copyright © 2010 pearson education, inc. tissues part i by the end of this lecture you will: be...

Copyright © 2010 Pearson Education, Inc.

Tissues Part I

• By the end of this lecture you will:

• Be able to define what a tissue is and the role tissues play in A&P

• Be able to describe and distinguish between the main categories of epithelial tissue


Tissues

• The study of tissues is known as __________?


Tissues

• The study of tissues is known as Histology.

• Histologists describe cells by their appearance:

• The size and shape of the cells

• How the cells are arranged in tissues (layers, scatterd, etc.)

• How the cells are connected to each other

• The amount of extracellular (EC) material in the tissue


Tissues

• Groups of cells similar in structure and function

• Types of tissues- 4 types in the human body

• 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


Epithelial Tissue (Epithelium)

• Epi (upon) thele (nipple)

• Protect and separate the internal and external environment of the organism

• Regulate exchange of materials between the internal and external environment

• What type of materials?



• Epi (upon) thele (nipple)

• Protect and separate the internal and external environment of the organism

• Regulate exchange of materials between the internal and external environment

• What type of materials?

• Any substance that enters or exits the body must cross an epithelium

• Significance- (disease, nutrition, homeostasis?)



• Two main types (by location):

1. Sheets of tissue covering and lining epithelia

• On external and internal surfaces and the lumen of hollow organs

2. Glandular (secretory) epithelia

• Secretory tissue in glands

• Synthesize and release substances into the EC space


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 (or basement membrane) made of glycoprotein and collagen lies adjacent to basal surface


Characteristics of Epithelial Tissue

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 (what does this mean?)

5. High rate of regeneration (why?)


Classification of Epithelia

• When classifying Epithelia, you need to ask two questions:

1. How many layers?

2. What type of cell?



• When classifying Epithelia, you need to ask two questions:

1. How many layers?

1 = Simple epithelium

>1 = Stratified epithelium

Copyright © 2010 Pearson Education, Inc. Figure 4.2a

?

? _______ surface

_____ surface

______ surface

_____ surface

(a) Classification based on number of cell layers.


Stratified

Simple

Apical surface

Basal surface

Apical surface

Basal surface

(a) Classification based on number of cell layers.



2. What type of cell?

• Squamous

• Cuboidal

• Columnar

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

Copyright © 2010 Pearson Education, Inc. Figure 4.2b

?

?

?(b) Classification based on cell shape.


Squamous

Cuboidal

Columnar(b) Classification based on cell shape.


Overview of Epithelial Tissues

• Additionally, there are 5 functional types of Epithelia:

• Exchange

• Transporting

• Ciliated

• Protective

• Secretory


Exchange Epithelial Tissues

• Exchange Epithelia

• Composed of simple, squamous layer that allows gases to pass rapidly across the epithelium (what gases do you think?)

• Found in the lungs, heart, blood vessels,

• The lining of heart and blood vessels is also called the Endothelium


Transporting Epithelial Tissues

• Transporting Epithelia

• Composed of simple, cuboidal or columnar layer

• Selectively and actively regulates the exchange of ions and nutrients between internal and external environments- shaped by needs and hormones

• Found in the kidneys and digestive system

• The lumen of each is exposed to the external environment


Transporting Epithelial Tissues

• Transporting Epithelia Characteristics:

• Cell Shape- thicker than exchange epithelia, though still one cell thick- columnar and cuboidal

• Membrane Modifications- large surface area on apical side (what structures?)

• Cell Junctions- Adjacent cells are tightly attached to each other (why?) –Materials must go through cells, rather than around

• Organelles- most need numerous mitochondria for energy requirements (why?)


Ciliated Epithelial Tissues

• Ciliated Epithelia

• Composed of simple, cuboidal or columnar layer

• Apical side contains cilia to move fluid across cell and tissue surface

• Found in the respiratory system and parts of female reproductive system


Protective Epithelial Tissues

• Protective Epithelia

• Composed of stratified layers- squamous in top layers, thicker in bottom layers

• Toughened by protein keratin (same protein found in hair and nails)

• Found in the epidermis (system?), and linings of mouth, pharynx (location?), esophagus, urethra, and vagina


Protective Epithelial Tissues

• Protective Epithelia

• Cells have short life span and are replaced by newer cells from deeper layers

• Why? Functionally, is this important?


Secretory Epithelial Tissues

• Secretory Epithelia

• Secrete a substance outside the cell

• Scattered throughout epithelia, or grouped to form glands

• Two main types:

• Exocrine

• Endocrine




• Exocrine:

• Release secretions to external environment through ducts

• Skin surface, lumen, etc.

• Can be harmful to life- stomach acid, digestive enzymes,

• Or beneficial- breast milk

• Sweat, salivary, and mammary glands, liver, pancreas, goblet cells




• Endocrine:

• Ductless glands

• Release secretions (hormones) to internal environment through blood and lymph

• Which type of glandular tissue is more common, Exocrine or Endocrine?


Overview of Epithelial Tissues

• For each of the following types of epithelia, note:

• Description

• Function

• Location


(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


Epithelia: Simple Squamous

• Two other locations

• Endothelium

• The lining of lymphatic vessels, blood vessels, and heart

• Mesothelium

• The epithelium of serous membranes in the ventral body cavity


(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 someglands; ciliated variety lines small bronchi, uterine tubes, and some regionsof the uterus.

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

Simplecolumnarepithelialcell

Basementmembrane

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

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


Epithelia: Stratified Cuboidal

• Quite rare in body

• Found in some sweat and mammary glands

• Typically two cell layers thick


Epithelia: Stratified Columnar

• 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


Glandular (Secretory) 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


Unicellular Exocrine Glands

• The only important unicellular gland is the goblet cell

• Cell that produces and secretes mucous

• Glycoproteins & Proteoglycans


(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)


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)

• Apocrine

• Products are secreted by a partial rupture of the apical cell surface (active in armpits, groin areas after puberty


Review Questions

• It is observed that the smoke from cigarettes and other tobacco products can paralyze cilia. From this observation, what tissue(s) will be most affected by the smoke, and what consequences could this have?

•What characteristics might you find on or in cells whose main function is absorption?

•What are Goblet cells and in what type of tissue will you most likely find them? Where is this tissue most common in the human body?

copyright © 2010 pearson education, inc. tissues part i by the end of this lecture you will: be...

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