Lymphatic System and Immunity

pathogens

microscopic organisms that cause disease

examples of pathogens

bacteria, viruses, fungi, parasites

lymphatic system (lymphoid system)

protects us against disease

lymphatic system cells respond to

Environmental pathogens, Toxins, Abnormal body cells, such as cancers

lymphocytes

A type of white blood cell that make antibodies to fight off infections

immunity

Resistance to disease

components of lymphatic system

lymph, lymphatic vessels, lymphatic tissue, lymphatic organs

lymphoid tissues and organs

the tissues and organs that work with the immune system to defend the body, including the thymus, bone marrow, lymph nodes, spleen, tonsils, adenoids, and other structures

lymphoid cells

Lymphocytes, phagocytes, and other cells

lymph nodes and lymphatic vessels

cervical lymph nodes, thoracic duct, right lymphatic duct, axillary lymph nodes, lymphatics of mammary gland, cisterna chyli, lymphatics of upper limb, lumbar lymph nodes, pelvic lymph nodes, inguinal lymph nodes, lymphatics of lower limb

Other lymphoid tissues and organs

spleen, tonsils, and mucosa-associated lymphoid tissue (MALT)

lymphocytes are produced in

Primary lymphoid tissues and organs (red bone marrow and thymus)

lymphocytes are activated in

Secondary lymphoid tissues and organs, Tonsils, lymph nodes, and spleen

Functions of the lymphatic system

Produce, maintain, and distribute lymphocytes and other lymphoid cells. Return excess fluid to bloodstream. Maintain normal blood volume. Transport hormones, nutrients, and wastes.

Lymphatic vessels (lymphatics)

carry lymph from peripheral tissues to the venous system

lymph

interstitial fluid once it has entered lymphatic vessels

lymphatic capillaries differ from

blood capillaries, they are closed at one end, have larger diameters, have thinner walls, typically flattened or irregular outline in sectional view, have overlapping endothelial cells

superficial and deep lymphatics

join to form large lymphatic trunks. the trunks empty into two major collecting vessels. the Thoracic duct and the Right Lymphatic duct

thoracic duct

receives lymph from the left side of the head, neck, chest, abdomen, left arm, and lower extremities

right lymphatic duct

receives lymph from right arm, right side of head and thorax; empties into right subclavian vein

lymphoid cells

lymphocytes, macrophages, dendritic cells, reticular cells

lymphocytes make up

20% to 35% of circulating WBCs

most lymphocytes are

stored, not circulating

types of lymphocytes

T cells, B cells, NK cells

t cells

thymus dependent

b cells

bone marrow derived

nk cells

natural killer cells

lymphoid nodules

Areolar tissue with densely packed lymphocytes. Germinal center contains dividing lymphocytes.

Five tonsils in wall of pharynx

Left and right palatine tonsils, Pharyngeal tonsil (adenoid), Two lingual tonsils

tonsilitis

inflammation of the tonsils (especially the palatine tonsils)

Mucosa-associated lymphoid tissue (MALT)

Lymphoid tissues associated with the digestive system

aggregated lymphoid nodules

clustered deep to intestinal epithelial lining

appendix (vermiform appendix)

contains a mass of fused lymphoid nodules

lymphoid organs

separated from surrounding tissues by fibrous connective tissue capsule

lymphoid organs

lymph nodes, spleen, and thymus gland

affarent lymphatics

carry lymph from peripheral tissues to lymph node

efferent lymphatics

leave lymph node at hilum and carry lymph to venous circulation

lymph node function

Retrieves excess fluid from tissue spaces and returns it to the blood stream

lymphoid tissues and lymph nodes

Monitor peripheral infections, Respond before infections reach vital organs

lymphadenopathy

disease of lymph nodes (characterized by abnormal enlargement of the lymph nodes associated with an infection or malignancy)

thymus

located in the mediastinum

thymus

An immune organ located near the heart. THe thymus is the site of T cell maturation and is larger in children and adolescents.

Atrophies after puberty

thymus

Thymus structure

two lobed gland in front of the heart

septa

the cells that make up hyphae are divided by these cross sections

thymic lobule

contains a dense outer cortex and a pale central medulla

Lymphocytes divide

cortex

mature t cells

leave thymus by medullary blood vessels

thymosin

an extract from the thymus that promotes development of lymphocytes

functions of the spleen

Site of lymphocyte proliferation and immune surveillance and response. Cleanses blood of aged blood cells and platelets; macrophages remove debris.

spleen function

Phagocytes and other lymphocytes in spleen. Identify and attack damaged and infected cells. In circulating blood.

splenectomy

surgical removal of the spleen

immunity

the ability of an organism to resist a particular infection or toxin by the action of specific antibodies or sensitized white blood cells.

resistance

ability to ward off disease

immune response

The body's defensive reaction to invasion by bacteria, viral agents, or other foreign substances.

Two types of immunity

innate and adaptive

innate immunity (nonspecific)

Immunity that is present before exposure and effective from birth. Responds to a broad range of pathogens.

Adaptive (specific) immunity

ability of the body to defend itself against specific invading agents

Lymphocyte distribution

Tissues maintain different T cell and B cell populations. Lymphocytes wander through tissues (Enter blood vessels or lymphatics for transport, Can survive many years).

lymphopoiesis

formation of lymph

lymphopoiesis involves

bone marrow, thymus, peripheral lymphoid tissues

Hemocytoblasts in bone marrow

divide into two types of lymphoid stem cells

lymphoid stem cells

group 1 and group 2

Group 1 lymphoid stem cells

Remain in bone marrow and develop with help of stromal cells, Produce B cells and NK cells, B cells differentiate with exposure to interleukin-7

Group 2 lymphoid stem cells

Migrates to thymus. Produces T cells in environment isolated by blood-thymus barrier.

t and b cells

Migrate throughout the body to defend peripheral tissues

Innate (nonspecific) defenses

Block or attack any foreign substance or pathogen. Cannot distinguish one pathogen from another.

innate defenses

physical barriers, phagocytes, immune surveillance, interferons, complement, inflammation, fever

physical barriers

Outer layer of skin, Hair, Epithelial layers of internal passageways, Secretions that flush away materials, Sweat glands, mucus, and urine, Secretions that kill or inhibit microorganisms, Enzymes, antibodies, and stomach acid

Phagocytes

Attack and remove dangerous microorganisms

types of phagocytes

microphages and macrophages

Macrophages

a large phagocytic cell found in stationary form in the tissues or as a mobile white blood cell, especially at sites of infection.

Microphages

Neutrophils and eosinophils. Enter peripheral tissues to fight infections.

monocyte-macrophage system

The relatively diffuse collection of phagocytic cells throughout the body

activated macrophages

enhanced to increase their phagocytic capabilities

types of macrophages

fixed macrophages and free macrophages

Fixed macrophages (histiocytes)

Stay in specific tissues and organs (e.g., dermis and bone marrow). Microglia found in central nervous system. Stellate macrophages found in liver sinusoids.

microglia

central nervous system

stellate macrophages

in liver sinusoids remove debris and old RBCs

free macrophages (wandering)

Travel throughout body, Alveolar macrophages (phagocytic dust cells)

free macrophages and microphages

Move through capillary walls (emigration), Are attracted or repelled by chemicals in surrounding fluids (chemotaxis), Phagocytosis begins: When phagocyte attaches to target (adhesion) And surrounds it with a vesicle

immune surveillance

carried out by natural killer (NK) cells

tumor specific antigens

unique protein on cell surface of tumors; measurement helps to track the extent of cancer as malignant cells mature and become less differentiated

cells infected with viruses

Present abnormal proteins on plasma membranes, Allow NK cells to identify and destroy them

interferons

small proteins secreted by virus-infected cells; tells other, uninfected cells to produce proteins that prevent infection

cytokines

Chemicals released by the immune system communicate with the brain.

types of interferons

alpha, beta, gamma

alpha interferon

produced by cells infected with viruses. Attract and stimulate NK cells and enhance resistance to viral infection.

interferon beta

secreted by fibroblasts and slows inflammation

interferon gamma

secreted by T cells and NK cells and stimulates macrophage activity

complement system

A group of about 30 blood proteins that may amplify the inflammatory response, enhance phagocytosis, or directly lyse extracellular pathogens.

three routes of activation of complement

classical pathway, lectin pathway, alternative pathway

classical pathway of complement activation

complement binds to an antibody that is bound to a foreign substance.

lectin pathway

mannose-binding lectin binds to pathogen surface

alternative pathway of complement activation

Begins when several complement proteins interact (Properdin (factor P), Factor B, Factor D)

C3 protein

When cleaved, it tags pathogens for destruction and recruit phagocytes, thus activating complement pathways

inflammation

a localized response to an injury or to the destruction of tissues

Cardinal signs of inflammation

redness, swelling, heat, pain, loss of function

products of inflammation

necrosis, pus, abscess

pus

mixture of debris, fluid, dead and dying cells, and necrotic tissue