The Tissue Level of Organization

Chapter 3

Tissue

• Definition – an aggregation of cells in which each cooperates with all others in the performance of a given function

• Examples of general functions– Movement– Protection– Support– Production of chemicals

Principal Tissue Types

• Epithelial

• Connective

• Muscular

• Nervous

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Epithelial Tissue• Functions

– Coverings and linings– Forms glands

• Characteristics– Closely packed cells – Basement membrane– Nerves– Avascular– Cell growth and

replacement by mitosis

• Classification– Simple or stratified– Squamous, cuboidal,

columnar, or transitional

Epithelia of Coverings and Linings

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Squamous Epithelium

• Simple Squamous Epithelium– Highly adapted to

diffusion, osmosis, & filtration

• Stratified Squamous Epithelium– Surface layer is flat– Function -

protection

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Cuboidal Epithelium• Simple cuboidal

epithelium• Lines glands and

their ducts• Function –

secretion and absorption

• Stratified Cuboidal epithelium– Surface layer cube-

shaped– Function –

protection

Transitional Epithelium

• Can be stretched

• Lines hollow structures that expand

• Function – prevents rupture of organ

http://www.mhhe.com/biosci/ap/histology_mh/stratepi.html

Human Anatomy, 3rd editionPrentice Hall, © 2001

Columnar Epithelia

• Simple columnar epithelium– Functions –

protection, absorption, secretion

• Stratified columnar epithelium– Surface layer is

column-shaped– Function – protection

Pseudostratified Columnar Epithelium

• Appear stratified but all cells connect to the basal lamina

• Functions – protection, secretion

http://bioweb.uwlax.edu/zoolab/Table_of_Contents/Lab-1b/Pseudostratified_Model_1/pseudostratified_model_1.htm

Glandular Epithelium• Gland – 1 or more cells

– Unicellular gland – goblet cell– Multicellular – secretory sheets or groups of

cells• Serous

• Mucous

• Mixed

• Function – secretion

• Types– Exocrine – to surface or ducts – Endocrine – to blood

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Mechanisms of Glandular Secretion

• Merocrine– Secretion is released

by exocytosis

• Apocrine– Secretion is released

by pinching off of vesicles

• Holocrine– Secretion is released

by entire cell bursting

Connective Tissue

• Most abundant tissue

• Functions are varied

• Characteristics– Specialized cells, widely scattered– Rich blood supply– Much matrix

• Extracellular fibers

• Ground substance

Human Anatomy, 3rd editionPrentice Hall, © 2001

Classification of Connective Tissues• Embryonic

– Mesenchymal cells

• Adult connective tissues

Human Anatomy, 3rd editionPrentice Hall, © 2001

Embryonic Connective Tissues

Cell Types Found in Connective Tissue

• Fibroblasts– Secrete the molecules that form the matrix– Fixed cells

• Fibrocytes

• Macrophages– “Big eaters”– May be fixed or wandering

Additional Connective Tissue Cells• Adipocytes

– Fixed fat cells• Mesenchymal cells

– Fixed cells that can divide (mitosis) to replace damaged connective tissue

• Melanocytes– Fixed cells that store melanin

• Lymphocytes– Wandering immune system cells

• Mast cells– Around blood vessels– Wandering cells that produce histamine & heparin

Connective Tissue Fibers• Collagen fibers

– Most common type– White– Strong, ropelike– Form ligaments, tendons

• Reticular fibers– Thin– Woven into rough, flexible network

• Elastic fibers– Yellow– Thin– Stretch

• Contain elastin

Ground Substance

• Extracellular fluid in connective tissue– Water– Glycoproteins

Types of Connective Tissue

Human Anatomy, 3rd editionPrentice Hall, © 2001

Loose (Areolar) Connective Tissue• Fibers not abundant• Contains all 3 types of fibers• Examples of locations

– Between skin and muscles

– Around digestive tract

– Around blood vessels

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Adipose Tissue

• Most of the volume is adipocytes• Provides padding, slows heat loss, food reserve• Locations

– Wherever there is loose connective tissue

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Reticular Tissue• Reticular fibers form a strong network• Provides strength and support• Forms the framework (stroma) of many organs• Binds together cells of smooth muscle

Dense Connective Tissue

• Types– Dense Regular Connective Tissue– Dense Irregular Connective Tissue– Elastic Connective Tissue

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Dense Regular Connective Tissue• Lots of collagen fibers in bundles• Cells – fibroblasts in rows between bundles• Examples

– Tendons, ligaments

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Dense Irregular Connective Tissue

• Tensions in various directions

• Occurs in sheets• Locations

– Periosteum

– Perichondrium

– Fibrous capsules of some organs

– Fasciae

– Dermis

Human Anatomy, 3rd editionPrentice Hall, © 2001

Elastic Tissue• Lots of elastic fibers• Fibroblasts in spaces between fibers• Provides stretch and strength

Cartilage

• Dense network of collagenous fibers & elastic fibers in a gel-like substance

• Cells – chondrocytes in lacunae– Chondroblasts

• Perichondrium – surrounds surface of cartilage

• Growth– Interstitial growth– Appositional growth

Growth of Cartilage

Types of Cartilage

• Hyaline cartilage

• Fibrocartilage

• Elastic cartilage

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Hyaline Cartilage

• Most common• Provides

flexibility and support

• Locations– Ends of bones

– Trachea

– Larynx

– Embryonic skeleton

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Fibrocartilage• Visible collagenous fibers with scattered chondrocytes• Provides strength and rigidity• Locations

– Intervertebral discs

– Symphysis pubis

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Elastic Cartilage• Threadlike network of elastic fibers with chondrocytes• Provides strength and maintains shape• Locations

– Pinna

– Eustacian tube

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Bone

• Solid matrix • Cells

– Osteocytes in lacunae

– Osteoblasts

– Osteoclasts

• Periosteum surrounds surface of bone

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Blood• Functions

– Transport medium

– Regulation

– Protection

• Composition– Plasma – fluid

– Formed elements – cells & cell fragments

• Erythrocyte

• Leukocyte

• Thrombocyte

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A Red Blood Cell

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SEM of RBCs

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Membranes

• Epithelial layer + underlying connective tissue = epithelial membrane

• Types– Mucous membrane

– Serous membrane

– Cutaneous membrane

– Synovial membrane

Fascia

• Fascia – collective term for sheets of connective tissue

• Functions– Provide strength and stability– Maintain positions of internal organs– Provide a route for the distribution of blood

vessels, lymphatics, and nerves

• 3 types

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Types of Fascia• Superficial Fascia

– Adipose tissue and loose connective tissue

– Immediately deep to the skin

• Deep Fascia– Dense connective

tissue– Strong internal

framework• Subserous Fascia

– Loose connective tissue

– Between deep fascia and serous membranes

Muscular Tissue

• Specialized cells

• Function - contraction

• 3 types– Skeletal muscle– Cardiac muscle– Smooth muscle

Human Anatomy, 3rd editionPrentice Hall, © 2001

Skeletal Muscle• Connected to bones• Striated• Multinucleated• Voluntary

Human Anatomy, 3rd editionPrentice Hall, © 2001

Cardiac Muscle• Found in the heart• Striations• Intercalated discs• Involuntary

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Smooth Muscle• Found in walls of internal organs• Nonstriated• Involuntary

Human Anatomy, 3rd editionPrentice Hall, © 2001

Nervous Tissue• Specialized cells• Function – conduction of electrical impulses• Cells

– Neurons– Neuroglia