Connective tissue is found throughout the body. It is usually characterized by large amounts of extracellular material that separates cells from one another.
Connective tissue consists of two basic elements:
- Extracellular matrix
The extracellular material, or extracellular matrix, has three major components:
(1) Protein fibers,
(2) Ground substance consisting of nonfibrous protein and other molecules, and
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)
Dense (more fibers, less ground substance)
Dense regular connective tissue
Dense irregular connective tissue
Elastic connective tissue
|Supporting connective tissue
Cartilage (semisolid matrix)
Bone (solid matrix)
|Fluid connective tissue
A. Loose Connective Tissue
The fibers of loose connective tissue are loosely arranged between cells.
|A. AREOLAR CONNECTIVE TISSUE|
|Structure||A 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.|
|Location||Skin, mucous membranes; around blood vessels, nerves, and body organs.|
|Function||Strength, elasticity, support.|
|B. ADIPOSE TISSUE|
|Structure||Little 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.|
|Location||Skin, around heart and kidneys, yellow bone marrow, padding etc.|
|Function||Reduces heat loss through skin; serves as an energy reserve; supports and protects organs.|
|C. RETICULAR CONNECTIVE TISSUE|
|Structure||Fine network of reticular fibers irregularly arranged.|
|Location||Stroma (supporting framework) of liver, spleen, lymph nodes; red bone marrow; reticular lamina of basement membrane; around blood vessels and muscles.|
|Function||Forms 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|
|Structure||Forms shiny white extracellular matrix; mainly collagen fibers regularly arranged in bundles with fibroblasts in rows between them.|
|Location||Forms tendons (attach muscle to bone), most ligaments (attach bone to bone) etc.|
|Function||Provides strong attachment between various structures.|
|B. DENSE IRREGULAR CONNECTIVE TISSUE|
|Structure||It is made up of collagen fibers; usually irregularly arranged with a few fibroblasts.|
|Location||Muscles, skin, heart, bone, cartilage etc.|
|Function||Provides tensile (pulling) strength in many directions.|
|C. ELASTIC CONNECTIVE TISSUE|
|Structure||Contains predominantly elastic fibers with fibroblasts between them.|
|Location||Lung tissue, walls of elastic arteries, trachea, bronchial tubes etc.|
|Function||Allows stretching of various organs.|
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|
|Structure||Collagen 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.|
|Location||Found 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.|
|Function||Provides smooth surfaces for movement at joints, flexibility, and support; weakest type of cartilage and can be fractured.|
|B. FIBRO CARTILAGE|
|Structure||Has chondrocytes among clearly visible thick bundles of collagen fibers within extracellular matrix.|
|Location||Symphysis pubis, in the inter-vertebral discs and knee.|
|Function||Support and joining structures together.|
|C. ELASTIC CARTILAGE|
|Structure||Has chondrocytes in threadlike network of elastic fibers within extracellular matrix.|
|Location||Larynx (epiglottis), part of external ear (auricle), auditory (eustachian) tubes.|
|Function||Provides 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.
|Structure||Hard, bony matrix predominates; many osteocytes are located within lacunae; the matrix contains mineral salts is organized into layers called lamellae.|
|Location||Various parts of bones of the body|
|Function||Support, 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.
|Structure||Blood plasma and formed elements: red blood cells (erythrocytes), white blood cells (leukocytes), platelets (thrombocytes).|
|Location||Within blood vessels & within chambers of heart.|
|Function||Red blood cells: transport O2 and some CO2;
White blood cells: phagocytosis and allergic reactions
Platelets: essential for blood clotting.