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The Biology of Climbing: Part 2, Connective Tissues and Body Support

Submitted by pianomahnn on 2001-10-01

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The Biology of Climbing

The Biology of Climbing


Part 2: Connective Tissues and Body Support


            Almost every organ in the body has a framework of connective tissue that supports and cushions it.  Cartilage and bone are examples of connective tissues that support your body and protect organs such as your heart and lungs.  Blood is also a connective tissue that transports materials, thereby connecting distant parts of the body.  Adipose tissue provides a protective cushion and stores fat.

            There are many kinds of connective tissues and many systems for classifying them.  Some of the main types, which will be the concentration of this article, are: (1) loose and dense connective tissues; (2) elastic connective tissue; (3) reticular connective tissue; (4) adipose tissue; (5) cartilage; (6) bone; and (7) blood, lymph, and tissues that produce blood cells.  The tissues vary widely in their structural details and in the functions they perform.

            Typically, connective tissues contain relatively few cells; these are embedded in an extensive intercellular substance consisting of threadlike, microscopic fibers scattered throughout a matrix, a thin gel composed of polysaccharides secreted by the cells.  The cells of different kinds of connective tissues differ in their shapes and structures and in the kinds of fibers and matrices they secrete.  The natures and function of each kind of connective tissue are determined in part by the structure and properties of the intercellular substance.


The basic contents of connective tissues


            Connective tissue typically contains three types of fibers; collagen, elastic, and reticular.  Collagen fibers, the most numerous type, are composed of collagens, the most abundant protein in the body.  Collagen is a very tough material.  The tensile strength (ability to be stretched without tearing) of collagen fibers is comparable to that of steel.  Collagen fibers are wavy and flexible, allowing them to remain intact when tissue is stretched.

            Elastic fibers branch and fuse to form networks.  They can be stretched by a force and then (like a stretched rubber band) return to their original size and shape when the force is removed.  Elastic fibers, composed of the protein elastin, are an important component of structures that must stretch.

            Reticular fibers are very small branched fibers that form delicate networks not visible when looked at under normal microscopes.  The framework of many organs such as the live and lymph nodes consists of reticular fibers.


Connective Tissues Contain Specialized Cells


            Fibroblasts are connective tissues cells that produce the fibers, as well as the protein and carbohydrate complexes of the matrix.  Fibroblasts release protein components that become arranged to form the characteristic fibers.  These cells are especially active in developing tissue and are important in healing wounds.  As tissues mature, the number of fibroblasts decreases and they become less active.

            Macrophages, the scavenger cells of the body, commonly wander through connective tissues, cleaning up cellular debris and getting rid of foreign matter, including bacteria.  Among the other types of cells seen in connective tissues are adipose (fat) cells; mast cells, which release histamine during allergic reactions; and plasma cells, which secrete antibodies for the immune system.


Loose Connective Tissues


            Loose connective tissue is the most widely distributed connective tissue in the body.  Found as a thin filling between body parts, it serves as a reservoir for fluid and salts.  Nerves, blood vessels, and muscles are wrapped in this tissue.  Together with adipose (fat) tissue, loose connective tissue forms the subcutaneous (below the skin) layer that attaches skin to the muscles and other structures beneath.  Loose connective tissue consists of fibers running in all directions through a semifluid matrix.  Its flexibility permits the parts it connects to move.


Dense Connective Tissues


            Dense connective tissue, found in the lower layer of the skin, is very strong, though somewhat less flexible than loose connective tissue.  Collagen fibers predominate.  In irregular dense connective tissue, the collagen fibers are arranged in bundles distributed in all directions throughout the tissue.

            In regular dense connective tissue, collagen bundles are arranged in a definite pattern, making the tissue greatly resistant to stress.  Tends, the cords that connect muscles to bones, and ligaments, the cables that connect bones to one another, consist of regular dense connective tissues.


Elastic Connective Tissues


            Elastic connective tissues consist mainly of bundles of parallel elastic fibers.  This tissue type is found in structures that must expand and then return to their original size, such as lung tissue and the walls of the large intestine.


Reticular Connective Tissue


            Reticular connective tissue is composed mainly of interlacing reticular fibers.  It forms a supporting framework in many organs, including the liver, spleen, and lymph nodes.


Adipose Tissue


            Adipose tissue is rich with fat cells that store fat and release it when fuel is needed for cellular respiration.  Adipose tissue is found in the subcutaneous layer and in tissue that cushions internal organs.


Article Three: Bones, Cartilage, Muscle


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