D3.3 - The Lymphatic System and Immunity

Lymphatic System and Immunity

• The lymphatic system is a network of vessels, glands, and nodes spread throughout the body
• It collects fluid (lymph) made of interstitial fluid
• Lymph connects to the circulatory system at the subclavian veins
• Lymph works with white blood cells to protect the body from infection
• Lymphocytes mature in lymph nodes
• Lymph nodes contain macrophages, which trap and destroy bacteria

Human Defense System

• The first line of defense prevents organisms from entering the body
• Skin and mucus lining respiratory passages keep out most microbes
• Stomach acids, oils in skin, and enzymes in tears break down bacteria

Non-Specific Defenses

• The second line of defense is cell-mediated immunity
• This includes neutrophils, monocytes, and macrophages
• Phagocytosis, where cells engulf bacteria, is used to kill bacteria
• Natural killer cells target cancerous or virus-infected body cells

Specific Defenses (Antibody Mediated Immunity)

• The third line of defense is immunity developed by specific defenses using antibodies
• Antibodies are proteins that recognize and destroy foreign substances
• Lymphocytes (T and B cells) are primarily responsible for the immune response
• The body recognizes its own molecules ("self") and protects against foreign invaders

T & B Cells – Lymphocytes

• Lymphocytes are divided into B-cells and T-cells based on where they mature
• B-cells mature in bone marrow and produce Y-shaped antibodies
• T-cells mature in the thymus gland and signal an attack from foreign invaders

Antigens & Antibodies

• Antigens are molecules found on cells and pathogens
• Antigens identify cells for T and B cells
• Antibodies are Y-shaped proteins that attach to specific antigens
• Antibody-antigen complexes make invaders visible to macrophages
• Antibodies prevent toxins from entering cells

Recognizing Antigens

• When an invader is destroyed, its antigen goes to the macrophage surface
• The macrophage couples with helper T-cells
• Helper T-cells release chemical signals to activate macrophages, B-cells, and T-cells
• Activated B-cells divide and produce antibodies

Recognizing Antigens (continued)

• Helper T-cells activate killer T-cells that destroy invading cells and body cells infected by viruses by puncturing their membranes
• Killer T-cells can be activated indirectly by chemical signals from helper T-cells or directly by invading pathogens
• Suppressor T-cells signal the immune system to shut down after the infection is fought off
• Phagocytes clean up dead/injured B and T-cells, and memory T-cells remain in the bloodstream for future responses to antigens

Blood Types

• Blood transfusion is the transfer of blood from one person to another
• Different blood types result from different groups of red blood cell antigens (ABO system)
• The ABO system determines blood type based on the presence of Type A and B antigens on red blood cells
• Agglutination is the clumping of red blood cells when incompatible blood types are mixed

Blood Groups – How They Work

• Blood types have specific antigens and antibodies, for example A blood type has "A" antigen and Anti-B antibodies in plasma
• Different blood types can receive blood from certain other types

Rhesus (Rh) Factor

• Rh factor is a second antigen found in red blood cells
• People can either have Rh+ (with antigens) or Rh- (without antigens) antigen
• An Rh- individual may form antibodies against Rh+ blood when exposed via transfusion or pregnancy

Rhesus Factor and Pregnancy

• If a Rh- mother carries a Rh+ baby, the mother's immune system can produce antibodies against the baby's blood cells.
• In subsequent pregnancies with Rh+ fetuses, this can cause clumping of blood in the fetus's veins
• Treatment may include blood transfusion for the child