Chapter 12 - The Lymphatic System and Body Defenses

What are the 2 semi-independent parts that make up the lymphatic system

1. lymphatic vessels

2. lymphatic tissues and organs

lymphatic system functions

transport escaped fluids back to blood

plays essential roles in body defense and resistance to disease

what is lymph

excess tissue fluid carried by lymphatic vessels

properties of lymphatic vessels

one way system toward the heart

no pump

lymph moves toward the heart by milking action of skeletal muscle and rhythmic contraction of smooth muscle in vessel walls

lymph capillaries

walls overlap to form flap-like minivalves

fluid leaks into lymph capillaries

capillaries are anchored to connective tissue by filaments

higher pressure on the inside closes minivalves

fluid is forced along the vessel

lymph collecting vessels

collect lymph from lymph capillaries

carry lymph to and away from lymph nodes

return fluid to circulatory veins near the heart

• right lymphatic duct

• thoracic duct

What part of the body is drained by the right lymphatic duct, thoracic duct?

right lymphatic duct drains right side of head, arm, and chest

thoracic duct drains everywhere else

What are some harmful materials that enter lymph vessels

bacteria, viruses, cancer cells, cell debris

lymph nodes

filter lymph before it is returned to the blood

what are 2 defense cells within lymph nodes

macrophages - engulf and destroy foreign substances

lymphocytes - provide immune response to antigens

lymph node structure

kidney-shaped, < 1 inch long

cortex = outer, contains follicles (collections of lymphocytes)

medulla = inner, contains phagocytic macrophages

Flow of lymph through lymph nodes

lymph enters the convex side through afferent lymphatic vessels → flows through a number of sinuses inside the node → exits through efferent lymphatic vessels

• fewer efferent than afferent vessels causes flow to be slowed

Organs that contribute to lymphatic function

spleen, thymus, tonsils, Peyer’s patches, appendix

Spleen

left side of abdomen

filters blood

destroys worn out RBCs

forms blood cells in fetus

acts as a blood reservoir

Thymus gland

located low in throat, overlying the heart

functions at peak levels only during childhood

produces hormones (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)

Peyer’s patches, tonsils, appendix

acts as a sentinel to protect respiratory and digestive tracts

What are the body’s 2 defense systems

1. Innate (nonspecific) defense system

2. Adaptive (specific) defense system

Immunity

specific resistance to disease

Innate defense system protect against a ___ of invaders and responds ___ to protect the body from foreign materials

variety, immediately

adaptive defense system requires ___ for each type of invader

specific defense

Innate body defenses are mechanical barriers to pathogens such as…

body surface coverings, intact skin, mucous membranes, specialized human cells, chemicals produced by the body

Body 1st line of defense

skin and mucous membranes (protective secretions)

stomach mucosa (HCl)

Saliva and lacrimal fluid (lysozymes)

Mucus (traps microorganisms)

Body 2nd line of defense

NK cells, inflammatory response, phagocytes, antimicrobal proteins, fever

NK cells

can lyse and kill cancer cells

can destroy virus infected cells

release a chemical called perforin to target the cells membrane and nucleus, causing disintegration

Inflammatory response

triggered when the body tissues are injured

results in a chain of events leading to protection and healing

4 most common indicators of acute inflammation

1. Redness

2. Heat

3. Swelling

4. Pain

Functions of the inflammatory response

prevent spread of damaging agents

disposes of cell debris and pathogens through phagocytosis

sets the stage for repair

Process of the inflammatory response

Neutrophils migrate to the area of inflammation by rolling along the vessel wall

squeeze through capillary walls by diapedesis to sites of inflammation

neutrophils gather (+ chemotaxis) and consume any foreign material present

Phagocytes

cells such as neutrophils and macrophages

engulf foreign material into a vacuole

enzymes from lysosomes digest the material

Phagocytosis

acute - neutrophils move by diapedesis to clean up damaged tissue and/or pathogens

chronic - monocytes become macrophages and complete disposal of cell debris

Antimicrobial proteins

attack microorganisms

hinder reproduction of microorganisms

complement proteins + nterferons

Complement proteins

a group of > 20 plasma proteins

activated when they encounter and attach to cells (complement fixation)

damage foreign cell surfaces

release vasodilators and chemotaxis chemicals, cause opsonization

Interferons

proteins secreted by virus-infected cells

bind to healthy cell surfaces to interfere with the ability of viruses to multiply

Fever

abnormally high body temperature

hypothalamus heat regulation can be reset by pyrogens (secreted by WBCs)

high temps inhibit the release of iron and zinc from the liver and spleen needed by bacteria

fever also increases the speed of tissue repair (inc. metabolic processes)

Immune response is the immune system’s response to a ___

threat

immunology is the study of ___

immunity

antibodies are proteins that

protect from pathogens

3 aspects of adaptive defense

1. antigen specific

2. systemic

3. memory

2 types of immunity

1. Humoral = antibody-mediated immunity. Provided by antibodies present in body fluids

2. Cellular Immunity = cell-mediated immunity. Targets virus-infected cells, cancer cells, and cells of foreign grafts

Antigens (nonself)

any substance capable of exciting the immune system and provoking an immune response

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

Allergies

many small molecules (haptens / incomplete antigens) are not antigenic, but can link up with our own proteins

the immune system may recognize and respond to a protein-hapten combination

the immune response is harmful rather than protective because it attacks our own cells

Cells of the adaptive defense system

Lymphocytes - respond to specific antigens

= T and B cells

Macrophages - help lymphocytes

Immunocompetent

cells become capable of responding to a specific antigen by bnding to it

Lymphocytes originate from…

hemocytoblasts in the red bone marrow

Where do T and B cells become immunocompetent

T cells - Thymus

B cells - Bone marrow

Macrophages arise from

monocytes

Macrophage functions

become widely distributed in lymphoid organs

secrete cytokines (proteins important in the immune response)

tend to remain fixed in the lymphoid organs (medulla)

Humoral (Ab-mediated) immune response

B cells with specific receptors bind to a specific antigen

binding activates the cell to undergo clonal selection

a large number of clones are produced (primary humoral response)

Most B cells become __ cells that…

plasma

produce antibodies to destroy antigens

activity lasts for 4-5 days

Some B cells become ___ cells

long-lived memory cells

(secondary humoral response)

Describe the secondary humoral responses

memory cells are long-lived

a second exposure causes a rapid response

the secondary response is stronger and longer lasting

Active Immunity

Occurs when B cells encounter antigens and produce antibodies

Naturally vs. Artificially acquired active immunity

natural = during bacterial and viral infections

artificially = vaccines

Passive Immunity

Occurs when antibodies are obtained from someone else

Naturally vs. Artificially acquired Passive immunity

naturally = mother to fetus (breast milk, placenta)

artificially = from immune serum or gamma globulin

*protection provided by “borrowed” antibodies

Does immunological memory occur during passive immunity

no, but it does occur during active immunity

Monoclonal antibodies

antibodies prepared for clinical testing or diagnostic services

produced from descendants of a single cell line

examples of use…

diagnosis of pregnancy

treatment after exposure to hepatitis and rabies

What are antibodies (immunoglobulins, Igs)

soluble proteins secreted by B cells (plasma cells)

carried in blood plasma

capable of binding specifically to an antigen

Describe antibody structure

4 amino acid chains linked by disulfide bonds

2 identical amino acid chains are linked to form a heavy chain

the other 2 identical chains are light chains

specific antigen-binding sites are present (variable regions)

what are the 5 major immunoglobulin classes

IgG, IgM, IgA, IgE, IgD

what is the function of the 5 different immunoglobulin classes

IgG = cross placental barrier, fix complement

IgM = fix complement

IgA = found mainly in mucus

IgE = involved in allergies

IgD = activation of B cells

Antibodies can inactivate antigens in 4 different ways

1. complement fixation

2. neutralization

3. agglutination

4. precipiation

Cellular (cell-mediated) immune response

antigens must be presented by macrophages to an immunocompetent T cell (Ag presentation)

T cells must recognize self and nonself (double recognition)

After Ag binding, clones form as with B cells, but different classes of cells are produced

Cytotoxic (killer) 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

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 T cell clone are ___

memory cells for secondary immune response

Autografts

tissue transplanted from one site to another on the same person

Isografts

tissue grafts from an identical person (twin)

Allografts

tissue taken from an unrelated person

Xenografts

tissue taken from a different animal species

What are ideal donors for grafts

Autografts and Isografts

What type of grafts are never successful

Xenografts

What type of grafts are more successful with a closer tissue match

Allografts

Allergies (Hypersensitivites)

abnormal, vigorous immune responses

Immediate Hypersensitivity

triggered by release of histamine from IgE binding to mast cells

reactions begin within seconds of contact with allergen

Anaphylactic shock

dangerous, systemic response to immediate hypersensitivity

Delayed hypersensitivity

triggered by the release of lymphokines from activated helper T cells

symptoms usually appear 1-3 days after contact with antigen

Immunodeficiencies

production or function of immune cells or complement is abnormal

congenital or acquired

includes AIDS

Autoimmune Diseases

the immune system does not distinguish between self and nonself

the body produces antibodies and sensitized T cells that attack its own tissues

Multiple sclerosis

white matter of brain and spinal cord are destroyed

Myasthenia gravis

impairs communication between nerves and skeletal muscles

Type I diabetes mellitus

destroys pancreatic beta cells that produce insulin

Rheumatoid arthritis

destroys joints

Systemic lupus erythematosus (SLE)

affects kidney, heart, lung, and skin

Glomerulonephritis

impairment of renal function

self tolerance breakdown

inefficient lymphocyte programming

appearance of self-proteins in the circulation that have not been exposed to the immune system

• eggs, sperm, eye lens, proteins in thyroid gland

Rheumatic fever

cross-reaction of antibodies produced against foreign antigens with self-antigens

What organs are developed vs. poorly developed before birth

developed = thymus, spleen

poorly = other lymphoid organs

do newborns have functioning lymphocytes at birth

no, only passive immunity from the mother

if lymphatics are removed or lost, what happens

sever edema (swelling), but vessels grow back in time