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Copyright 2009, John Wiley & Sons, Inc.

Chapter 4

The Tissue Level of

Organization

BIOL 2210 : Dr. Yoga Sundram

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What is a Tissue?

A tissue is a group of cells

Common embryonic origin

Function together to carry out specialized

activities

Hard (bone), semisolid (fat), or liquid (blood)

Histology is the science that deals with the

study of tissues. Pathologist specialized in laboratory studies

of cells and tissue for diagnoses

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4 Types of Tissues

Epithelial Covers body surfaces and lines hollow organs,

body cavities, duct, and forms glands

Connective

Protects, supports, and binds organs. Stores energy as fat, provides immunity

Muscular

Generates the physical force needed to make body

structures move and generate body heat Nervous

Detect changes in body and responds by

generating nerve impulses

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Development of Tissues

Tissues of the body develop from three primary

germ layers:

Ectoderm, Endoderm, and Mesoderm

Epithelial tissues develop from all three germ

layers

All connective tissue and most muscle tissues

drive from mesoderm Nervous tissue develops from ectoderm

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Cell Junctions

Contact points between the

plasma membranes of

tissue cells

5 most common types:

Tight junctions

Adherens junctions

Desmosomes

Hemidesmosomes Gap junctions

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Tight Junctions

Web-like strands of

transmembrane proteins

Fuse cells together

Seal off passageways

between adjacent cells

Common in epithelial

tissues of the stomach,

intestines, and urinary

bladder

Help to retard the passageof substances between

cells and leaking into the

blood or surrounding

tissues

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Adherens Junctions

Dense layer of proteins calledplaque

Resist separation of cellsduring contractile activities

Located inside of the plasmamembrane attached to both

membrane proteins andmicrofilaments of thecytoskeleton

Transmembrane glycoproteinscalled cadherinsinsert into theplaque and join cells

In epithelial cells, adhesionbelts encircle the cell

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Desmosomes

Contain plaque andcadherins that extends intothe intercellular space toattach adjacent cells

together Desmosome plaque

attaches to intermediatefilaments that containprotein keratin

Prevent epidermal cells

from separating undertension and cardiacmuscles cells from pullingapart during contraction

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Hemidesmosomes

Resemble half of a

desmosome

Do not link adjacent cells

but anchor cells to thebasement membrane

Contains transmembrane

glycoprotein integrin

Integrins attach to

intermediate filamentsand the protein laminin

present in the basement

membrane

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Gap Junctions

Connect neighboring cellsvia tiny fluid-filled tunnelscalled connexons Contain membrane proteins

called connexins

Plasma membranes of gapjunctions are separated bya very narrow intercellulargap (space) Communication of cells

within a tissue

Ions, nutrients, waste,chemical and electricalsignals travel through theconnexons from one cell toanother

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Epithelial Tissues

Epithelial tissue consists of cells arranged in

continuous sheets, in either single or multiple layers

Closely packed and held tightly together

Covering and lining of the body Free surface

3 major functions:

Selective barrier that regulates the movement of materials

in and out of the body Secretory surfaces that release products onto the free

surface

Protective surfaces against the environment

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General Features of Epithelial Cells

Surfaces of epithelial cells differ in structure and

have specialized functions

Apical (free) surface

Faces the body surface, body cavity, lumen, or duct

Lateral surfaces

Faces adjacent cells

Basal surface

Opposite of apical layer and adhere to extracellular

materials

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General Features of Epithelial Cells

Basement membrane

Thin double extracellular layer that serves as the point of

attachment and support for overlying epithelial tissue

Basal lamina Closer to and secreted by the epithelial cells

Contains laminin, collagen, glycoproteins, and proteoglycans

Reticular lamina

Closer to the underlying connective tissue

Contains collagen secreted by the connective tissue cells

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Epithelial Cells

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Epithelial Tissues Own nerve supply

Avascularor lacks its own blood supply

Blood vessels in the connective tissue bring innutrients and eliminate waste

High rate of cell division for renew and repair

Numerous roles in the body (i.e. protection andfiltration)

Covering and lining epithelium Outer covering of skin and some internal organs

Glandular epithelium Secreting portion of glands (thyroid, adrenal, and sweat

glands)

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Covering and Lining Epithelium

Normally classified according to:

Arrangement of cells into layers

Shapes of cells

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Arrangement of cells in layers

Consist of one or more layers depending on function

Simple epithelium

Single layer of cells that function in diffusion, osmosis,filtration, secretion, or absorption

Pseudostratified epithelium

Appear to have multiple layers because cell nuclei at different

levels

All cells do not reach the apical surface

Stratified epithelium

Two or more layers of cells that protect underlying tissues in

areas of wear and tear

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Different Types of Covering and Lining

Epithelium Cells vary in shape depending on their

function

Squamous

Thin cells, arranged like floor tiles

Allows for rapid passage of substances

Cuboidal

As tall as they are wide, shaped like cubes or hexagons

May have microvilli

Function in secretion or absorption

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Different Types of Covering and Lining

Epithelium Columnar

Much taller than they are wide, like columns

May have cilia or microvilli

Specialized function for secretion and absorption Transitional

Cells change shape, transition for flat to cuboidal

Organs such as urinary bladder stretch to larger size

and collapse to a smaller size

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Simple Epithelium

Simple squamous epithelium

Simple cuboidal epithelium

Simple columnar epithelium (nonciliated and

ciliated)

Pseudostratified columnar epithelium (nonciliated

and cilated)

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Simple squamous epithelium

Single layer of cells that resembles a tiled floor on the

surface

Nucleus is centrally located and appears flattened oval or

sphere

Found at sites for filtration or diffusion

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Endothelium

The type of simple squamous that lines the heart,

blood vessels, and lymphatic vessels

Mesothelium

The type of epithelial layer of serous membranes

such as the pericardium, pleura, or peritoneum

Unlike other epithelial tissue, Both arederived from embryonic mesoderm

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Simple cuboidal epithelium

Cuboidal shaped cells

Cell nuclei round and centrally located

Found in thyroid gland and kidneys Functions in secretion and absorption

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Simple columnar epithelium

Column shaped cells

Oval nuclei at near base

Nonciliated and ciliated

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Nonciliated simple columnar epithelium

Contains columnar cells

with microvilli at their

apical surface and goblet

cells

Secreted mucus serves

as lubricant for the lining

of digestive, respiratory,

reproductive and urinary

tracts Also prevents the

destruction of the

stomach lining by acidic

gastric juices

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Ciliated simple columnar epithelium Columnar epithelial cells

with cilia at the apicalsurface

In respiratory tract,goblet cells areinterspersed amongciliated columnarepithelia

Secreted mucus on thesurface traps inhaledforeign particles.Beating cilia movesparticles to the throat forremoval by coughing,swallowing, or sneezing

Cilia also moves oocytesto the uterine tubes

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Pseudostratified columnar epithelium

Appears to have several layers due to nuclei are

various depths

All cells are attached to the basement membranein a single layer but some do not extend to the

apical surface

Ciliated cells secrete mucus and bear cilia

Nonciliated cells lack cilia and goblet cells

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Stratified Epithelium

Two or more layers of cells

Specific kind of stratified epithelium depends

on the shape of cells in the apical layer

Stratified squamous epithelium

Stratified cuboidal epithelium

Stratified columunar epithelium

Transitional epithelium

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Stratified Squamous Epithelium Several layers of cells that are flat in the apical layer

New cells are pushed up toward apical layer

As cells move further from the blood supply they dehydrate, harden,and die

Keratinized form contain the fibrous protein keratin

Found in superficial layers of the skin

Nonkeratinized form does not contain keratin

Found in mouth and esophagus

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Stratified Cuboidal Epithelium

Fairly rare type of epithelium

Apical layers are cuboidal

Functions in protection

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Stratified columnar epithelium

Also very uncommon

Columnar cells in apical layer only

Basal layers has shorten, irregular shaped cells

Functions in protection and secretion

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Transitional Epithelium

Found only in the urinary system Variable appearance

In relaxed state, cells appear cuboidal

Upon stretching, cells become flattened and appear

squamous

Ideal for hollow structure subjected to expansion

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Glandular Epithelium: Endocrine

Glands Secretions, called hormones, diffuse directly into the

bloodstream

Function in maintaining homeostasis

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Glandular Epithelium: Exocrine Glands

Secrete products into ducts that empty onto the surfaces ofepithelium

Skin surface or lumen of a hollow organ

Secretions of the exocrine gland include mucus, sweat, oil,

earwax, saliva, and digestive enzymes Examples of glands include sudoriferous (sweat) glands

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Structural Classification of Exocrine

Glands

Multicellular glands are categorized

according to two criteria:

Ducts are branched or unbranched

Shape of the secretory portion of the gland

Simple gland duct does not branch

Compound gland duct branches

Tubular glands have tubular secretory parts

Acinar glands have rounded secretory parts

Tubuloacinar glands have both tubular and rounded

secretory parts

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Structural Classification of Exocrine

Glands

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Functional Classification of Exocrine

Glands

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Connective Tissue

Most abundant and widely distributed tissues

in the body

Numerous functions

Binds tissues together

Supports and strengthen tissue

Protects and insulates internal organs

Compartmentalize and transport Energy reserves and immune responses

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Extracellular matrix of Connective

Tissue Extracellular matrix is the material located

between the cells

Consist of protein fibers and ground substance

Connective tissue is highly vascular

Supplied with nerves

Exception is cartilage and tendon. Both have little

or no blood supply and no nerves

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Cells and Fibers in Connective Tissue

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Connective Tissue Cells Fibroblasts

Secrete fibers and components of ground substance

Adipocytes (fat cells)

Store triglycerides (fat)

Mast cells

Produce histamine White blood cells

Immune response

Neutrophil and Eosinophils

MacrophagesEngulf bacteria and cellular debris by phagocytosis

Plasma cells

Secrete antibodies

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Connective Tissue Extracellular Matrix

Ground substance

Between cells and fibers

Fluid, semifluid, gelatinous, or calcified

Functions to support and bind cells, store water, and allow

exchange between blood and cells

Complex combination of proteins and polysaccharides

Fibers

Collagen fibers

Elastic fibers

Reticular fibers

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Classification of Connective Tissues

Embryonic connective tissue Mesenchyme and mucous connective tissue

Mature connective tissue Loose connective tissue

Areolar, adipose, and reticular

Dense connective tissue

Dense regular, dense irregular, and elastic

Cartilage

Hyaline, fibrocartilage, and elastic cartilage Bone tissue

Liquid connective tissue

Blood and lymph

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Embryonic Connective Tissue

Mesenchyme

Gives rise to all other connective tissues

Mucous (Whartons Jelly)

Found in umbilical cord of the fetus

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Loose Connective Tissue: Areolar

Connective Tissue

Most widely distributed in the body

Contains several types of cells and all three fibers

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Loose Connective Tissue: Adipose Tissue

Contains adipocytes Good for insulation and energy reserves

White (common) and brown adipose tissue

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Loose Connective Tissue: Reticular

Connective Tissue

Fine interlacing reticular fibers and cells

Forms the stroma of liver, spleen, and lymph nodes

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Dense Connective Tissue

Dense connec

tive

tissue

Contains numerous, thicker, and denser fibers

Packed closely with fewer cells than loose connective tissue

Dense regular connective tissue

Bundles of collagen fibers are regularly arranged in parallel

patterns for strength Tendons and most ligaments

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Types of Mature Connective Tissue:

Dense Irregular Connective Tissue Collagen fibers are usually irregularly arranged

Found where pulling forces are exerted in many directions

Dermis of skin and heart

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Dense Connective Tissue: Elastic

Connective Tissue Contain branching elastic fibers

Strong and can recoil to original shape after stretching

Lung tissue and arteries

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Types of Mature Connective Tissue:

Cartilage

Cartilage is a dense network of collagenfibers and elastic fibers firmly embedded inchondroitin sulfate

Chondrocytes Cartilage cells found in the spaces called lucunae

Perichondrium Covering of dense irregular connective tissue that

surrounds the cartilage

Two layers: outer fibrous layer and inner cellular layer

No blood vessels or nerves, exceptperichondrium

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Hyaline cartilage

Most abundant cartilage in the body

Surrounding by perichondrium (some exceptions like

articular cartilage)

Provide flexibility and support. Reduces friction

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Fibrocartilage Chondrocytes are scattered among bundles of collagen

fibers within the extracellular matrix Lack a perichondrium

Strongest type of cartilage

Found in intervertebral disc (between vertebrae)

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Elastic Cartilage

Chrondrocytes are located within a threadlike network of

elastic fibers

Perichondrium is present

Provides strength and elasticity

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Repair and Growth of Cartilage

Cartilage grows slowly

When injured or inflamed, repairs is slow due

to its avascular nature.

Two patterns of cartilage growth:

Interstitial growth

Growth from within the tissue

Appositional growth Growth at the outer surface of the tissue

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Bone tissue Bones are organs composed of several different

connective tissues: bone (osseous) tissue,periosteum, and endosteum.

Compact or spongy

Osteon or haversian system

Spongy bone lacks osteons. They have columns called

trabeculae

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Liquid Connective Tissue

Blood tissue

Connective tissue with liquid extracellular matrix called blood

plasma

Lymph

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Membranes

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Epithelial Membranes

Mucous membranes

Lines a body cavity that opens directly to the

exterior

Epithelial layer is important for the bodys defenseagainst pathogens

Connective tissue layer is areolar connective

tissue and is called lamina propria

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Epithelial Membranes

Serous membranes orserosa

Lines a body cavity that does not open directly to

the exterior. Also covers the organs that lie within

the cavity Consist of areolar connective tissue covered by

mesothelium (simple squamous epithelium) that

secrete a serous fluid for lubrication

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Epithelial membranes: Mucous

Membranes

Membranes are flat sheets of pliable tissue

that cover or line a part of the body

Epithelial membranes are a combination of

an epithelial layer and an underlyingconnective tissue layer

Mucous, Serous, and Cutaneous membranes

Synovial membranes Lines joints and contains connective tissue but not

epithelium

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Muscular Tissue

Consists of elongated cells called muscle

fibers or myocytes

Cells use ATP to generate force

Several functions of muscle tissue

Classified into 3 types: skeletal, cardiac,and

smooth musculartissue

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Skeletal Muscle Tissue

Attached to bones of the skeleton

Have striations

Voluntary movement or contractions by conscious control

Vary in length (up to 40 cm) and are roughly cylindrical in

shape

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Cardiac Muscular Tissue

Have striations

Involuntary movement or contraction is not consciously

controlled

Intercalated disc unique to cardiac muscle tissue

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Smooth Muscle Tissue

Walls of hollow internal structures

Blood vessels, airways of lungs, stomach, and intestines

Nonstriated

Usually involuntary control

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Nervous Tissue

Consists of two principle types of cells

Neurons or nerve cells

Neuroglia

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Excitable Cells

Neurons and muscle fibers

Exhibit electrical excitability

The ability to respond to certain stimuli by

producing electrical signals such as actionpotentials

Actions potentials propagate along a nerve or

muscle plasma membrane to cause a response

Release of neurotransmitters

Muscle contraction

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Tissue Repair: Restoring Homeostasis

When tissue damage is extensive both

stroma and parenchymal cells are active in

repair

Fibroblast divide rapidly

New collagen fibers are manufactured

New blood capillaries supply materials for healing

All of these process create an activelygrowing connective tissue called granulation

tissue

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Aging and Tissues

Tissue heal faster in young adults

Surgery of a fetus normally leaves no scars

Young tissues have a better nutritional state,

blood supply, and higher metabolic rate Extracellular components also changes with

age

Changes in the bodys use of glucose,collagen, and elastic fibers contribute to theaging process

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End of Chapter 4

Copyright 2009 John Wiley & Sons, Inc.All rights reserved. Reproduction or translation of thiswork beyond that permitted in section 117 of the 1976United States Copyright Act without express permission

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