Lymphatic System & Immunity - PCL and Diploma Students
1. Introduction
The lymphatic system is a network of vessels, nodes, and organs that returns interstitial fluid to blood, absorbs dietary fats, and participates in immune defense.
Functions:
Fluid balance: Returns 2–3 L interstitial fluid/day to circulation
Fat absorption: Via lacteals in small intestine
Immune surveillance: Filters pathogens via lymph nodes and spleen
Main components: Lymph, Lymphatic vessels, Lymph nodes, Tonsils, Spleen, Thymus, Bone marrow
2. Lymphatic System Anatomy
2.1 Lymph
Colorless fluid, similar to plasma but lower in proteins, contains lymphocytes and chyle after meals.
Flow: Interstitial space → Lymph capillaries → Lymph vessels → Lymph nodes → Thoracic duct / Right lymphatic duct → Subclavian veins
2.2 Lymphatic Vessels
Structure: Thin-walled, valves prevent backflow, composed of endothelial lining.
Types:
Lymphatic capillaries → blind-ended, permeable to proteins and cells
Collecting vessels → drain into lymph nodes
Trunks: Jugular, Subclavian, Bronchomediastinal, Intestinal, Lumbar
Ducts:
Thoracic duct: Drains most of body into left subclavian vein
Right lymphatic duct: Drains right upper limb, right thorax, head/neck
Clinical correlation: Blockage → lymphedema, e.g., post-mastectomy
2.3 Lymph Nodes
Small, bean-shaped structures filtering lymph, located along vessels.
Structure: Capsule → Cortex → Paracortex → Medulla
Cell types:
Cortex → B lymphocytes
Paracortex → T lymphocytes
Medulla → Plasma cells, macrophages
Major groups: Cervical, Axillary, Inguinal, Mesenteric
Atlas-style diagram placeholder: Label cortex, paracortex, medulla, afferent/efferent vessels.
2.4 Primary Lymphoid Organs
Bone marrow: Hematopoiesis, B cell maturation
Thymus: T cell maturation, located in anterior mediastinum
2.5 Secondary Lymphoid Organs
Spleen: Filters blood, stores platelets, site of immune response
Red pulp → removes old RBCs
White pulp → lymphoid tissue (T and B cells)
Tonsils: Pharyngeal, palatine, lingual → first line of defense in oropharynx
Mucosa-associated lymphoid tissue (MALT): Peyer’s patches, appendix
3. Lymphatic Physiology
3.1 Lymph Formation and Flow
Interstitial fluid → Lymph via hydrostatic and osmotic pressures
One-way flow aided by:
Valves
Skeletal muscle contraction
Respiratory movements
Pulsation of adjacent arteries
3.2 Immune Cell Trafficking
Lymph transports antigen-presenting cells (APCs) to lymph nodes
B and T cells enter nodes via high endothelial venules
4. Immunity Overview
4.1 Innate (Non-specific) Immunity
First line of defense, rapid, no memory
Components:
Physical: Skin, mucous
Chemical: Lysozyme, acidic pH, complement proteins
Cellular: Neutrophils, macrophages, NK cells, dendritic cells
4.2 Adaptive (Specific) Immunity
Slower, highly specific, immunological memory
Components:
Humoral immunity (B cells/antibodies)
Plasma cells produce antibodies: IgG, IgA, IgM, IgE, IgD
Functions: Neutralization, opsonization, complement activation
Cell-mediated immunity (T cells)
CD4+ helper T cells → activate B cells, macrophages
CD8+ cytotoxic T cells → kill infected cells
4.3 Antigen Presentation
APCs: Dendritic cells, macrophages, B cells
Present processed antigen with MHC molecules to T cells
6. MCQs
Primary site of T cell maturation → Thymus
Main antibody in mucosal secretions → IgA
Lymphatic duct draining left upper limb, left thorax → Thoracic duct
APC presenting antigen to helper T cells → Dendritic cells
Bean-shaped organ filtering lymph → Lymph nodes
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