A) Overview

Lymphatic System Functions and Components

The lymphatic system is a vital part of the circulatory and immune systems, responsible for maintaining fluid balance and defending the body against pathogens. It consists of a network of vessels, lymphoid tissues, and organs.

• Lymphatic vessels: Collect approximately 10% of extracellular fluid that leaks out from cardiovascular capillaries and return this fluid (now termed lymph) to the venous blood.

• Lymph nodes: Along the vessels, lymph is filtered by lymph nodes, which contain T & B lymphocytes that identify and remove bacteria, viruses, and cancer cells.

• Lymphatic cells, tissues, and organs: Support the functions of the lymphatic system.

B) Body Fluid Compartments

Distribution of Body Fluids

Body fluids are divided into intracellular and extracellular compartments, each with distinct locations and functions.

• Intracellular Fluid (ICF): Fluid found within cells, accounting for about 40% of body weight.

• Extracellular Fluid (ECF): Fluid found outside of cells (~20% of body weight), further divided into:

  • Blood plasma: Fluid portion of blood.

  • Interstitial fluid (ISF): Fluid between cells, derived from plasma via capillary filtration.

  • Lymph: ISF that enters lymphatic capillaries to form lymph. Lymph is returned to blood plasma via lymphatic vessels.

Example: Lymphatic capillaries collect excess ISF from tissues, which is then filtered and returned to the bloodstream, helping to prevent edema.

C) Lymphatic Circulation

Pathway of Lymph Flow

Lymphatic circulation involves the movement of lymph from tissues back to the cardiovascular system, ensuring fluid balance and immune surveillance.

• Lymphatic capillaries: Closed-ended vessels that collect ISF and project into cardiovascular capillary beds.

• Lymphatic collecting vessels: Contain valves to prevent backflow and transport lymph toward larger ducts.

• Lymphatic ducts: Drain lymph into subclavian veins, returning it to the blood circulation.

• Thoracic duct: The largest lymphatic duct, drains lymph from below the ribs and the entire left side of the body into the left subclavian vein.

• Cisterna chyli: The most inferior portion of the thoracic duct, collecting lymph from the lower body.

Equation:

Example: During exercise, increased muscle contractions enhance lymph flow through the vessels.

D) Lymphoid Tissues & Organs

Structure and Function of Lymphoid Organs

Lymphoid tissues and organs are essential for immune function, containing numerous lymphocytes that detect and respond to pathogens.

• Primary lymphoid organs and tissues: Sites where lymphoid stem cells divide and mature.

  • Red bone marrow: All lymphocyte stem cells originate here.

  • Thymus: Site of T lymphocyte proliferation and maturation. Immature T cells migrate here for development, then move into the blood stream and secondary lymphoid organs.

• Secondary lymphoid organs and tissues: Locations where lymphocytes detect pathogens and become activated.

  • Lymph nodes: Small masses of lymphoid tissue along lymphatic collecting vessels. High concentrations found in cervical, axillary, inguinal, intestinal, and pelvic regions.

  • Spleen: Located in the left side of the abdominal cavity, just below the diaphragm, next to the stomach. Functions include filtering blood, removing pathogens, and old blood cells.

  • Mucosal Associated Lymphoid Tissue (MALT): Includes tonsils, adenoids, and other lymphoid tissues on mucous membranes. Protects against pathogens entering the body via the mouth, nose, and digestive tract.

    • Palatine tonsils: Located at the posterior oral cavity.

    • Pharyngeal tonsil (adenoid): Located at the roof of the nasopharynx.

    • Lingual tonsil: Bumpy nodules on the posterior part (base) of the tongue.

Example: Swelling of lymph nodes during infection is a sign of immune activation.

Table: Comparison of Primary and Secondary Lymphoid Organs

Additional info: The notes have been expanded to include definitions, examples, and a comparison table for clarity and completeness.