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DrX Whiz Niraj
The Lymphatic System & Immunity
A complete guide to Lymphatic organs, Lymph circulation, and functions of the lymphatic system for B.Pharm and GPAT exams.
The Lymphatic System consists of a fluid called lymph, vessels that transport lymph, a number of organs containing lymphatic tissue (like lymph nodes, spleen, thymus), and red bone marrow. It works closely with the cardiovascular system.
3 Major Functions:
- 1. Drains excess interstitial fluid: It returns leaked blood plasma proteins and fluid from tissue spaces back to the bloodstream.
- 2. Transports dietary lipids: Lymphatic vessels called Lacteals in the gastrointestinal tract absorb lipids and fat-soluble vitamins (A, D, E, K).
- 3. Carries out immune responses: Lymphatic tissue initiates highly specific responses directed against particular microbes or abnormal cells (via T cells and B cells).
Lymphatic vessels begin as closed-ended lymphatic capillaries located in the spaces between cells. These capillaries merge to form larger lymphatic vessels, which pass through lymph nodes.
The Two Main Lymphatic Ducts:
- 1. Thoracic Duct (Left Lymphatic Duct): The main duct. It receives lymph from the entire left side of the body and the entire lower body, emptying into the Left Subclavian Vein.
- 2. Right Lymphatic Duct: Drains lymph only from the upper right side of the body, emptying into the Right Subclavian Vein.
Widely distributed throughout the body, lymphatic organs are classified into two groups based on their functions:
| Type | Description | Organs Included |
|---|---|---|
| Primary Lymphatic Organs | Sites where stem cells divide and become immunocompetent (capable of mounting an immune response). | Red Bone Marrow (B-cells mature here) Thymus (T-cells mature here) |
| Secondary Lymphatic Organs & Tissues | Sites where most immune responses actually occur against foreign invaders. | Lymph Nodes, Spleen, and Lymphatic Nodules (e.g., Tonsils, MALT). |
A. Lymph Nodes
Bean-shaped structures located along lymphatic vessels. They act as filters. Lymph enters through afferent vessels, macrophages destroy foreign substances, and clean lymph exits through efferent vessels.
B. Spleen
The largest single mass of lymphatic tissue in the body, located in the left hypochondriac region. It filters blood (not lymph). It removes ruptured/worn-out RBCs and stores platelets.
Clinical Correlation (Applied Physiology)
- Edema: An abnormal increase in interstitial fluid volume. It occurs when filtration exceeds reabsorption, or when lymphatic vessels are blocked, causing tissues to swell.
- Elephantiasis: A tropical disease caused by a parasitic roundworm (transmitted by mosquitoes) that blocks lymphatic vessels, leading to massive, irreversible edema in the limbs.
- Lymphadenopathy: Enlarged, sometimes painful lymph nodes, often indicating a local infection or, if painless, possibly a sign of lymphoma (cancer of lymphatic organs).