Lympathic System

Enlist the Functions of the Lympathic System

1. Fluid balance 2. Lipid absorption 3. Defense

Lymphatic capillaries

-tiny, closed-ended vessels consisting of simple squamous epithelium -more permeable than blood capillaries because they lack a basement membrane, and fluid moves easily into them ‑ joins to form larger lymphatic vessels

Lymphatic vessels

‑ resemble small veins ‑ have a beaded appearance because they have one-way valves that are similar to the valves of veins

Factors that make compression of the Lymphatic vessels

1. contraction of surrounding skeletal muscle during activity 2. contraction of smooth muscle in the lymphatic vessel wall 3. pressure changes in the thorax during breathing

thoracic duct

-where lymphatic vessels from the rest of the body enters; empties into the left subclavian vein

right lymphatic duct

lymphatic vessels from the right upper limb and the right half of the head, neck, and chest; empties into the right subclavian vein

Lymphatic Organs

include the tonsils, the lymph nodes, the spleen, and the thymus

Lymphatic tissue

characterized by housing many lymphocytes and other defense cells, such as macrophages

Tonsils

form a protective ring of lymphatic tissue around the openings between the nasal and oral cavities and the pharynx

Three groups of tonsils

palatine tonsils pharyngeal tonsil lingual tonsil

palatine tonsils

located on each side of the posterior opening of the oral cavity; these are the ones usually referred to as “the tonsils.

pharyngeal tonsil

located near the internal opening of the nasal cavity

lingual tonsil

located on the posterior surface of the tongue

tonsillectomy

-removal of the pharyngeal tonsils

adenoidectomy

-removal of the palatine tonsil

Lymph Nodes

rounded structures, varying from the size of a small seed to that of a shelled almond

Parts if the Lymph node

Capsule -a dense connective tissue that surrounds each lymph node Trabeculae -extensions of the capsule; subdivide a lymph node into compartments containing lymphatic tissue and lymphatic sinuses Lymphatic nodules -lymphocytes and other cells that can form dense aggregations of tissue Lymphatic sinuses -spaces between the lymphatic tissue that contain macrophages on a network of fibers Germinal centers -lymphatic nodules containing the rapidly dividing lymphocytes; sites of lymphocyte production

Three superficial aggregations of lymph nodes

• inguinal nodes in the groin • axillary nodes in the axilla • the cervical nodes in the neck

functions of lymph nodes

activate the immune system • remove pathogens from the lymph through the action of macrophages

Spleen

‑ roughly the size of a clenched fist and is located in the left, superior corner of the abdominal cavity ‑ filters blood instead of lymph ‑ blood reservoir ‑ has an outer capsule of dense connective tissue and a small amount of smooth muscle

Trabeculae

-divide the spleen into small, interconnected compartments containing two specialized types of lymphatic tissue: o white pulp -lymphatic tissue surrounding the arteries within the spleen o red pulp -associated with the veins

Splenectomy

-removal of the spleen

Thymus

‑ a bilobed gland roughly triangular in shape ‑ located in the superior mediastinum ‑ site for the maturation of a class of lymphocytes called T cells ‑ surrounded by a thin connective tissue capsule

Thymus' parts

• trabeculae -divide each lobe into lobules • cortex -where lymphocytes are numerous and form darkstaining areas • medulla -lighter-staining, central portion of the lobules; fewer lymphocytes

Lymph

the fluid that lympathic capillaries remove from the blood stream

Valves of lymphatic vessels

prevents backflow of lymph

Lacteals

found in the small intestine absorb lipids, which enter the thoracic duct.

Chyle

lymph containing lipids, enters the blood.

function of spleen

filters blood and is a site where lymphocytes respond to infections

Lymphocytes

(pre-B and pre-T cells) originate from stem cells in the red bone marrow. The pre-B cells become mature B cells in the red bone marrow and are released into the blood. The pre-T cells enter the blood and migrate to the thymus

where pre-T cells derived from red bone marrow increase in number and become mature T cells that are released into the blood.

thymus

B cells and T cells

populates all lymphatic tissues. These lymphocytes can remain in tissues or pass through them and return to the blood. B cells and T cells can also respond to infections by dividing and increasing in number. Some of the newly formed cells enter the blood and circulate to other tissues.

Immunity

‑ the ability to resist damage from pathogens, such as microorganisms; harmful chemicals, such as toxins released by microorganisms; and internal threats, such as cancer cells

two immunity systems

innate immunity (nonspecific resistance) - body recognizes and destroys certain pathogens, but the response to them is the same each time the body is exposed • adaptive immunity (specific immunity) -body recognizes and destroys pathogens, but the response to them improves each time the pathogen is encountered o specificity -the ability of adaptive immunity to recognize a particular substance o memory -the ability of adaptive immunity to “remember” previous encounters with a particular substance

Physical Barriers

‑ prevent pathogens and chemicals from entering the body in two ways: 1. the skin and mucous membranes form barriers that prevent their entry 2. tears, saliva, and urine wash these substances from body surfaces

Chemical Mediators

‑ molecules responsible for many aspects of innate immunity. ‑ some chemicals on the surface of cells destroy pathogens or prevent their entry into the cells • Complement -a group of more than 20 proteins found in plasma; can be activated by combining with foreign substances or antibodies; once activated, it can promote inflammation, phagocytosis, and lyse (rupture) bacterial cells • Interferons -are proteins that protect the body against viral infections

White Blood Cells

‑ most important cellular components of immunity ‑ produced in red bone marrow and lymphatic tissue and released into the blood chemotaxis -movement of WBC toward chemicals such as complement, leukotrienes, kinins, and histamine

Types of WBC

Phagocytic Cells = Neutrophils and Macrophages Cells of Inflammation = Basophils, Mast cells, and Eosinophils Natural Killer Cells = type of lymphocyte produced in red bone marrow that account up to 15% off lymphocytes

Phagocytosis

-ingestion and destruction of particles by cells called phagocytes

small phagocytic WBC; usually the first WBC to enter infected tissues from the blood in large numbers

Neutrophils

Pus

an accumulation of fluid, dead neutrophils, and other cells at a site of infection

Macrophages

-are monocytes that leave the blood, enter tissues, and enlarge about fivefold o mononuclear phagocytic system -formed by monocytes and macrophages because they are phagocytes with a single, unlobed nucleus o dust cells -lungs o Kupffer cells -liver o microglia -CNS

derived from red bone marrow; motile WBCs that can leave the blood and enter infected tissues

Basophils

derived from red bone marrow, are nonmotile cells in connective tissue, especially near capillaries

Mast cells

Eosinophils

participate in inflammation associated with allergies and asthma

-recognize classes of cells, such as tumor cells or virus -infected cells, in general, rather than specific tumor cells or cells infected by a specific virus ‑ do not exhibit memory response

Natural Killer Cells

. Inflammatory Response

Bacteria cause tissue damage that stimulates the release or activation of chemical mediators, such as histamine, prostaglandins, leukotrienes, complement, and kinins.

Local inflammation

-an inflammatory response confined to a specific area of the body

Systemic inflammation

-an inflammatory response that is generally distributed throughout the body o Pyrogens -chemicals released by microorganisms, neutrophils, and other cells, stimulate fever production

Antigens

-substances that stimulate adaptive immune responses; can be divided into two groups: • Foreign antigens -introduced from outside the body (bacteria and viruses) • Self-antigens -molecules the body produces to stimulate an immune system response o Autoimmune disease -results when self-antigens stimulate unwanted destruction of normal tissue

Adaptive immunity can be divided into

Antibody-mediated immunity & Cell-mediated immunity

Antibody-mediated immunity

involves a group of lymphocytes called B cells and proteins called antibodies, which are found in the plasma o Antibodies -produced by plasma cells, which are derived from the B cells

Cell-mediated immunity

-involves the actions of a second type of lymphocyte, called T cells o cytotoxic T cells-produce the effects of cell-mediated immunity o helper T cells can promote or inhibit the activities of both antibody-mediated immunity and cell-mediated immunity

Origin and Development of Lymphocytes

• Both B cells and T cells originate from stem cells in red bone marrow. • B cells are processed from pre-B cells in the red marrow. • T cells are processed from pre-T cells in the thymus. • Both B cells and T cells circulate to other lymphatic tissues, such as lymph nodes. • clones -small groups of identical B cells or T cells; form during embryonic development

Ways of Activation and Multiplication of Lymphocytes

Antigen Recognition Lymphocyte Proliferation

Antigen Recognition

Antigen receptors -cell membrane proteins on the surfaces of lymphocytes • B-cell receptors -antigen receptors on B cells • T-cell receptors -antigen receptors on T cells Major histocompatibility complex (MHC) molecules -are glycoproteins that have binding sites for antigens • MHC class I molecules -found on the membranes of most nucleated cells • MHC class II molecules -found on the membranes of antigen-presenting cells, B lymphocytes, and other defense cells

Lymphocyte Proliferation

-important process that generates the needed defense cells to protect the body

Proliferation of Helper T Cells

1. Antigen-presenting cells, such as macrophages, phagocytize, process, and display antigens on the cell’s surface. 2. The antigens are bound to MHC class II molecules, which present the processed antigen to the T-cell receptor of the helper T cell. 3. Costimulation results from interleukin-1, secreted by the macrophage, and the CD4 glycoprotein of the helper T cell. 4. Interleukin-1 stimulates the helper T cell to secrete interleukin-2 and to produce interleukin-2 receptors. Chapter 13: Lymphatic System and Immunity 5. The helper T cell stimulates itself to divide when interleukin-2 binds to interleukin-2 receptors. 6. The “daughter” helper T cells resulting from this division can be stimulated to divide again if they are exposed to the same antigen that stimulated the “parent” helper T cell. This greatly increases the number of helper T cells. 7. The increased number of helper T cells can facilitate the activation of B cells or effector T cells.

Proliferation of B Cells

1. Before a B cell can be activated by a helper T cell, the B cell must phagocytize and process the same antigen that activated the helper T cell. The antigen binds to a B-cell receptor, and both the receptor and the antigen are taken into the cell by endocytosis. 2. The B cell uses an MHC class II molecule to present the processed antigen to the helper T cell. 3. The T-cell receptor binds to the MHC class II/antigen complex. 4. There is costimulation of the B cell by CD4 and other surface molecules. 5. There is costimulation by interleukins (cytokines) released from the helper T cell. 6. The B cell divides, the resulting daughter cells divide, and so on, eventually producing many cells that recognize the same antigen. 7. Many of the daughter cells differentiate to become plasma cells, which produce antibodies. Antibodies are part of the immune response that eliminates the antigen.

Antibody-Mediated Immunity

effective against extracellular antigens, such as bacteria, viruses (when they are outside cells), and toxins

Antibodies

-proteins produced in response to an antigen. They are Y-shaped molecules consisting of four polypeptide chains: two identical heavy chains and two identical light chains

Structure of Antibodies

variable region -end of each “arm” of the antibody; part that combines with the antigen • constant region -rest of the antibody • gamma globulins -found mostly in the gamma globulin part of plasma • immunoglobulins (Ig) -globulin proteins involved in immunity.

Effects of Antibodies

Antibodies directly affect antigens by inactivating the antigens or by binding the antigens together. • Antibodies indirectly affect antigens by activating other mechanisms through the constant region of the antibody. 1. Inactivate the antigen 2. Bind antigens together 3. Activate the complement cascade. An antigen binds to an antibody. As a result, the antibody can activate complement proteins, which can produce inflammation, chemotaxis, and lysis. 4. Initiate the release of inflammatory chemicals. An antibody binds to a mast cell or a basophil. When an antigen binds to the antibody, it triggers the release of chemicals that cause inflammation. 5. Facilitate phagocytosis. An antibody binds to an antigen and then to a macrophage, which phagocytizes the antibody and antigen.

Antibody Production

• primary response -results from the first exposure of a B cell to an antigen; B cell proliferates to form plasma cells and memory cells; plasma cells produce antibodies. • memory B cells are responsible for the secondary response • secondary response/memory response -occurs when the immune system is exposed to an antigen against which it has already produced a primary response

Cell-Mediated Immunity

‑ a function of cytotoxic T cells and is most effective against microorganisms that live inside body cells; involved with allergic reactions, control of tumors, and graft rejection

Cytotoxic T cells have two main effects:

• When activated, cytotoxic T cells form many additional cytotoxic T cells, as well as memory T cells. • The cytotoxic T cells release cytokines that promote the destruction of the antigen or cause the lysis of target cells, such as virally infected cells, tumor cells, or transplanted cells. The memory T cells are responsible for the secondary response.

ACQUIRED IMMUNITY

• Natural -contact with the antigen or transfer of antibodies occurs as part of everyday living and is not deliberate • Artificial -deliberate introduction of an antigen or antibody into the body has occurred

Active immunity

-immunity is provided by the individual’s own immune system • active natural immunity -antigens are introduced through natural exposure such as disease-causing microorganism • active artificial immunity -antigens are deliberately introduced in a vaccine

Passive immunity

-immunity is transferred from another person or an animal • passive natural immunity -antibodies from the mother are transferred to her child across the placenta or in milk • passive artificial immunity -antibodies produced by another person or an animal are injected antiserum -antibodies that provide passive artificial immunity

Innate immunity

-general response that does not improve with subsequent exposure

Adaptive immunity

-specific response that improves with subsequent exposure; begins with a macrophage presenting an antigen to a helper T cell • Antibody-mediated immunity -antibodies act against antigens in solution or on the surfaces of extracellular microorganisms • Cell-mediated immunity -cytotoxic T cells act against antigens bound to MHC molecules on the surface of cells; they are effective against intracellular microorganisms, tumors, and transplanted cells.

Immunotherapy

-treats disease by altering immune system function or by directly attacking harmful cells

Aging has little effect on the lymphatic system’s ability to remove fluid from tissues, absorb lipids from the digestive tract, or remove defective red blood cells from the blood. • Decreased helper T-cell proliferation results in decreased antibody-mediated and cell-mediated immune responses. • The primary and secondary antibody responses decrease with age. • The ability to resist intracellular pathogens decreases with age.

EFFECTS OF AGING ON THE LYMPHATIC SYSTEM AND IMMUNITY

DISEASES of lymphatic system

Lymphedema - Abnormal accumulation of lymph in tissues, often the limbs; 70%– 90% cases in women; can be caused by developmental defects, disease, or damage to the lymphatic system Lymphoma - Cancer of lymphocytes that often begins in lymph nodes; immune system becomes depressed, with increased susceptibility to infections

Immediate Allergic Reactions

Asthma - Symptoms occur within a few minutes of exposure to an antigen because antibodies are already present from prior exposure Antigen combines with antibodies on mast cells or basophils in the lungs, which then release inflammatory chemicals that cause constriction of the air tubes, so that the patient has trouble breathing Anaphylaxis - Systemic allergic reaction, often resulting from insect stings or drugs such as penicillin; chemicals released from mast cells and basophils cause systemic vasodilation, increased vascular permeability, drop in blood pressure, an possibly death

Delayed Allergic Reactions

Symptoms occur in hours to days following exposure to the antigen because these types of reactions involve migration of T cells to the antigen, followed by release of cytokines

Immunodeficiencies

Severe combined immunodeficiency (SCID) - Congenital; both B cells and T cells fail to form; unless patient kept in a sterile environment or provided with a compatible bone marrow transplant, death from infection results Acquired immunodeficiency syndrome (AIDS) - Life-threatening disease caused by the human immunodeficiency virus (HIV)