The Lymphatic System and Body Defenses Ms. Dunishiya de Silva

Waugh, A. & Grant, A., anatomy and Physiology in Health and Illness 9th Ed (Edinburgh: Churchill Livingstone, 2003) Fig 6.1 “A. The lymphatic system.” P 130

The Lymphatic System Lymphatic system functions Transport excess interstitial fluids (and proteins) back to the blood Transporting dietary fats. Play essential roles in body defense and resistance to disease

Lymphatic Vessels Lymph Capillaries Walls overlap to form flap-like minivalves Fluid leaks into lymph capillaries Figure 12.2

Lymphatic Vessels Lymph Capillaries Capillaries are anchored to connective tissue by filaments Higher pressure on the inside closes minivalves

Lymphatic Vessels Lymphatic collecting vessels Collects lymph from lymph capillaries Carries lymph to and away from lymph nodes Figure 12.1

Lymphatic Vessels Lymphatic collecting vessels (continued) Returns fluid to circulatory veins near the heart Right lymphatic duct Thoracic duct

Movement of lymph towards the heart This is aided by: Valves in the vessel walls Milking action of skeletal muscle Pressure changes in the chest during breathing Rhythmic contraction of smooth muscle in vessel

Lymph Materials returned to the blood Water Blood cells Proteins

Lymph Harmful materials that enter lymph vessels Bacteria Viruses Cancer cells Cell debris

Lymph Nodes Figure 12.3

Lymph Node Structure Most are kidney-shaped, less than 1 inch long Cortex Outer part Contains follicles – collections of lymphocytes Medulla Inner part Contains phagocytic macrophages

Lymph Node Structure Figure 12.4

Flow of Lymph Through Nodes Lymph enters the convex side through afferent lymphatic vessels Lymph flows through a number of sinuses inside the node Lymph exits through efferent lymphatic vessels Fewer efferent than afferent vessels causes flow to be slowed

Other Lymphoid Organs Several other organs contribute to lymphatic function Spleen Thymus Tonsils Peyer’s patches Figure 12.5

The Spleen Located on the left side of the abdomen Filters blood Destroys worn out blood cells Forms blood cells in the fetus Acts as a blood reservoir

Herlihy, B. & Maeblus, N K. , The Human Body in Health and Illness (St Herlihy, B. & Maeblus, N K., The Human Body in Health and Illness (St. Louis: Elsevier Science, 2003) Fig 17-7 “Spleen, composed of white pulp and red pulp” P 328

The Thymus Located in the upper thorax behind the sternum and below the thyroid gland Functions at peak levels only during childhood Produces hormones (like thymosin) to program lymphocytes

Tonsils Small masses of lymphoid tissue around the pharynx Trap and remove bacteria and other foreign materials Tonsillitis is caused by congestion with bacteria

Peyer’s Patches Found in the wall of the small intestine Resemble tonsils in structure Capture and destroy bacteria in the intestine

Mucosa-Associated Lymphatic Tissue (MALT) Includes: Peyer’s patches Tonsils Other small accumulations of lymphoid tissue Acts as a sentinal to protect respiratory and digestive tracts

Antigens (Nonself) Any substance capable of exciting the immune system and provoking an immune response Examples of common antigens Foreign proteins Nucleic acids Large carbohydrates Some lipids Pollen grains Microorganisms

Self-Antigens Human cells have many surface proteins Our immune cells do not attack our own proteins Our cells in another person’s body can trigger an immune response because they are foreign Restricts donors for transplants

Antibody - A blood protein produced in lymphoid tissue that can provide immunity against a specific antigen Pathogen – a disease causing microorganism (e.g. some bacteria, fungi, viruses, etc)

First line of defense Herlihy, B. & Maeblus, N K., The Human Body in Health and Illness (St. Louis: Elsevier Science, 2003) Fig 18-1 “Nonspecific immunity” P 333

Surface Membrane Barriers – First Line of Defense The skin Physical barrier to foreign materials pH of the skin is acidic to inhibit bacterial growth Sebum is toxic to bacteria Vaginal secretions are very acidic

Surface Membrane Barriers – First Line of Defense Stomach mucosa Secretes hydrochloric acid Has protein-digesting enzymes Saliva, perspiration and lacrimal fluid contain lysozyme Mucus traps microogranisms in digestive and respiratory pathways

Surface Membrane Barriers – First Line of Defense Cilia sweep dust and bacterial laden mucus towards the mouth Flow of urine cleanses the urethra Reflexes assist in the removal of pathogens:- Coughing and sneezing (the respiratory tract) Vomiting and diarrhea (the gastrointestinal tract)

Defensive Cells Phagocytes Engulfs foreign material into a vacuole Enzymes from lysosomes digest the material Figure 12.7a

Events of Phagocytosis Figure 12.7b

Inflammatory Response - Second Line of Defense Triggered when body tissues are injured Produces four cardinal signs Redness Heat Swelling Pain Results in a chain of events leading to protection and healing

Functions of the Inflammatory Response Prevents spread of damaging agents Disposes of cell debris and pathogens Sets the stage for repair

Steps in the Inflammatory Response Figure 12.8

Defensive Cells Natural killer cells Can lyse and kill cancer cells Can destroy virus- infected cells

Antimicrobial Chemicals Complement A group of at least 20 plasma proteins Activated when they bind to immune complexes or the foreign sugars found on bacterial cell walls (called complement fixation) Figure 12.10

Antimicrobial Chemicals Complement acts in a variety of ways: Damage foreign cell surfaces Vasodilators Chemotaxis Opsonization Figure 12.10

Antimicrobial Chemicals Interferon Secreted proteins of virus-infected cells Bind to healthy cell surfaces to inhibit viruses binding Transferrins Inhibit bacterial growth by reducing the amount of available iron

Fever Abnormally high body temperature Hypothalmus heat regulation can be reset by pyrogens (secreted by white blood cells) High temperatures inhibit the release of iron and zinc from liver and spleen needed by bacteria Fever also increases the speed of tissue repair

Specific Defense: The Immune System – Third Line of Defense Antigen specific – recognizes and acts against particular foreign substances Systemic – not restricted to the initial infection site Has memory – recognizes and mounts a stronger attack on previously encountered pathogens

Cells of the Immune System Lymphocytes Originate from hemocytoblasts in the red bone marrow B lymphocytes become immunocompetent in the bone marrow T lymphocytes become immunocompetent in the thymus Macrophages Arise from monocytes Become widely distributed in lymphoid organs

Humoral (Antibody-Mediated) Immune Response B cells with the proper receptors recognize and bind antigen particles (without having to be presented with them by an antigen-presenting cell) The B cell is activated (and along with the stimulus from helper T cells) begins to form a clone A large number of clones are produced (primary humoral response)

Humoral (Antibody Mediated) Immune Response Most B cells become plasma cells Produce antibodies to destroy antigens Activity lasts for four or five days Some B cells become long-lived memory cells (secondary humoral response)

Humoral Immune Response Figure 12.12

Secondary Response Memory cells are long-lived A second exposure causes a rapid response The secondary response is stronger and longer lasting Figure 12.13

Active Immunity Your B cells encounter antigens and produce antibodies Active immunity can be naturally or artificially acquired Figure 12.14

Passive Immunity Antibodies are obtained from someone else Conferred naturally from a mother to her fetus Conferred artificially from immune serum or gamma globulin Immunological memory does not occur Protection provided by “borrowed antibodies”

Genetic or innate (inborn) Acquired Immunity Genetic or innate (inborn) Acquired Naturally acquired Active (getting the disease) Passive (from mother) Artificially acquired Active: vaccine Passive: immunoglobulins A Kitson

Antibody Function Antibodies are Y or T shaped soluble proteins. Each has two antigen binding sites particular to specific antigens. The remaining end is similar in all antibodies. Antibodies inactivate antigens in a number of ways Complement fixation Neutralization Agglutination Precipitation

Antibody Function Figure 12.16

Cellular (Cell-Mediated) Immune Response a macrophage engulfs and digests a pathogen the macrophage then pushes to its membrane surface the antigen from the digested pathogen (called antigen presentation) a T cell that has receptor sites for that particular antigen then binds to the antigen on the macrophage’s surface and becomes activated (called T cell activation) The activated T cell then clones resulting in a large number of T cells.

Cellular (Cell-Mediated) Immune Response Figure 12.17

T Cell Clones Cytotoxic T cells Specialize in killing infected cells Insert a toxic chemical (perforin) Helper T cells Recruit other cells to fight the invaders Interact directly with B cells

T Cell Clones Regulatory T cells Release chemicals to suppress the activity of T and B cells Stop the immune response to prevent uncontrolled activity A few members of each clone are Memory T cells

Summary of the Immune Response Figure 12.19