Lymphatic system

Anatomy and Physiology

The Lymphatic System

• Prevalence categories:

  • >20%

  • 15-20%

  • 10-15%

  • 5-10%

  • 2-5%

  • 1-2%

  • 0.5-1.0%

  • 0.1-0.5%

  • <0.1%

• Categories indicate levels of HIV prevalence in various populations.

• Aids free area indicates regions without recorded cases.

• Areas with no data on HIV are also marked.

The Lymphatic System Functions

• Primary Functions:

  • Remove Excess Interstitial Fluid:

  • Helps maintain fluid balance in the tissues by draining excess fluid.

  • House and Transport Lymphocytes:

  • Lymphocytes are critical for immune responses, aiding in defense against pathogens.

  • Transport Dietary Lipids and Fat-Soluble Vitamins:

  • Absorbs these nutrients in the gut and transports them throughout the body.

Lymphatic System Components

• Core Components Include:

  • Lymphocytes

  • Lymph nodes

  • Lymphatic vessels

  • Lymphatic capillaries

  • Lymphatic fluid

  • Bone marrow

  • Thymus

  • Spleen

  • Tonsils

  • Peyer’s patches

Lymphatic Capillaries

Structure and Function

• Location and Features:

  • Nestled among blood capillaries.

  • Composed of a single layer of endothelial cells.

  • Contain one-way flap valves tethered to collagen fibers.

• Mechanism of Fluid Entry:

  • As interstitial fluid accumulates, collagen fibers pull valves open, allowing fluid to enter.

  • Lymph capillaries drain into lymphatic vessels.

  • Lymph fluid is filtered by lymph nodes before entering blood circulation via subclavian veins.

Visual Anatomy of Lymphatic Capillaries

• Components:

  • Arterioles and venules

  • Tissue fluid

  • Endothelial 'flaps' for backflow prevention

  • Macrophages and lymphocytes in the fluid.

Lymphatic Capillaries in the Small Intestines

• Function of Lacteals:

  • Specialized lymphatic capillaries called lacteals transport dietary lipids and lipid-soluble vitamins.

• Formation of Chyle:

  • Dietary triglycerides combine with lipids and proteins to form a milky fluid called chyle.

• Travel Path:

  • Chyle travels through the lymphatic system, eventually entering the bloodstream to send lipids to the liver.

Lymphatic Vessels & Ducts

Structure

• Three tunic layers similar to veins.

• Mechanism of Movement:

  • Skeletal muscle massage aids lymph fluid movement, analogous to how blood is returned in veins.

• One-way valves prevent reverse flow of fluid when muscles relax.

Duct Functions

• Right Lymphatic Duct:

  • Receives lymph from the upper right side of the body (head, arm, chest on right).

• Thoracic Duct:

  • Receives lymph from the remaining body (legs, abdomen, left chest, arm, head).

  • The cisterna chyli drains the intestines into the thoracic duct.

Visual Diagram Components

• Right and Left internal jugular veins

• Draining pathways of the thoracic duct and right lymphatic duct into subclavian veins.

Lymphocytes

Development and Function

• Primary Cells:

  • Key immune cells in lymphoid organs developed from lymphoblasts in hematopoiesis.

• Types of Lymphocytes:

  • B Lymphocytes:

  • Clone into plasma cells that produce antibodies binding to foreign antigens during immune responses (requires vitamin A).

  • T Lymphocytes:

  • Differentiate into:

    • CD4 T Cells (Helper Cells): Direct the immune response by secreting factors for communication with immune cells.

    • Natural Killer Cells (CD8 Cytotoxic Cells): Destroy cells infected with intracellular pathogens.

Primary Lymphoid Organs

Red Bone Marrow

• Hematopoiesis Site:

  • B lymphocytes develop and mature here, moving to the spleen and lymph nodes to await infection.

• T Lymphocyte Development:

  • T lymphocytes leave immature and travel to the thymus for maturation.

Thymus

• Location and Structure:

  • Located anterior to the heart in thoracic cavity, made of reticular connective tissue providing a framework for lymphocytes.

• Hormonal Function:

  • Produces hormones that induce:

  • T Cell Maturation: Thymosin, thymic factor, thymulin.

  • Proliferation: Thymopoietin.

• Post-Maturation:

  • Mature T cells migrate to the spleen or lymph nodes until infection occurs.

Secondary Lymphoid Organs

Spleen

• Location:

  • Found in the left upper quadrant of the abdomen.

• Composition:

  • Made of reticular connective tissue surrounded by a weak connective tissue capsule.

• Functional Regions:

  • White Pulp:

  • Framework for T and B lymphocytes awaiting activation; organized with germinal centers (B cells) and medullary regions (T cells).

  • Red Pulp:

  • Contains sinusoidal capillaries; resident macrophages degrade old erythrocytes.

Lymph Nodes

• Location:

  • Found in cervical, axillary, and inguinal regions among other places near organs.

• Structure:

  • Composed of reticular connective tissue with a dense irregular connective tissue capsule.

• Medulla:

  • Contains incoming afferent and outgoing efferent lymph vessels and resident macrophages potentially becoming antigen-presenting cells (APCs).

• Activation Process:

  • CD4 T cells activated by APCs and migrate to outer cortex where they activate specific B cells to proliferate into plasma cells in germinal centers producing antibodies.

Lymphoid Nodules (Tonsils)

• Types:

  • Pharyngeal (adenoids), palatine, and lingual tonsils.

• Structure:

  • Similar to lymph nodes but lack a dense outer capsule.

• Function:

  • Tonsillar crypts trap pathogens, triggering active immune responses and lymphoid follicle activation during infections.

• Clinical Implications:

  • Swollen palatine tonsils can impair swallowing; swollen pharyngeal tonsils may block Eustachian tubes, leading to middle ear infections.

Mucosa Associated Lymphoid Tissue (MALT)

• Location:

  • Found in digestive or respiratory tract beneath mucosal lining.

• Peyer’s Patches:

  • Located in the GI tract, primarily in the terminal ileum, help to prevent bacteria from entering the bloodstream.

• Bronchus Associated Lymphoid Tissue (BALT):

  • Found at branching points of bronchi (large airways), protecting respiratory system.