Lymphatic and Immune System

The Lymphatic and Immune Systems

• The lymphatic system is responsible for maintaining blood volume and protecting the body from infection, while the immune system is responsible for protecting the body from foreign substances and disease.

Fluid Compartments

• The body contains two main fluid compartments: intracellular fluid and extracellular fluid.
• Intracellular fluid is the fluid within cells, making up about 40% of the body's water content.
• Extracellular fluid is the fluid outside of cells, making up about 20% of the body's water content.
• Extracellular fluid is further divided into:
  • Plasma (the fluid portion of blood, making up about 5% of the body's water content)
  • Interstitial fluid (the fluid surrounding tissue cells, making up about 15% of the body's water content)
  • Lymph (a clear fluid that circulates through the lymphatic vessels, making up about 5% of the body's water content)

Lymphatic System Function

• The lymphatic system has two main functions:
  • To return fluid that has leaked from blood vessels back to the bloodstream (maintaining blood volume)
  • To protect the body from infection (immune function)

Lymphatic System Organs

• The lymphatic system includes the following organs:
  • Thymus gland
  • Bone marrow
  • Spleen
  • Lymph nodes
  • Lymphatic vessels
  • Lymphatic ducts
  • Tonsils
  • Lymphoid tissues (found in the mucous membranes of the digestive, respiratory, urinary, and reproductive tracts)

Spleen

• The spleen is the largest mass of lymphatic tissue in the body.
• The spleen filters the blood, removing old or damaged red blood cells and platelets.
• The spleen also stores red blood cells and platelets, releasing them into the bloodstream as needed.

Thymus Gland

• The thymus gland is responsible for the maturation of T-lymphocytes (a type of white blood cell involved in the immune response).
• The thymus gland is located in the superior mediastinum, superior to the heart.
• The thymus gland is large in infancy and atrophies with age.

Bone Marrow

• Bone marrow is responsible for the production of blood cells, including red blood cells, platelets, and white blood cells.
• Bone marrow is found in the medullary cavity of bones.
• There are two types of bone marrow: red bone marrow and yellow bone marrow.
• Red bone marrow is responsible for the production of blood cells, while yellow bone marrow is primarily composed of fat cells.

Immune Response

• The immune response involves the recognition of pathogens (foreign substances) by the immune system and the activation of immune cells to eliminate the pathogen.
• There are two main types of immune responses:
  • Humoral immune response (involving B-lymphocytes and antibodies)
  • Cell-mediated immune response (involving T-lymphocytes)

Humoral Immune Response

• B-lymphocytes recognize pathogens and produce antibodies, which bind to the pathogen, marking it for destruction.
• There are two types of B-cells:
  • Plasma cells (produce antibodies)
  • Memory B-cells (remember the pathogen and can rapidly produce antibodies upon re-exposure)

Cell-Mediated Immune Response

• T-lymphocytes recognize pathogens and directly kill infected cells or produce chemical signals that activate other immune cells.
• There are several types of T-cells, including:
  • Cytotoxic T-cells (kill infected cells)
  • Helper T-cells (activate other immune cells)
  • Regulatory T-cells (regulate the immune response)

Antigens and Antibodies

• Antigens are substances that can trigger an immune response.
• Antibodies are proteins produced by B-cells that bind to specific antigens.
• Antibodies have a specific shape that allows them to bind to a particular antigen.

Inflammation

• Inflammation is a generic response to tissue damage or infection.
• The inflammatory response involves the activation of immune cells, the dilation of blood vessels, and the movement of immune cells to the site of injury or infection.

Three Lines of Defense

• The body has three lines of defense against infection:
  1. Intact skin and mucous membranes (physical barrier)
  2. Inflammatory response (non-specific immune response)
  3. Immune response (specific immune response)

Lymphatic Tissue Composition

• Lymphatic tissue is composed of reticular connective tissue
• Fibroblasts are a type of cell found in lymphatic tissue
• Macrophages, derived from monocytes that have left the blood, are present in lymphatic tissue
• Lymphocytes are abundant in lymphatic tissue
• Lymphocytes serve as a defense mechanism, interacting with harmful substances

cell function

• Macrophages are monocytes that have migrated out of the blood
• Lymphocytes play a crucial role in responding to harmful substances

Thymus Gland Functions

• The thymus gland does not produce blood cells; only the red bone marrow produces blood cells.
• Bone marrow produces immature T-cells, also known as pre-thymocytes, which then migrate to the thymus gland.
• In the thymus gland, pre-thymocytes differentiate into mature T-cells, making them ready to perform their immune functions.

Development of T-Cells

• Pre-thymocytes leave the red bone marrow and circulate to the thymus gland, where they mature into T-cells.
• The thymus gland plays a crucial role in the maturation of T-cells, ensuring they can recognize and distinguish between self and non-self.

Immune System Functions

• The thymus gland is responsible for half of the immune system's functions, particularly in recognizing self vs. non-self T-cells.
• The thymus gland helps the body distinguish between its own tissues and foreign substances, preventing autoimmune responses.

Autoimmune Diseases

• Autoimmune diseases, such as psoriasis and arthritis, occur when the body's immune system mistakenly attacks its own tissues.
• Early exposure to various substances in childhood may help the body develop a stronger immune system, reducing the risk of autoimmune diseases later in life.