".,LYMPHATIC AND IMMUNE SYSTEM,."

The lymphatic system is both the transport system and barracks of your immune system. It is a second circulatory system parallel to the cardiovascular system.

The lymphatic system has four functions:
* storage and maturation of some types of white blood cells
*recycling of lost fluids from the cardiovascular system
*absorption of glycerol and fatty acids from food
*transporting pathogens to the lymph nodes.

Given that the lymphatic system is intimately connected to the function of cardiovascular system, it should come no surprise that the smallest pipes of the lymphatic system, called lymph capillaries, run parallel to blood capillaries. The fluid filling the lymph capillaries is called lymphatic fluid, or simply lymph. The lymphatic vessels is where several lymph capillary networks. Structurally similar veins, including valves. The lymph nodes is where the larges lymphatic vessels empty.

Lymphatic vessels exiting lymph nodes empty into one of several lymphatic trunks.These trunks, named for their locations, are lumbar, intestinal, bronchomediastinal, subclavian, jugular and intercostal. There are two larger collections of lymphatic tissue, known as lymph organs. These lymph organs are the thymus and the spleen. The spleen is a spongy organ and has blood sinuses. Surrounded by the blood sinuses are islands of white pulp containing lymphocytes and islands of red pulp. The thymus is a soft organ. It is bigger in the children and becomes smaller or even disappears in adults. The thymus is packed with lymphocyte.

The immune system defends the body on two fronts, by innate and adaptive. Innate immunity is the first line of defense against invasion while the adaptive immunity is the back up.

COMPONENTS OF THE IMMUNE SYSTEM

BARRIER : Anything that prevents invaders from getting inside your body prevents infection. Your body has many barriers located in the places where invaders are most likely to gain entrance. Physical barrier include skin and mucous membranes of the eyes, digestive system, respiratory, and reproductive system. The fluids associated with these chemicals are contain chemicals that act as chemical barriers. These chemicals are contained in tears, saliva, urine, mucous secretion, and sweat.

CELLS : White blood cells ( leukocytes ) are responsible for defending the body against invaders. Red blood cells are responsible for carrying oxygen throughout the body. And platelets are responsible for blood's ability to clot. The immune system uses a dozen or more different types of cells to combat pathogens. All of these cells are leukocytes or modified leukocytes. Leukocytes can be divided into two groups. Polymorphonuclear granulocytes are cells with granules or spots in their cytoplasm. Agranulocytes or mononuclear cells have no granulocytes in their cytoplasm. These two groups contains several different types of cells that play a role in the body's defense against infection.

*POLYMURPHONUCLEAR GRANULOCYTES

** NEUTROPHILS
- whose function is phagocytosis
- most common leukocytes in the blood stream
- originate in the bone marrow
- release chemical that increase tissue damage of inflammation
- part of innate immunity

** BASOPHILS
- release chemicals to promote inflammation
- mobile, entering infected tissues from the bloodstream
- low in number

**MAST CELLS
- not mobile
- found stationed throughout the body
- also found in connective tissue

**EOSINOPHILS
- counteract the activities of basophils and mast cells
- break down the chemicals released by basophils and mast cells
- also have role in fighting invasion by parasitic worms


*MONONUCLEAR ( AGRANULOCYTES )
** MONOCYTES
> MACROPHAGES
- modified monocytes
- phagocytic cells, which are active in the later stages of an infection
- release chemicals to stimulate the immune system

>DENDRITIC CELLS
- weakly phogocytic
- most important job is as antigen displaying cells or ADC's
- able to ingest a foreign cell and place the foreign antigens into their own membrane

**LYMPHOCYTES
>NATURAL KILLER CELLS
- kills any cells displaying foreign bodies part of innate immunity
-early symptoms of a cold or flu are due to the action of NK cells

>T- LYMPHOCYTES ( T- CELLS )
- responsible for a portion of adaptive immunity known as cell- mediated immunity
- TYPES:
= CYTOTOXIC T CELLS ( CELL POISON )
- kills infected cells and release immune stimulating chemicals

= HELPER T CELLS
- help activate other parts of adaptive immunity

= REGULATORY T CELLS
- regulate immune response

= MEMORY T CELLS
- remember pathogens after exposure

>B LYMPHOCYTES ( B- CELLS )
- known as antibody- mediated immunity
- TYPES:
= PLASMA CELLS
- produce antibodies to nonself-antigens

= MEMORY B CELLS
- remember pathogens