LYMPHATIC SYSTEM ASSIGNMENT
13.1 Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphatic organs. The three main functions of the lymphatic
system are fluid balance, fat absorption, and defense against disease. The lymphatic system aids in fluid balance by
taking up excess tissue fluid and returning it to the bloodstream. The lymphatic system absorbs fats from the digestive
system. The special capillaries that transport fats are celled lacteals.
Lymphatic Vessels
The fluid inside of lymphatic vessels is called lymph. The smallest lymphatic vessels are called lymphatic capillaries.
These smaller vessels join together to form larger lymphatic vessels which eventually enter either the thoracic duct or
the right lymphatic duct. These ducts return the lymph fluid to either the left or right subclavian vein.
13.2 Organs, Tissues, and Cells of the Immune System
Primary Lymphatic Organs
The primary lymphatic organs are the red bone marrow and the thymus gland. Red bone marrow is found in the
sternum, vertebrae, ribs, skull, pelvic girdle, and the proximal ends of the humerus and femur. The thymus gland is
located in the thoracic cavity. Lymphocytes originate and/or mature in the primary lymphatic organs.
Secondary Lymphatic Organs
The secondary lymphatic organs are where lymphocytes bind to foreign proteins that are known as antigens. The
largest lymphatic organ is the spleen, which is found in the left upper quadrant of the abdomen. The small oval organs
that are located along lymphatic vessels are the lymph nodes. A cluster of lymphatic tissue that is not enclosed by a
capsule is called a lymphatic nodule. Examples of this type of organ that are found in the pharynx are the tonsils. There
are pharyngeal, lingual, and palatine tonsils. Additional modules are found in the wall of the intestine. These are known
as Peyer patches. Additional nodules are found in the appendix.
13.3 Nonspecific and Specific Defenses
Nonspecific Defenses
Barriers to Entry
Physical barriers to entry of pathogens include intact skin and mucous membranes. Chemical barriers include
secretions of the sebaceous glands and the sweat glands in the skin. An enzyme called lysozyme helps to kill bacteria.
The microbes that usually are found on the skin and in body cavities compete with disease-causing microbes. These
harmless microbes are referred to as normal flora.
Inflammatory Reaction
Inflammation reaction is a general response to tissue injury; the response is the same whether physical agents, chemical
agents, or pathogens cause the injury. The four signs of inflammation are redness, swelling, heat, and pain.
Natural Killer Cells
These are special white blood cells, which kill virus-infected cells and tumor cells.
Protective Proteins
Protective proteins in the blood plasma include the complement system and interferon.
Specific Defenses
Specific defenses involve lymphocytes responding to specific foreign antigens. B lymphocytes mature in the bone
marrow, while T lymphocytes mature in the thymus gland. B lymphocytes form plasma cells which produce antibodies;
these are proteins that neutralize specific antigens. IgG, IgM, IgA, IgD, and IgE are all examples of categories of
antibodies. T lymphocytes include cytotoxic T cells, which destroy virus-infected cells and cancer cells and helper T cells,
which secrete chemical that enhance the immune response of macrophages, B lymphocytes, and other T lymphocytes.