Chapter 3--Tissues

Biology 110

Tri-County Technical College

Pendleton, SC

Definition and Types

Tissue is group of cells that are “similar” in structure and function

There are four primary tissue types in the human body: Epithelium Connective Nervous Muscle

Epithelial Tissue Function

Is the lining, covering, and glandular tissue of the body

Functions include: Protection, absorption, filtration, and secretion

Epithelium has some special characteristics Cells fit close together to form continuous

sheets Neighboring cells bound together by cell

junctions including desmosomes and tight junctions

Epithelial Functions, ctd.

Membranes all have ONE free (unattached) surface or edge This apical surface exposed to body’s exterior

or to cavity of internal organs May be slick/smooth or covered with

microvilli or cilia Lower surface rests on BASEMENT

MEMBRANE-structureless material secreted by cells

Epithelial cells have NO blood supply of their own (avascular)-depend on diffusion from capillaries in underlying connective tissue

Classifying Epithelium (layering)

Each epithelium is given two names First indicates relative number of cell

layers it has Second describes the shape of its cells SIMPLE is composed of only ONE layer

of cells STRATIFIED is composed of MORE than

one cell layer Stratified named for cells at free surface and

NOT those resting on basement membrane

Epithelium Classification, ctd.

SQUAMOUS epithelium cells are flattened like fish scales

CUBOIDAL epithelium cells are cube-shaped like dice

COLUMNAR epithelium cells are shaped like columns

Terms describing arrangement and shape are combined to describe epithelium fully

Use arrangement name first and shape name second

Simple Squamous Single layer of thin squamous cells resting

on basement membrane Usually forms membranes where filtration

or exchange of substances by rapid diffusion occurs

Composes air sacs of lungs, walls of capillaries, and the SEROUS MEMBRANES (serosae), the slick membranes that line ventral body cavities and cover organs in that cavity

Simple Cuboidal

ONE layer of cuboidal cells resting on BM Common in glands and their ducts

Salivary glands and pancreas for examples Forms wall of kidney tubules and covers

surface of the ovaries

Simple Columnar ONE layer of columnar cells resting on BM Tall cells that fit closely together Specialized for absorption and secretion GOBLET CELLS often found in this

epithelium type—produce lubricating mucus Line entire digestive tract from stomach to

anus Epithelial membranes that line body cavities

open to body exterior called MUCOSAE or mucous membranes

Pseudostratified Columnar All pseudostratified columnar epithelium

cells rest on basement membrane Some shorter than others and their nuclei

appear at different heights above BM Results in psuedo (false) impression that its

stratified Specialized for absorption and secretion Ciliated variety lines most of respiratory

tract Mucus produced by GC traps dust/debris

and cilia propel mucus upward away from lungs

Stratified Squamous Most common stratified epithelium in body Cells close to edge are squamous whereas

cells close to BM are cuboidal/columnar Usually consists of several layers of cells Found in sites that receive abuse or friction Esophagus, mouth, and outer portion of

skin

Stratified Cuboidal & Columnar

Stratified Cuboidal usually 2 layers thick Found along ducts of sweat glands and

larger ducts of mammary glands Stratified Columnar basal cells vary in size

and shape Provides protection along portions of

pharynx, epiglottis, urethra, anus, salivary gland ducts, and along few large excretory ducts

Both are fairly rare in the human body

Transitional Epithelium

Is highly modified stratified squamous epithelium that forms lining of only few organs

Found in urinary bladder, ureters, and part of urethra

Found where “stretching” is necessary Basal cells are cuboidal/columnar while those at

surface vary in appearance Ability of cells to “slide past” each other and

change shape allows “stretching” Ureter wall/urethra/urinary bladder…enough said

Glandular Epithelium Gland consists of one or more cells that

make/secrete particular product (secretion) Usually proteins in aqueous fluid

Two major types of glands form from epithelial sheets

ENDOCRINE glands lose connection to surface; called “ductless glands” Their secretions (hormones) diffuse directly

in blood vessels that run through the glands THYROID, ADRENALS, PITUITARY,

ETC.

Glandular Epithelium, ctd. EXOCRINE glands retain their ducts and

their secretions empty through ducts to epithelial surface

Glands located both internally/externally Sweat and oil glands Liver and pancreas (be careful with

pancreas, it also has endocrine function)

Connective Tissue Overview

Connects body parts and is most abundant and widely distributed of tissue types

Connective tissue has some common characteristics

Most are well vascularized (good blood supply) but there are exceptions Tendons and ligaments have poor blood

supply Cartilages are avascular

As result, these structures heal very slowly (if at all) when injured

CT Overview, ctd. Connective tissues composed of many different cell

types plus varying amounts of nonliving substances found outside cells called EXTRACELLULAR MATRIX Is what makes connective tissue so different

Matrix produced by CT cells and secreted to exterior May be liquid, semisolid/gel-like, or very hard

Because of EC matrix, CT able to stand stretching and other abuses (abrasion) that no other tissue could endure

As always, there are exceptions

CT Overview, ctd. Fat tissue (adipose) mostly cells with soft

EC matrix Bone and cartilage tissue has very few cells

and large amounts of hard EC matrix which makes them very strong

Various types/amounts of fibers deposited in and form part of EC matrix

Collagen (white) fibers, Elastic (yellow) fibers, and Reticular (fine collagen) fibers Made by CT cells and secreted to outside

CT Overview, ctd. Connective tissue performs many

functions: Protecting, Supporting, & Binding together other body tissues

All CT consist of living cells surround by a matrix

Their major differences reflecdt fiber type and number of fibers in their matrix

From the overview to the specific-let us discuss the Connective Tissue

Bone Tissue Often called “osseous tissue” Composed of bone cells in cavities called

LUCUNAE Surrounded by layers of very hard matrix

containing calcium salts and large numbers of collagen fibers

Because of this hardness, bone has exceptional ability to protect/support other body organs

Hyaline Cartilage Less hard and more flexible than bone Hyaline cartilage is most widespread Has abundant collagen fibers hidden by

rubbery matrix with blue-white appearance Forms supporting structures of larynx

(voice box), attaches ribs to breastbone, and covers ends of bones where they form joints

**skeleton of fetus made of hyaline cartilage

More Cartilage…Yeah!!

ELASTIC cartilage found where structure with elasticity desired Supports external ear

FIBROCARTILAGE highly compressable Forms cushionlike disks between vertebrae of

spinal column

Dense Fibrous Tissue Also known as Dense Connective Tissue Has collagen fibers as main matrix Crowded between collagen fibers are rows of

FIBROBLASTS (fiber-forming cells) Forms strong, ropelike structures such as tendons

and ligaments TENDONS attach skeletal muscles to bone Ligaments connect bone to bone at joints

More stretchy/contains more elastic fibers

Makes up lower layers of skin (arranged in sheets)

Areolar Tissue

Also known as Loose Connective tissue & is most widely distributed CT variety

Soft & pliable tissue that cushions/protects body organs it wraps

Functions as universal packing tissue and “glue” because it helps hold internal organs together and in their proper positions

Soft layer of areolar tissue (LAMINA PROPRIA) underlies all mucous membranes

Areolar Tissue, ctd. Fluid matrix contains all types of fibers in

loose network Provides reservoir of water and salts for

surrounding tissues **Essentially all body cells obtain their

nutrients from and release their wastes into this “tissue fluid”

When body region inflamed, areolar tissues in area soak up excess fluid like sponge and area swells and becomes puffy This condition is called EDEMA

Adipose Tissue

Is an areolar tissue in which fat cells predominate Glistening drop of fat occupies most of cell’s

volume Often called “signet ring cells” Forms subcutaneous tissue beneath skin

Insulates body Protects some organs individually Kidneys surrounded by capsule of fat; cushions

eyeballs in sockets

Fat “depots” in body (hips/breasts) store fat (fuel)

Reticular Connective Tissue

Consists of delicate network of interwoven reticular fibers associated with RETICULAR CELLS which resemble fibroblasts

Limited to certain sites Forms STROMA (bed/mattress) which is internal

supporting framework Stroma can support many free blood cells (mostly

lumphocytes) in lymph organs such as lymph nodes, spleen, and bone marrow

Blood Connective Tissue Blood (vascular tissue) composed of blood

cells surrounded by nonliving matrix (blood plasma)

Fibers are soluble protein molecules that become visible only during blood clotting

Transport vehicle for cardiovascular system

Carries nutrients, wastes, respiratory gases, and many other substances throughout body

Nervous Tissue Functional unit is the NEURON Neurons receive and conduct electrochemical

impulses from one part of body to another IRRITABILITY and CONDUCTIVITY are two

major functions of nervous tissue Neurons may be quite long (up to 3 feet) because

cytoplasm may be drawn out into extensions Neurons along with supporting cells (called glial

or neuroglial cells that insulate, support, and protect neurons) make up structures of nervous system Brain, spinal cord, and nerves

Muscle Tissue Overview Highly specialized to contract (shorten) Muscle cells elongated to provide long axis

for contraction Called muscle “fibers”

Three types of muscle tissue SKELETAL, CARDIAC, and SMOOTH

Skeletal Muscle, and more…

Packaged by connective tissue sheets into organs called skeletal muscles which are attached to skeleton

Can be controlled voluntarily and form flesh of body (word of caution here)

When contract, they pull on bones or skin Result is body movement of change in facial

expressions Cells are long, cylindrical, and

multinucleate Have obvious striations (stripes)

That’s the beat of a heart…

Cardiac muscle found only in the heart Has striations, uninucleate, branching cells

that fit tightly together at junctions called INTERCALATED DISKS

Contain gap junctions that allow ions to free pass from cell to cell

Results in rapid conduction of exciting electrical impulse across heart

Involuntary/not under conscious control

Smooth Muscle Tissue Also called VISCERAL muscle because NO

striations are visible Spindle shaped cells with single nucleus Found in walls of hollow organs (stomach,

bladder, uterus, and blood vessels) When contracts, cavity of organ constricts or

dilates so that substances are propelled through organ along specific pathway

Contracts much more slowly than skeletal/cardiac PERISTALSIS is wavelike motion that keeps

food moving through small intestine (typical of smooth muscle tissue)

Tissue Repair Tissue injury stimulates body’s inflammatory and

immune responses and healing process begins almost immediately

Tissue repair (wound healing) occurs in 2 major ways

REGENERATION is replaced of destroyed tissue by the same kind of cell

FIBROSIS involves repair by dense (fibrous) CT; i.e., formation of SCAR tissue

Which of these occurs depends on TYPE of tissue damaged and SEVERITY of injury

Tissue Repair, ctd. Clean cuts (incisions) heal more

successfully that ragged tears (lacerations) Tissue injury triggers series of events CAPILLAIRES become very permeable

allowing fluids rich in clotting proteins to seep into injured area

Leaked clotting proteins form clot, stopping blood loss, holds edges of wound together, and seals off damaged area Prevents bacteria (other harmful stuff) from

spreading to surrounding tissues

Tissue Repair, ctd. Clot exposed to air, dries and hardens to

form scab GRANULATION tissue next phase

Delicate, pink tissue composed largely of capillaries that grow into damaged area

Capillaries are delicate and bleed freely Also contains phagocytes and connective

tissue cells (fibroblasts) that synthesize collagen fibers (scar tissue) to permanently bridge the gap

Tissue Repair, ctd.

Surface epithelium begins to regenerate and cover granulation tissue beneath scab

Final result is fully regenerated surface epithelium that covers area of fibrous scar

Scar is either invisible or visible as white line depending on severity of wound

Epithelial tissues such as skin epidermins, mucous membranes, and fibrous connective tissue regenerate beautifully

Tissue Repair, ctd. Skeletal muscle regenerates poorly, if at all Cardiac and nervous tissue replaced only

by SCAR tissue Scar tissue is strong but lacks flexibility of

more normal tissues Is unable to perform normal functioning of

tissue it replaces May hamper functioning of an organ

(bladder, heart, etc.)