THE LYMPHATIC SYSTEM

Anatomy & Physiology

LYMPHATIC SYSTEM-GENERAL 2 Main Parts

Lymphatic vessels Lymphoid tissues/organs

FUNCTIONS:Drain excess fluid (edema) and returns it to

bloodPlays essential roles in body defense and

resistance to disease

LYMPHATIC SYSTEM-GENERAL Lymph—excess tissue fluid Properties of lymphatic vessels

One way system toward the heartNo pumpLymph moves toward the heart

Transported through milking action of skeletal muscle

Rhythmic contraction of smooth muscle in vessel walls helps pump the lymph through the system

RELATIONSHIP OF LYMPHATIC VESSELS TO BLOOD VESSELS

LYMPHATIC VESSELS Lymph capillaries

Walls overlap to form flap-like minivalves to allow entrance for lymph Fluid leaks into lymph capillaries

Lymph Capillaries are anchored to connective tissue by filaments

Higher pressure on the inside of the capillary closes minivalves Fluid is forced along the vessel for examination

Examined by cells of immune system for any potential threats

LYMPHATIC VESSELS Lymphatic 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

Drains lymph to right arm/head/thorax

Thoracic duct Drains rest of body that

R.Lymph duct doesn’t

LYMPH Harmful materials that enter lymph

vesselsBacteriaVirusesCancer cellsCell debris

LYMPH NODES Filter lymph before it is returned to the

blood Areas of high concentration?

Inguinal, axillary, and cervical regions Defense cells within lymph nodes

Macrophages—engulf and destroy foreign substances

Lymphocytes—provide immune response to antigens

Nodes swell when fighting infection because nodes have engulfed the foreign substance to prevent it from spreading

LYMPH NODE STRUCTURE Most are kidney-

shaped and less than 1 inch long

Cortex Outer part Contains follicles—

collections of lymphocytes

Medulla Inner part Contains phagocytic

macrophages

OTHER LYMPHOID ORGANS Several other

organs contribute to lymphatic functionSpleenThymusTonsilsPeyer’s patches

SPLEEN Blood filled organ which

filters blood Location: Left side of

abdomen above diaphragm

Functions: Filters/cleanses blood of

foreign substances Destroy worn-out blood

cells Recycles components of

worn out blood cells (i.e. hemoglobin)

Stores platelets Protect body during

hemorrhage

THYMUS GLAND Lymphoid mass

found in throat Function:

Programs lymphocytes with the help of thymosin (hormone)

TONSILS Small, lymphoid

tissue in back of throat

Function: Capture and remove any foreign pathogens(substances)Reason they

become swollen during colds/viruses

PEYER’S PATCHES Location: Wall of

small intestine Function:

Capture and destroy bacteriaPrevent foreign

pathogens from penetrating intestinal wall

BODY DEFENSES The body is constantly in contact with

bacteria, fungi, and viruses The body has two defense systems for

foreign materials Innate (nonspecific) defense system

Attacks ANY foreign pathogenAdaptive (specific) defense system

Attacks SPECIFIC substances

Immunity—specific resistance to disease -Immun=free

IMMUNE SYSTEM

INNATE BODY DEFENSES AKA “non-specific defense system” Innate body defenses are mechanical

barriers to pathogens such asBody surface coverings

Intact skin Mucous membranes

Line all body cavities that are exposed (i.e. digestive, respiratory, urinary, and reproductive tracts)

Specialized human cellsChemicals produced by the body

SURFACE MEMBRANE BARRIERS:FIRST LINE OF DEFENSE Skin and mucous membranes

Physical barrier to foreign materialsAlso provide protective secretions

pH of the skin is acidic to inhibit bacterial growth Sebum is toxic to bacteria Stomach releases hydrochloric acid to kill

pathogens Saliva and lacrimal fluid contain lysozymes

which kill bacteria Mucus traps microorganisms and prevent them

from entering the digestive or respiratory tract

CELLS AND CHEMICALS:SECOND LINE OF DEFENSE Phagocytes

I.e. macrophage or neutrophilSwallows foreign pathogen

Natural killer cellsKill cancer and virus cells Fight off these pathogens by detecting

sugar molecules on pathogen’s surface

CELLS AND CHEMICALS:SECOND LINE OF DEFENSE CONT’D Inflammatory response

Happens when tissue is injured4 signs: Redness, heat, inflammation,

swelling painHistamine & Kinins causes:

Vessels to dilate causing inflammation Activate pain receptors to alert body of problem Attract WBCs and phagocytes to clean cellular

debris from tissue damage

CELLS AND CHEMICALS:SECOND LINE OF DEFENSE CONT’D Antimicrobial proteins

Help fight pathogens by attacking them or inhibiting their progress through the use of? Complement proteins

Bind to sugar receptors on pathogen’s cell and causes holes which allow water to enter the cell and cause it to burst

Interferon: Bind to viruses’ cells and cause proliferation of

interferon molecules which hinder the viruses’ cell replication

CELLS AND CHEMICALS:SECOND LINE OF DEFENSE CONT’D Fever

Effects of fever include: Prohibiting iron or zinc availability which bacteria

require to multiply Increases metabolic rate which in turn increases

the repair process HIGH fevers can denature proteins and enzymes

causing breakdowns within the body

ADAPTIVE DEFENSE SYSTEM: THIRD LINE OF DEFENSE Immune response is the immune

system’s response to a threatProvides protection by the use of antigens

through specificity Immunology is the study of immunity Antibodies are proteins that protect from

pathogens

THIRD LINE OF DEFENSE When the body is exposed to a pathogen

it builds “antibodies”Less likely the body will acquire that same

pathogen again Immune response becomes stronger when

faced with this invading pathogen in the future

3 steps involved in immune response:1. Antigen specific: It attacks particular

pathogens/foreign substances2. Systemic: Immunity is not confined to only

the “initial infection site.” Can work through the circulatory system

3. Memory: Has stronger attacks against previously fought pathogens

THIRD LINE OF DEFENSE Humoral Immunity/Antibody-mediated

immunityAntibodies fight off infection in the blood

stream (humors/fluids)

Cellular Immunity/Cell-mediated immunityFights off viral cells, cancer cells, and

foreign graft cells either directly or indirectly

THIRD LINE OF DEFENSE Antigen:

Any substance responsible for initiating an immune response

Examples of common antigens Foreign proteins (strongest) Nucleic acids Large carbohydrates Some lipids Pollen grains Microorganisms

THIRD LINE OF DEFENSE Self-antigens

Human cells have many surface proteins

Our immune cells do not attack our own proteins because they are recognizable in our bodies

Our cells in another person’s body can trigger an immune response because they are foreign Restricts donors for

transplants Unless…medications are

taken to suppress immune system

Hapten/Incomplete Antigen: A small molecule

antigen that cannot initiate the creation of antibodies

Instead, it binds with our proteins

The body doesn’t not recognize combination and attacks it

Examples: Poison ivy, detergents,

hair dyes, etc

THIRD LINE OF DEFENSE-CELLS B lymphocytes/B-cells

Create antibodies and direct humoral immunity

T lymphocytes/T-cellsThese cells do not produce antibodies Mature T-cells are the most effective in

fighting off foreign antigens

THIRD LINE OF DEFENSE-CELLS Immunocompetent—cell becomes

capable of responding to a specific antigen by binding to it

Cells of the adaptive defense system Lymphocytes

Originate from hemocytoblasts in the red bone marrow

B lymphocytes become immunocompetent in the bone marrow (remember B for Bone marrow)

T lymphocytes become immunocompetent in the thymus (remember T for Thymus)

THIRD LINE OF DEFENSE-CELLS Cells of the adaptive defense system

(continued)Macrophages

Arise from monocytes found in bone marrow Become widely distributed in lymphoid organs Secrete cytokines (proteins important in the

immune response) Tend to remain fixed in the lymphoid organs

Unlike lymphocytes that circulate

HUMORAL (ANTIBODY-MEDIATED) IMMUNE RESPONSE B lymphocytes with specific receptors

bind to a specific antigen The binding event activates the

lymphocyte to undergo clonal selectionLymphocyte grows and multiplies

Most B cells turn into plasma cells The remaining B cells are stored as

memory cells for future encounters with that antigen

HUMORAL (ANTIBODY-MEDIATED) IMMUNE RESPONSE Secondary humoral responses

Memory cells are long-livedA second exposure causes a rapid responseThe secondary response is stronger and

longer lasting

ACTIVE IMMUNITY Occurs when B cells encounter antigens

and produce antibodies Active immunity can be

Naturally acquired during bacterial and viral infections

Artificially acquired from vaccines

PASSIVE IMMUNITY Occurs when antibodies are obtained

from someone elseAcquired naturally from a mother to her

fetus (naturally acquired) when passing through placenta

Conferred artificially from immune serum or gamma globulin (artificially acquired) Shots given after exposure to certain pathogens

Immunological memory does not occur Protection provided by “borrowed

antibodies” Lasts 2-3 weeks

TYPES OF ACQUIRED IMMUNITY

ANTIBODIES (IMMUNOGLOBULINS OR IGS) Secreted by

activated B cells Respond to a

specific antigen

ANTIBODIES (IMMUNOGLOBULINS OR IGS) Antibody classes

Antibodies of each class have slightly different roles

Five major immunoglobulin classes (MADGE) IgM—can fix complement IgA—found mainly in mucus IgD—important in activation of B cell IgG—can cross the placental barrier and fix

complement IgE—involved in allergies

ANTIBODIES Antibody function

Antibodies inactivate antigens in a number of ways Complement fixation

Causes lysis of the cell Neutralization

Bind to bacterial cells to block the release of that cell’s toxic chemicals

AgglutinationClumping of foreign cells

PrecipitationWhen antigen-antibodies combine forming

large complexes that settle out a solution that was agglutinated

ANTIBODY FUNCTION

CELLULAR (CELL-MEDIATED) IMMUNE RESPONSE

Antigens must be presented by macrophages to an immunocompetent T cell

T cells must recognize nonself and self (double recognition)

After antigen binding, clones form as with B cells, but different classes of cells are producedCytotoxic (killer T cells): Attack virus infected,

cancer, or foreign graft cellsHelper T cells: Directors of immune systemRecruit other cells to fight pathogens Regulatory T cells: Stop the immune response

once antigen is destroyed

ORGAN TRANSPLANTS AND REJECTION

Major types of graftsAutografts—tissue transplanted from one

site to another on the same person Isografts—tissue grafts from an identical

person (identical twin)Allografts—tissue taken from an unrelated

personXenografts—tissue taken from a different

animal species

ORGAN TRANSPLANTS AND REJECTION Autografts and isografts are ideal donors Xenografts are never successful Allografts are more successful with a

closer tissue match

DISORDERS OF IMMUNITY: ALLERGIES (HYPERSENSITIVITY) Abnormal, vigorous immune responses Types of allergies

Immediate hypersensitivity Triggered by release of histamine from IgE

binding to mast cellsCauses dilation of small blood vesselsLeads to: itchy, watery, runny nose/eyes

Reactions begin within seconds of contact with allergen

Anaphylactic shock—dangerous, systemic responseThroat closes in response to allergy, blocking

airway

DISORDERS OF IMMUNITY: IMMUNODEFICIENCIES Production or function of immune cells or

complement is abnormal May be congenital or acquired Includes AIDS (Acquired Immune Deficiency

Syndrome) Kills of Helper T-cells

Includes Severe Combined Immunodeficiency Disease (SCID) Congenital condition

The immune system does not distinguish between self and nonself

The body produces antibodies and sensitized T lymphocytes that attack its own tissues