Khady Guiro C2PRISM

REVIEW

 Human beings are one of the most complex organisms on this planet.  Imagine billions of microscopic parts, each with its own identity, working together in an organized manner for the benefit of the total being.  The human body is a single structure but it is made up of billions of smaller structures of four major kinds: cells, tissues, organs, and systems.

 CELLS  Cells recognized as the simplest units of living matter that can maintain life and reproduce themselves.  The human body, which is made up of numerous cells, begins as a single, newly fertilized cell.  TISSUES  Tissues are somewhat more complex units than cells.  By definition, a tissue is an organization of a great many similar cells with varying amounts and kinds of nonliving, intercellular substance between them.  ORGANS  Organs are more complex units than tissues.  An organ is an organization of several different kinds of tissues so arranged that together they can perform a special function.  SYSTEMS  Systems are the most complex of the component units of the human body.  A system is an organization of varying numbers and kinds of organs so arranged that together they can perform complex functions for the body.

Illustration Cells organize into tissues Organs organize into organ systems Tissues organize into organs Organ systems are organized into make up the organism

TISSUES

Body Tissues  Tissue is a group of cells that have similar structure and that function together as a unit.  A nonliving material, called the intercellular matrix, fills the spaces between the cells.  This may be abundant in some tissues and minimal in others.  The intercellular matrix may contain special substances such as salts and fibers that are unique to a specific tissue and gives that tissue distinctive characteristics.  There are four main tissue types in the body: epithelial, connective, muscle, and nervous.  Each is designed for specific functions.

Example The stomach is an organization of muscle, connective, epithelial, and nervous tissues. Muscle and connective tissues form its wall, epithelial and connective tissues form its lining, and nervous tissue extends throughout both its wall and its lining.

Epithelial tissues

 Epithelial tissues cover surfaces.  For instance, they cover the external body surface, line its cavities, and generally mark off our “insides” from our outsides.  Epithelial tissues are widespread throughout the body.  They are the major tissue in glands.  Functions:  Protection,  absorption,  filtration,  excretion,  secretion,  sometimes sensory reception.

General characteristics  Cells fit closely together to form membranes, or sheets of cells, and are bound together by specialized junctions.  The membranes always have one exposed surface called the apical surface.  The cells are attached to and supported by an adhesive basement membrane.  Epithelial tissues have no blood supply of their own  (avascular)  but depend on diffusion of nutrients from the underlying connective tissue.  If well nourished, epithelial cells can easily regenerate themselves.

Classification  The covering and lining of epithelial tissues are classified according to two criteria: cell shape and relative number of layers.  On the basis of shape:  Squamous  Scale-like  Cuboidal  Cube-like  Columnar  Column-shaped  On the basis of arrangement:  Simple epithelia  consisting of one layer of cells attached to the basement membrane.  Stratified epithelia  consisting of more than one layer of cells with only the deepest layer resting on the basement membrane.  The terms denoting the shape and arrangement of the epithelial cells are combined to describe the epithelium fully.

Classification based on number of layers

Classification based on cell shape

Categories of epithelia  There are two categorized types of epithelia: pseudo-stratified epithelium and transitional epithelium.  Pseudo-stratified epithelium  Simple columnar epithelium (one layer of cells with all cells attached to the basement membrane)  But its cells extend various distance from the basement membrane so it gives the false appearance of being stratified  Transitional epithelium  Described as stratified squamous epithelium formed of rounded cells  With the ability to slide over one another to allow the organ to be stretched.  Transitional epithelium is only found in urinary system organs.