Tissues

Groups of cells similar in structure and function

Types of tissues Epithelial tissue Connective tissue Muscle tissue Nerve tissue

Connective Tissues

Epithelial Tissue Muscular Tissue Nervous Tissue

Nervous tissue: Internal communication (electrical impulses)• Brain, spinal cord, and nervesMuscle tissue: Contracts to cause movement• Muscles attached to bones (skeletal)• Muscles of heart (cardiac)• Muscles of walls of hollow organs (smooth)

Epithelial tissue: Forms boundaries between different environments, protects, secretes, absorbs, filters• Skin surface (epidermis)• Lining of GI tract organs and other hollow organs

Connective tissue: Supports, protects, bindsother tissues together• Bones• Tendons• Fat and other soft padding tissue•Store energy

Two main types (by location):1. Covering and lining epithelia

On external and internal surfaces

2. Glandular epithelia Secretory tissue in glands

1. Cells are bound closely together2. A free (apical) surface exposed to the

environment or to some internal chamber or passageway

3. Attachment to underlying connective tissue by a basement membrane

4. The absence of blood vessels5. Continual replacement/regeneration of

epithelial cells that are damaged or lost at the exposed surface

1. Provide physical protection2. Control permeability3. Provide sensation4. Produce specialized secretions

Epithelial cells that produce secretions are called gland cells – usually scattered amongst other cells

In glandular epithelium, most or all of the cells produce secretions. Classified according to where they are discharged:

• Exocrine – secretions are discharged onto the surface of the epithelium

• Endocrine – secretions are released into the surrounding tissue fluid and the blood (hormones)

Tight junction (occluding junction) – lipid layers of adjacent plasma membranes are tightly bound together by interlocking membrane proteins Inferior to this is an adhesion belt – encircles cells and

binds them to their neighbors Prevents the passage of water and solutes between cells

Gap junction – 2 cells are held together by embedded membrane protein groups (connexons) Most abundant in cardiac muscle and smooth muscle

Desmosome – here the plasma membranes of 2 cells are locked together by intercellular cement and by membrane proteins connected to a network of intermediate filaments

How many layers? 1 = simple epithelium >1 = stratified epithelium

Simple – thin and fragile. Characteristic of where secretion and absorption occurs

Stratified – several layers of cells. More protection. Found in areas subject to mechanical and chemical stresses

Stratified

Simple

Apical surface

Basal surface

Apical surface

Basal surface

(a) Classification based on number of cell layers.

• What type of cell?• Squamous – thin and flat with nucleus

occupying the thickest portion of the cell• Cuboidal – nuclei lie near the center of each

cell and the cells form a neat row• Columnar - very tall with their nuclei close

to the basal side of the cell (If stratified, name according to apical

layer of cells)

Squamous

Cuboidal

Columnar(b) Classification based on cell shape.

(a) Simple squamous epithelium

Description: Single layer of flattenedcells with disc-shaped central nucleiand sparse cytoplasm; the simplestof the epithelia.

Function: Allows passage ofmaterials by diffusion and filtrationin sites where protection is notimportant; secretes lubricatingsubstances in serosae.

Location: Kidney glomeruli; air sacsof lungs; lining of heart, bloodvessels, and lymphatic vessels; liningof ventral body cavity (serosae).

Photomicrograph: Simple squamous epitheliumforming part of the alveolar (air sac) walls (125x).

Air sacs oflung tissue

Nuclei ofsquamousepithelialcells

(b) Simple cuboidal epithelium

Description: Single layer ofcubelike cells with large,spherical central nuclei.

Function: Secretion andabsorption.

Location: Kidney tubules;ducts and secretory portionsof small glands; ovary surface.

Photomicrograph: Simple cuboidalepithelium in kidney tubules (430x).

Basementmembrane

Connectivetissue

Simplecuboidalepithelialcells

(c) Simple columnar epithelium

Description: Single layer of tall cells with round to oval nuclei; some cells bear cilia; layer may contain mucus-secreting unicellular glands (goblet cells).

Function: Absorption; secretion of mucus, enzymes, and other substances; ciliated type propels mucus (or reproductive cells) by ciliary action.

Location: Nonciliated type lines most of the digestive tract (stomach to anal canal),gallbladder, and excretory ducts of someglands; ciliated variety lines small bronchi, uterine tubes, and some regionsof the uterus.

Photomicrograph: Simple columnar epitheliumof the stomach mucosa (860X).

Simplecolumnarepithelialcell

Basementmembrane

(d) Pseudostratified columnar epithelium

Description: Single layer of cells ofdiffering heights, some not reachingthe free surface; nuclei seen atdifferent levels; may contain mucus-secreting cells and bear cilia.

Function: Secretion, particularly ofmucus; propulsion of mucus byciliary action.

Location: Nonciliated type in male’ssperm-carrying ducts and ducts oflarge glands; ciliated variety linesthe trachea, most of the upperrespiratory tract.

Photomicrograph: Pseudostratified ciliatedcolumnar epithelium lining the human trachea (570x).

Trachea

Cilia

Pseudo-stratifiedepitheliallayer

Basementmembrane

Mucus ofmucous cell

(e) Stratified squamous epithelium

Description: Thick membranecomposed of several cell layers;basal cells are cuboidal or columnarand metabolically active; surfacecells are flattened (squamous); in thekeratinized type, the surface cells arefull of keratin and dead; basal cellsare active in mitosis and produce thecells of the more superficial layers.

Function: Protects underlyingtissues in areas subjected to abrasion.

Location: Nonkeratinized type formsthe moist linings of the esophagus,mouth, and vagina; keratinized varietyforms the epidermis of the skin, a drymembrane.

Photomicrograph: Stratified squamous epitheliumlining the esophagus (285x).

Stratifiedsquamousepithelium

Nuclei

Basementmembrane

Connectivetissue

Columnar Limited distribution in

body Small amounts in

pharynx, male urethra, and lining some glandular ducts

Also occurs at transition areas between two other types of epithelia

Cuboidal Quite rare in body Found in some

sweat and mammary glands

Typically two cell layers thick

(f) Transitional epithelium

Description: Resembles both stratified squamous and stratified cuboidal; basal cells cuboidal or columnar; surface cells domeshaped or squamouslike, depending on degree of organ stretch.

Function: Stretches readily and permits distension of urinary organ by contained urine.

Location: Lines the ureters, urinary bladder, and part of the urethra.

Photomicrograph: Transitional epithelium lining the urinary bladder, relaxed state (360X); note the bulbous, or rounded, appearance of the cells at the surface; these cells flatten and become elongated when the bladder is filled with urine.

BasementmembraneConnectivetissue

Transitionalepithelium

A gland is one or more cells that makes and secretes an aqueous fluid

Classified by: Site of product release—endocrine or exocrine Relative number of cells forming the gland—unicellular or

multicellular Endocrine glands

Ductless glands Secrete hormones that travel through lymph or blood to target

organs Exocrine glands

More numerous than endocrine glands Secrete products into ducts Secretions released onto body surfaces (skin) or into body cavities Examples include mucous, sweat, oil, and salivary glands

Unicellular exocrine glands The only important unicellular exocrine gland is the goblet cell

Multicellular exocrine glands are composed of a duct and a secretory unit

Classified according to: Duct type (simple or compound) Structure of their secretory units (tubular, alveolar, or

tubuloalveolar) Modes of secretion

Merocrine Products are secreted by exocytosis (e.g., pancreas, sweat and

salivary glands) Holocrine

Products are secreted by rupture of gland cells (e.g., sebaceous glands)

Compound duct structure(duct branches)

Simple tubular

ExampleIntestinal glands

Simple branchedtubular

ExampleStomach (gastric)glands

Compound tubular

ExampleDuodenal glands of small intestine

Compound alveolar

ExampleMammary glands

Simplealveolar

ExampleNo importantexample in humans

Simple branchedalveolar

ExampleSebaceous (oil)glands

Compoundtubuloalveolar

ExampleSalivary glands

Tubularsecretorystructure

Alveolarsecretorystructure

Surface epithelium Duct Secretory epithelium

Simple duct structure(duct does not branch)

Most abundant and widely distributed tissue type

Four classes Connective tissue proper Cartilage Bone tissue Blood

Functions Support and protection Storage of energy reserves Defense of the body Transportation

Characteristics Connective tissues have:

Mesenchyme as their common tissue of origin Varying degrees of vascularity Cells separated by nonliving extracellular matrix (ground

substance and fibers)

Three types of fibers Collagen (white fibers)

Strongest and most abundant type Provides high tensile strength

Elastic Networks of long, thin, elastin fibers that allow

for stretch Reticular

Short, fine, highly branched collagenous fibers

Cells Mitotically active and secretory cells = “blasts” Mature cells = “cytes”

Fibroblasts in connective tissue proper Chondroblasts and chondrocytes in cartilage Osteoblasts and osteocytes in bone Hematopoietic stem cells in bone marrow Fat cells, white blood cells, mast cells, and

macrophages

Macrophage

Fibroblast

Lymphocyte

Fat cell

Mast cell

Neutrophil

Capillary

Cell typesExtracellularmatrix

Fibers• Collagen fiber• Elastic fiber• Reticular fiber

Ground substance

For each of the following examples of connective tissue, note: Description Function Location

Types Loose connective tissue

Areolar, adipose, and reticular Dense connective tissue

Dense regular, dense irregular, and elastic

(a) Connective tissue proper: loose connective tissue, areolar

Description: Gel-like matrix with allthree fiber types; cells: fibroblasts,macrophages, mast cells, and somewhite blood cells.

Function: Wraps and cushionsorgans; its macrophages phagocytizebacteria; plays important role ininflammation; holds and conveystissue fluid.

Location: Widely distributed underepithelia of body, e.g., forms laminapropria of mucous membranes;packages organs; surroundscapillaries.

Photomicrograph: Areolar connective tissue, asoft packaging tissue of the body (300x).

Epithelium

Laminapropria

Fibroblastnuclei

Elasticfibers

Collagenfibers

(b) Connective tissue proper: loose connective tissue, adipose

Description: Matrix as in areolar,but very sparse; closely packedadipocytes, or fat cells, havenucleus pushed to the side by largefat droplet.

Function: Provides reserve foodfuel; insulates against heat loss;supports and protects organs.

Location: Under skin in thehypodermis; around kidneys andeyeballs; within abdomen; in breasts.

Photomicrograph: Adipose tissue from thesubcutaneous layer under the skin (350x).

Nucleus offat cell

Vacuolecontainingfat droplet

Adiposetissue

Mammaryglands

(c) Connective tissue proper: loose connective tissue, reticular

Description: Network of reticularfibers in a typical loose groundsubstance; reticular cells lie on thenetwork.

Function: Fibers form a soft internalskeleton (stroma) that supports othercell types including white blood cells,mast cells, and macrophages.

Location: Lymphoid organs (lymphnodes, bone marrow, and spleen).

Photomicrograph: Dark-staining network of reticularconnective tissue fibers forming the internal skeletonof the spleen (350x).

Spleen

White bloodcell(lymphocyte)

Reticularfibers

(d) Connective tissue proper: dense connective tissue, dense regular

Description: Primarily parallelcollagen fibers; a few elastic fibers;major cell type is the fibroblast.

Function: Attaches muscles tobones or to muscles; attaches bonesto bones; withstands great tensilestress when pulling force is appliedin one direction.

Location: Tendons, mostligaments, aponeuroses.

Photomicrograph: Dense regular connectivetissue from a tendon (500x).

Shoulderjoint

Ligament

Tendon

Collagenfibers

Nuclei offibroblasts

(e) Connective tissue proper: dense connective tissue, dense irregular

Description: Primarilyirregularly arranged collagenfibers; some elastic fibers;major cell type is the fibroblast.

Function: Able to withstandtension exerted in manydirections; provides structuralstrength.

Location: Fibrous capsules oforgans and of joints; dermis ofthe skin; submucosa ofdigestive tract.

Photomicrograph: Dense irregularconnective tissue from the dermis of theskin (400x).

Collagenfibers

Nuclei offibroblasts

Fibrousjointcapsule

(f) Connective tissue proper: dense connective tissue, elastic

Description: Dense regularconnective tissue containing a highproportion of elastic fibers.

Function: Allows recoil of tissuefollowing stretching; maintainspulsatile flow of blood througharteries; aids passive recoil of lungsfollowing inspiration.

Location: Walls of large arteries;within certain ligaments associatedwith the vertebral column; within thewalls of the bronchial tubes.

Elastic fibers

Aorta

HeartPhotomicrograph: Elastic connective tissue inthe wall of the aorta (250x).

Three types of cartilage: Hyaline cartilage Elastic cartilage Fibrocartilage

(g) Cartilage: hyaline

Description: Amorphous but firmmatrix; collagen fibers form animperceptible network; chondroblastsproduce the matrix and when mature(chondrocytes) lie in lacunae.

Function: Supports and reinforces;has resilient cushioning properties;resists compressive stress.

Location: Forms most of theembryonic skeleton; covers the endsof long bones in joint cavities; formscostal cartilages of the ribs; cartilagesof the nose, trachea, and larynx.

Photomicrograph: Hyaline cartilage from thetrachea (750x).

Costalcartilages

Chondrocytein lacuna

Matrix

(h) Cartilage: elastic

Description: Similar to hyalinecartilage, but more elastic fibersin matrix.

Function: Maintains the shapeof a structure while allowinggreat flexibility.

Location: Supports the externalear (pinna); epiglottis.

Photomicrograph: Elastic cartilage fromthe human ear pinna; forms the flexibleskeleton of the ear (800x).

Chondrocytein lacuna

Matrix

(i) Cartilage: fibrocartilage

Description: Matrix similar tobut less firm than that in hyalinecartilage; thick collagen fiberspredominate.

Function: Tensile strengthwith the ability to absorbcompressive shock.

Location: Intervertebral discs;pubic symphysis; discs of kneejoint.

Photomicrograph: Fibrocartilage of anintervertebral disc (125x). Special stainingproduced the blue color seen.

Intervertebraldiscs

Chondrocytesin lacunae

Collagenfiber

(j) Others: bone (osseous tissue)

Description: Hard, calcifiedmatrix containing many collagenfibers; osteocytes lie in lacunae.Very well vascularized.

Function: Bone supports andprotects (by enclosing);provides levers for the musclesto act on; stores calcium andother minerals and fat; marrowinside bones is the site for bloodcell formation (hematopoiesis).Location: Bones

Photomicrograph: Cross-sectional viewof bone (125x).

Lacunae

Lamella

Centralcanal

(k) Others: blood

Description: Red and whiteblood cells in a fluid matrix(plasma).

Function: Transport ofrespiratory gases, nutrients,wastes, and other substances.

Location: Contained withinblood vessels.

Photomicrograph: Smear of human blood (1860x); twowhite blood cells (neutrophil in upper left and lymphocytein lower right) are seen surrounded by red blood cells.

Neutrophil

Red bloodcells

Lymphocyte

Plasma

Photomicrograph: Neurons (350x)

Function: Transmit electricalsignals from sensory receptorsand to effectors (muscles andglands) which control their activity.

Location: Brain, spinalcord, and nerves.

Description: Neurons arebranching cells; cell processesthat may be quite long extend fromthe nucleus-containing cell body;also contributing to nervous tissueare nonirritable supporting cells(not illustrated).

Dendrites

Neuron processes Cell body

Axon

Nuclei ofsupportingcells

Cell bodyof a neuron

Neuronprocesses

Nervous tissue

(a) Skeletal muscle

Description: Long, cylindrical,multinucleate cells; obviousstriations.

Function: Voluntary movement;locomotion; manipulation of theenvironment; facial expression;voluntary control.

Location: In skeletal musclesattached to bones oroccasionally to skin.

Photomicrograph: Skeletal muscle (approx. 460x).Notice the obvious banding pattern and thefact that these large cells are multinucleate.

Nuclei

Striations

Part ofmuscle fiber (cell)

Figure 4.10b

(b) Cardiac muscle

Description: Branching, striated, generally uninucleate cells that interdigitate atspecialized junctions (intercalated discs).

Function: As it contracts, it propels blood into the circulation; involuntary control.Location: The walls of the heart.

Photomicrograph: Cardiac muscle (500X);notice the striations, branching of cells, andthe intercalated discs.

Intercalateddiscs

Striations

Nucleus

Figure 4.10c

(c) Smooth muscle

Description: Spindle-shapedcells with central nuclei; nostriations; cells arranged closely to form sheets.

Function: Propels substancesor objects (foodstuffs, urine,a baby) along internal passage-ways; involuntary control.Location: Mostly in the wallsof hollow organs.

Photomicrograph: Sheet of smooth muscle (200x).

Smoothmusclecell

Nuclei