Discovery Science: Humans – Cell types and the Lymphatic System

Earth Science: Biology – Humans – Immune System

The human immune system is responsible for protecting the body from pathogens.

There are two types of immune systems: the innate nonspecific resistance fights germs by means of low pH values (stomach) or macrophages (leuocytes in the blood and tissue); the specific resistance is an acquired resistance to specific pathogens.

Earth Science: Biology – Humans – Cell types and the Lymphatic System

On a cellular level the immune system is supported by three main cell types, three groups of serum proteins (humoral defense system), and the lymphatic system with its lymphatic organs.

Leuocytes (white blood cells) play a major role in attacking pathogens. These mobile cells originate from the stem cells of the bone marrow and can pass through the walls of blood vessels. Leuocytes are mostly divided into granulocytes and monocytes (they develop into macro-phages) for nonspecific immune responses as well as lymphocytes.

The former are responsible for destroying germs by phago-cytosis (ingestion). The latter can be grouped into B- and T-lymphocytes which are of varying life spans. T-lymphocytes may reach 500 days old and serve as memory cells, as they can “remember” pathogens after a defeated infection.

Three types of serum proteins ensure immunity: antibodies (immunoglobulins), cytokines, and complement proteins. Anti-bodies are produced by B-lymphocytes and consist of a constant region and a variable region. Antibodies of the same type have identical constant regions.

The variable region recognizes antigens, for example, certain areas on the surface of bacteria. The constant region determines functional properties of the antibody. Cytokines are messenger substances produced and released by immune and nonimmune cells.

They function to stimulate and coordinate immune responses. The complement system is also involved in cell destruction and consists of several plasma proteins, which form a network with more than 30 different components.

The lymphatic system

The lymphatic system consists of lymphatic vessels as well as primary (for example, bone marrow and thymus) and secondary lymphatic organs (including the spleen and lymph nodes).

The lymphatic organs produce and store cells of the immune system and regulate lymphatic vessels (via lymph nodes) and blood circulation (via the spleen). A dense network of lymphatic vessels traverses the entire body. Its function is the discharge of lymph fluid.


Normally we take little notice of our palatine tonsils, except when they are sore. They have a good side that may be less obvious to us, but they are still important to our immune system.

In concert with the pharyngeal and lingual tonsils they recognize pathogens entering through the mouth and nose and help initiate an immune response.

A few decades ago it was still common practice to remove the tonsils for preventative reasons. Today a removal of the tonsils is viewed with much more caution.