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Connective Tissue

Connective tissue is found throughout the body. It is usually characterized by large amounts of extracellular material that separates cells from one another.

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Connective tissue consists of two basic elements:

Extracellular matrixCells

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The extracellular material, or extracellular matrix, has three major components:

(1) Protein fibers,

(2) Ground substance consisting of nonfibrous protein and other molecules, and

(3) Fluid

Three types of protein fibers help form most connective tissues.

Collagen (glue-producing) fibers, which resemble microscopic ropes, are flexible but resist stretching.

Reticular fibers are very fine, short collagen fibers that branch to form a supporting network.

Elastic fibers have a structure similar to that of coiled metal bed springs; after being stretched, they can recoil to their original shape.

Ground substance is the shapeless background against which cells and collagen fibers can be seen when using a light microscope.

Connective tissue cells are named according to their functions.

Cells whose names contain the suffix -blast (germ) produce the matrix; cells ending in –cyte (cell) maintain it; and cells ending in -clast (break) break it down for remodeling.

Classification of Connective Tissue
Connective tissue proper

Loose (fewer fibers, more ground substance)

Areolar

Adipose

Reticular

Dense (more fibers, less ground substance)

Dense regular connective tissue

Dense irregular connective tissue

Elastic connective tissue

Supporting connective tissue

Cartilage (semisolid matrix)

Hyaline

Fibrocartilage

Elastic

Bone (solid matrix)

Fluid connective tissue

Blood

A. Loose Connective Tissue

The fibers of loose connective tissue are loosely arranged between cells.

A. AREOLAR CONNECTIVE TISSUE
StructureA fine network of fibers (mostly collagen fibers with a few elastic fibers) with spaces between the fibers; fibroblasts, macrophages, and lymphocytes are located in the spaces.
LocationSkin, mucous membranes; around blood vessels, nerves, and body organs.
FunctionStrength, elasticity, support.
B. ADIPOSE TISSUE
StructureLittle extracellular matrix surrounding cells; the adipocytes, or fat cells, are so full of lipid that the cytoplasm is pushed to the periphery of the cell.
LocationSkin, around heart and kidneys, yellow bone marrow, padding etc.
FunctionReduces heat loss through skin; serves as an energy reserve; supports and protects organs.
C. RETICULAR CONNECTIVE TISSUE
StructureFine network of reticular fibers irregularly arranged.
LocationStroma (supporting framework) of liver, spleen, lymph nodes; red bone marrow; reticular lamina of basement membrane; around blood vessels and muscles.
FunctionForms stroma of organs; binds smooth muscle tissue cells; filters and removes worn-out blood cells in spleen and microbes in lymph nodes.

B. Dense Connective Tissue

Dense connective tissue contains more fibers, which are thicker and more densely packed, but have considerably fewer cells than loose connective tissue.

A. DENSE REGULAR CONNECTIVE TISSUE
StructureForms shiny white extracellular matrix; mainly collagen fibers regularly arranged in bundles with fibroblasts in rows between them.
LocationForms tendons (attach muscle to bone), most ligaments (attach bone to bone) etc.
FunctionProvides strong attachment between various structures.
B. DENSE IRREGULAR CONNECTIVE TISSUE
StructureIt is made up of collagen fibers; usually irregularly arranged with a few fibroblasts.
LocationMuscles, skin, heart, bone, cartilage etc.
FunctionProvides tensile (pulling) strength in many directions.
C. ELASTIC CONNECTIVE TISSUE
StructureContains predominantly elastic fibers with fibroblasts between them.
LocationLung tissue, walls of elastic arteries, trachea, bronchial tubes etc.
FunctionAllows stretching of various organs.

C. Cartilage

Unlike other connective tissue, cartilages have no blood vessels and nerves. It consists of a dense network of collagenous fibers and elastic fibers firmly embedded in chondriotin sulfate. The strength is because of collagenous fibers. The cells of a matured cartilage are called chondrocyte. The surface of a cartilage is surrounded by irregularly arranged dense connective tissue called perichondrium.

A. HYALINE CARTILAGE
StructureCollagen fibers are small and evenly dispersed in the matrix, making the matrix appear transparent; the chondrocytes are found in spaces, or lacunae, within the firm but flexible matrix.
LocationFound at joints over long bones as articlar cartilage and forms costal cartilage (at ventral end of ribs). It also forms nose, larynx, trachea, bronchi and bronchial tubes.
FunctionProvides smooth surfaces for movement at joints, flexibility, and support; weakest type of cartilage and can be fractured.
B. FIBRO CARTILAGE
StructureHas chondrocytes among clearly visible thick bundles of collagen fibers within extracellular matrix.
LocationSymphysis pubis, in the inter-vertebral discs and knee.
FunctionSupport and joining structures together.
C. ELASTIC CARTILAGE
StructureHas chondrocytes in threadlike network of elastic fibers within extracellular matrix.
LocationLarynx (epiglottis), part of external ear (auricle), auditory (eustachian) tubes.
FunctionProvides strength and elasticity; maintains shape of certain structures.

D. Osseous tissue (Bone)

The matured bone cell osteocytes, embedded in the intercellular substance consisting mineral salts (calcium phosphate and calcium carbonate) with collagenous fibers. The osseous tissue together with cartilage and joints it comprises the skeletal system.

BONE TISSUE
StructureHard, bony matrix predominates; many osteocytes are located within lacunae; the matrix contains mineral salts is organized into layers called lamellae.
LocationVarious parts of bones of the body
FunctionSupport, protection, storage.

E. Vascular tissue (Blood Tissue or Liquid Connective Tissue)

It is a liquid connective tissue. It contains intercellular substance plasma. Plasma is a straw colored liquid, consists water and dissolved material.

BLOOD
StructureBlood plasma and formed elements: red blood cells (erythrocytes), white blood cells (leukocytes), platelets (thrombocytes).

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LocationWithin blood vessels & within chambers of heart.
FunctionRed blood cells: transport O2 and some CO2;

White blood cells: phagocytosis and allergic reactions