chapter 4 the tissue level of organization

Copyright 2009, John Wiley & Sons, Inc.

Chapter 4

The Tissue Level of

Organization


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


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


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


Cell Junctions

Contact points between the

plasma membranes of

tissue cells

5 most common types:

Tight junctions

Adherens junctions

Desmosomes

Hemidesmosomes

Gap junctions


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 passage

of substances between

cells and leaking into the

blood or surrounding

tissues


Adherens Junctions

Dense layer of proteins called plaque

Resist separation of cells during contractile activities

Located inside of the plasma membrane attached to both membrane proteins and microfilaments of the cytoskeleton

Transmembrane glycoproteins called cadherins insert into the plaque and join cells

In epithelial cells, adhesion belts encircle the cell


Desmosomes

Contain plaque and cadherins that extends into the intercellular space to attach adjacent cells together

Desmosome plaque attaches to intermediate filaments that contain protein keratin

Prevent epidermal cells from separating under tension and cardiac muscles cells from pulling apart during contraction


Hemidesmosomes

Resemble half of a

desmosome

Do not link adjacent cells

but anchor cells to the

basement membrane

Contains transmembrane

glycoprotein integrin

Integrins attach to

intermediate filaments

and the protein laminin

present in the basement

membrane


Gap Junctions

Connect neighboring cells via tiny fluid-filled tunnels called connexons Contain membrane proteins

called connexins

Plasma membranes of gap junctions are separated by a very narrow intercellular gap (space) Communication of cells

within a tissue

Ions, nutrients, waste, chemical and electrical signals travel through the connexons from one cell to another


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


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


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


Epithelial Cells


Epithelial Tissues

Own nerve supply

Avascular or lacks its own blood supply

Blood vessels in the connective tissue bring in nutrients and eliminate waste

High rate of cell division for renew and repair

Numerous roles in the body (i.e. protection and filtration)

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

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

glands)


Covering and Lining Epithelium

Normally classified according to:

Arrangement of cells into layers

Shapes of cells



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


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


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


Simple Epithelium

Simple squamous epithelium

Simple cuboidal epithelium

Simple columnar epithelium (nonciliated and

ciliated)

Pseudostratified columnar epithelium (nonciliated

and cilated)


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



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 are

derived from embryonic mesoderm


Simple cuboidal epithelium

Cuboidal shaped cells

Cell nuclei round and centrally located

Found in thyroid gland and kidneys

Functions in secretion and absorption


Simple columnar epithelium

Column shaped cells

Oval nuclei at near base

Nonciliated and ciliated


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


Ciliated simple columnar epithelium

Columnar epithelial cells with cilia at the apical surface

In respiratory tract, goblet cells are interspersed among ciliated columnar epithelia

Secreted mucus on the surface traps inhaled foreign particles. Beating cilia moves particles to the throat for removal by coughing, swallowing, or sneezing

Cilia also moves oocytes to the uterine tubes



Pseudostratified columnar epithelium

Appears to have several layers due to nuclei are

various depths

All cells are attached to the basement membrane

in 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


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


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


Stratified Cuboidal Epithelium

Fairly rare type of epithelium

Apical layers are cuboidal

Functions in protection


Stratified columnar epithelium

Also very uncommon

Columnar cells in apical layer only

Basal layers has shorten, irregular shaped cells

Functions in protection and secretion


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


Glandular Epithelium: Endocrine

Glands

Secretions, called hormones, diffuse directly into the

bloodstream

Function in maintaining homeostasis


Glandular Epithelium: Exocrine Glands

Secrete products into ducts that empty onto the surfaces of

epithelium

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


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


Structural Classification of Exocrine

Glands


Functional Classification of Exocrine

Glands


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


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


Cells and Fibers in Connective Tissue


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

Macrophages

Engulf bacteria and cellular debris by phagocytosis

Plasma cells

Secrete antibodies


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


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


Embryonic Connective Tissue

Mesenchyme

Gives rise to all other connective tissues

Mucous (Wharton’s Jelly)

Found in umbilical cord of the fetus


Loose Connective Tissue: Areolar

Connective Tissue

Most widely distributed in the body

Contains several types of cells and all three fibers


Loose Connective Tissue: Adipose Tissue

Contains adipocytes

Good for insulation and energy reserves

White (common) and brown adipose tissue


Loose Connective Tissue: Reticular

Connective Tissue

Fine interlacing reticular fibers and cells

Forms the stroma of liver, spleen, and lymph nodes


Dense Connective Tissue

Dense connective 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


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


Dense Connective Tissue: Elastic

Connective Tissue

Contain branching elastic fibers

Strong and can recoil to original shape after stretching

Lung tissue and arteries


Types of Mature Connective Tissue:

Cartilage

Cartilage is a dense network of collagen fibers and elastic fibers firmly embedded in chondroitin sulfate

Chrondrocytes Cartilage cells found in the spaces called lucunae

Pericondrium Covering of dense irregular connective tissue that

surrounds the cartilage

Two layers: outer fibrous layer and inner cellular layer

No blood vessels or nerves, except pericondrium


Hyaline cartilage

Most abundant cartilage in the body

Surrounding by perichondrium (some exceptions like

articular cartilage)

Provide flexibility and support. Reduces friction


Fibrocartilage

Chondrocytes are scattered among bundles of collagen

fibers within the extracellular matrix

Lack a perchondrium

Strongest type of cartilage

Found in intervertebral disc (between vertebrae)


Elastic Cartilage

Chrondrocytes are located within a threadlike network of

elastic fibers

Pericondrium is present

Provides strength and elasticity


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


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


Liquid Connective Tissue

Blood tissue

Connective tissue with liquid extracellular matrix called blood

plasma

Lymph


Membranes


Epithelial Membranes

Mucous membranes

Lines a body cavity that opens directly to the

exterior

Epithelial layer is important for the body’s defense

against pathogens

Connective tissue layer is areolar connective

tissue and is called lamina propria


Epithelial Membranes

Serous membranes or serosa

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


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 underlying

connective tissue layer

Mucous, Serous, and Cutaneous membranes

Synovial membranes

Lines joints and contains connective tissue but not

epithelium


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 muscular tissue


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


Muscular Tissue

Cardiac muscle tissue

Have striations

Involuntary movement or contraction is not consciously

controlled

Intercalated disc unique to cardiac muscle tissue


Smooth Muscle Tissue

Walls of hollow internal structures

Blood vessels, airways of lungs, stomach, and intestines

Nonstriated

Usually involuntary control


Nervous Tissue

Consists of two principle types of cells

Neurons or nerve cells

Neuroglia


Excitable Cells

Neurons and muscle fibers

Exhibit electrical excitability

The ability to respond to certain stimuli by

producing electrical signals such as action

potentials

Actions potentials propagate along a nerve or

muscle plasma membrane to cause a response

Release of neurotransmitters

Muscle contraction


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 actively

growing connective tissue called granulation

tissue


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 body’s use of glucose, collagen, and elastic fibers contribute to the aging process


End of Chapter 4

Copyright 2009 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of theses programs or from the use of the information herein.

chapter 4 the tissue level of organization

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