Copyright © 2010 Pearson Education, Inc. Connective Tissue Most abundant and widely distributed...

Copyright © 2010 Pearson Education, Inc.

Connective Tissue

•Most abundant and widely distributed tissue type

• Four classes

• Connective tissue proper

• Cartilage

• Bone tissue

• Blood



Major Functions of Connective Tissue

• Binding and support

• Protection

• Insulation

• Transportation (blood)


Characteristics of Connective Tissue

• Connective tissues have:

• Mesenchyme as their common tissue of origin

• Varying degrees of vascularity

• Cells separated by nonliving extracellular matrix (ground substance and fibers)


Structural Elements of Connective Tissue• Ground substance

• Medium through which solutes diffuse between blood capillaries and cells

• Components:

• Interstitial fluid

• Adhesion proteins (“glue”)

• Proteoglycans

• Protein core + large polysaccharides (chrondroitin sulfate and hyaluronic acid)

• Trap water in varying amounts, affecting the viscosity of the ground substance


Structural Elements of Connective Tissue• 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


Structural Elements of Connective Tissue

• 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

Copyright © 2010 Pearson Education, Inc. Figure 4.7

Macrophage

Fibroblast

Lymphocyte

Fat cell

Mast cell

Neutrophil

Capillary

Cell types Extracellularmatrix

Fibers• Collagen fiber• Elastic fiber• Reticular fiber

Ground substance


Connective Tissue: Embryonic

•Mesenchyme—embryonic connective tissue

• Gives rise to all other connective tissues

• Gel-like ground substance with fibers and star-shaped mesenchymal cells


Overview of Connective Tissues

• For each of the following examples of connective tissue, note:

• Description

• Function

• Location


Connective Tissue Proper

• Loose connective

• Areolar

• Adipose

• Reticular

• Dense connective

• Dense regular

• Dense irregular

• 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

Figure 4.8a

Copyright © 2010 Pearson Education, Inc. Figure 4.8b

(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

Copyright © 2010 Pearson Education, Inc. Figure 4.8c

(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

Copyright © 2010 Pearson Education, Inc. Figure 4.8d

(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

Copyright © 2010 Pearson Education, Inc. Figure 4.8e

(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

Copyright © 2010 Pearson Education, Inc. Figure 4.8f

(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).


Connective Tissue: Cartilage

• Three types of cartilage:

• Hyaline cartilage

• Elastic cartilage

• Fibrocartilage

Copyright © 2010 Pearson Education, Inc. Figure 4.8g

(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

Copyright © 2010 Pearson Education, Inc. Figure 4.8h

(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

Copyright © 2010 Pearson Education, Inc. Figure 4.8i

(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

Copyright © 2010 Pearson Education, Inc. Figure 4.8j

(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

Copyright © 2010 Pearson Education, Inc. Figure 4.8k

(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


Nervous Tissue

•Nervous system (more detail with the Nervous System)


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


Muscle Tissue

• Skeletal muscle

• Cardiac muscle

• Smooth muscle

• (more detail with the Muscular System)

Copyright © 2010 Pearson Education, Inc. Figure 4.10a

(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)


(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


(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


Epithelial Membranes

• Cutaneous membrane (skin) (More detail with the Integumentary System, Chapter 5)

• Mucous membranes

• Mucosae

• Line body cavities open to the exterior (e.g., digestive and respiratory tracts)

• Serous membranes

• Serosae

• Line internal body cavities (pleural membranes, visceral membranes, peritoneum etc.)

Copyright © 2010 Pearson Education, Inc. Figure 4.11a

Cutaneousmembrane(skin)

(a) Cutaneous membrane (the skin)covers the body surface.


Mucosa ofnasal cavity

Mucosa oflung bronchi

Mucosa ofmouth

Esophaguslining

(b) Mucous membranes line body cavitiesopen to the exterior.


Parietalpericardium

Visceralpericardium

(c) Serous membranes line body cavitiesclosed to the exterior.

Parietalperitoneum

Visceralperitoneum

ParietalpleuraVisceralpleura


Tissue Injury

• Tissue injury = penetration of one of the bodies primary defense barriers (skin & mucosae)

• Injury triggers two types of responses:

• Inflammation: rapid, but not specific

• Immune: slower, but specific

• Tissue repair involves two major processes:

• Regeneration: replace damaged tissue with the same type of tissue

• Fibrosis: production of fibrous connective tissue called scar tissue

• Which process occurs depends on the location and severity of the tissue damage


Steps in Tissue Repair

1. Inflammation

• Trauma triggers the release of inflammatory chemicals from injured cells as well as macrophages & mast cells

• These chemicals trigger the dilation of blood vessels

• Dilation increases vessel permeability, allowing WBCs & plasma w/ clotting proteins and antibodies to seep into injured area

• Clotting occurs, stopping the loss of blood, holding edges of wound together and isolating it from bacteria, toxins etc.

Copyright © 2010 Pearson Education, Inc. Figure 4.12, step 1

Scab

Blood clot inincised wound

Epidermis

Vein

Inflammatorychemicals

Inflammation sets the stage:• Severed blood vessels bleed and inflammatory chemicals arereleased.

• Local blood vessels become more permeable, allowing whiteblood cells, fluid, clotting proteins and other plasma proteinsto seep into the injured area.

• Clotting occurs; surface dries and forms a scab.

Migrating whiteblood cell

Artery

1


Steps in Tissue Repair2. Organization and restored blood supply (beginning of actual repair)

• The blood clot is replaced with granulation tissue, which lays down a new capillary bed

• Fibroblasts within the granulation tissue produce growth factors, collagen fibers & contractile proteins to pull edges of wound together

• Epithelium begins to regenerate

• Debris is phagocytized by macrophages and undelying fibrous patch becomes scar tissue resistant to infection because it produces bacteria inhibiting fibers


Regeneratingepithelium

Area ofgranulationtissueingrowth

FibroblastMacrophage

Organization restores the blood supply:• The clot is replaced by granulation tissue, which restoresthe vascular supply.

• Fibroblasts produce collagen fibers that bridge the gap.• Macrophages phagocytize cell debris.• Surface epithelial cells multiply and migrate over thegranulation tissue.

2


Steps in Tissue Repair3. Regeneration and fibrosis

• The scab detaches as epithelial tissue regenerates

• Fibrous tissue matures; epithelium thickens and begins to resemble adjacent tissue

• Results in a fully regenerated epithelium with underlying scar tissue

NOTE: In “pure infections” where there is no wound, puncture or scrape, repair is carried out by regeneration alone and there is generally not any clot formation or scarring.


Regeneratedepithelium

Fibrosedarea

Regeneration and fibrosis effect permanent repair:• The fibrosed area matures and contracts; the epitheliumthickens.• A fully regenerated epithelium with an underlying area ofscar tissue results.

3


Developmental Aspects of Tissues

• There are three primary germ layers: ectoderm, mesoderm, and endoderm

• Formed early in embryonic development (by the end of the second month)

• Specialize to form the four primary tissues

• Nerve tissue arises from ectoderm (mitosis basically stops after birth)

• Muscle and connective tissues arise from mesoderm (continue to divide after both)

• Epithelial tissues arise from all three germ layers (continue to divide after both)


MesodermEndoderm

16-day-old embryo(dorsal surface view)

Epithelium

Nervous tissue(from ectoderm)

Muscle and connectivetissue (mostly frommesoderm)

Ectoderm

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