Lymphatic System

Lymphatic System

• The lymphatic system is a critical network of vessels, cells, and organs that helps maintain fluid balance and filter harmful substances from the blood.

• It works closely with the blood vessels, collecting excess fluid from tissues and returning it to the bloodstream via vessels, trunks, and ducts.

Functions of the Lymphatic System

• Fluid Drainage and Homeostasis: Drains excess interstitial fluid, preventing swelling (edema). Returns fluid (lymph) to the bloodstream, preventing depletion of blood volume.

• Interstitial Fluid and Cellular Health: Plasma that leaks from capillaries becomes interstitial fluid, bathing cells. Facilitates nutrient delivery and waste removal for cellular homeostasis.

• Edema: Accumulation of fluid in tissues due to lymphatic blockage or injury. Can cause swelling and serious medical consequences.

Structure of the Lymphatic System

• Lymphatic Capillaries: The smallest vessels in the lymphatic system that collect interstitial fluid; it is referred to as lymph once inside.

• Lymphatic Vessels: Lymphatic capillaries lead to larger lymphatic vessels that eventually return lymph to the bloodstream via ducts. Lymph passes through lymph nodes along the way.

• Lymph Nodes: Humans have approximately 500–600 lymph nodes; commonly found near the groin, armpits, neck, chest, and abdomen.

Flow of Lymph

• Lymph is not actively pumped by the heart. Movement of lymph relies on skeletal muscle contraction, body movements, and breathing.

• Lymphatic vessels have one-way valves preventing backflow as lymph moves toward the heart.

• Lymph eventually empties into the bloodstream through the lymphatic ducts located at the junction of the jugular and subclavian veins in the neck.

Lymphatic Capillaries

• Located in almost all tissues of the body; intertwined with the arterioles and venules of the circulatory system, especially in soft connective tissues.

• Some parts of the body do not have lymphatic capillaries, including the central nervous system (CNS), bone marrow, bones, teeth, and the cornea of the eye.

• These capillaries are only one cell thick, similar to blood vessel capillaries but with a distinct structure.

• Endothelial Cells: Cells overlap slightly, forming a one-way system where fluid can flow in but not out.

• Pressure Mechanism: When pressure in the tissue increases, it pushes the cells open allowing fluid to flow into the capillaries. Once pressure builds inside the capillaries, the cells close to prevent fluid from leaking back out.

Lacteals

• Lymphatic capillaries known as lacteals are vital for transporting dietary lipids and lipid-soluble vitamins into the bloodstream.

Lymph Nodes

• Lymph Flow:

  • Afferent Vessels: Lymph enters the node through afferent lymphatic vessels.
  • Efferent Vessels: Lymph, cells, and any remaining fluid exit the node through efferent lymphatic vessels.
  • Filtration Pathway: Lymph flows through the subcapsular sinus (filtration zone) within the node where cells engulf harmful invaders.

• Cortex: Lymph moves into the cortex, which contains rapidly dividing lymphocytes that can replicate in response to pathogens.

• Medulla: Lymph flows through the medulla; contains cells specializing in antibody production before leaving through efferent vessels.

Lymphoid Nodules

• Lack a capsule and consist of a dense cluster of lymphocytes found in other tissues.

• Common in the respiratory and digestive tracts, areas frequently exposed to pathogens.

Tonsils

• Lymphoid nodules located in the throat; help the body develop immunity to oral pathogens.

• Swollen tonsils (adenoids) indicate an active immune response.

• Lack a complete capsule and contain tonsillar crypts, deep invaginations that collect food particles, mucus, and microbes.

• Play a key role in helping children's bodies recognize and develop immunity to pathogens, protecting them later in life.

Mucosa-Associated Lymphoid Tissue (MALT)

• A group of lymphoid nodules found in various organs, including the gastrointestinal tract, breast tissue, lungs, and eyes.

• MALT cells sample materials from the organ's lumen, triggering immune responses to potential pathogens while also helping the body develop tolerance to harmless substances like food.

Bronchus-Associated Lymphoid Tissue (BALT)

• Consists of lymphoid follicles located along the walls of the bronchi in the lungs.

• Like the tonsils, BALT helps protect the body from inhaled pathogens.

Thymus

• A small gland in the lymphatic system that makes and trains special white blood cells called T-cells.

• Found in the space between the sternum and aorta of the heart.

• The outer region of the organ is known as the cortex, and the inner region is the medulla.

Spleen

• A major lymphoid organ; found in the posterior abdominal cavity (left upper quadrant).

• Divided into nodules by strips of connective tissue; each nodule contains a reddish area (red pulp) and a purplish area (white pulp).

• Red Pulp: Consists mostly of red blood cells.

• White Pulp: Filled with leukocytes.

Overview of the Immune Response

• Barriers: First line of defense, such as the skin and mucous membranes, which act instantaneously to prevent pathogenic invasion into the body tissues.

• Innate Immune Response: Rapid "Emergency responders" of the immune system. It involves a variety of cells and soluble factors that activate quickly.

• Adaptive Immune Response: Involves many cell types and soluble factors. Notable for its long-lasting memory capability.

White Blood Cells (Leukocytes)

• Functionally divided into three broad classes:
  • Phagocytic cells: Ingest pathogens or other cellular debris for destruction.
  • Lymphocytes: Responsible for antibody production, direct cell-mediated killing of virus-infected and tumor cells, and regulation of the immune response.
  • Granular cells: Two main types: Hodgkin lymphoma and non-Hodgkin lymphoma.

Lymphatic System Cancers

• Symptoms: Swollen lymph nodes, fever, night sweats, weight loss, fatigue, itching.

• Treatment: Chemotherapy, radiation therapy, immunotherapy, targeted therapy, stem cell transplantation.

• Duration: Treatment might last for several months with continuous follow-up care afterward.