lymphatic

TOPIC XIII: LYMPHATIC SYSTEM

A) Overview

  • The lymphatic system comprises a one-way network of lymphatic vessels.
  • Function: Collects approximately 10% of extracellular fluid (ECF) that leaks out from cardiovascular capillaries and returns this fluid, known as lymph, to the venous blood. (Refer to Fig. 20.2 and Fig. 20.3)
  • Lymph Nodes: Located along the vessel network; these nodes cleanse lymph as it passes through. (Refer to Fig. 20.2 and Fig. 20.3)
Lymphocytes
  • Description: Small cells characterized by a large spherical nucleus and a thin rim of pale blue cytoplasm.
  • Function: Lymph nodes contain T and B lymphocytes, which help identify and remove bacteria, viruses, and cancer cells. (Refer to Fig. 20.2)
  • The lymphoid cells, tissues, and organs support various functions of the lymphatic system. (Refer to Fig. 20.2 and Fig. 20.3)

B) Body Fluid Compartments

  1. Intracellular Fluid (ICF)

    • Definition: Fluid found within cells - accounts for approximately 40% of body weight.
    • Composition: Includes plasma (55%), white blood cells and platelets (<1%), red blood cells (45%).

  2. Extracellular Fluid (ECF)

    • Definition: Fluid found outside of cells.

    • a) Blood Plasma:

      • Accounts for approximately 5% of body weight.
      • It is the fluid component of blood and some of it exits capillaries to form interstitial fluid (ISF).

    • b) Interstitial Fluid (ISF):

      • Accounts for approximately 15% of body weight.
      • It is the fluid between cells within the body (excluding blood cells surrounded by plasma).
      • Some ISF moves into lymphatic capillaries to form lymph. (Refer to Fig. 20.1)

    • c) Lymph:

      • Accounts for approximately 1% of body weight.
      • This is the fluid contained within lymphatic vessels, which is eventually returned to blood plasma. (Refer to Fig. 20.3)

C) Lymphatic Circulation

  • General Flow: Lymph enters, flows through lymphatic capillaries, and then proceeds to lymphatic collecting vessels.

  • Characteristics of Lymphatic Capillaries:

    • These are closed-ended vessels that are interspersed within cardiovascular capillary beds.
    • The capillaries have thin walls and use anchoring filaments to maintain their structure. (Refer to Fig. 20.1)

  • Collecting Vessels:

    • Connects lymphatic capillaries and have one-way valves to ensure lymph flows in one direction.
    • Lymph nodes located along these vessels filter lymph for bacteria and debris. (Refer to Fig. 20.2)
Major Ducts in Lymphatic Circulation

  1. Right Lymphatic Duct:

    • Responsible for draining lymph from the right side of the head, chest, and right arm. (Refer to Fig. 20.3)
    • Drains into the right subclavian vein, thus reentering the blood circulation.

  2. Thoracic Duct:

    • Drains lymph from below the ribs and the left side of the body. (Refer to Fig. 20.3)
    • Collecting vessels from below the ribs converge to form an enlarged lymph vessel known as the cisterna chyli, which is the most inferior part of the thoracic duct.
    • Drains into the left subclavian vein, allowing reentry into the blood circulation. (Refer to Fig. 20.2 and Fig. 20.3)

D) Lymphatic Tissues & Organs

  • Contains numerous lymphocytes and plays a crucial role in the immune system of the body.
1) Primary Lymphoid Organs and Tissues:

  • These are locations where lymphoid stem cells divide and mature to become immunocompetent.

    • Includes:

    a) Red Bone Marrow:

    • All lymphocyte stem cells arise here.
    • B lymphocytes mature and proliferate (mitosis) here.

    b) Thymus Gland:

    • Early in development (fetal stage), lymphocyte stem cells migrate here.
    • T lymphocytes mature and further proliferate in this gland. (Refer to Fig. 20.5)

    c) Mature Lymphocytes:

    • Once mature, these lymphocytes move into the bloodstream and migrate to secondary lymphoid organs/tissues. (Refer to Fig. 20.5)
2) Secondary Lymphoid Organs and Tissues:

  • Functions in detecting and removing pathogens.

  • Locations for lymphocytes to activate and proliferate.

  • Includes:

    a) Lymph Nodes:

    • Small masses of lymphoid tissue found along the lymphatic collecting vessels.
    • Highly concentrated in cervical (neck), axillary (armpit), inguinal (groin), intestinal, and pelvic regions. (Refer to Fig. 20.3)

    b) Spleen:

    • Located in the left side of the abdominal cavity, below the diaphragm, next to the stomach.
    • Function: Filters blood by removing bacteria, viruses, old and defective blood cells, and cellular debris. (Refer to Fig. 20.5)

    c) Mucosal Associated Lymphoid Tissue (MALT):

    • Serves to trap and remove pathogens at entry points into the body. (Refer to Fig. 20.5)
    • Examples: Tonsils, appendix, and lymphoid tissues associated with mucous membranes.
    • Specific Structures: Aggregated lymphoid nodules known as Peyer's patches in the small intestine, tonsils forming a ring around the pharynx, including:
      • Pharyngeal (1): Located in the posterior nasopharynx and referred to as adenoids when infected/swollen.
      • Palatine (2): Found in the oropharynx, commonly removed in surgeries.
      • Lingual (1): Formed from bumpy nodules at the posterior part (base) of the tongue. (Refer to Fig. 20.8)

Summary

  • The lymphatic system forms a one-way route back to the blood, connecting the:
    • Venous System
    • Arterial System
    • Heart
    • Components include:
      • Lymph Ducts
      • Lymph Nodes
      • Collecting Lymphatic Vessels (with valves)
      • Blood Capillaries
      • Lymphatic Capillaries
      • Lymph Trunks (Refer to Fig. 20.1)
    • Coverage completed for all material relevant to the upcoming lecture midterm exam. Questions can be addressed for further clarification if needed.