Lymphatic System Notes

General Structure and Functions of the Lymphatic System

• Major Functions:

  • Returns excess interstitial fluid to the bloodstream.

  • Transports dietary lipids and fat-soluble vitamins from the gastrointestinal tract.

  • Facilitates immune responses (house immune cells).

• Components of the Lymphatic System:

  • Lymph

  • Lymphatic vessels

  • Lymph nodes

  • Spleen

  • Thymus

  • Tonsils

  • Red bone marrow

Lymph & Lymphatic Vessels

• Lymph:

  • A clear fluid that contains lymphocytes (white blood cells) and is derived from interstitial fluid.

  • Components include water, electrolytes, immune cells, and proteins.

• Comparison of Body Fluids:

  • Whole Blood: Composed of plasma, red blood cells, white blood cells, and platelets.

  • Plasma: Fluid component of blood containing water, electrolytes, proteins.

  • Interstitial Fluid: Fluid found in the spaces between cells; similar to plasma but has a lower protein content.

  • Lymph: Similar to interstitial fluid but contains more lymphocytes.

• Anatomic Structure of Lymphatic Capillaries:

  • Blind-ended (open at one end) capillaries found in most tissues.

  • Have walls that are one cell thick and allow for the entrance of interstitial fluid.

• Comparison of Capillaries:

  • Lymphatic Capillaries:

    • Larger in diameter and more permeable than blood capillaries.

    • Endothelial cells overlap to create one-way valves.

  • Blood Capillaries:

    • Thinner walls and are not as permeable as lymphatic capillaries.

• Fluid Entry into Lymphatic Capillaries:

  • When interstitial fluid pressure increases, fluid enters the lymphatic capillaries due to the high permeability of their walls.

• Structure and Function of Lacteals:

  • Specialized lymphatic capillaries located in the small intestine.

  • Function to absorb dietary fats and fat-soluble vitamins, resulting in a milky fluid called chyle.

• Chyle vs. Normal Lymph:

  • Chyle is a milky fluid containing fat particles absorbed from the intestine, while normal lymph does not contain significant amounts of fat.

• Lymphatic Collecting Vessels vs. Blood Vessels:

  • Lymphatic Collecting Vessels:

    • Thinner walls, more valves, and larger diameter than blood vessels.

  • Blood Vessels:

    • Thicker walls and carry blood under higher pressure.

• Lymphatic Trunks:

  • Major Trunks:

    • Jugular trunks (head and neck)

    • Subclavian trunks (upper limbs)

    • Bronchomediastinal trunks (thoracic organs)

    • Intestinal trunk (digestive organs)

    • Lumbar trunks (lower limbs and pelvic organs)

• Lymphatic Ducts:

  • Major Ducts:

    • Thoracic duct: drains into the left subclavian vein, covering the left side of the head, neck, thorax, left arm, and lower body.

    • Right lymphatic duct: drains into the right subclavian vein, covering the right arm, right side of the head and neck.

• Cisterna Chyli:

  • A dilated sac that serves as a major collecting basin for lymph from the lower body and intestines. It receives lymph from the lumbar and intestinal trunks, facilitating its return to the bloodstream.

• Pathway of Lymph Circulation:

  • Lymph flows from lymphatic capillaries to lymphatic vessels, to trunks, and finally through ducts into venous circulation (subclavian veins).

• Mechanisms that Move Lymph:

  • Lymph flow is aided by skeletal muscle contractions, respiratory movements, and the presence of one-way valves in lymphatic vessels.

Lymphatic Tissues and Organs

• Two Categories of Lymphatic Tissue:

  • Primary Lymphatic Organs:

    • Red bone marrow, Thymus

  • Secondary Lymphatic Organs:

    • Lymph Nodes, Spleen, Tonsils, Lymphatic nodules, MALT (Mucosa-associated lymphoid tissue)

Red Bone Marrow

• Location:

  • Found within the cavities of certain bones.

• Functions:

  • Site of hematopoiesis (blood cell formation), including B cell maturation.

Thymus

• Location:

  • Located in the superior mediastinum, posterior to the sternum.

• Structure:

  • Consists of lobules with an outer cortex and inner medulla.

• Function:

  • Site of T cell maturation and differentiation, essential for adaptive immunity.

• Thymus Changes:

  • Reaches its maximum size during childhood and gradually involutes and decreases in size in adulthood.

Lymph Nodes

• Location:

  • Distributed throughout the body, commonly found in the neck, armpits, and groin.

• Palpable Areas:

  • Cervical, axillary, and inguinal regions.

• Function:

  • Filter lymph, trap pathogens, and facilitate immune responses (activate lymphocytes).

• Structure:

  • Bean-shaped organs with a capsule, cortex, germinal centers, and medulla.

• Lymph Circulation:

  • Lymph enters through afferent lymphatics, passes through sinuses in the nodes, and exits via efferent lymphatics.

• Slow Flow in Nodes:

  • Lymph flows slowly to allow time for immune processing and filtraion.

Spleen

• Location:

  • Located in the upper left quadrant of the abdomen, posterior to the stomach.

• Structure:

  • Comprised of white pulp (lymphatic tissue) and red pulp (blood filtering).

• Functions:

  • Filters blood, provides immune responses, recycles iron, and stores red blood cells.

Tonsils

• Location:

  • Positioned in the oropharynx (palatine tonsils), nasopharynx (pharyngeal tonsil), and lingual tonsils at the base of the tongue.

• Structure:

  • Composed of lymphoid tissue with crypts to trap pathogens.

• Function:

  • Protect against pathogens entering through the oral and nasal cavities.

Lymphatic Nodules and MALT

• Composition of Lymphatic Nodules:

  • Clusters of lymphoid tissue found throughout the body, especially in mucosal areas.

• MALT:

  • Stands for Mucosa-associated lymphoid tissue.

• Location of MALT:

  • Found in mucous membranes of the gastrointestinal, respiratory, and urogenital tracts.

• Peyer’s Patches:

  • Located in the ileum of the small intestine, they protect against pathogens in ingested food.

• Appendix:

  • Located at the junction of the small and large intestines, functions in immune response to gut flora.