Lymphatic System: Key Structures, Functions, and Immune Roles

What is the primary function of the lymphatic system?

To return fluids that leaked from blood vessels back to the blood.

What are the three main components of the lymphatic system?

1. Network of lymphatic vessels (lymphatics), 2. Lymph (the fluid in vessels), 3. Lymph nodes (filter and cleanse lymph).

What is lymph?

Interstitial fluid that has entered lymphatic vessels, consisting of plasma, other fluids, cellular debris, and potential pathogens.

What is the structure of lymphatic capillaries?

They are very permeable, take up proteins, cell debris, potential pathogens, and cancer cells, and have overlapping endothelial cells forming one-way minivalves.

Where are lymphatic capillaries absent?

In bones, teeth, bone marrow, and the central nervous system (CNS).

What specialized lymphatic capillaries are present in the intestinal mucosa?

Lacteals, which absorb digested fat and deliver fatty lymph (chyle) to the blood.

How do lymphatic collecting vessels differ from veins?

They have thinner walls, more internal valves, and anastomose more frequently.

What are the main lymphatic trunks?

1. Jugular trunk, 2. Subclavian trunk, 3. Bronchomediastinal trunk, 4. Lumbar trunk, 5. Intestinal trunk.

What are the two large lymphatic ducts?

1. Right lymphatic duct, which drains the right upper arm and right side of the head and thorax; 2. Thoracic duct, which drains the rest of the body.

How is lymph propelled through the lymphatic system?

By the milking action of skeletal muscles, pressure changes during breathing, valves to prevent backflow, pulsations of nearby arteries, and contractions of smooth muscle in larger lymphatics.

What are the main types of lymphocytes?

1. T lymphocytes (T cells), which act against virus-infected cells and tumor cells; 2. B lymphocytes (B cells), which give rise to plasma cells that produce antibodies.

Where do lymphocytes arise and mature?

They arise in red bone marrow and mature into T cells or B cells.

What role do lymph nodes play in the lymphatic system?

They filter and cleanse lymph as it passes through.

What happens to lymph during inhalation?

The diaphragm moves inferiorly, increasing abdominal pressure and forcing lymph to move from the abdominal cavity to the thoracic cavity.

What prevents lymph from flowing backward during exhalation?

Valves in lymphatic vessels act as one-way gates, preventing backflow.

What is the function of the cisterna chyli?

It is the starting point of the thoracic duct, which drains lymph from the lower body.

What is the significance of the overlap of endothelial cells in lymphatic capillaries?

It allows for the uptake of larger molecules and pathogens while preventing backflow.

What is the role of phagocytic cells in lymphoid organs?

They help in the immune response by engulfing and destroying pathogens.

What is the difference between interstitial fluid and lymph?

Interstitial fluid becomes lymph once it enters the lymphatic vessels.

What are the primary lymphoid organs?

Spleen, thymus, and tonsils, which provide the structural basis of the immune system.

What is the lymphatic system's relationship with the circulatory system?

Lymphatic vessels return lymph to the circulatory system, mixing it with blood before it reaches the heart.

What is the pressure relationship in the lymphatic system?

Fluid moves from areas of higher pressure to lower pressure within the system.

What do antibodies do in the immune response?

Antibodies attach to bacteria and mark them for destruction.

What are lymphocytes and their main types?

Lymphocytes are white blood cells that protect against antigens; the main types are T cells and B cells.

What is the role of T cells in the immune response?

T cells manage the immune response and attack infected cells.

What do B cells produce in response to antigens?

B cells produce plasma cells, which secrete antibodies.

What are macrophages and their function?

Macrophages phagocytize foreign substances and help activate T cells.

What is the function of dendritic cells?

Dendritic cells capture antigens and deliver them to lymph nodes.

What type of tissue primarily makes up lymphoid tissue?

Lymphoid tissue is largely composed of reticular connective tissue.

What are the two main types of lymphoid tissue?

The two main types are diffuse lymphoid tissue and lymphoid follicles.

What are the primary locations for lymphatic organs?

Primary locations include red bone marrow, spleen, thymus, tonsils, Peyer's patches, and appendix.

What is the primary function of lymph nodes?

Lymph nodes filter lymph and activate the immune system.

Describe the structure of a lymph node.

Lymph nodes have an external fibrous capsule, trabeculae, and two distinct regions: cortex and medulla.

What is the role of the spleen in the lymphatic system?

The spleen is involved in lymphocyte proliferation, immune surveillance, and cleansing blood of aged cells.

What are the two distinct areas of the spleen?

The two areas are white pulp, which is involved in immune functions, and red pulp, which disposes of worn-out RBCs.

What is the thymus and its role in the immune system?

The thymus is crucial for T cell maturation and is most active during childhood.

What is Mucosa-associated Lymphoid Tissue (MALT)?

MALT is lymphoid tissue in mucous membranes that protects against pathogens entering the body.

What are the main types of tonsils and their functions?

The main types are palatine, lingual, pharyngeal, and tubal tonsils, which gather and remove pathogens in food or air.

What are Peyer's patches and their function?

Peyer's patches are clusters of lymphoid follicles in the intestines that destroy bacteria and generate memory lymphocytes.

What is the significance of germinal centers in lymphoid follicles?

Germinal centers are sites of proliferating B cells within lymphoid follicles.

How do lymph nodes facilitate immune response?

Lymph nodes allow lymphocytes and macrophages time to function by having fewer efferent vessels, which slows lymph flow.

What is the blood-thymus barrier?

The blood-thymus barrier isolates the thymus to provide a controlled environment for T lymphocyte maturation.

What happens to the thymus during adolescence?

The thymus stops growing and gradually atrophies, but it continues to produce immunocompetent cells slowly.

What is the function of reticular cells in lymphoid organs?

Reticular cells produce reticular fibers that support other cells in lymphoid organs.

What is the role of the appendix in the lymphatic system?

The appendix contains lymphoid tissue that helps destroy bacteria and generate memory lymphocytes.

What is the primary function of lymphatic vessels?

Lymphatic vessels transport lymph, which contains immune cells, throughout the body.