Tissue Types Overview Tissue Definitions

Epithelial Tissue

• Simple and Stratified

Connective Tissue

• Characteristics

• Bone, Cartilage, Dense

• Connective, Loose Connective

Blood

Muscle Tissue

• Skeletal, Cardiac, and Smooth

Nervous Tissue

Tissue Repair

Tissue Development and Aging

Body Tissues Cells are specialized for particular functions

Tissues

• Groups of cells with similar structure and function

• Four primary types

Epithelium

Connective tissue

Muscle

Nervous tissue

Epithelial Tissues Found in different areas

• Body coverings

• Body linings

• Glandular tissue

Functions

• Protection

• Absorption

• Filtration

• Secretion

Epithelium Characteristics Cells fit closely together

Tissue layer always has one free surface

The lower surface is bounded

by a basement membrane

Avascular (have no blood supply)

Regenerate easily if well nourished

Classification of Epithelium: Layering

Classification of Epithelium: Shape

(a) Simple squamous epithelium

Description: Single layer of flattenedcells with disc-shaped central nucleiand sparse cytoplasm; the simplestof the epithelia.

Function: Allows passage ofmaterials by diffusion and filtrationin sites where protection is notimportant; secretes lubricatingsubstances in serosae.

Location: Kidney glomeruli; air sacsof lungs; lining of heart, bloodvessels, and lymphatic vessels; liningof ventral body cavity (serosae).

Photomicrograph: Simple squamous epitheliumforming part of the alveolar (air sac) walls (125x).

Air sacs oflung tissue

Nuclei ofsquamousepithelialcells

Other important locations:

Endothelium- the lining of lymphatic vessels, blood vessels, and heart

Mesothelium- the epithelium of serous membranes in the ventral body cavity

Figure 4.3b

(b) Simple cuboidal epithelium

Description: Single layer ofcubelike cells with large,spherical central nuclei.

Function: Secretion andabsorption.

Location: Kidney tubules;ducts and secretory portionsof small glands; ovary surface.

Photomicrograph: Simple cuboidalepithelium in kidney tubules (430x).

Basementmembrane

Connectivetissue

Simplecuboidalepithelialcells

Figure 4.3c

(c) Simple columnar epithelium

Description: Single layer of tall cells with round to oval nuclei; some cells bear cilia; layer may contain mucus-secreting unicellular glands (goblet cells).

Function: Absorption; secretion of mucus, enzymes, and other substances; ciliated type propels mucus (or reproductive cells) by ciliary action.

Location: Nonciliated type lines most of the digestive tract (stomach to anal canal),gallbladder, and excretory ducts of someglands; ciliated variety lines small bronchi, uterine tubes, and some regionsof the uterus.

Photomicrograph: Simple columnar epitheliumof the stomach mucosa (860X).

Simplecolumnarepithelialcell

Basementmembrane

Figure 4.3d

(d) Pseudostratified columnar epithelium

Description: Single layer of cells ofdiffering heights, some not reachingthe free surface; nuclei seen atdifferent levels; may contain mucus-secreting cells and bear cilia.

Function: Secretion, particularly ofmucus; propulsion of mucus byciliary action.

Location: Nonciliated type in male’ssperm-carrying ducts and ducts oflarge glands; ciliated variety linesthe trachea, most of the upperrespiratory tract.

Photomicrograph: Pseudostratified ciliatedcolumnar epithelium lining the human trachea (570x).

Trachea

Cilia

Pseudo-stratifiedepitheliallayer

Basementmembrane

Mucus ofmucous cell

Figure 4.3e

(e) Stratified squamous epithelium

Description: Thick membranecomposed of several cell layers;basal cells are cuboidal or columnarand metabolically active; surfacecells are flattened (squamous); in thekeratinized type, the surface cells arefull of keratin and dead; basal cellsare active in mitosis and produce thecells of the more superficial layers.

Function: Protects underlyingtissues in areas subjected to abrasion.

Location: Nonkeratinized type formsthe moist linings of the esophagus,mouth, and vagina; keratinized varietyforms the epidermis of the skin, a drymembrane.

Photomicrograph: Stratified squamous epitheliumlining the esophagus (285x).

Stratifiedsquamousepithelium

Nuclei

Basementmembrane

Connectivetissue

Stratified Epithelium, Other Types

Stratified cuboidal

Stratified columnar

Mucous gland duct, tongue

•Quite rare in body

•Found in some sweat and mammary glands

•Typically two cell layers thick

•Limited distribution in body

•Small amounts in pharynx, male urethra, and lining some glandular ducts

•Also occurs at transition areas between two other types of epithelia

Figure 4.3f

(f) Transitional epithelium

Description: Resembles both stratified squamous and stratified cuboidal; basal cells cuboidal or columnar; surface cells domeshaped or squamouslike, depending on degree of organ stretch.

Function: Stretches readily and permits distension of urinary organ by contained urine.

Location: Lines the ureters, urinary bladder, and part of the urethra.

Photomicrograph: Transitional epithelium lining the urinary bladder, relaxed state (360X); note the bulbous, or rounded, appearance of the cells at the surface; these cells flatten and become elongated when the bladder is filled with urine.

BasementmembraneConnectivetissue

Transitionalepithelium

Glandular Epithelium Gland – one or more cells that secretes a

particular product

Two major gland types

• Endocrine gland

Ductless

Secretions are hormones

• Exocrine gland

Empty through ducts to the epithelial surface

Include sweat and oil glands

Found as unicellular and multicellular types

Unicellular Exocrine Glands: Goblet Cell The only important unicellular gland is the

goblet cell

Figure 4.4

(b)(a)

Microvilli

Secretoryvesiclescontainingmucin

Golgiapparatus

Rough ER

Nucleus

Multicellular Exocrine Glands Multicellular exocrine glands are

composed of a duct and a secretory unit

Classified according to:

• Duct type (simple or compound)

• Structure of their secretory units (tubular, alveolar, or tubuloalveolar)

Figure 4.5

Compound duct structure(duct branches)

Simple tubular

ExampleIntestinal glands

Simple branchedtubular

ExampleStomach (gastric)glands

Compound tubular

ExampleDuodenal glands of small intestine

Compound alveolar

ExampleMammary glands

Simplealveolar

ExampleNo importantexample in humans

Simple branchedalveolar

ExampleSebaceous (oil)glands

Compoundtubuloalveolar

ExampleSalivary glands

Tubularsecretorystructure

Alveolarsecretorystructure

Surface epithelium Duct Secretory epithelium

Simple duct structure(duct does not branch)

Modes of Secretion Merocrine

• Products are secreted by exocytosis (e.g., pancreas, sweat and salivary glands)

Holocrine

• Products are secreted by rupture of gland cells (e.g., sebaceous glands)

Tissue Types Overview Tissue Definitions

Epithelial Tissue

• Simple and Stratified

Connective Tissue

• Characteristics

• Bone, Cartilage, Dense

• Connective, Loose Connective

Blood

Muscle Tissue

• Skeletal, Cardiac, and Smooth

Nervous Tissue

Tissue Repair

Tissue Development and Aging

Connective Tissue Found everywhere in the body

Includes the most abundant and widely distributed tissues

Functions

• Binds body tissues together

• Supports the body

• Provides protection

Connective Tissue Characteristics Variations in blood supply

• Some tissue types are well vascularized

• Some have poor blood supply or are avascular

Extracellular matrix

• Non-living material that surrounds living cells

Extracellular Matrix Two main elements

• Ground substance - Gel like, high water content

Proteoglycans

Glycosaminoglycans (GAGs like hyaluronan), chondroitin sulfate as dietary supplement for osteoarthritis

Glycoproteins

• Fibers

Produced by the cells

Three types

Collagen fibers

Elastic fibers

Reticular fibers

Reticular fibers

Table 4.1

Connective Tissue Types: Areolar Areolar connective tissue

Generic organ packaging tissue, soaks up water

Connective Tissue Types: Bone Bone (osseous tissue)

Has both an organic and a mineral component

Tissue Types Overview Tissue Definitions

Epithelial Tissue

• Simple and Stratified

Connective Tissue

• Characteristics

• Bone, Cartilage, Dense

• Connective, Loose Connective

Blood

Muscle Tissue

• Skeletal, Cardiac, and Smooth

Nervous Tissue

Tissue Repair

Tissue Development and Aging