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The TissueLevel of

Organization4.1-4.4

August 27, 2012

Chapter 4: The Tissue Level of Organization 4.1 Types of Tissue 4.2 Cell Junctions

4.3 Comparison between Epithelial and Connective Tissues 4.4 Epithelial Tissues 4.5 Connective Tissues

4.6 Membranes 4.7 Muscular Tissues

4.8 Nervous Tissues 4.9 Excitable Tissues 4.10 Tissue Repair: Homeostasis

4.11 Aging & Tissues

The Big Idea Tissues & Homeostasis

The four basic types of tissues in the humanbody contribute to homeostasis by providingdiverse functions including protection, support,communication among cells, and resistance todisease

4.1 Types of Tissue Objectives

Name the four basic types of tissues thatmake up the human body, and state thecharacteristics of each

Tissues are a group of cells with a commonembryonic origin that function together to carryout specialized activities

They include various types, ranging from hard(bone) to semisolid (fat) to liquid (blood)

They are classified into four basic types:epithelial, connective, muscular, and nervoustissue

• Histology is the study of the microscopic anatomyof cells and tissues – it is a branch of pathology

A trained histologist can recognize over 200distinct human cell types under the microscopeand is able to distinguish a cell from pancreatictissue as opposed to a cell from the skin

• Each cell type has features particular to itsfunction

4.2 Cell Junctions Objectives

Describe the structure and functions of thefive main types of cell junctions

Tissues are formed bygrouping cells togetherusing a variety ofIntercellular Junctions

Connect adjacentcells mechanically atthe cell membranesor throughcytoskeletal elementswithin and betweencells

Tight Junctions Tight Junctions are

found where a leakproofseal is needed betweencells

They keep materialsfrom leaking out oforgans like thestomach and bladder

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Adherens Junctions Adherens Junctions make

an adhesion belt that keepstissues from separating asthey stretch and contract

Cadherin is aglycoprotein that formsthe belt-like “plaque”

Desmosomes Desmosomes act as

“spot welds”

They also use cadheringlycoprotein (plusintermediatefilaments) to hookinto the cytoplasm

Hemidesmosomes Hemidesmosomes

are half-welds thatjoin cells to thebasementmembrane

Gap Junctions Gap Junctions are pores

(connexons) that allowsmall substances like ionsto pass between cells

If one of the cells gets sickor dies, these seal like ahatch to prevent damageto other cells

4.3 Comparisons Between Epithelial &Connective Tissues

Objectives

State the main differences between epithelialand connective tissues

Of all the cells in thebody, they combineto make only 4 basictissue types:

Epithelial tissues Connective tissues

Muscular tissues

Nervous tissues

Epithelial tissues cover body surfaces and formglands and line hollow organs, body cavities, andducts

Many cells are tightly packed together and areavascular

Connective tissues (CT) protect,support, and bind organs

Have relatively few cells with lots ofextracellular material

Fat is a type of CT that stores energy

Red blood cells, white blood cells,and platelets are all CT

Muscular tissues generate the physical forceneeded to make body structures move

They also generate heat used by the body

Nervous tissues detect changes in the body andrespond by generating nerve impulses

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Tissues of the bodydevelop from threeprimary germ layers:Endoderm, Mesoderm,and Ectoderm Epithelial tissues from all

three germ layers CT and muscle are

derived from mesoderm Nervous tissue develops

from ectoderm

4.4 Epithelial Tissues Objectives

Describe the general features of epithelialcells

List the location, structure, and function ofeach different type of epithelial tissues

Epithelial tissues include covering and lining epitheliaand glandular epithelia Epithelium is used to line surfaces and form

protective barriers Good at secreting things like mucous, hormones,

and other substances Epithelial tissues consist mostly of cells with little

extracellular material Epithelium is arranged in sheets and attached to a

basement membrane Avasucular with their own nerve supply A high rate of cell division allows for a high capacity

of renewal

Apical (free) surfaces face the body surface, abody cavity, the lumen (interior space) of anorgan, or a tubular duct that receives secretions

Lateral surfaces face adjacent cells on either side,may contain tight junctions, adherens junctions,desmosomes, and/or gap junctions

Basal surfaces are opposite the apical surface The basal surfaces of the deepest layer of

epithelial cells adhere to extracellular materialssuch as the basement membrane

The basal layer of the epithelium secretes abasal lamina; the underlying CT secretes areticular lamina

Together the basal lamina and the reticularlamina form a non-cellular basementmembrane on which the epithelium sits

Classification of Epithelial Tissues Epithelia are named according to the shape of

their cells, and the thickness or arrangement oftheir layers (of cells)

Naming epithelia according to shape

Flat, wide “pavingstone” cells; allowsfor rapid passage of

substances

Cells as tall as they arewide; may have

microvilli at the apicalsurface; for secretion or

absorption

Cells taller than theyare wide; protect

underlying tissue; mayhave cilia or microvilliat the apical surface;

for secretion orabsorption

Naming epithelia according to arrangement

One layer; all cells incontact withbasement

membrane;secretion and

absorption, diffusionand osmosis

Appears to havelayers, but in reality allcells go from the apex

to the base; maycontain cillia; gobletcells secret mucus

Two or more layers;only basal layer in

contact with basementmembrane; protect

underlying tissuewhere there is

considerable wear andtear

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

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Covering & Lining Epithelium Forms the outer covering of the skin and

some internal organs Also forms the inner lining of blood vessels,

ducts, body cavities, and the interior of therespiratory, digestive, urinary, andreproductive systems

• Endothelium is a specialized simple squamousepithelium that lines the entire circulatory systemfrom the heart to the smallest capillary – it isextremely important in reducing turbulence offlow of blood

• Mesothelium is found in serous membranes suchas the pericardium, pleura, and peritoneum.

• Unlike other epithelial tissue, both are derivedfrom embryonic mesoderm (the middle layer ofthe 3 primary germ layers of the embryo)

Simple Squamous Epithelium is composed of a singlelayer of flat cells found in parts of the body wherefiltration or diffusion is a priority process In the air sacs of lungs Endothelium in the lining of blood vessels, the heart,

and lymphatic vessels In all capillaries, including those of the kidney Mesothelium forms the serous membranes in the

thoracic and abdominopelvic cavities

Simple Cuboidal Epithelium is composed of a singlelayer of cube shaped cells that function in secretionand absorption

It is often found lining tubules of the kidneys andmany other glandular ducts

Also found covering the ovaries and in the eyes

Nonciliated Simple Columnar Epithelium forms a singlelayer of nonciliated rectangular cells Lines most of the gastrointestinal tract and contains

specialized cells that perform absorption and secretemucus

Ciliated Simple Columnar Epithelium forms a single layerof ciliated rectangular cells Found in portions of the upper respiratory tract, where

it moves foreign particles trapped in mucus out of therespiratory tract

Pseudostratified Columnar Epithelium appears tohave layers, due to nuclei which are at various depths In reality, all cells are attached to the basement

membrane in a single layer, but some do notextend to the apical surface

Ciliated tissue has goblet cells that secretemucous

Stratified Squamous Epithelium has an apical surface thatis made up of squamous (flat) cells The other layers have different shapes, but the name is

based on the apical layer The many layers are ideal for protection against strong

friction forces, water loss, uv radiation, and foreigninvasion

A nonkeratinized variety lines wet surfaces A keratinized variety forms the epidermis

Stratified Cuboidal Epithelium has an apical surfacemade up of two or more layers of cube-shaped cells Locations include the sweat glands and part of the

male urethra Stratified Columnar Epithelium cells are columnar in

shape Also found in the portions of the male urethra and

in large excretory ducts of some glands

Transitional Epithelium change shapedepending on the state of stretch in the tissue

The apical “dome cells” of the top layer arean identifiable feature and signify an emptybladder

In a full bladder, the cells are flattened

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Although epithelia arefound throughout thebody, certain ones areassociated with specificbody locations Stratified squamous

epithelium is aprominent feature ofthe outer layers ofthe skin

Simple squamous makes upepithelial membranes and linesthe blood vessels

Columnar is common in thedigestive tract

Pseudostratified ciliatedcolumnar is characteristic of theupper respiratory tract

Transitional is found in thebladder

Cuboidal lines ducts and sweatglands

Glandular Epithelium A gland is a single cell or a group of epithelial cells

adapted for secretion Makes up the secreting portion of glands such as the

thyroid, adrenal, and sweat glands Epithelial glands are another example of simple

organs Glands that secrete their contents directly into the

blood are called endocrine glands Glands that secrete their contents into a lumen or

duct are called exocrine glands

Endocrine glands, called hormones, enterinterstitial fluid and then diffuse directly into thebloodstream without flowing through a duct

Exocrine glands secrete substances through ductsto the surface of the skin or into the lumen of ahollow organ

Secretions of the exocrine gland include mucus,sweat, oil, earwax, saliva, and digestive enzymes

Examples of exocrine glands are sudoriferous(sweat) glands

The two criteria for categorizing multicellularglands according to structure: Whether the ducts are branched or

unbranched In a simple gland the duct does not branch In a compound gland the duct branches

And the shape of the secretory portion of theglandTubular glands have tubular secretory partsAcinar glands have rounded secretory partsTubuloacinar glands have features of both

unbranchedduct

(simple)

branchedduct

(compound)

The criteria for categorizing multicellular glandsaccording to function is based on the mannerin which the gland secretes its product frominside the cell to the outside environment

Merocrine

Apocrine

Holocrine

Merocrine secretion is the most commonmanner of secretion The gland releases its product by

exocytosis and no part of the gland is lostor damaged

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Apocrine glands “bud” their secretions off through theplasma membrane, producing membrane-boundvesicles in the lumen of the gland The end of the cell breaks off by “decapitation”,

leaving a milky, viscous odorless fluid This type of sweat only develops a strong odor

when it comes into contact with bacteria on theskin surface

Holocrine secretions are produced by rupture ofthe plasma membrane, releasing the entire cellularcontents into the lumen and killing the cell (cellsare replaced by rapid division of stem cells)

The sebaceous gland is an exampleof aholocrine gland, because its secretion (sebum) isreleased with remnants of dead cells