Overview
This lecture covers the lymphatic (immune) system, its major functions, structures, fluid movement, and related disorders.
Functions of the Lymphatic System
- Transports excess tissue fluid back to the bloodstream.
- Defends the body by filtering body fluids for bacteria, viruses, and cell debris.
- Absorbs and transports large lipids from the digestive tract that cannot enter blood capillaries directly.
Lymphatic Pathways and Fluid Movement
- Lymphatic vessels resemble veins but carry lymph, a watery fluid with dissolved substances.
- Lymphatic capillaries have dead ends and are highly permeable, allowing proteins and fats to enter.
- Lymphatic vessels drain into the subclavian veins, returning lymph to blood circulation.
- Fluid movement depends on muscle contraction, breathing, one-way valves, and new lymph formation—no pump like the heart.
Key Lymphatic Organs and Tissues
- Lymph nodes cluster at vessel junctions; contain lymphocytes and macrophages for immune defense.
- Thymus gland produces thymosin hormone to mature lymphocytes into T cells; shrinks with age.
- Spleen is the largest lymphatic organ; filters blood, removes old red blood cells, and stores blood.
- Tonsils (palatine, pharyngeal/adenoids, lingual) filter inhaled and swallowed pathogens at vulnerable entry points.
- Appendix is a vestigial lymphatic tissue, possibly once aided digestion and immunity.
Lymphatic vs. Blood Circulation
- Lymphatic flow is much slower (≈3 liters/day) than blood (≈5 liters/minute).
- Lymphatic vessels have thin, permeable walls and one-way valves; unlike blood, lymph moves in only one direction.
- Movement is aided by skeletal muscle, body movement, and breathing.
Disorders: Edema and Causes
- Edema (fluid buildup) occurs when excess fluid is not returned to the bloodstream.
- Causes include immobility, gravity, heat, high salt intake, heart failure, and kidney disease.
Key Terms & Definitions
- Lymph — fluid collected by lymphatic vessels from tissues.
- Lymphatic vessels — transport lymph toward the bloodstream, similar to veins.
- Lymph node — small structures that filter lymph and house immune cells.
- Thymus — gland that matures T lymphocytes.
- Spleen — organ that filters blood and destroys old red blood cells.
- Tonsils — lymphatic tissues that protect the throat and nasal passages.
- Edema — swelling from excess fluid in tissues.
- Vestigial structure — body part that has lost its original function.
Action Items / Next Steps
- Review the anatomy of lymphatic organs (nodes, spleen, tonsils, appendix) in lab models.
- Understand fluid movement mechanisms and causes of edema for upcoming assessments.