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1
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