Chapter 13: Lymphatic System And Immunity

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 Trabeculae Lymphatic nodules Lymphatic sinuses Germinal centers

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 o red pulp

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

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

thymus

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

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) • adaptive immunity (specific immunity) o specificity o memory

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 • Interferons

White Blood Cells

‑ most important cellular components of immunity ‑ produced in red bone marrow and lymphatic tissue and released into the blood

Types of WBC

Phagocytic Cells = Neutrophils and Macrophages Cells of Inflammation = Basophils, Mast cells, and Eosinophils Natural Killer Cells

Phagocytosis

ingestion and destruction of particles by cells called phagocytes

Neutrophils

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

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 o dust cells o Kupffer cells o microglia

Basophils

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

Mast cells

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

Eosinophils

participate in inflammation associated with allergies and asthma

Natural Killer Cells

‑ a type of lymphocyte produced in red bone marrow, and they account for up to 15% of lymphocytes

• 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

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

Antigens

-substances that stimulate adaptive immune responses; can be divided into two groups: • Foreign antigens • Self-antigens o Autoimmune disease

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

Cell-mediated immunity

-involves the actions of a second type of lymphocyte, called T cells o cytotoxic T cells o helper T cells

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.

Ways of Activation and Multiplication of Lymphocytes

Antigen Recognition Lymphocyte Proliferation

Antigen Receptor

cell membrane proteins on the surfaces of lymphocytes

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.

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

variable region

end of each “arm” of the antibody; part that combines with the antigen

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 • memory B cells • secondary response/memory 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 • Artificial

Active immunity

-immunity is provided by the individual’s own immune system • active natural immunity • active artificial immunity

Passive immunity

-immunity is transferred from another person or an animal • passive natural immunity • 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 • Cell-mediated immunity

Immunotherapy

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

EFFECTS OF AGING ON THE LYMPHATIC SYSTEM AND IMMUNITY

• 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.

DISEASES of lymphatic system

• Lymphedema • Lymphoma

Immediate Allergic Reactions

• Asthma • Anaphylaxis

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) • Acquired immunodeficiency syndrome (AIDS)

pathogen

any substance or microorganism that causes disease or damage to the tissues of the body

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

white pulp

lymphatic tissue surrounding the arteries within the spleen

red pulp

associated with the veins

trabeculae

divide each lobe into lobules

cortex

where lymphocytes are numerous and form dark-staining areas

medulla

lighter-staining, central portion of the lobules; fewer lymphocytea

Lymph nodes

filter lymph and are sites where lymphocytes respond to infections

innate immunity

body recognizes and destroys certain pathogens, but the response to them is the same each time the body is exposed

adaptive immunity

body recognizes and destroys pathogens, but the response to them improves each time the pathogen is encountered

specificity

the ability of adaptive immunity to recognize a particular substance

memory

the ability of adaptive immunity to “remember” previous encounters with a particular substance

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

chemotaxis

movement of WBC toward chemicals such as complement, leukotrienes, kinins, and histamine

mononuclear phagocytic system

formed by monocytes and macrophages because they are phagocytes with a single, unlobed nucleus

dust cells

lungs

Kupffer cells

liver

microglia

Central Nervous System (CNS)

Pyrogens

chemicals released by microorganisms, neutrophils, and other cells, stimulate fever production