Lymphatic and Immune Systems Review
Lymphatic System and Immunity
Organization of the Lymphatic System
Anatomy of the Lymphatic System
- Lymph: Fluid similar to plasma but lacks plasma proteins.
- Lymphatic Vessels (Lymphatics): Network carrying lymph from peripheral tissues to the venous system.
- Lymphoid Tissues and Lymphoid Organs: Includes tonsils, lymph nodes, thymus, spleen, etc.
- Immune System Cells: White blood cells (WBCs).
Function of the Lymphatic System
- Produces, maintains, and distributes lymphocytes.
Lymphatic Vessels
- Lymphatic Capillaries: Smallest vessels, starting as blind sacs where interstitial fluid diffuses in.
- Large diameter, thin-walled.
- Cells act as one-way valves, allowing fluid in but not out.
- Lymphatic vessels travel along the same pathways as veins; divided into deep and superficial lymphatics.
- Larger lymphatic vessels contain valves to prevent backflow.
- Main Lymphatic Vessels
- Thoracic Duct: Receives lymph from the lower body and left side of the upper body; drains into the left subclavian vein.
- Right Lymphatic Duct: Receives lymph from the right side of the upper body and head; drains into the right subclavian vein.
- Lymphatic Capillaries: Smallest vessels, starting as blind sacs where interstitial fluid diffuses in.
Lymphocytes
- Classes of Circulating Lymphocytes:
- T-cells (Thymus-dependent)
- Cytotoxic T-cells: Mediate cell-mediated immunity; attack virus-infected cells.
- Helper T-cells: Stimulate T-cell and B-cell function.
- Suppressor T-cells: Inhibit T-cell and B-cell function.
- B-cells (Bone Marrow-derived)
- Differentiate into plasma cells, which secrete antibodies (immunoglobulins); mediate antibody-mediated immunity.
- NK Cells (Natural Killer Cells)
- Responsible for immune surveillance.
- T-cells (Thymus-dependent)
- Life Span and Circulation of Lymphocytes
- Can survive for many years.
- Travel throughout the bloodstream, migrate through tissues, and return to the circulatory or lymphatic system.
- Lymphocyte Production
- Two types of lymphoid stem cells:
- In red bone marrow: gives rise to B-cells and NK cells.
- In the thymus: gives rise to T-cells; isolated from general circulation during development by the blood-thymus barrier.
- Thymosins (thymus hormones) alter T-cells.
- Two types of lymphoid stem cells:
- Classes of Circulating Lymphocytes:
Lymphoid Tissues
- Concentrations of lymphocytes within other body tissues.
- Example: Lymphoid nodules in the wall of the intestines called Peyer’s patches or MALT.
- Another example: Tonsils.
Lymphoid Organs
- Lymph Nodes: Lymphatic vessels carry lymph to lymph nodes for filtration and then away to the venous system.
- Contain T-cells, B-cells, and macrophages which remove debris, pathogens, and antigens.
- Clustered in specific areas to prevent the spread of infection (e.g., axillary, inguinal lymph nodes).
- Thymus: Located in the mediastinum; deteriorates after puberty.
- Has two lobes.
- Secretes thymosins, important for T-cell maturation.
- Spleen
- Anatomy
- Red Pulp: Contains large numbers of RBCs.
- White Pulp: Resembles lymphoid nodules.
- Functions
- Removes abnormal blood cells and other blood components via phagocytosis.
- Stores iron recycled from RBCs.
- Initiates immune response by T-cells and B-cells to circulating antigens in the blood.
- Splenectomy: Surgical removal of the spleen.
- Increases susceptibility to pneumococcal infections.
- Pneumococcal vaccination is recommended post-splenectomy.
- Anatomy
*NOTE: Lymphoid tissues and organs contain both T and B cells; organs have fibrous outer capsules and are more organized in their internal structure.
- Lymph Nodes: Lymphatic vessels carry lymph to lymph nodes for filtration and then away to the venous system.
Lymphatic System and Body Defenses
Non-Specific Defenses (Innate Immunity)
- Attacks all invaders in the same way.
- Physical and Chemical Barriers
- Skin
- Hair
- Epithelial layers of internal passageways
- Secretions that flush away materials (sweat glands, mucus)
- Secretions that kill or inhibit microorganisms (enzymes, stomach acid).
- Phagocytes
- Microphages: Neutrophils and eosinophils.
- Macrophages
- Fixed Macrophages: Stay in specific tissues or organs.
- Free Macrophages: Travel through the body.
- Microphages and free macrophages respond to chemotactic signals; all can leave the bloodstream and enter tissues.
- Immunological Surveillance: Constant monitoring of normal tissues by NK cells.
- NK cells attack abnormal cells anywhere in the body, including cancer cells and virus-infected cells.
- Interferons: Proteins that signal the presence of viruses and stimulate cells to produce antiviral proteins, which block viral replication.
- Complement: A group of proteins that complements the action of antibodies.
- Activation of complement:
- Stimulation of inflammation.
- Attraction of phagocytes.
- Enhancement of phagocytosis through opsonization (antibodies coat antigens).
- Destruction of target cell membranes via membrane attack complex (MAC). MAC involves 5 complement proteins that punch holes in the cell membrane.
- Activation of complement:
- Inflammation: Localized response to injury.
- Signs of Inflammation
- Swelling: Accumulation of excess fluid in interstitial spaces.
- Redness: Increased blood flow (vasodilation).
- Heat: Increased blood flow.
- Pain: Distortion/destruction of cell membranes.
- Necrosis: Local tissue destruction in the area of injury.
- Pus: Debris and necrotic tissue, including dead WBCs.
- Abscess: Pus accumulation in an enclosed space.
- Signs of Inflammation
- Fever: Maintained body temperature above 99° F.
- Pyrogens: Substances that cause fever.
- Endogenous Pyrogen: Released by macrophages.
Specific Defenses (Adaptive Immunity)
- General
- Designed to attack only the invader for which it is programmed, ignoring all others.
- Relies on the action of specific lymphocytes – T-cells and B-cells.
- Forms of Immunity
- Innate: Present at birth; non-specific immunity.
- Acquired: Appears after birth upon exposure to an antigen.
- Active: The person has been exposed to the antigen, and their body actively makes antibodies against it.
- Naturally acquired: exposure to the disease itself.
- Artificially acquired: immunization.
- Passive: A person is given antibodies manufactured by another organism.
- The person's immune system never sees the antigen and cannot produce antibodies.
- Naturally acquired: Antibodies received through mother’s milk or across the placenta.
- Artificially acquired: Receiving hepatitis A immunoglobulin to prevent infection.
- Active: The person has been exposed to the antigen, and their body actively makes antibodies against it.
- General
Properties of Immunity
- Specificity: Each T or B-cell responds only to one antigen, based on its molecular structure, and ignores all others.
- Versatility: The body produces a small number of many differently coded lymphocytes (T-cells and B-cells), so the immune system can fight many different types of antigens.
- Once a lymphocyte has been