Chapter 20 – The Lymphatic System and Lymphoid Organs and Tissues

These flashcards cover important vocabulary and concepts related to the lymphatic system and lymphoid organs and tissues.

What are the three parts of the lymphatic system?

(1) Network of lymphatic vessels, (2) Lymph (the fluid), (3) Lymph nodes.

What are the main functions of the lymphatic system?

Returns fluids leaked from blood vessels back to the blood and provides the structural basis of the immune system.

What are the main lymphoid organs and tissues?

Spleen, thymus, tonsils, lymph nodes, and other lymphoid tissues.

How much interstitial fluid does the lymphatic system circulate per day?

Approximately 3 liters per day.

Once interstitial fluid enters lymphatic vessels, what is it called?

Lymph.

What direction does lymph flow in the body?

It flows in a one-way system toward the heart.

What are the two main types of lymphatic vessels?

Lymphatic capillaries and larger lymphatic vessels.

Where are lymphatic capillaries absent?

In bones, teeth, bone marrow, and the CNS.

Why are lymphatic capillaries more permeable than blood capillaries?

Because of overlapping endothelial cells forming one-way minivalves and anchoring collagen filaments.

What are lacteals?

Specialized lymph capillaries in the intestinal mucosa that absorb digested fats and deliver fatty lymph (chyle) to the blood.

What do collecting lymphatic vessels consist of?

Collecting vessels, lymphatic trunks, and ducts.

What are the five major lymphatic trunks?

Paired lumbar, bronchomediastinal, subclavian, jugular trunks, and a single intestinal trunk.

What areas are drained by the right lymphatic duct?

Right upper arm and right side of head and thorax.

What areas are drained by the thoracic duct?

The rest of the body.

Where do lymphatic ducts empty lymph into venous circulation?

At the junction of the internal jugular and subclavian veins.

What is lymphangitis?

Inflammation of larger lymphatic vessels appearing as painful red lines under the skin.

What causes lymphangitis?

Inflammation of vessels containing vasa vasorum that become congested with blood.

What is lymphedema?

Severe localized edema caused by blockage or removal of lymphatics.

What mechanisms help propel lymph through vessels?

Skeletal muscle contraction, breathing pressure changes, valves preventing backflow, nearby artery pulsations, and smooth muscle contractions.

How does physical activity affect lymph flow?

It increases lymph flow.

What two main cell types are found in lymphoid tissue?

Immune system cells and supporting cells.

What are the two types of lymphocytes?

T cells (T lymphocytes) and B cells (B lymphocytes).

What are antigens?

Anything the body perceives as foreign (bacteria, viruses, toxins, mismatched RBCs, etc.).

What do T cells do?

Manage the immune response and attack infected cells.

What do B cells do?

Produce plasma cells that secrete antibodies to mark antigens for destruction.

What is the function of macrophages?

Phagocytize foreign substances and help activate T cells.

What is the function of dendritic cells?

Capture antigens and deliver them to lymph nodes; activate T cells.

What do reticular cells produce?

Reticular fibers (stroma), providing a supportive framework for immune cells.

What are the main functions of lymphoid tissue?

Houses and provides proliferation sites for lymphocytes and offers surveillance points for lymphocytes and macrophages.

What type of connective tissue makes up lymphoid tissue?

Reticular connective tissue (a loose connective tissue).

What are the two types of lymphoid tissues?

Diffuse lymphoid tissue and lymphoid follicles (nodules).

What are lymphoid follicles?

Spherical bodies of tightly packed lymphoid cells containing germinal centers of proliferating B cells.

What are primary lymphoid organs?

Red bone marrow and thymus (where T and B cells mature).

What are secondary lymphoid organs?

Lymph nodes, spleen, MALT, and diffuse lymphoid tissue (where lymphocytes encounter antigens).

What are lymph nodes?

Principal secondary lymphoid organs that filter lymph and activate the immune system.

Where are lymph nodes located?

Along lymphatic vessels; clustered in inguinal, axillary, and cervical regions.

What are the two main functions of lymph nodes?

(1) Cleansing the lymph, (2) Immune system activation.

What are the two regions of a lymph node?

Cortex and medulla.

What cells are found in the cortex?

B cells (in follicles) and T cells (in transit).

What cells are found in the medulla?

B cells, T cells, and plasma cells.

How does lymph circulate through a lymph node?

Enters via afferent vessels → subcapsular sinus → cortex/medulla sinuses → exits at hilum via efferent vessels.

Why is lymph flow slow through a node?

Fewer efferent vessels cause stagnation, allowing time for filtration and immune response.

What are buboes?

Inflamed, swollen lymph nodes overwhelmed by infection (common in bubonic plague).

How can lymph nodes indicate cancer?

Cancerous nodes are swollen but not painful, unlike infected nodes.

What is the spleen’s function?

Filters blood, recycles aged RBCs, stores platelets and monocytes, and aids immune responses.

What are the two structural regions of the spleen?

White pulp (immune function) and red pulp (RBC destruction).

What is white pulp made of?

Lymphocytes on reticular fibers clustered around central arteries.

What is red pulp made of?

Splenic cords and sinusoids containing RBCs and macrophages.

What is splenectomy?

Surgical removal of the spleen.

What organs take over spleen functions if it is removed?

Liver and bone marrow.

What is MALT?

Lymphoid tissue in mucous membranes that protects against pathogens entering the body.

Where is MALT found?

In mucosa of respiratory, digestive, and genitourinary tracts.

What are the major MALT structures?

Tonsils, Peyer’s patches, and appendix.

What is the function of tonsils?

Trap and remove pathogens in food or air.

Name the four types of tonsils.

Palatine, lingual, pharyngeal (adenoids), and tubal tonsils.

What are tonsillar crypts?

Invaginations that trap bacteria to activate immune cells.

What are Peyer’s patches?

Clusters of lymphoid follicles in the wall of the distal small intestine.

What are Peyer’s patches’ functions?

Destroy bacteria and generate memory lymphocytes.

What are the functions of the appendix?

Destroy bacteria and generate memory lymphocytes.

What is the function of the thymus?

Site of T cell maturation.

When is the thymus most active?

During childhood.

What are the two thymic regions?

Cortex (dense with lymphocytes) and medulla (fewer lymphocytes and thymic corpuscles).

What are thymic corpuscles?

Sites where regulatory T cells develop.

How is the thymus different from other lymphoid organs?

(1) No follicles (lacks B cells); (2) Does not directly fight antigens; (3) Stroma made of epithelial cells, not reticular fibers.

What is the blood-thymus barrier?

Prevents premature exposure of immature T cells to antigens.

When do lymphatic vessels begin forming?

Around week 5 of embryonic development.

Which lymphoid organ has endodermal origin?

Thymus.

Which organs can regenerate after partial removal in children?

The spleen.