20 Lymphatic

Lymphatic System Notes

Overview of the Lymphatic System

  • Importance of the Lymphatic System

    • Two main functions:

      • Maintain fluid balance in the internal environment

      • Promote body immunity

    • Lymph vessels function as drains, collecting excess tissue fluid and returning it to the venous blood before it reaches the heart.

    • The lymphatic system is a specialized component of the circulatory system consisting of lymph, lymphatic vessels, and lymphoid tissue structures (e.g., lymph nodes, tonsils, thymus, spleen, bone marrow).

    • Transports tissue fluid, proteins, fats, and other substances to general circulation.

    • Lymphatic vessels begin in the intercellular spaces of soft tissues and form an open system.

Components of the Lymphatic System

  • Major Structures:

    • Right lymphatic duct: Empties lymph into the right subclavian vein.

    • Thoracic duct: Empties lymph into the left subclavian vein; originates from cisterna chyli.

    • Axillary lymph nodes: Located in the underarm region; cleanse lymph and alert immunity.

    • Inguinal lymph nodes: Located in the groin; cleanse lymph and alert immunity.

    • Tonsils: Lymphatic tissue that helps block pathogens from entering the body via nose and mouth.

    • Red bone marrow: Site of blood cell origin.

    • Thymus: Maturation site for T lymphocytes that differentiate self from non-self.

    • Spleen: Cleanses blood of debris and bacteria while stimulating resident lymphocytes.

Lymph and Interstitial Fluid

  • Lymph:

    • Clear, watery fluid found in lymphatic vessels, resembling blood plasma but with a lower percentage of protein; isotonic.

    • Elevated protein concentration occurs in thoracic duct lymph due to absorption from the liver and small intestine.

  • Interstitial Fluid (IF):

    • Fills spaces between cells, part of the extracellular matrix (ECM).

    • Resembles blood plasma with less protein; together with blood plasma, constitutes extracellular fluid.

Lymphatic Vessels

  • Structure and Distribution:

    • Lymphatic Capillaries:

      • Microscopic, blind-end vessels originating lymphatic vessels; consist of a single layer of flattened endothelial cells.

    • Capillaries merge to form larger lymphatics, leading to lymphatic trunks (right lymphatic duct and thoracic duct).

    • Lymph from the upper right quadrant empties into the right lymphatic duct, while lymph from the rest of the body flows into the thoracic duct.

  • Functions of Lymphatic Vessels:

    • Remove high-molecular weight substances and particulate matter from interstitial spaces.

    • Lacteals: Special lymphatic vessels in the intestines that absorb fats and nutrients from digestion.

Circulation of Lymph

  • Lymph flows from capillaries to larger vessels and eventually re-enters blood at the internal jugular and subclavian vein junction.

  • Lymphatic Pump (Lymphokinesis):

    • Movement of lymph facilitated by valves, breathing, and skeletal muscle contractions which create fluid pressure gradients.

    • Lymphokinetic actions involve activities propelling the flow of lymph.

Lymph Nodes

  • Structure of Lymph Nodes:

    • Oval structures surrounded by a fibrous capsule that act as biological filters.

    • Lymph enters nodes and flows through sinuses before draining into efferent vessels.

    • Comprised of trabeculae and lined with reticuloendothelial cells that perform phagocytosis.

  • Functions of Lymph Nodes:

    • Defense Functions:

      • Mechanical filtration prevents particles from progressing.

      • Biological activity of cells destroys/remove particles (phagocytosis).

    • Hematopoiesis:

      • Lymphoid tissue serves as the maturation site for lymphocytes.

Lymphatic Drainage of the Breast

  • Important clinically as cancer and infections can spread through lymphatic pathways.

  • Lymph Node Associations:

    • Over 85% of lymph from breasts enters axillary lymph nodes; the remainder drains to nodes along the sternum.

Tonsils

  • Form a protective ring under the mucous membranes of the mouth/throat (pharyngeal lymphoid ring).

    • Types of Tonsils:

      • Palatine tonsils: On each side of the throat.

      • Pharyngeal tonsils: Near the nasal cavity.

      • Lingual tonsils: At the base of the tongue.

Thymus

  • Location: Central organ located in the mediastinum, above the heart and lungs.

  • Structure: Subdivided into lobules with a dense cellular cortex and a less dense medulla.

  • Function:

    • Vital for immunity; source of lymphocytes before birth.

    • Produces thymosin which aids in T cell development shortly after birth.

Spleen

  • Location: Below the diaphragm, above the left kidney.

  • Structure: Ovoid shape with a fibrous capsule and compartments.

    • White pulp: Contains developing lymphocytes.

    • Red pulp: Network of reticular fibers submerged in blood.

  • Functions:

    • Remove microorganisms via macrophages; participate in hematopoiesis; destroy old RBCs; act as a blood reservoir.

Cycle of Life: Lymphatic System

  • Major changes from birth to late adulthood.

    • Organs with lymphocytes appear before birth and develop until puberty.

    • Post-puberty atrophy occurs; organs shrink in size, becoming fatty/fibrous.

    • Risk of infection and cancer increases with age; potential for autoimmune conditions increases.