1 chapter 5 tissues – epithelial. 2 introduction similar cells with a common function are called...

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Chapter 5

Tissues – Epithelial

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Introduction

• Similar cells with a common function are called tissues.

• The study of tissues is called histology.

• There are four (4) primary or major tissue types:

1. Epithelial Tissue (covering/lining; ET)2. Connective Tissue (support; CT)3. Muscle Tissue (movement; MT)4. Nervous Tissue (control; NT)

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

Epithelial Tissue (Epithelium)

Two main types (by location):1. Covering and lining epithelia

• On external and internal surfaces o body (i.e. epidermis) and

o ventral cavity organs (i.e. visceral serous membranes)

2. Glandular epithelia• Secretory tissue in glands

o internal spaces (i.e. lumen of the intestine), o line body cavities (i.e. parietal membranes),o line ducts of exocrine glands (i.e. sweat glands).

Epithelial Tissue

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Functions of Epithelial Tissue

• Protection• Absorption• Filtration• Secretion

1. Cells exibit 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).

– Apical surfaces always have a free space, which opens to the outside or to an internal space (lumen)

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

Characteristics of Epithelial Tissue

2. Cellularity - cells are in close contact with each other with little or no intercellular space between them.

3. Supported by a connective tissue - reticular lamina (under the basal lamina) at the basal surface, both the epithelial tissue and the connective tissue contribute to the basement membrane

4. Avascular (no blood supply).

5. Innervated (supplied with nerves)

6. Rely on diffusion and underlying connective tissue for nutrients and O2

7. High rate of regeneration

Characteristics of Epithelial Tissue

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Cellularity - Intercellular Junctions

Gap junctions• Tubular channels between cells• Located in cardiac muscle cells

• cardiac muscle cells• digestive smooth muscle cells

Tight junction

Cell membrane

Cell membrane

Cell membrane

Desmosome

Gap junction

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Tight junctions• Close space between cells• Located among cells that form linings

• lining cells in small intestine• kidney tubules• blood-brain barrier

Desmosomes• Form “spot welds” between cells• Found in tissues that undergo repeated episodes of tension and stretching

• skin, heart, uterus

Basement Membrane: The Basal Lamina

• Noncellular supporting sheet between the epithelium and the connective tissue deep to it

• Consists of proteins secreted by the epithelial cells • Functions:

– Acts as a selective filter, determining which molecules from capillaries enter the epithelium

– Acts as scaffolding along which regenerating epithelial cells can migrate

• Basal lamina and reticular layers of the underlying connective tissue form the basement membrane

• First name of tissue indicates number of layers

– Simple – one layer of cells

– Stratified – more than one layer of cells

Classifications of Epithelia

- Pseudostratified- tissue appears to be stratified, but all cells contact basement membrane so it is in fact simple

• Last name of tissue describes shape of cells– Squamous – cells wider than

tall (plate or “scale” like)

– Cuboidal – cells are as wide as tall, as in cubes

- Columnar – cells are taller than they are wide, like columns

Classifications of Epithelia

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Epithelial Tissue

• Simple squamous:• Single layer of flat cells• Substances pass easily through• Line air sacs• Line blood vessels• Line lymphatic vessels

• Simple cuboidal:• Single layer of cube-shaped cells• Line kidney tubules• Cover ovaries• Line ducts of some glands

(b)(a)

Free surfaceof tissue

Simplesquamousepithelium

Basement

Nucleus

Connectivetissue


b,d: © Ed Reschke

Nucleus

Basementmembrane


Simplecuboidalepithelium

Connectivetissue

Lumen

(a) (b)


b: © The McGraw-Hill Companies, Inc./Al Telser, photographer

Simple Squamous Epithelium

Figure 4.3a

Simple Cuboidal Epithelium

Figure 4.3b

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• Simple columnar:• Single layer of elongated cells• Nuclei usually near the basement• Membrane at same level• Sometimes possess cilia• Sometimes possess microvilli• Often have goblet cells• Line uterus, stomach, intestines

• Pseudostratified columnar:• Single layer of elongated cells• Nuclei at two or more levels• Appear striated• Often have cilia• Often have goblet cells• Line respiratory passageways

Nucleus

Basementmembrane

Microvilli(free surfaceof tissue)

Connectivetissue

Mucus

Cytoplasm

Goblet cell

(a) (b)


b: © The McGraw-Hill Companies, Inc./Al Telser, photographer.

(a) (b)

Cilia(free surfaceof tissue)

Goblet cell

Basementmembrane

Nucleus

Connectivetissue

Cytoplasm


b: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer

Epithelial Tissue

Simple Columnar Epithelium

Figure 4.3c

Pseudostratified Ciliated Columnar Epithelium

Figure 4.3d

• Contain two or more layers of cells

• Regenerate from below

• Major role is protection

• Are named according to the shape of cells at apical layer

Stratified Epithelial Tissue

• Specific types – Keratinized – contain the protective protein keratin

• Surface cells are dead and full of keratin

– Non-keratinized – forms moist lining of body openings

• Function– Protects underlying tissues in areas subject to abrasion

• Location – Keratinized – forms epidermis

– Non-keratinized – forms lining of esophagus, mouth, and vagina

Stratified Squamous Epithelium

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• Stratified squamous: • Many cell layers• Top cells are flat• Can accumulate keratin• Outer layer of skin• Line oral cavity, vagina, and anal canal

• Stratified cuboidal: • 2-3 layers• Cube-shaped cells• Line ducts of mammary glands, sweat glands, salivary glands, and the pancreas

Basementmembrane

Layer ofdividingcells

Connectivetissue


Squamouscells

(b)(a)



(a) (b)

Stratifiedcuboidalepithelium


Lumen

Basementmembrane

Connectivetissue

Nucleus


b: © The McGraw-Hill Companies, Inc./Al Telser, photographer.

Epithelial Tissue

Stratified Squamous Epithelium

Figure 4.3e

Stratified Cuboidal Epithelium

• Description– generally two layers

of cube-shaped cells

• Function– protection

• Location– Forms largest ducts

of sweat glands– Forms ducts of

mammary glands and salivary glands

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• Stratified columnar:• Top layer of elongated cells• Cube-shaped cells in deeper layers• Line part of male urethra and part of pharynx

• Transitional:• Many cell layers• Cube-shaped and elongated cells• Line urinary bladder, ureters, and part of urethra

(b)(a)

Lumen

Stratifiedcolumnarepithelium

Connectivetissue

Basementmembrane




Stretchedtransitionalepithelium

Basementmembrane

Underlyingconnective tissue

Basementmembrane

Underlyingconnective tissue

Unstretchedtransitionalepithelium

(b)(a)

(d)(c)




b,d: © Ed Reschke

Epithelial Tissue

Stratified Columnar Epithelium

• Description– several layers; basal

cells usually cuboidal; superficial cells elongated

• Function– protection and secretion

• Location – Rare tissue type– Found in male urethra

and vas deferens, largest ducts of salivary glands, nasopharynx

Figure 4.3h

Transitional Epithelium

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Glandular Epithelium

• Composed of cells that are specialized to produce and secrete substances

• There are two (2) types:• Endocrine glands are ductless (key word: hormone)• Exocrine glands have ducts

• Unicellular exocrine gland: • Composed of one cell • Goblet cell

• Multicellular exocrine gland: • Composed of many cells• Sweat glands, salivary glands, etc.• Simple and compound

Endocrine Glands

• Glands that do not have ducts or tubules and whose secretions are distributed throughout the body• Produce and secrete hormones into the bloodstream or the lymphatic system• Part of a complex, biochemical network known as the endocrine system

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Unicellular Exocrine Glands (The Goblet Cell)

• Goblet cells produce mucin

• Mucin + water mucus

• Protects and lubricates many internal body surfaces

Multicellular Exocrine Glands

• Have two basic parts– Epithelium-walled duct

– Secretory unit

• Classified by structure of duct– Simple

– Compound

• Categorized by secretory unit– Tubular

– Alveolar

– Tubuloalveolar

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Types of Glandular Secretions

• Merocrine Glands • Fluid product• Salivary glands• Pancreas gland • Sweat glands

• Apocrine Glands • Cellular product• Portions of cells• Mammary glands• Ceruminous glands

• Holocrine Glands• Secretory products• Whole cells• Sebaceous glands

(a) Merocrine gland (b) Apocrine gland (c) Holocrine gland

Secretion

Pinched offportion of cell(secretion)

Intactcell

Disintegrating celland its contents(secretion)

New cellforming bymitosis andcytokinesis


Multicellular Exocrine Glands

• Classified by structure (branching & shape) of duct

• Can also be classified by mode or type of secretion– Merocrine secretion – secretory vesicles

released via exocytosis (saliviary glands)– Apocrine secretion – apical portion of the

cell is lost, cytoplasm + secretory product (mammary glands)

– Holocrine secretion – entire cell is destroyed during secretion (sebaceous gland)

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Structural Types of Exocrine Glands

Duct

Secretory portion

Tissue surface

Simple tubular Simple branchedtubular

Simple branchedalveolar

Simple coiledtubular

Compound tubular Compound alveolar


May also be classified by types of secretions from exocrine glands

• Serous– mostly water but also contains some enzymes– Ex. parotid glands, pancreas

• Mucous– mucus secretions– Ex. sublingual glands, goblet cells

• Mixes– serous & mucus combined– Ex. submandibular gland

1 chapter 5 tissues – epithelial. 2 introduction similar cells with a common function are called...

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