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Chapter 4 Tissue: The Living FabricPart A

Shilla Chakrabarty, Ph.D.

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Tissues

• Groups of cells that are similar in structure and function

• Types of tissues

Epithelial tissue

Connective tissue

Muscle tissue

Nerve tissue

Copyright © 2010 Pearson Education, Inc. Figure 4.1

Nervous tissue: Internal communication• Brain, spinal cord, and nerves

Muscle tissue: Contracts to cause movement• Muscles attached to bones (skeletal)• Muscles of heart (cardiac)• Muscles of walls of hollow organs (smooth)

Epithelial tissue: Forms boundaries between different environments, protects, secretes, absorbs, filters• Skin surface (epidermis)• Lining of GI tract organs and other hollow organs

Connective tissue: Supports, protects, bindsother tissues together• Bones• Tendons• Fat and other soft padding tissue

Overview Of Tissues In The Body

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Epithelial Tissue (Epithelium)

Two main types (by location):

1. Covering and lining epithelia

• On external and internal surfaces

2. Glandular epithelia

• Secretory tissue in glands

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Characteristics of Epithelial Tissue

1. Cells have polarity—apical (upper, free) and basal (lower, attached) surfaces

Apical surfaces may bear microvilli (e.g., brush border of intestinal lining) or cilia (e.g., lining of trachea)

Noncellular basal lamina of glycoprotein and collagen lies adjacent to basal surface

2. Are composed of closely packed cells: Continuous sheets held together by tight junctions and desmosomes

3. Supported by a connective tissue reticular lamina (under the basal lamina)

4. Avascular but innervated

5. Rate of regeneration high

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Classification of Epithelia

• Based on number of layers:

1. 1 layer = simple epithelium

>1 = stratified epithelium

Copyright © 2010 Pearson Education, Inc. Figure 4.2a

Stratified

Simple

Apical surface

Basal surface

Apical surface

Basal surface

(a) Classification based on number of cell layers.

Classification of Epithelia1. Based on number of layers:

1 layer = simple epithelium

>1 layer = stratified epithelium

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Classification of Epithelia

Based on type of cell:

•Squamous

•Cuboidal

•Columnar

(If stratified, name according to shape of cells in apical layer)

Squamous

Cuboidal

Columnar

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Types of Epithelial Tissues

1. Simple squamous epithelium

2. Simple cuboidal epithelium

3. Simple columnar epithelium

4. Pseudostratified columnar epithelium

5. Stratified squamous epithelium

6. Stratified cuboidal epithelium

7. Stratified columnar epithelium

8. Transitional epithelium

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(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

NOTE: Endothelium refers to the epithelial lining for blood vessels, lymph vessels and heartMesothelium refers to the epithelium of serous membranes in ventral body cavity

Copyright © 2010 Pearson Education, Inc. 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

Copyright © 2010 Pearson Education, Inc. 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 some glands; ciliated variety lines small bronchi, uterine tubes, and some regions of the uterus.

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

Simplecolumnarepithelialcell

Basementmembrane

Mucus ofmucouscell

Microvilli

Copyright © 2010 Pearson Education, Inc. 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

Copyright © 2010 Pearson Education, Inc. 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

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Stratified Cuboidal Epithelium

• Quite rare in body

• Found in some sweat and mammary glands

• Typically two cell layers thick

Stratified Columnar Epithelium

• 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

Copyright © 2010 Pearson Education, Inc. 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

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Glandular Epithelia

• A gland is one or more cells that makes and secretes an aqueous fluid

• Classified by:

• Site of product release—endocrine or exocrine

• Relative number of cells forming the gland—unicellular (e.g., goblet cells) or multicellular

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Endocrine And Exocrine Glands

Endocrine glands:

•Ductless

•Secrete hormones that travel through lymph or blood to target organs

Exocrine glands:

•More numerous than endocrine glands

•Secrete products into ducts

•Secretions released onto body surfaces (skin) or into body cavities

Examples: mucous, sweat, oil, and salivary glands

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(b)(a)

Microvilli

Secretoryvesiclescontainingmucin

Golgiapparatus

Rough ER

Nucleus

Unicellular Exocrine Glands

The only important unicellular gland is the goblet cell

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Multicellular Exocrine Glands• 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)

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Compound duct structure(duct branches)

Simple tubular

ExampleIntestinal glands

Simple branchedtubularExampleStomach (gastric)glands

Compound tubularExampleDuodenal glands of small intestine

Compound alveolarExampleMammary glands

SimplealveolarExampleNo importantexample in humans

Simple branchedalveolarExampleSebaceous (oil)glands

CompoundtubuloalveolarExampleSalivary glands

Tubularsecretorystructure

Alveolarsecretorystructure

Surface epithelium Duct Secretory epithelium

Simple duct structure(duct does not branch)

Multicellular Exocrine GlandsComposed of a duct and a secretory unitClassified according to:

Duct type (simple or compound) Structure of their secretory units (tubular, alveolar, or tubuloalveolar)

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Modes of Secretion• Merocrine

• Products are secreted by exocytosis (e.g., pancreas, sweat and salivary glands); gland cells remain intact

• Apocrine

• Products are released by pinching off portions of cells

(e.g. milk secretion)

• Holocrine

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