Chapter 4: Human Tissue Types and Microscopy Techniques

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Tissue

Groups of cells similar in structure that perform common or related function.

Histology

Study of tissues.

Epithelial tissue

Covers surfaces, lines cavities, forms glands.

Connective tissue

Supports and protects, stores energy, immunity.

Muscle tissue

Produces movement.

Nervous tissue

Controls (generates signals that coordinate body's activities).

Fixed tissue

Tissue preserved with solvent.

Sectioned tissue

Cut into slices thin enough to transmit light or electrons.

Stained tissue

Enhanced contrast using dyes or coatings.

Covering and lining epithelium

Outer layer of the skin and lines open cavities of the urogenital, digestive, and respiratory systems.

Glandular epithelium

Secretory tissue in glands (example: salivary glands).

Polarity

Cells have polarity (top and bottom).

Apical surface

Upper free side exposed to surface or cavity.

Basal surface

Lower attached side facing inwards toward body.

Basal lamina

An adhesive sheet that holds basal surface of epithelial cells to underlying cells.

Microvilli

Specialized fingerlike projections on apical surfaces that increase surface area.

Cilia

Tiny hairlike projections that push substances along their free surface.

Basal lamina function

Acts as a selective filter and scaffolding for cell migration in wound repair.

Specialized contacts

Points that bind adjacent epithelial cells together.

Tight junctions

Prevent substances from leaking through spaces between cells.

Desmosomes

Keep cells from pulling apart.

Basement membrane

Reinforces the epithelial sheet and defines the epithelial boundary.

Reticular lamina

Lower layer of the basement membrane produced by connective tissue.

Cancerous epithelial cells

Not contained by the basement membrane boundary like other cells; they penetrate the boundary and invade underlying tissues, resulting in the spread of cancer.

Avascular

No blood vessels in epithelial tissue; must be nourished by diffusion from underlying connective tissues.

Innervated

Epithelial tissue is supplied by nerve fibers.

Regeneration of epithelial cells

Epithelial cells have high regenerative capacity; if adequate nutrients are available, they can replace lost cells by cell division.

Simple epithelia

A single layer thick.

Stratified epithelia

Two or more layers thick and involved in protection (example: skin).

Squamous cells

Flattened and scale-like cells.

Cuboidal cells

Box-like, cube-shaped cells.

Columnar cells

Tall, column-shaped cells.

Simple squamous epithelium

Single layer of flattened cells sitting on the basement membrane; functions where rapid diffusion is a priority (kidney, lungs).

Endothelium

Lining of lymphatic vessels, blood vessels, and heart; a special name for simple squamous epithelium.

Mesothelium

The epithelium found in serous membranes in the ventral body cavity; a special name for simple squamous epithelium.

Simple cuboidal epithelium

Single layer of cubelike cells with large, spherical central nuclei; involved in secretion and absorption.

Simple columnar epithelium

Single layer of tall, closely packed cells; some have microvilli and cilia, involved in absorption and secretion.

Ciliated cells

Cells that move mucus; found in simple columnar epithelium.

Pseudostratified columnar epithelium

Cells vary in height and appear stratified, but are actually a single layer; involved in secretion and movement of mucus.

Stratified squamous epithelium

Most widespread of stratified epithelia; free surface is squamous with deeper cuboidal or columnar layers; located in areas of high wear and tear.

Keratinized stratified squamous epithelium

Forms the external part of the skin and contains keratin, a tough protective protein.

Nonkeratinized stratified squamous epithelium

Found in moist linings such as the mouth.

Stratified cuboidal epithelium

Quite rare; found in some sweat and mammary glands; typically has two cell layers thick.

Stratified columnar epithelium

Very limited distribution in the body; small amounts found in pharynx, male urethra, and lining some glandular ducts.

Transitional Epithelium

Forms lining of hollow urinary organs, which stretch as they fill with urine. Found in bladder, ureters, and urethra.

Apical Layer

Only apical layer is columnar in transitional epithelium.

Basal Layer Cells

Basal layer cells are cuboidal or columnar in transitional epithelium.

Dome Shape Apical Cells

The apical (surface) cells vary in appearance, depending on the degree of distension (stretching) of the organ.

Gland

One or more cells that makes and secretes an aqueous fluid called a secretion.

Endocrine Glands

Ductless glands that secrete hormones into surrounding interstitial fluid, which is picked up by the circulatory system.

Exocrine Glands

Glands that release secretions onto body surfaces or into body cavities.

Unicellular Exocrine Glands

The only important unicellular glands are mucous cells and goblet cells, found in epithelial linings of intestinal and respiratory tracts.

Mucin

A glycoprotein produced by goblet cells that can dissolve in water to form mucus, a slimy protective, lubricating coating.

Multicellular Exocrine Glands

Composed of a duct and a secretory unit (acinus), usually surrounded by supportive connective tissue.

Simple Exocrine Glands

Have unbranched ducts.

Compound Glands

Have branched ducts.

Tubular Gland

Secretory cells form a duct.

Alveolar Glands

Secretory cells form sacs.

Tubuloalveolar Glands

Glands that have both tubular and alveolar types.

Merocrine Secretion

Most secrete products by exocytosis as secretions are produced (e.g., sweat, pancreas).

Holocrine Secretion

Accumulated products fill the whole cell, which then ruptures; the cell is replaced by other cells from below (e.g., sebaceous oil glands).

Apocrine Secretion

Only apex of the cell ruptures; controversial existence in humans (e.g., lactating mammary cells).

Four Main Classes of Connective Tissue

Connective tissue proper, Cartilage, Bone, Blood.

Common Embryonic Origin

All connective tissues arise from an embryonic tissue called mesenchyme.

Degrees of Vascularity

Connective tissues differ in amount of vascularity, from avascular (e.g., cartilage) to very vascular (e.g., bone).

Extracellular matrix

Nonliving material that separates living cells of connective tissues and supports them.

Ground substance

Unstructured material that fills space between cells and contains fibers, composed of interstitial fluid, cell adhesion proteins, and proteoglycans.

Interstitial fluid

Fluid that exists between the cells in connective tissues.

Cell adhesion proteins

Proteins that act as 'glue' for attachment of cells within the ground substance.

Proteoglycans

Sugar proteins made up of a protein core and large polysaccharides called glycosaminoglycans (GAGs).

Glycosaminoglycans (GAGs)

Large polysaccharides that include chrondroitin sulfate and hyaluronic acid, affecting the viscosity of the ground substance.

Collagen fibers

The strongest and most abundant type of fiber in connective tissues, providing high tensile strength.

Elastic fibers

Networks of long, thin elastin fibers that allow for stretch and recoil.

Reticular fibers

Short, fine fibers made of a different type of collagen that support soft tissue of organs.

Blast cells

Immature cells that actively secrete ground substance and fibers.

Fibroblasts

Blast cells found in connective tissue proper that become fibrocytes.

Chondroblasts

Blast cells found in cartilage that become chondrocytes.

Osteoblasts

Blast cells found in bone that become osteocytes.

Cyte cells

Mature, less active form of 'blast' cells that help maintain the health of the matrix.

Fat cells

Cells that store nutrients.

White blood cells

Cells such as neutrophils, eosinophils, and lymphocytes involved in immune response.

Mast cells

Cells that initiate local inflammatory response against foreign microorganisms.

Macrophages

Phagocytic cells that 'eat' dead cells and microorganisms, functioning in the immune system.

Connective Tissue Proper

Consists of all connective tissues except bone, cartilage, and blood.

Loose connective tissues

Subclasses of connective tissue proper that include Areolar, Adipose, and Reticular tissues.

Dense connective tissues

Also called fibrous connective tissue, includes Dense regular, Dense irregular, and Elastic tissues.

Areolar connective tissue

Most widely distributed connective tissue that supports and binds other tissues.

Adipose tissue

A type of loose connective tissue that stores fat and has little matrix with closely packed cells.

Richly vascularized

Functions in shock absorption, insulation, and energy storage.

Brown fat

Uses lipid fuels to heat bloodstream rather than to produce ATP, as does white fat.

Loose CT: Reticular Connective Tissue

Resembles areolar tissue, but fibers are thinner reticular fibers.

Reticular cells

Fibroblast cells that secrete reticular fibers made up of thin collagen.

Dense Regular Connective Tissue

Very high tensile strength; can withstand high tension and stretching.

Collagen fibers in Dense Regular CT

Closely packed bundles run parallel to direction of pull, appearing as white structures.

Fibroblasts in Dense Regular CT

Manufacture collagen fibers and ground substance.

Tendons

Attach muscles to bones.

Aponeuroses

Flat, sheetlike tendons that attach muscles to other muscles or to bones.

Ligaments

Connect bones.

Dense Irregular Connective Tissue

Same elements as the regular, but bundles of collagen are thicker and irregularly arranged.

Elastic Connective Tissue

Contains elastic fibers; some ligaments are very elastic.