific C.T.


Embryonic connective tissueEmbryonic connective tissue MesenchymeMesenchyme Mucous connective tissueMucous connective tissue

Mature connective tissueMature connective tissue Loose connective tissueLoose connective tissue Dense connective tissueDense connective tissue CartilageCartilage BoneBone LiquidLiquid

Connective Tissue Connective Tissue ClassificationClassification

There are 2 Embryonic Connective There are 2 Embryonic Connective Tissues:Tissues: MesenchymeMesenchyme gives rise to all other connective gives rise to all other connective

tissues.tissues. Mucous C.T. Mucous C.T. (Wharton's Jelly) is a gelatinous (Wharton's Jelly) is a gelatinous

substance within the umbilical cord and is a substance within the umbilical cord and is a rich source of stem cells.rich source of stem cells.

Embryonic Connective Embryonic Connective TissuesTissues

Loose Connective TissuesLoose Connective Tissues

Areolar Connective Tissue Areolar Connective Tissue is the most is the most

widely distributed in the body. It contains widely distributed in the body. It contains

several types of cells and all three fiber several types of cells and all three fiber

types.types.

AdiposeAdipose

ReticularReticular

Mature Connective Mature Connective TissuesTissues


Loose areolarLoose areolar

Adipose tissue Adipose tissue is located in the is located in the

subcutaneous layer deep to the skin and subcutaneous layer deep to the skin and

around organs and joints.around organs and joints.

ReticularReticular



Loose areolarLoose areolar

AdiposeAdipose

Reticular connective tissue Reticular connective tissue is a is a

network of interlacing reticular fibers and network of interlacing reticular fibers and

cells.cells.


Dense Connective TissuesDense Connective Tissues

Dense Irregular Connective Tissue Dense Irregular Connective Tissue

consists predominantly of fibroblasts and consists predominantly of fibroblasts and

collagen fibers randomly arranged.collagen fibers randomly arranged.

Dense regularDense regular

ElasticElastic

Mature Connective TissuesMature Connective Tissues


Dense IrregularDense Irregular

Dense regular Connective Tissue Dense regular Connective Tissue comprise comprise

tendons, ligaments, and other strong tendons, ligaments, and other strong

attachments where the need for strength along attachments where the need for strength along

one axis is mandatory (a muscle pulling on a one axis is mandatory (a muscle pulling on a

bone).bone).

ElasticElastic



Dense IrregularDense Irregular

Dense regularDense regular

Elastic Connective Tissue Elastic Connective Tissue consists consists

predominantly of fibroblasts and freely predominantly of fibroblasts and freely

branching elastic fibers.branching elastic fibers.


Cartilage Cartilage is a tissue with poor blood is a tissue with poor blood

supply that grows slowly. When injured supply that grows slowly. When injured

or inflamed, repair is slow.or inflamed, repair is slow. Hyaline cartilage Hyaline cartilage is the most abundant is the most abundant

type of cartilage; it covers the ends of long type of cartilage; it covers the ends of long

bones and parts of the ribs, nose, trachea, bones and parts of the ribs, nose, trachea,

bronchi, and larynx.bronchi, and larynx.

FibrocartilageFibrocartilage

Elastic cartilageElastic cartilage


CartilageCartilage

Hyaline cartilageHyaline cartilage

Fibrocartilage, Fibrocartilage, with its thick bundles of with its thick bundles of

collagen fibers, is a very strong, tough collagen fibers, is a very strong, tough

cartilage.cartilage.

Elastic cartilageElastic cartilage


CartilageCartilage

Hyaline cartilageHyaline cartilage

FibrocartilageFibrocartilage

Elastic cartilage Elastic cartilage consists of consists of

chondrocytes located in a threadlike chondrocytes located in a threadlike

network of elastic fibers. network of elastic fibers.


BoneBone is a connective tissue with a calcified is a connective tissue with a calcified

intracellular matrix. In the right circumstances, intracellular matrix. In the right circumstances,

the chondrocytes of cartilage are capable of the chondrocytes of cartilage are capable of

turning into the osteocytes that make up bone turning into the osteocytes that make up bone

tissue.tissue.

We will study bone in detail in Chapter 6.We will study bone in detail in Chapter 6.


Blood and lymph Blood and lymph are atypical liquid are atypical liquid connective tissues that we will study in connective tissues that we will study in Chapters 19 and 22. As we have seen, Chapters 19 and 22. As we have seen, blood has many cells. It also has blood has many cells. It also has fibers (such as fibrin that makes blood fibers (such as fibrin that makes blood clot).clot).


Summary of Mature Connective Summary of Mature Connective TissuesTissues

Combining two tissues creates an organ. However, Combining two tissues creates an organ. However,

most of the organs and all of the organs systems most of the organs and all of the organs systems

studied this year contain all 4 basic types of tissues.studied this year contain all 4 basic types of tissues.

Epithelial membranes are the simplest organs in Epithelial membranes are the simplest organs in

the body, constructed of the body, constructed of onlyonly epithelium and a epithelium and a

little bit of connective tissue.little bit of connective tissue.

Epithelial MembranesEpithelial Membranes

Epithelial membranes = epithelium + Epithelial membranes = epithelium +

connective tissueconnective tissue Mucous membranesMucous membranes

Serous membranesSerous membranes

Cutaneous membrane = skin Cutaneous membrane = skin


Mucous membranes line “interior” body surfaces Mucous membranes line “interior” body surfaces

open to the outside:open to the outside:

Digestive tractDigestive tract

Respiratory tractRespiratory tract

Reproductive tractReproductive tract

Serous membranes line some internal surfaces:Serous membranes line some internal surfaces:

Parietal layer next to body wallParietal layer next to body wall

Serous fluid between layersSerous fluid between layers

Visceral layer next to organVisceral layer next to organ


Skin as a cutaneous membrane is studied in Chapter 5.Skin as a cutaneous membrane is studied in Chapter 5.

Epithelial Epithelial MembranesMembranes

Synovial membranes enclose certain joints Synovial membranes enclose certain joints and are made of and are made of connective tissue only.connective tissue only.

Synovial MembranesSynovial Membranes

Muscles and nerve tissues are the last of the 4 basic Muscles and nerve tissues are the last of the 4 basic

tissue types. Neurons and muscle fibers are considered tissue types. Neurons and muscle fibers are considered

excitable cellsexcitable cells because they exhibit because they exhibit electrical electrical

excitability,excitability, the ability to respond to certain stimuli the ability to respond to certain stimuli

by producing electrical signals such as by producing electrical signals such as action action

potentials.potentials.

Action potentials can propagate (travel) along the Action potentials can propagate (travel) along the

plasma membrane of a neuron or muscle fiber due to plasma membrane of a neuron or muscle fiber due to

the presence of specific voltage-gated ion channels.the presence of specific voltage-gated ion channels.

Each will be studied in depth in upcoming chapters.Each will be studied in depth in upcoming chapters.

Muscle and Nerve TissuesMuscle and Nerve Tissues

Muscle and Nerve Muscle and Nerve TissuesTissues

Science

Chapter 4