130539583 Histology Powerpoint

7/27/2019 130539583 Histology Powerpoint

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Philip Mathew


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Histology is the study of tissues in terms ofstructure, function, and classification.


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Tissues are groups of closely associated cellsthat are similar in terms of structure andfunction.

Four types of tissues:1. Epithelial2. Connective

3. Muscle4. Nervous


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Epithelial tissue occurs as(1) covering and lining epithelium(2) glandular epithelium

Covering and lining epithelium is found on allfree surfaces.

Glandular epithelium fashions the glands of thebody.


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Epithelium is highly specialized to accomplishmany functions, including:- protection- absorption

- filtration- excretion- secretion


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Special Characteristics of Epithelium(1) Cellularity

- composed almost entirely of cells with littleextracellular material between adjacent cells.

(2) Specialized Contacts- fit close together to form continuous

sheets.

- adjacent cells are bound together by lateralcontacts (tight junctions and desmosomes).


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(3) Polarity- free surface (apical surface) is alwaysexposed to the body exterior or the cavity ofan internal organ.

(4) Avascularity- supplied by nerve fibers but devoid of

vasculature. Epithelial cells are nourished bysubstances diffusing from the blood vesselsin the underlying connective tissue.


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(5) Basement Membrane- the lower (or basal) surface of anepithelium rests on a thin supporting basallamina.

The basal lamina separates the basal surfacefrom the underlying connective tissue andconsists of nonliving, adhesive materialcomposed of glycoproteins.


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The connective tissue cells, just deep to thebasal lamina, secrete a similar extracellularmaterial containing find collagenous fibers(the reticular lamina).

The basal lamina and the reticular lamina forthe basement membrane (which reinforces

the epithelial sheet).


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(6) Regeneration

- high regenerative capacity.- particularly important in cases whereepithelial cells are exposed to friction.


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Primary classification scheme is based on twocriteria:

- The number of cell layers

- The shape of the cell

Simple epithelia consists of a single layer.

Stratified epithelia consists of many layers.


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The nucleus shape conforms to the shape ofthe cell.


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Major classes of simple epithelia:- Simple Squamous- Simple Cuboidal- Simple Columnar

- Pseudostratified

Major classes of stratified epithelia:- Stratified Squamous

- Stratified Cuboidal- Stratified Columnar- Transitional


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Cell shape may vary in stratified epithelia andso classification is based on the cell shape atthe apical surface.


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I. Simple Squamous

- Single layer of squamous cells.

- Fragile (so no protective function).- Main function is to ease diffusion/filtration

- Found in capillaries and air sacs in the lungs.


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III. Simple Columnar

- Single layer of columnar cells.

- Functions include secretion and/orabsorption.- possess cytoplasmic projections

(microvili) that increase surface area.

- Found in the stomach, intestines.- Some serve as a form of protection (ie. the

uterus).


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IV. Pseudostratified

- Appears to be stratified because the nucleiare scattered.

- Used for protection.- All cells are attached to the basement

membrane,- Always has cilia on its apical surface.

- Found in the respiratory tract.- Associated with mucous-producing goblet

cells.


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V. Stratified Squamous

- Several layers of squamous cells.

- Thick, protective tissue.

- Youngest cells are near the basementmembrane. Oldest cells are near the apicalsurface.

- Commonly found where the body is exposed toan external environment (ie. oral cavity, vaginalcanal, anal canal, skin).

- In skin, the outer layers are dead andkeratnized (keratin is a water-proofing protein).


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VI. Stratified Cuboidal

- Several layers of cuboidal cells.

- Functions for protection.- Protects human egg.

- Line large glandular ducts.


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VII. Stratified Columnar

- Several layers of columnar cells noted fortheir scattered nuclei.

- Cells are more cuboidal near basal surface.

- Protection is a primary function.

- Found in the male reproductive tract.


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VIII. Transitional

- Shape changes over spatial variation.

- Able to expand (distend) and contract.- Provides a flexible barrier.

- Found in the urinary tract (primarily in theureters and the lining of the bladder).


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A gland consists of one or more cells thatmake and secrete a particular product (asecretion).

Endocrine glands => produce regulatorychemicals (hormones) that secreted directlyinto the extracellular space.

Exocrine glands => secrete their products viaducts onto body surfaces or into bodycavities.


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Simple glands: possess a single unbranchedduct.

Compound glands: possess a branching duct.


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Tubular Glands: secretory cells form a tube.

Alveolar Glands: secretory cells form small,flask-like sacs (alveoli).

Tubuloalveolar Glands: glands have bothtubular and alveolar secretory units.


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Merocrine glands secrete their products byexocytosis shortly after the products areproduced.

Holocrine glands accumulate their products withinthem until they rupture. Consequently holocrinegland secretions contain the product in additionto dead cell fragments.

Apocrine glands accumulate products just belowtheir free surface. The apex of the cell pinchesoff and the secretion is released.


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Connective tissue is the most abundant andwidely distributed of the primary tissues.

Major functions of connective tissue:- Binding and support- Protection- Insulation- Transportation of substances within thebody.


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Characteristics of Connective Tissue:(1) Common Origin

All connective tissue is derived from themesenchyme (an embryonic tissue derived fromthe mesoderm germ layer).

(2) Degrees of Vascularity

Connective tissue can be avascular or possessa rich supply of vessels (and everything inbetween).


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2. Fibers

Three distinct types of fibers:- Collagen fibers- Elastic fibers- Reticular fibers


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a. Collagen Fibers

Constructed primarily of collagen.

Extremely tough and provide high tensilestrength.

White fibers


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b. Elastic Fibers

Presence of the fibrous protein elastic impartsa rubbery and resilient characteristic to thefibers.

Found in locations where greater elasticity is

required.

Yellow fibers


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3. Cells

Each major class of connective tissue had afundamental cell type that exists in

immature and mature forms.

blast => undifferentiated, activesecrete both ground substance and fibers

characteristic of their particular matrix.

cyte => less active, mature.


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Mucous connective tissue is a temporarymesenchyme-derived tissue that appears inthe fetus in very limited amounts.

Whartons jelly (a type of mucous connectivetissue) supports the umbilical cord.


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II. Connective Tissue Proper

A. Loose Connective Tissue- areolar, adipose, reticular

B. Dense Connective Tissue- dense regular, dense irregular, elastic


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III. Areolar Connective Tissue

Areolar connective tissue has a semifluidground substance formed primarily of

hyaluronic acid in which all three types offiber types are loosely dispersed.

Fibroblasts are the predominant cell type of

this tissue. Fibroblasts are flat, branchingcells that appear spindle-shaped in profile.


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Obvious structural feature is the loosearrangement of its supportive fibers.

In event of inflammation, the aerolarconnective tissue fills with water, leading toedema.

Aerolar connective tissue also serves as acellular packaging material between othertissues.


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IV. Adipose Tissue

Adipose tissue is basically an aerolar connectivetissue in which the nutrient-storing function isgreatly increased (as a result, adipocytes

predominates).Adipocytes = signet rings

Adipocytes are packed tightly together, givingrise to a chicken wire appearance.

Richly vascular, indicating high metabolic activity.


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V. Reticular Connective Tissue

Reticular connective tissue consists of adelicate network of interwoven reticular fibers

associated with reticular cells.


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VI. Dense Fibrous Connective Tissue

Dense regular connective tissue containsregularly arranged bundles of closely packed

collagen fibers running parallel to oneanother.

Poorly vascularized.


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Dense regular connective tissue has a very hightensile strength. Due to this, it forms thetendons (cords that attach muscles to bones)and aponeuroses (flat, sheetlike tendons),

and ligaments (connective tissue that bindsbones together at joints).


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VII. Dense Irregular Connective Tissue

Similar to dense regular connective tissueexcept for much thicker collagen fibers and

irregular interwoven arrangement.

Forms sheets in body areas where tension isexerted from many different directions.


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VIII. Elastic Connective Tissue

Elastic connective tissues are composedalmost entirely of elastin fibers.


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IX. Cartilage

Cartilage has qualities intermediate betweendense connective tissue and bone.

Avascular and devoid of nerve fibers.

Perichondrium surrounds cartilage structures

and allows diffusion of nutrients from thematrix to the chondrocytes.


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Interstitial Growth: chondroblasts within thecartilage divide and secrete new matrix.

Appositional Growth: chondroblasts locateddeep to the perichondrium secrete newmatrix elements on the external face of thecartilage structure.


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X. Hyaline Cartilage

Most widely distributed cartilage in thehuman body.

Matrix appears glassy (hyalin = glass) blue-white.

Hyaline cartilage covers the ends of long

bones as articular cartilage and persistsduring childhood as the epiphyseal plates.


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XI. Elastic Cartilage

Nearly identical to hyaline cartilage with theexception that elastic cartilage has a higher

concentration of elastin fibers.

Found in locations where strength andexceptional ability to stretch are needed.


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XIII. Bone (Osseous Tissue)

Osseous tissue has the exceptional ability tosupport and protect softer tissues.

Osteoblasts => produce the organic portionof the matrix.


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XIV. Blood

Blood consists of living blood cellssurrounded by a nonliving fluid matrix called

blood plasma.

Fibers of blood are soluble proteinmolecules.


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Primary blast cells types by connective tissueclass:

1. Connective tissue proper (fibroblast)

2. Cartilage (chondroblast)

3. Bone (osteoblast)

4. Blood (hemocytoblast or hematopoietic stem

cell)


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Class of Connective

Tissue Resulting:

Cellular

Descendants:

Common

Embryonic Origin:Mesenchyme

Fibroblast

Fibrocyte

Connective

Tissue Proper

Chondroblast

Chondrocyte

Cartilage

Osteoblast

Osteocyte

Osseous

(bone)

Hemocytoblast

Blood Cells,

Macrophages

Blood


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Epithelial Membranes = a continuousmulticellular sheet composed of at least twoprimary tissue types: an epithelium bound toa discrete underlying connective tissue layer.

Three common types of epithelial membranes:

- Cutaneous- Mucous (or mucosae)- Serous (or serosae)


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A. Cutaneous Membrane

The cutaneous membrane is the skin.

It consists of a keratinized stratifiedsquamous epithelium (the epidermis) firmlyattached to a thick layer of dense irregular

connective tissue (dermis).


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B. Mucous Membranes

The mucous membranes line body cavities thatare open to the exterior.

The term mucosa refers to the location of theepithelial membrane (not the composition).

All mucosae consist of an epithelial sheet directlyunderlain by a lamina propria.

The lamina propria is a layer of loose connectivetissue just deep to the basement membrane.


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C. Serous Membranes

The serous membranes are the moist membranes found inthe closed bentral body cavities.

Each serosa consists of a parietal layer (which lines the

cavity wall) and then reflects back as the visceral layer(which covers the outer surface of organs within the body).

Each of these layers consists of mesothelium resting on athin layer of loose connective (areolar) tissue. Themesothelial cells secrete thin, clear serous fluid that

lubricates the facing surfaces of the parietal and viscerallayers.


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Muscle tissues are highly cellular, well-vascularized tissues that are responsible formost types of body movement.

Due to the elongated shape, muscle cells arealso referred to as fibers.

Muscle cells possess myofilaments (elaborateversions of the actin and myosin filamentsthat promote movement).


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B. Cardiac Muscle- found in the walls of the heart (and nowhereelse).

- striated in appearance.

- uninucleated.

- fit together tightly at unique junctions(intercalated discs).

- involuntary.


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C. Smooth Muscle

- located in the walls of hollow organs.

- no external visible striations.

- spindle-shaped.

- one central nucleus.

- involuntary.


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- Highly specialized.- Detects internal/external changes and

coordinates responses to the stimuli.

- Little (if any) reproductive ability.


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Neurons- Perform most of the work

(communication).

- Distributed end-to-end.

Neuroglial Cells- Helper cells (provide support).- Supply neurons with nutrients.- Fight off invaders.


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130539583 Histology Powerpoint

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