Lymphatic and Immune System: Innate Immunity

• The following are study notes on the lymphatic/immune system with an emphasis on the innate system

Lymphatic/Immune System Terms

• Lymph is extracellular body fluid found in lymphatic vessels and nodes.
• Lymphatic capillaries are microscopic, very permeable vessels of the lymphatic system.
• Lymph nodes are lymphatic system structures that filter unwanted substances like pathogens and cancer cells from lymph.
• Macrophages are white blood cells developed from monocytes to engulf and destroy bacteria and other foreign substances.
• Lymphocytes are white blood cells that monitor body fluids for antigens and can trigger an immune response.
• Metastasis occurs when cancer spreads to a new location in the body from its original site.
• Tonsils trap pathogens entering the throat.
• The thymus gland produces lymphocytes in children.
• The spleen filters pathogens and debris from blood.
• Nonspecific defenses protect the body from all foreign invaders, regardless of type or location.
• Specific defenses produce specially formulated substances to attack specific antigens to which the body has been previously exposed.
• Mechanical barriers include skin and mucous membranes, which form physical barriers to pathogens.
• Phagocytes are specialized white blood cells like macrophages and neutrophils that engulf and destroy foreign particles.
• Natural killer cells are lymphocytes that bind to tumor cells and virus-infected cells, injecting special proteins to create holes in the plasma membrane.
• The inflammatory response is triggered by injury to body tissues, in which damaged cells release inflammatory chemicals like histamine and kinins, leading to redness, heat, swelling, pain, and loss of function.
• Chemotaxis is the movement of cells towards or away from a chemical stimulus.
• Diapedesis is the movement of white blood cells through capillary walls into tissues.
• Complement proteins are plasma proteins that attach to foreign cells and destroy or tag them.
• Interferons are small proteins secreted by virus-infected cells that protect nearby cells from being infected.
• Fever is an abnormally high body temperature, a response to invading microbes.

The Immune System

• Immunity is the ability to resist infection and disease.
• Immunity includes all body cells and tissues involved in production of immunity.
• The function of the immune system is to protect against disease.
• The immune system responds to toxins, abnormal body cells (cancer), and pathogens like viruses, bacteria, fungi, and parasites.
• Mechanisms of protection vary because each pathogen attacks in a specific way.

The Lymphatic System

• The lymphatic system consists of vessels, nodes, and other organs.
• The function is to transport, filter, and cleanse body fluids of pathogens, toxins, and unwanted substances.
• The lymphatic system produces, maintains, and distributes lymphocytes, providing specific immunity.
• Red bone marrow produces formed elements called lymphocytes: T-cells mature in the thymus and B-cells mature in bone marrow.
• Lymphatic structures house secondary structures: lymph nodes, spleen, tonsils, lymphatic nodules, and MALT.
• Lymphatic networks begin with lymphatic capillaries.
• Lymph movement is one way, always toward the heart, and returns to the venous system through ducts.
• Lymph empties into the junction of the right jugular and right subclavian vein via the right lymphatic duct.
• Lymph empties into the junction of the left jugular and left subclavian vein via the thoracic duct.
• Lymph flow is aided by semilunar valves that prevent backflow.
• Skeletal muscle contraction, thoracic cavity pressure, smooth muscle contractions, and pulsatile blood in arteries also assist lymph flow.

Lymphatic Structures and Functions

• Red bone marrow is primary.
  • It is in spongy bone and is the site of formation of all formed elements and B-lymphocyte maturation.
• The thymus is primary.
  • It is in the superior mediastinum and is the site of T-lymphocyte maturation and differentiation.
• Lymph nodes are secondary.
  • They are along lymphatic vessels, clustered in axillary, inguinal, and cervical regions
  • They filter lymph, where the immune response is initiated against substances in the lymph.
• The spleen is secondary.
  • It is in the left upper quadrant of the abdomen, near the 9th-11th ribs, partially "wraps" around the stomach.
  • It filters blood, initiating immune response; removes aged erythrocytes and platelets, and serves as an erythrocyte and platelet reservoir.
• Tonsils are secondary.
  • They are oral cavity and pharynx protectors against inhaled and ingested substances.
• Lymphatic nodules are secondary.
  • They are in every body organ and protect body organs.
• MALT (mucosa-associated lymphatic tissue) is secondary.
  • They include clusters of lymphatic nodules within the walls of the gastrointestinal (GI), respiratory, urinary, and reproductive tracts
  • They protect mucosal membranes against foreign substances.
• Hundreds of lymph nodes filter unwanted substances and initiate immune responses
• Afferent vessels bring lymph into lymph nodes efferent vessels allow lymph to exit.
• Lymph movement is slow.

Spleen and Tonsils

• The spleen filters blood, not lymph.
• The spleen facilitates phagocytosis of foreign materials, old red blood cells (RBCs), and platelets.
• They are blood reservoirs for RBCs and platelets.
• The red pulp contains erythrocytes, platelets, macrophages, and B lymphocytes and acts as a blood reservoir.
• The white pulp contains clusters of T cells, B cells, and macrophages and is involved in mounting an immune response.
• Tonsils are located in the oral cavity and pharynx.
• The phagocytosis of foreign materials trap foreign substances
• Tonsillitis is inflammation of the tonsils.

Immune System Defense Overview

• Primary lymphatic structures which assist the immune system are: red bone marrow and the thymus
• Secondary lymphatic structures which assist the immune system are: lymph nodes, spleen, and tonsils
• Innate immune system provides innate immunity using multiple components that protect a wide array of substances.
• Adaptive Immune System Provides Adaptive Immunity: Lymphocytes that are activated; replicate and respond when stimulated by a specific antigen

Innate, Nonspecific Immunity

• Innate defenses involves using physical barriers which Prevent the entry Of infectious agents.
  • Skin: is acidic, hypertonic and produces sebum
  • Mucous membranes: cavities open to the exterior, ciliated or secrete acids
• Second type of defense involves cells to use phagocytes (First line of cellular defense)
  • Microphages (neutrophils and eosinophils)-leave bloodstream into peripheral tissues
  • Macrophages- (derived from monocytes)-free or fixed to connective tissue -Immunological Surveillance: Natural killer cells-destroys abnormal cells and virally infected cells

Interferons

• Chemical messengers and trigger antiviral proteins
• Stimulate NK cells and macrophages
• Complement Proteins
• Circulating proteins assist (complement) antibodies in the destruction of pathogens
• Inflammatory Response: Local response to limit spread of pathogens
• Basophils: dilate blood vessels and increase permeability
• Allergies: anti-histamine reduces inflammatory response
• Fever which is when a response causes Pyrogens to alter hypothalamus temperature set point