Saturday, June 5, 2010

Tissues... Part II

Connective tissue is everywhere! It can be found in all parts of the body or as a part of various organs!  The primary function is for protection, support and binding different tissues together.
 For the most part, connective tissues are highly vascular.  The exceptions include tendons and ligaments.  Connective tissues are composed of many, many different cells.  Between the cells of connective tissue, there is a large amount of noncellular, nonliving material.

Before getting into the different types of connective tissue, I'm going to explain the extracellular matrix.  The matrix is produced by the cells around it and then extruded.  There are two components of the extracellular matrix: ground substance and fibers.  The ground substance is made of interstitial fluid, cell adhesion proteins and proteoglycans.  The ground substance, depending on its location and function, can be in any state of matter.  The ground substance functions as a medium for nutrients and things to diffuse between the blood capillaries and the cells. The fibers provide support and come in different forms: collagen, elastic or reticular fibers.  Fibers make diffusion a little more difficult because there is less pliability.

Areolar (connective tissue proper: loose connective tissue)
description: Areolar tissue has a gel-like matrix.  All three fiber types are present: fibroblasts, macrophages and some red blood cells.
function: This tissue wraps and cushions organs  The macrophages phagocytize bacteria.  This tissue plays an important role in inflammation and conveys tissue fluid.
location:  It is most commonly found underneath the epithelia, because forms the lamina propria of mucous membranes, packages organs and surrounds our capillaries.

Adipose (connective tissue proper; loose connective tissue)
description: This tissue is in a matrix form similar to areolar tissue, but it is very sparse.  These fat cells have pushed the nucleus to the outer edge of the cell.
function: Adipose tissue provides reserve fuel.  It insulates against heat loss and supports and protects our organs.
location: We can find adipose tissue under the skin, around our kidneys and eye balls, within our abdomen and in breasts.

Reticular (connective tissue proper, loose connective tissue)
description: The reticular tissue is full of reticular fibers! They are in a typically loose ground substance.
function: The reticular fibers form a soft internal skeleton that supports other cell types.
location: You'll find reticular tissue in the lymphoid organs.

Dense Regular (connective tissue proper, dense connective tissue)
description: This tissue is full of parallel collagen fibers.  There are a few elastin fibers.  The major cell type is the fibroblast.
function: this tissue, dense regular, attaches muscles to bones or vice versa.  It is very, very strong and withstands a great tensile strength when a force is applied in one direction.
location: You'll find this tissue making up tendons and ligaments and aponeuroses.  (remember tendons and ligaments are mostly avascular.)

Dense Irregular (connective tissue proper, dense connective tissue)
description: This irregular tissue is also mostly collagen fibers.  There are some elastic fibers.  The major cell is the fibroblast.  
function: The dense irregular tissue can withstand tension in many directions.  It also provides structural strength.
location: This tissue is found as the dermis of the skin.  It is also the submucosa of the digestive tract and the fibrous capsules of the organs and joints.  

Hyaline (cartilage)
description: Hyaline cartilage is amorphous but firm matrix.  The matrix, made from collagen fibers, in imperceptible.  
function: This cartilage supports and reinforces.  There are some built in cushioning properties.  It also resists compressive stress.
location: Most of the embryonic skeleton is made from hyaline cartilage.  In mature humans, it will be the covering of long bones in joint cavities, form the costal cartilages of the ribs, and will also be in the nose, trachea and larynx.  

Elastic cartilage 
description: this is an elastic version of the hyaline cartilage, the major difference is that there are more elastic fibers here.  
function: this cartilage maintains the shape of a structure, but allows for great flexibility. 
location: It's in the ear and the epiglottis.  

description: This cartilage is a less firm form of hyaline cartilage.  It's thick collagen fibers are predominate.  
function: They are able to provide tensile strength and absorb compressive shock.
location: The fibrocartilage is located in the intervertebral discs, the pubic symphysis and the discs of the knee joint.  

Bone (osseous tissue)
description: Bones are made of hard calcified matrix containing many collagen fibers.  Osteocytes lie in lacunae.  Bones are very vascularized. 
function: Bones support and protect. They provide levers for muscles to act on.  They store calcium and other minerals and fat.  Marrow inside the bone is for blood cell formation.  
location: Bones!  

description: Red and white blood cells are in a fluid matrix.  
function: Blood transports oxygen and carbon dioxide, nutrients, wastes and some other stuff.  
location:  Blood is typically contained within blood vessels.  

Nervous Tissue is composed of two major cell populations.  They are the neuroglia and neurons.  The neuroglia are the special supporting cells that protect, support and insulate the delicate neurons.  Neurons are highly specialized cells.  They receive stimuli and then conduct impulses to all parts of the body.  They are located in the brain, spinal cord and nerves.  

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