The Tissue Level of Organization

Chapter 4

Ch 4 Outline

4 major tissue types- functions, features 4 types of membranes & functions Injury Aging

Four Types of Tissues

Tissues- collections of cells that perform specific, limited functions

Histology- study of tissues

4 Types of tissue: Epithelial tissue Connective tissue Muscle tissue Neural tissue

Four Types of Tissues Epithelial tissue

Covers exposed surfaces Lines internal passageways Forms glands

Connective tissue Fills internal spaces Supports other tissues Transports materials Stores energy

Four Types of Tissues

Muscle tissue Specialized for contraction Skeletal muscle, heart muscle, and walls of

hollow organs

Neural tissue Carries electrical signals from one part of the

body to another

Epithelial Tissues

Epithelia- layers of cells covering internal or

external surfaces

Glands- structures that

produce fluid secretions, either

attached or derived from

epithelia

Characteristics of Epithelia

Cellularity- composed almost entirely of cells held together by cell junctions

Polarity- exposed surface faces exterior of body or internal space (apical) and side attached to base- (basal), structural & functional differences

Polarity of Epithelial Cells

Characteristics of Epithelia

Attachment- base of epithelium bound to basement membrane (basal lamina)

Avascularity- lack blood vessels, obtain nutrients by diffusion

Regeneration- damaged & lost cells continuously replaced through stem cell division, very high rates

Functions of Epithelial Tissues

Provide physical protection- abrasion, dehydration, biological/chemical agent

Control permeability- ions, nutrients

Provide sensation- sensory nerves provide info about external environment

Produce specialized secretions (glandular epithelium)- physical protection, temp regulation, chemical messengers

Specializations of Epithelial Cells

In order to perform functions, highly specialized structure- polarity: cell divided into 2 distinct regions

Apical surfaces: exposed to internal or external environment Microvilli increase absorption or secretion Cilia (ciliated epithelium) move fluid

Basolateral surfaces: Base- cellular attachment Sides- cells contact neighbors

Maintaining the Integrity of Epithelia

To be an effective barrier must form a complete cover:

Intercellular connections

Attachment to basal lamina

Epithelial maintenance and repair

Intercellular Connections Epithelial cells tightly bound together CAMs (cell adhesion molecules)- transmembrane

proteins

Intercellular cement- proteoglycans contain hyaluronan (hyaluronic acid)

Intercellular Connections

Cell junctions- form bonds with other cells or extracellular material: Occluding (tight) junctions Gap junctions Macula adherens (desmosomes)

Occluding (Tight) junctions Between two plasma membranes

Adhesion belt attaches to terminal web Prevents passage of water and solutes Isolates wastes in the lumen of GI tract

Occluding Junctions

Gap junctions Allow rapid communication

Held together by connexons (channel proteins) Allow ions to pass between cells Coordinate contractions in heart muscle

Gap Junctions

Macula adherens (Desmosomes) CAMs, dense areas, intercellular cement link plasma

membranes Spot desmosomes- tie cells together & allow

bending, twisting Hemidesmosomes- attach cells to the basal lamina

Attached to cytoskeleton

Spot Desmosomes

CAMS

Intercellular cement

Small discs connected to intermediate

filaments, which function to

stabilize cell shape

Hemidesmosome

Attach cell to extracellular filaments in basal lamina

Stabilize cell position and anchor to underlying tissues

Attachment to the Basal Lamina

Lamina lucida- clear layer closest to epithelium Glycoproteins & fine protein filaments Thin layer secreted by epithelia Restricts movement of proteins from underlying

connective tissue into epithelium

Lamina densa- dense layer Thick fibers produced by connective tissue Strength and filtration

Epithelial Maintenance and Repair

Constantly replaced by division of germinative cells (stem cells) near basal lamina

Exposure to enzymes, toxic chemicals, bacteria, mechanical abrasion

Classification of Epithelia

Singular epithelium; plural epithelia

Classes of Epithelia Based on shape

Squamous epithelia: thin and flat

Cuboidal epithelia: square shaped

Columnar epithelia: tall, slender rectangles

Based on layers

Simple epithelium: single layer of cells, no polarity

Stratified epithelium: several layers of cells

Simple Epithelia

Stratified Epithelia

Simple Squamous Epithelia Thin, flat, irregular- smooth surface Simple squamous epithelium

Absorption and diffusion Aveoli, lining body cavities, lining heart &

blood vessels

Mesothelium- lines body cavities

Endothelium- lines heart and blood vessels

Simple Squamous Epithelia

Located where mechanical stress is severe- skin surface, lining of mouth, esophagus, anus

Protects against attacks Keratin- protein adds strength & water resistant

Simple cuboidal epithelium- secretion and absorption (kidney tubules)

Sratified Cuboidal EpitheliaSimple Cuboidal Epithelia

Stratified Cuboidal Epithelia

Stratified cuboidal epithelia- sweat ducts and mammary ducts

-Tolerates repeated cycles of stretching and recoiling and returns to its previous shape without damage

-Appearance changes as stretching occurs

Columnar Epithelia

Simple columnar epithelium Absorption and secretion

Pseudostratified columnar epithelium Cilia movement

Stratified columnar epithelium Protection

Simple Columnar Epithelia

Absorption and secretion- small intestine

Pseudostratified CiliatedColumnar Epithelia

-Several cell types, varying shapes & functions-Not truly stratified-Cilia movement- nasal cavity, trachea, bronchi

Stratified Columnar Epithelia

-Relatively rare-Protection along pharynx, epiglottis, anus, urethra

Glandular Epithelia Specialized for secretion

Endocrine glands Release hormones into interstitial fluid

No ducts Thyroid gland, pituitary gland

Exocrine glands Produce secretions onto epithelial surfaces

Through ducts Saliva, sweat, tears, milk Categorized by mode & type of secretion, structure

Modes of Glandular Secretionby Exocrine Glands

Merocrine Secretion

Produced in Golgi apparatus Released by vesicles- exocytosis Most common secretion mode Sweat glands, salivary glands

Apocrine Secretion

Produced in Golgi apparatus Released by shedding cytoplasm Mammary gland

Holocrine Secretion

Released by cells bursting, killing gland cells Gland cells replaced by stem cells Sebaceous gland- oil coating on hair

Types of Secretion by Exocrine Glands

Serous glands: watery secretions- saliva

Mucous glands: secrete mucins- mucus

Mixed exocrine glands: both serous and mucous

Gland Structure- Exocrine Glands

Unicellular glands- independent, scattered cells Mucous (goblet) cells- intestinal lining

Multicellular glands- glandular epithelia & aggregations of gland cells Structure of the duct- simple or compound

Shape of secretory portion of the gland Tubular (straight/coiled) or blind pockets

Relationship between ducts & glandular areas Branched

Simple Multicellular Exocrine Glands

Simple- single duct does not

divide on way to gland cell

Compound Multicellular Exocrine Glands

Compound- duct divides one or more times on

way to gland cell

Tubular Exocrine Glands

Tubular- form tubes, straight or

coiled

Alveolar/Acinar Exocrine Glands

Alveolar- blind pocketsTubuloalveolar- both tubes and

pockets

Connective Tissues

Connect epithelium to the rest of the body Dense layer of basal lamina produced by connective

tissue

Functions: Provide structure, support- bone Store energy- fat Transport materials- blood Defending body from microbes Protect organs

Have no contact with outside environment

Connective Tissues

Characteristics of Connective Tissues Specialized cells

Solid extracellular protein fibers

Fluid extracellular ground substance

Extracellular components make up the matrix

Majority of connective tissue volume

Determines specialized function

Classification of Connective Tissues Connective tissue proper- connect & protect

Many cell types & extracellular fibers in syrupy ground substance Loose & dense connective tissue (adipose, tendons)

Fluid connective tissues- transport Distinctive cell populations, watery matrix, dissolved

proteins (blood, lymph)

Supportive connective tissues- structural strength Protect soft tissue, support weight of body (cartilage, bone) Matrix- gel or calcified (bone)

Connective Tissues

Fibroblasts Fibrocytes Adipocytes Mesenchymal cells Melanocytes

Macrophages Mast cells Lymphocytes Microphages

Nine Cell Types of Connective Tissue Proper

Connective Tissue Proper Cells

Fibroblasts Most abundant cell type:

Always found in all connective tissue proper

Secrete proteins and hyaluronan (cellular cement)

Fibrocytes 2nd most abundant cell type:

Found in all connective tissue proper Maintain the fibers of connective tissue

proper

Connective Tissue Proper Cells

Macrophages “Big eaters” immune system:

Eat pathogens & damaged cells Fixed macrophages- stay in tissue Free macrophages- migrate

Adipocytes Fat cells- each cell stores a single, large fat droplet

Mesenchymal Cells Stem cells that respond to injury or infection:

Differentiate into fibroblasts, macrophages

Connective Tissue Proper Cells

Melanocytes Synthesize and store the brown pigment

melanin

Mast Cells Stimulate inflammation after injury or infection:

Release histamine and heparin

Basophils (white blood cells) also contain histamine and heparin

Connective Tissue Proper Cells Lymphocytes

Specialized immune cells in lymphatic system: B-cells (plasma cells)- produce antibodies T-cells

Microphages (neutrophils, eosinophils) Phagocytic white blood cells:

Respond to signals from macrophages & mast cells

Connective Tissue Fibers

Collagen fibers

Most common fibers in connective tissue proper

Long, straight, unbranched

Strong and flexible

Tendons & ligaments

Connective Tissue Fibers

Reticular fibers Network of interwoven fibers- stroma Strong & flexible Stabilize functional cells (parenchyma) &

blood vessels, nerves Sheaths around organs

Connective Tissue Fibers

Elastic fibers

Contain elastin

Branched and wavy Return to original length after

stretching

Elastic ligaments of vertebrae

Connective Tissues

Ground Substance

Clear, colorless, viscous (thick)

Fills spaces between cells & slows pathogen

movement

Cells and Fibers of Connective Tissue Proper

Cells and Fibers of Connective Tissue Proper

Embryonic Connective Tissues

Not found in adults

Mesenchyme Embryonic stem cells 1st connective tissue

in embryos Gives rise to all other

connective tissue

Embryonic Connective Tissues

Mucous connective tissue Wharton’s jelly Loose embryonic

connective tissue

Loose Connective Tissues

Packing materials of the body

Fill spaces between organs, cushion, stabilize specialized cells in organs, support epithelia, blood vessels, nerves, store lipids

Three types in adults Areolar Adipose Reticular

Areolar TissueLoose Connective Tissues

Least specialized

Open framework Viscous ground substance

most volume

Elastic fibers

Holds blood vessels & capillary beds

Under skin (subcutaneous layer), padding

Adipose TissueLoose Connective Tissues

Contains many adipocytes (fat cells)

Types of adipose tissue White fat:

Most common Stores fat, absorbs shocks, slows heat loss (insulation)

Brown fat: More vascularized Adipocytes have many mitochondria When stimulated by nervous system, fat break down

accelerates, releasing energy Energy absorbed from surrounding tissues- heats body

Adipose Tissue

Adipose cells Adipocytes in adults do not divide:

Expand to store fat

Shrink as fats are released

Mesenchymal cells divide and differentiate: Produce more fat cells when more storage is

needed

Adipose Tissues

Functions- padding, absorbs shock, insulation, packing/filler around structures

Reticular TissueLoose Connective Tissues

Provides support Complex, 3D network- stroma

Support functional cells (parenchyma) Reticular organs

Spleen, liver, lymph nodes, and bone marrow

Dense Connective Tissues

Connective tissues proper, tightly packed with high numbers of collagen or elastic fibers

Dense regular connective tissue

Dense irregular connective tissue

Elastic tissue

Dense Regular Connective Tissues

Tightly packed, parallel collagen fibers Tendons- attach muscles to bones Ligaments- connect bone to bone & stabilize organs Aponeuroses- tendinous sheet that attaches a broad,

flat muscles to another muscle or

Dense Irregular Connective Tissues

Interwoven networks of collagen fibers

Strengthen &support areas subjected to stress from multiple directions, gives skin strength

Sheaths cartilage- perichondrium Sheaths bones- periosteum

Form capsules around some organs (liver, kidneys, spleen)

Elastic TissueDense Regular Connective Tissues

Made of elastic fibers

Elastic ligaments of spinal vertebrae

Fluid Connective Tissues

Blood & lymph Watery matrix of dissolved proteins Fluid Elements- extracellular

Plasma Interstitial fluid Lymph

Formed Elements- specific cell types Formed elements of blood

Red blood cells- erythrocytes White blood cells- leukocytes Platelets

Formed Elements of the Blood

Connective Tissues

Lymph- extracellular fluid

Collected from interstitial space

Monitored by immune system

Transported by lymphatic

system

Returned to venous system

Fluid Tissue Transport Systems

Cardiovascular system (blood)

Arteries

Capillaries

Veins

Lymphatic system (lymph)

Lymphatic vessels

Supportive Connective Tissues

Support soft tissues and body weight Cartilage - gel-type ground substance

For shock absorption and protection

Bone- calcified (made rigid by calcium salts, minerals) For weight support

Cartilage Characteristics

Cartilage Matrix- firm gel contains proteoglycans derived from chondroitin sulfates complexed with ground substance proteins Chondrocytes (cartilage cells)- occupy small

chambers- lacunae

Cartilage Structure- no blood vessels, exchange by diffusion only Chondrocytes produce antiangiogenesis factor

Perichondrium- sets cartilage apart from surrounding tissues

Outer, fibrous layer- strength Inner, cellular layer- growth and maintenance

Interstitial Growth of Cartilage

*Most important during

development

- Enlarges cartilage from

within

Appositional Growth of Cartilage

- Adds new layers of

cartilage to the surface

Hyaline Cartilage

Hyaline cartilage (most common) Stiff, flexible support Reduces friction between bones Found in synovial joints, rib tips, sternum, trachea,

elbows, knees

Elastic Cartilage

Elastic cartilage Supportive but bends easily Found in external ear and epiglottis

Fibrous Cartilage

Fibrous cartilage (fibrocartilage) Limits movement Prevents bone-to-bone contact Pads knee joints Found between pubic bones and intervertebral discs

Bone (Osseous) Tissue

Strong (calcified: calcium salt deposits) Resists shattering (flexible collagen fibers)

Osteocytes (bone cells)- in lacunae Arranged around central canals within matrix Small channels through matrix (canaliculi) access

blood supply

Periosteum Covers bone surfaces except in joint cavities Fibrous layer Cellular layer

Supportive Connective Tissue- Bone

Matrix- mixture of calcium salts (calcium phosphate, carbonate) and collagen fibers

Supportive Connective Tissues

Membranes

Membranes- physical barriers that line or cover portions of the body Consist of epithelium supported by connective

tissues

Four Types of Membranes Mucous membranes Serous membranes Cutaneous membrane Synovial membranes

Mucous Membranes

Line passageways with external connections Digestive, respiratory, urinary, reproductive tracts

Epithelial surfaces must be moist Reduce friction & facilitate absorption and excretion

Lamina propria- areolar tissue

Serous Membranes Line cavities not open to outside Thin but strong Have fluid, transudate, to reduce friction Parietal portion- covers cavity Visceral portion, serosa- covers organs

Three Serous Membranes

Pleura: Lines pleural cavities Covers lungs

Peritoneum: Lines peritoneal cavity Covers abdominal organs

Pericardium: Lines pericardial cavity Covers heart

Cutaneous Membrane

Skin, surface of the body

Thick, waterproof, dry

Synovial Membranes

Articulating joint cavities (bones very close or touching) Produce synovial fluid (lubricant)- joint movement is

important in stimulating formation & circulation of fluid

Protect the ends of bones

Internal Framework of the Body

Connective tissues Provide strength and stability Maintain positions of internal organs Provide routes for blood vessels, lymphatic vessels,

and nerves

Fasciae (singular form is fascia)

Connective tissue layers surround, support organs Three types of fasciae

– Superficial fascia– Deep fascia– Subserous fascia

Muscle Tissue

Specialized for contraction

Produces all body movement

Three types of muscle tissue Skeletal muscle

Large body muscles responsible for movement

Cardiac muscle

Found only in the heart

Smooth muscle

Found in walls of hollow, contracting organs (blood vessels; urinary bladder; respiratory, digestive,

reproductive tracts), contractility & support

Classification of Muscle Cells

Striated- muscle cells with a banded appearance

Nonstriated- not banded; smooth

Muscle cells- single nucleus or multinucleate

Muscle cells can be controlled voluntarily or involuntarily

Striated Muscle Nonstriated Muscle

Muscle Tissue- Skeletal Long, thin, very large- muscle

fibers Several hundred nuclei! Do NOT divide New fibers- myosatellite cells Striated voluntary muscle-

nervous system

Muscle Tissue- CardiacCardiac cells- cardiocytesForm branching networks connected at intercalated discsRegulated by pacemaker cellsStriated involuntary muscle

Muscle Tissue- Smooth

Smooth muscle cells Small and tapered Divide and regenerate No striations

Nonstriated involuntary muscle

Neural Tissue

Specialized for conducting electrical impulses

Rapidly senses internal or external environment

Processes information and controls responses

Central nervous system Brain Spinal cord

Two Kinds of Neural Cells

Neurons Nerve cells Perform electrical communication

Neuroglia Supporting cells Repair and supply nutrients to neurons

Cell Parts of a Neuron Cell body- nucleus Dendrites- short branches extending from cell body

Receive incoming signals

Axon (nerve fiber)- long, thin extension of cell body Carries outgoing electrical signals

http://www.greenspine.ca/media/mGFP_neuron2.jpg

Tissue Injuries and Repair

Tissues respond to injuries to maintain homeostasis

Cells restore homeostasis with two processes

Inflammation- tissues 1st response to injury Regeneration

Inflammation

Inflammation = inflammatory response

Inflammatory response (signs & symptoms): Swelling

Redness

Heat

Pain

Can be triggered by trauma (physical injury) or infection

Process of Inflammation Damaged cells release chemical signals into

surrounding interstitial fluid Prostaglandins, proteins, potassium ions

Process of Inflammation

Damaged cells break down, lyse- contents leak out Lysosomes release hydrolytic enzymes Tissue destruction surrounding tissues- necrosis

Process of Inflammation

Necrotic tissues and cellular debris (pus) accumulate in the wound Abscess: pus trapped in an enclosed area

Process of Inflammation

Injury stimulates mast cells to release:

Histamine Heparin Prostaglandins

Process of Inflammation

Dilation of blood vessels (redness & heat) Increases blood circulation Brings more nutrients and oxygen to the area Removes wastes

Plasma diffuses into the area Swelling and pain

Phagocytic white blood cells Clean up the area- damaged cells, pathogens

An Introduction to Inflammation

Regeneration Injury or infection is cleaned up healing begins Fibrocytes move into necrotic area

Lay down collagen fibers- bind area together (scar tissue)

New cells migrate into area or mesenchymal stem cells produce them

Not all tissues can regenerate Epithelia & connective tissues regenerate well Cardiac cells & neurons do not regenerate (or regenerate

poorly)

Aging and Tissue Tissue repair speed, efficiency decreases with age:

Slower rate of energy consumption (metabolism) Hormonal alterations Reduced physical activity

Chemical & structural tissue changes Thinning epithelia and connective tissues Increased bruising and bone brittleness Cardiovascular disease- cumulative damage Mental deterioration

Aging and Cancer Incidence

Cancer rates increase with age 1 in 4 people in US develops cancer Cancer is the #2 cause of death in US Environmental chemicals, cigarette smoke

cause cancer Longer exposure, accumulate mutations

– 7 mutations in 1 cell

Plastics (food); pesticides (air, water, soil, food); air pollution (industry, vehicles)