Lymphatic System Overview

Lymphatic System Components

• The lymphatic system consists of lymphatic vessels and lymphoid tissues and organs.

Lymphatic Vessels

• A network of vessels that transport lymph, including excess interstitial fluid, proteins, and waste products back to the bloodstream.

Lymphoid Tissues and Organs

• Structures involved in immune responses, such as lymph nodes, spleen, thymus, and tonsils, which produce, maintain, and distribute lymphocytes, and filter lymph to remove pathogens and debris.

Plasma, Interstitial Fluid, and Lymph Fluid

• Plasma: The liquid component of blood, consisting of water, proteins, electrolytes, and other substances.
• Interstitial fluid: Fluid that surrounds tissue cells, derived from plasma that has leaked out of capillaries.
• Lymph fluid: Interstitial fluid that enters the lymphatic vessels, containing lymphocytes and other immune cells.

Hydrostatic and Osmotic Pressures

• Hydrostatic pressure: Generated by the pumping action of the heart, pushes fluid out of the capillaries.
• Osmotic pressure: Created by plasma proteins (mainly albumin), pulls fluid back into the capillaries.

Source of Interstitial Fluid and Lymph Fluid

• Interstitial fluid is derived from plasma that leaks out of the blood capillaries into the surrounding tissues.
• Lymph fluid is derived from interstitial fluid that enters the lymphatic capillaries.

Smallest Lymphatic Vessels

• The smallest lymphatic vessels are the lymphatic capillaries.

Permeability of Lymph Capillaries vs. Blood Capillaries

• Lymph capillaries are more permeable than blood capillaries, allowing larger molecules and particles (e.g., proteins, pathogens) to enter.

Route of Lymph Flow

• Lymph capillaries → Lymphatic vessels → Lymph nodes → Larger lymphatic vessels → Lymphatic trunks → Lymphatic ducts → Circulatory system (subclavian veins).

Largest Lymphatic Vessels

• Thoracic duct: Drains lymph from the majority of the body.
• Right lymphatic duct: Drains lymph from the right upper quadrant of the body.

Lymphatic Ducts

• Dump lymph into the subclavian veins, specifically at the junction of the internal jugular and subclavian veins.

Lymphatic Trunks and Their Drainage Areas

• Jugular trunks (left and right): Drain the head and neck.
• Subclavian trunks (left and right): Drain the upper limbs.
• Bronchomediastinal trunks (left and right): Drain the thoracic cavity and lungs.
• Intercostal trunks: Drain the intercostal spaces.
• Intestinal trunk: Drains the digestive organs.
• Lumbar trunks (left and right): Drain the lower limbs and pelvic region.

Factors Helping the Flow of Lymph

• Contraction of skeletal muscles.
• Pressure changes in the thorax during breathing.
• Contraction of smooth muscle in the walls of lymphatic vessels.
• Presence of valves in lymphatic vessels to prevent backflow.

Functions of Lymphocytes, Macrophages, and Dendritic Cells

• Lymphocytes: Involved in immune responses; T cells attack infected cells, B cells produce antibodies.
• Macrophages: Phagocytose pathogens and debris, present antigens to T cells.
• Dendritic cells: Capture antigens and present them to T cells, initiating immune responses.

Lymphoid Tissue Components

• Reticular fibers (framework).
• Lymphocytes (T cells and B cells).
• Macrophages and dendritic cells.

Location of Lymph Nodes

• Located along the lymphatic vessels, distributed throughout the body.

Large Clusters of Lymph Nodes

• Found in the cervical (neck), axillary (armpit), and inguinal (groin) regions.

Functions of Lymph Nodes

• Filter lymph to remove pathogens and debris.
• House lymphocytes and macrophages that initiate immune responses.

Afferent vs. Efferent Vessels of Lymph Nodes

• Afferent vessels: Bring lymph into the lymph node.
• Efferent vessels: Carry lymph away from the lymph node.