Post on 29-Dec-2015
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