Lymphatic System and Immunity: Study Notes for Anatomy & Physiology

Lymphatic System

Overview of the Lymphatic System

The lymphatic system is a network of tissues and organs that help rid the body of toxins, waste, and other unwanted materials. Its primary function is to transport lymph, a fluid containing infection-fighting white blood cells, throughout the body.

• Main Organs: Lymph nodes, spleen, thymus gland, tonsils, and lymphatic vessels.

• Functions: Fluid balance, immune defense, absorption of dietary fats.

• Lymph: A clear fluid that circulates through lymphatic vessels and is eventually returned to the bloodstream.

Lymphatic Organs and Their Functions

• Lymph Nodes: Small, bean-shaped structures that filter lymph and house lymphocytes. They are key sites for immune responses.

• Spleen: The largest lymphatic organ; filters blood, removes old red blood cells, and stores white blood cells and platelets.

• Thymus Gland: Located in the upper chest; site of T cell maturation, especially active in childhood.

• Tonsils: Lymphatic tissue in the pharynx that protects against inhaled or ingested pathogens.

Lymphatic Vessels and Circulation

Lymphatic vessels transport lymph from tissues to the bloodstream. Most lymph returns to the systemic circulation via the thoracic duct, which drains into the left subclavian vein.

• Difference from Blood Vessels: Lymphatic vessels are more permeable and have valves to prevent backflow.

• Flow of Lymph: Lymph flows in one direction, aided by muscle contractions and valves.

• Thoracic Duct: The main lymphatic vessel that drains lymph from most of the body.

Cells of the Lymphatic and Immune Systems

Lymphocytes

Lymphocytes are a type of white blood cell crucial for immune responses. The two main types are B cells and T cells.

• B Cells: Mature in the bone marrow; responsible for humoral immunity (antibody production).

• T Cells: Mature in the thymus gland; responsible for cellular immunity.

• Cytotoxic T Cells: Destroy virus-infected cells and tumor cells.

• Helper T Cells: Activate other immune cells.

Other Immune Cells

• Macrophages: Found in the spleen and other tissues; engulf and digest pathogens and cellular debris.

• Antigen-Presenting Cells: Cells that process and present antigens to lymphocytes, initiating immune responses.

Immunity and Defense Mechanisms

Types of Immunity

• Humoral Immunity: Mediated by B cells and antibodies; defends against extracellular pathogens.

• Cellular Immunity: Mediated by T cells; defends against intracellular pathogens.

• Innate Defense: Non-specific, immediate defense mechanisms such as skin, mucous membranes, and phagocytic cells.

Functions of Lymphatic System Components

• Lymph Nodes: Filter lymph, trap pathogens, and facilitate immune cell activation.

• Cytotoxic Cells: Destroy infected or abnormal cells.

• Lymphocytes: Recognize and respond to specific antigens.

Key Terms and Definitions

• Antigen: Any substance that can induce an immune response.

• Immunoglobulins: Antibodies produced by B cells; bind to antigens and neutralize them.

• Red Bone Marrow: Site of hematopoiesis (formation of blood cells), including B cell maturation.

• Thymus: Site of T cell maturation.

Table: Comparison of Humoral and Cellular Immunity

Feature	Humoral Immunity	Cellular Immunity
Main Cell Type	B cells	T cells
Effector Molecule	Antibodies (Immunoglobulins)	Cytokines, cytotoxic granules
Target	Extracellular pathogens	Intracellular pathogens, infected cells
Site of Maturation	Bone marrow	Thymus

Additional info:

• Some questions referenced the role of lymphatic tissue in the small intestine; this refers to Peyer’s patches, which are lymphoid nodules important for gut immunity.

• The lymphatic system also plays a role in the absorption of dietary fats via specialized lymphatic vessels called lacteals in the small intestine.