Chapter 15The Lymphatic System

and Immunity

Function of the Lymphatic System

Protect body from pathological bacteria, foreign tissue cells, and

cancerous cells

Lymph

• Fluid in the tissue spaces that carries protein molecules and other substances back to the blood

• Created from fluids that do not get back into capillaries during cardiovascular circulation

Lymphatic Capillaries

– Tiny closed-ended tubes

– Microscopic in size

– One cell layer of simple squamous epithelium

– Called lacteals in the intestinal wall (for fat transportation)

Lymphatic Vessels

• Permit only one-way movement of lymph

• Gradually get larger as they move toward the heart

Lymph Nodes

– Located in clusters along the pathway of lymphatic vessels

– Filter lymph – Lymph fluid flows in from several points, out

through one vessel– Lymph flows through many nodes along the

pathway and is filtered in each node

Structure of Lymph nodes

Lymphatic Ducts

– Right lymphatic duct• Drains lymph from the right upper extremity and

right side of head, neck, and upper torso• Empties cleansed lymph into right subclavian vein

– Thoracic duct• Largest lymphatic vessel• Drains lymph from about three fourths of the body

– Right lower quadrant, Left upper and lower quadrants

• Empties cleansed lymph into left subclavian vein

Process

1. Lymph absorbed from tissues

2. Lymph capillaries carry fluid to lymph vessels

3. Fluid is cleansed in lymph nodes as it flows through vessels

4. Vessels deliver fluids to ducts

5. Ducts empty fluids into subclavian veins

MORE LYMPH STRUCTURES

Thymus

– Located in mediastinum

– Secretes hormone called thymosin• Stimulates production of T-lymphocytes or T cells

– Large at birth• Shrinks over lifetime as less Tcell production is

needed

Tonsils

Spleen

– Largest lymphoid organ in body

– In upper left quadrant of abdomen

– Functions include phagocytosis of bacteria and old RBCs; acts as a blood reservoir

IMMUNITY

Types of Immunity

• Nonspecific immunity– General things the body does to protect itself

from pathogens– Not targeted at a specific pathogen– i.e. membranes that protect organs

eyes tearing to wash substances out

inflammation

The Immune System

• Specific immunity—

– Ability of body to recognize and remember harmful substances or bacteria

– Allows body to respond to a pathogen before we become ill from it

Terms related to immunity

• Natural immunity— • Active—active disease produces immunity• Passive—immunity passes from mother to fetus

through placenta or from mother to child through mother’s milk

• Artificial immunity• Active—vaccination results in immunity• Passive—protective material developed in another

individual’s immune system and given to previously nonimmune individual

Immune System Molecules

• Antibodies – Protein compounds– Attach to specific antigens

• humoral or antibody-mediated immunity

– Antigen-antibody complexes may:• Neutralize toxins• Clump or agglutinate enemy cells• Promote phagocytosis

Lymphcytes

• Two types– B cells

• Produce antibodies• Related to humoral (antibody mediated) immunity

– T cells• Related to cell mediated immunity• Play a role in killing individual cells of the pathogen

Hypersensitivity

• Allergy—– hypersensitivity to harmless environmental

antigens (allergens)

• Autoimmunity—– inappropriate, excessive response to tissues

within the body• Body attacks its own tissues • Results in “autoimmune disorders”

Hypersensitivity (cont)

• Isoimmunity—– excessive reaction to antigens from another

human• May occur between mother and fetus during

pregnancy• Common with tissue transplants