Lymphatic system

• Includes the cells, tissues, and organs responsible for defending the body
• Lymphocytes are the primary cells of the lymphatic system

The ability to resist infection and disease is immunity

• _Lymph__ – fluid that is similar to blood plasma but has a lower concentration of proteins
• A network of lymphatic vessels (called lymphatics) that connect to veins
• Lymphoid tissues and lymphoid organs throughout the body
• Lymphocytes

produce, maintain, and distribute lymphocytes throughout the body

Lymphatic vessels:

Lymphatic capillaries – branch throughout the peripheral tissues

Differ from blood capillaries:

a.)Originate as pockets rather than continuous tubes

b.)They have thinner walls than capillaries

c.)Have larger diameters

Endothelial cells not tightly bound together but they do overlap and only allow fluids to enter the capillaries, not exit

From the lymphatic capillaries, lymph flows into larger lymphatic vessels that lead towards the body’s trunk

• superficial
• Located in the skin

Deep lymphatics

Larger lymphatic vessels that are around skeletal muscles and organs

Superficial and deep lymphatics converge to form larger vessels called lymphatic trunks

• Trunks enter into 2 large collecting vessels: Thoracic duct and right lymphatic duct
• Thoracic duct drains the majority of the body

t cells, b cells, nk cells

• Most lymphocytes are T cells
• T cells involved in the production of cell-mediated immunity

• B cells differentiate into plasma proteins that secrete antibodies
• B cells are responsible for antibody-mediated immunity

• NK cells attack foreign cells, normal cells infected with viruses, and cancer cells that appear in normal tissues
• NK cells responsible for immunological surveillance

T cells are quicker (more common) than B cells

1 stays in the __bone marrow__

Produces B cells and NK cells

• B cells move into lymphatic tissues
• NK cells are continually migrating

1 migrates to the _thymus__

Where T cells mature

Once T cells are mature, they enter blood and migrate to red bone marrow and other lymphatic tissues

T cells isolated once they are in the thymus by the blood-thymus barrier

Lymphoid tissues are connective tissues dominated by lymphocytes

A lymphoid nodule occurs when there lymphocytes densely packed in an area of areolar tissue

Tonsils are large lymphoid nodules in the walls of the pharynx (throat)

• Small lymphoid organs scattered throughout the body
• Greatest number in the neck, armpits, and groin

Shaped like a kidney bean

Blood vessels and nerves enter/exit lymph node at shallow indentation called ______hilum__________________

Afferent lymphatics bring lymph to the lymph node from peripheral tissues

carry lymph from the lymph node to the peripheral circulation

Enters the subcapsular space from the afferent lymphatic









Then flows through the outer cortex of the node:outer cortex contains B cells 

Next, lymph passes through lymph sinuses in the deep cortex: Deep cortex contains T cells

Lymph next travels through the medulla (core) of the lymph node: Medulla contains B cells

After medulla, lymph enters the __efferent lymphatic_ to leave the node

– they remove foreign antigens that pass through the nodes

Thymus 

Pink grainy organ located in the mediastinum, just posterior to the sternum

Much larger in newborns and infants

Gets smaller after puberty

• T cells in the cortex are actively dividing
• T cells migrate into the medulla as they mature

Clusters surrounded by reticular epithelial cells which form the blood-thymus barrier

Reticular epithelial cells are still present and cluster together to form distinctive structures called Hassall’s corpuscles

1.)Removing abnormal blood cells

2.) Storing iron recycled form RBC

3.)Initiating immune responses by B and T cells in response to antigens

The spleen is located in the upper left region of the abdominal cavity

In contact with the diaphragm, stomach, and left kidney

Inside the spleen the cellular components are referred to as pulp

• Red pulp contains RBCs
• White pulp is lymphatic

Lymphocytes are scattered throughout the red and white pulp, and any foreign particle is quickly recognized by lymphocytes

Macrophages are also present

Prevent the approach, deny the entry, or limit the spread of microorganisms or other environmental hazards

Your skin, in addition to the linings of your digestive, respiratory, urinary, and reproductive tracts defend against foreign materials

neutrophils & eosinophils

large, much more active phagocytic cells

• Derived from monocytes
• Can be either fixed in a tissue (fixed macrophage) or freely mobile throughout the body (free macrophage)

Fixed macrophages can become mobile during an infection

Phagocytes can move through capillary walls by squeezing through adjacent cells

Phagocytes are attracted or repelled by chemicals in the surrounding fluids

adhesion of the phagocyte to the target

Vesicle then forms around entire target – lysosome or peroxisome degrades target

Natural killer cells are responsible for recognizing and destroying normal body cells when they become abnormal

NK cells recognize abnormal antigens on the plasma membrane

• 1.)NK cell first recognizes and attaches to the target cell
• 2.)The Golgi apparatus of the NK cell moves to face directly at the abnormal cell

• 3.)Golgi apparatus produces a flood of secretory vesicles that contain the proteins called perforins
• 4.)Perforins are releases and cause the formation of __pores in the abnormal cell which will kill the cell

Interferons are small proteins released by activated lymphocytes and macrophages, and by tissue cells infected with viruses

Interferons cause a normal cell to produce antiviral proteins that help protect the cell

Your body’s plasma contains 11 special complement proteins that interact with one another in a cascade of reactions to ‘complement’ the actions of antibodies

Helps destroy antigens by forming pores in the infected cells and increasing phagocytosis

Produces local swelling, redness, heat, and pain

• 1.)Injury is temporarily repaired
• 2.)Additional pathogens are prevented from entering wound
• 3.)Spread of pathogens away from injury is slowed
• 4.)Other immune defenses are activated

1.)Mast cells are activated by injury and release histamine, heparin, and prostaglandins into the environment surrounding the cell

2.)Increased blood flow raises local temperature which accelerates activity of phagocytes

3)Blood vessel permeability increases – clotting and complement factors can enter the injured area

4)Neutrophils are drawn to area by chemotaxis

5)Fixed and free macrophages engulf pathogens and cell debris

6.)Active phagocytes release proteins known as cytokines which stimulate local cells to repair the damaged tissue

• Body temperature greater than 99°F (37.2°C)
• Fevers can be beneficial, within certain limits
• High body temperatures may inhibit some viruses and bacteria
• Also, higher body temperatures can increase body metabolism

• Adaptive defenses result from the coordinated activities of T cells and B cells
• T cells bring about cell-mediated immunity and B cells provide antibody-mediated immunity

cells are enter peripheral tissues and directly attack antigens

Memory T cells respond to antigens that they have encountered by cloning more lymphocytes to fight off future pathogens

stimulate responses of T and B cells

inhibit T and B cells

T cells need to recognize an antigen bound to glycoproteins on the plasma membrane of another cell

These glycoproteins are referred to as majory histocompatibilty complex (MHC) proteins

T cells recognize MHC Class I proteins and ignore these cells – signals that cell is healthy

If the cell is not healthy, the abnormal proteins are displayed by the Class I MHC proteins on the cell’s surface

The presence of the abnormal protein signals that cell needs to be destroyed

Antigen presenting cells are responsible for activating T cell defenses against foreign cells

All the phagocytes are antigen-presenting cells

Phagocytic APCs engulf and break down the foreign pathogens and then the Class II MHC molecules are bound to the plasma membrane

Class II MHC proteins appear on the plasma membrane only when the cell is processing antigens

• Inactive T cells have receptors for either Class I or Class II MHC proteins
• When a T cell detects its appropriate antigen, the T cell is activated

The markers on the T cells that respond to the antigens are called CD markers

Respond to antigens presented by Class I MHC proteins

Cytotoxic T cells will seek out and destroy the cell with the specific antigen

Memory T cells will ‘remember’ the antigen so if it comes along again they will produce cytotoxic T cells to destroy that cell

Suppressor T cells will eventually suppress the immune response

• respond to class II mhc2
• Helper T cells secrete cytokines that coordinate immune responses

• B cells produce specific antibodies
• Each B cell carries its own particular antibody on the plasma membrane

When the particular B cell recognizes the appropriate antigen, it begins the process of activation – this process is called sensitization

usually occurs in lymph nodes 

Prevents the virus or toxin from attaching to a cell

Antibodies can link large numbers of antigens together and form clumps that prevent further damage

Increased phagocytosis when the foreign particle is coated by antibodies and complement proteins

Antibodies can produce inflammation by stimulating basophils and mast cells