Rachel+-+Excretory+System

=Excretory System= =Skin: The Integumentary System=

== source: http://www.essentialdayspa.com/images/emerginc/Skin_Anathomy_and_Physiology.gif

Made up of all four tissue types:
 * 1) Epithelial Tissue (or Epithelium) - lines hollow organs and covers surfaces.
 * 2) Connective Tissue - binds structures, supports and protects, fills spaces, stores fat, and forms blood cells. Adipose tissue, cartilage, bone, and blood are different types.
 * 3) Muscle Tissue (or Contractile Tissue) - composed of fibers that can shorten and thicken.
 * 4) Nervous Tissue - contains nerve cells (neurons); conduct impulses and neuroglia (supports, protects, and provides nutrients to neurons).


 * Skin** is referred to as the integumentary system because it is made up of many different accessory organs such as hair, nails, sweat glands, and sebaceous glands.
 * Accounts for 15% of average human body's weight
 * Provides protection fro underlying tissue
 * Helps regulate body temperature.
 * Two Regions:
 * 1) Epidermis (Top layer)
 * 2) Dermis (Bottom layer)
 * Under both regions: Subcutaneous layer - between the skin and bone/muscle.

Epidermis
 * New epidermal cells are made from stem cells
 * Damaged tissue produces more cells and skin grafting begins in order to make new skin.
 * Pushing to the surface skin cells harden and flatten.
 * Cells harden because of keratin, a waterproof protein.
 * Skin is waterproof because skin cells are dead and keratinized.
 * Two Specialized Cells
 * Langerhan cell - macrophages
 * Melanocytes - produce melanin (responsible for skin color)

Dermis
 * Region beneath epidermis.
 * Made of dense fibrous connective tissue.
 * Collagen Fibers - prevents tears
 * Elastic Fibers - allows movement; maintains normal skin tension.
 * Contains blood vessels that nourish skin.
 * Sensory receptors primary location.
 * Supply information to nervous system about external temperature

Blood Vessels in the Dermis and their Role in Temperature Regulation
 * When blood rushes into vessels a person turns red.


 * When body temperature rises blood vessels dilate.
 * Dilated vessels allow more blood to be brought to surface of skin for cooling.
 * More blood in vessels in the skin more red the person appears.
 * During exercise or extreme heat a persons body temperature rises thus dilating blood vessels in the dermis, making the skin appear more red.
 * When body temperature is low the vessels constrict blood flow.
 * Less blood in the vessel, less red the skin will appear.
 * Reason why people who are cold are referred to as looking "blue."