BIO 004 · Human Anatomy
The Lymphatic System
Block 3 · Module 6: The Lymphatic System
A reference for the lymphatic system video and lab. This page covers lymph and the pathway it follows, the lymphatic vessels, lymph nodes, the lymphatic organs, and common disorders of the system.
How to use this sheet Toggle the toolbar above. Notes prints the full reference for review. Study prints as a fill-in-the-blank worksheet. Print it, then write each definition while you watch the video or read your book. Quiz me is on-screen typing practice: type the term, click Reveal to check yourself. The comparison grids respond to Study and Quiz too, with a Reveal button on each row.
The Foundations video gives you a complete foundational understanding of this topic, enough on its own for a foundational course. Learn it first, then move on to the Deep dive, which adds the majors-level material: the lymph node, the lymphatic organs, and the disorders of the system.
- Define lymph and trace the pathway it follows back to the blood.
- Describe the structure of lymphatic vessels and a lymph node.
- Sort the lymphatic organs into primary and secondary.
- Name common disorders of the lymphatic system.
Your pre-work
Work through these the evening before class. None of it is turned in. It is how you learn the material and build your spaced recall.
This is more than a checklist. Ticking these boxes is the start, not the finish. Committing this material to memory and being able to apply it takes considerable time and repeated effort. You are not done when the boxes are checked. Put in the real hours, and keep coming back for frequent recall and review until the material is genuinely yours.
The lymphatic vessels of the body
Add a labeled whole-body view of the lymphatic vessels, trunks, ducts, and node clusters.
A lymph node
Add a labeled section of a lymph node showing the capsule, cortex, medulla, and afferent and efferent vessels.
The lymphatic organs
Add a labeled view locating the thymus, spleen, tonsils, and node clusters.
The Lymphatic System, an Overview
The lymphatic system is a one-way drainage network. It collects fluid that leaks out of the blood capillaries, filters it, and returns it to the bloodstream, while also housing the body's defenses.
- Lymphatic systema network of vessels, tissues, and organs that drains tissue fluid and defends the body
- Interstitial fluidthe fluid in the spaces between cells, filtered out of the blood capillaries
- Lymphthe interstitial fluid once it has entered the lymphatic vessels; a clear, watery fluid
- Three functionsdraining excess interstitial fluid back to the blood, absorbing dietary fats from the small intestine, and housing the immune defenses
- A one-way systemlymphatic vessels carry lymph in one direction only, toward the heart; the system has no pump of its own
The Pathway of Lymph
Lymph travels a fixed route from the tissue spaces back to the bloodstream, growing into larger and larger vessels along the way. Follow it in order.
- Lymphatic capillariesblind-ended tubes that take up excess interstitial fluid from the tissue spaces
- Lymphatic collecting vesselslarger vessels, with valves, that carry the lymph onward
- Lymph nodesthe lymph is filtered as it passes through nodes spaced along the vessels
- Lymphatic trunkscollecting vessels merge into large trunks, each draining a major region of the body
- Lymphatic ductsthe trunks empty into two ducts: the right lymphatic duct and the larger thoracic duct
- Subclavian veinsthe ducts return the lymph to the bloodstream where the subclavian and internal jugular veins meet
Lymphatic Vessels
Lymphatic vessels resemble veins, but they begin as blind-ended capillaries and they move fluid without a pump.
- Lymphatic capillariesthe smallest lymphatic vessels, blind-ended and more permeable than blood capillaries
- Overlapping endothelial cellsthe cells of a lymphatic capillary overlap as one-way flap valves, letting fluid in but not back out
- Lactealsspecialized lymphatic capillaries in the lining of the small intestine that absorb dietary fat
- Lymphatic valvesone-way valves in the collecting vessels that keep lymph moving in a single direction
- How lymph moveswith no pump, lymph is pushed along by the squeeze of nearby skeletal muscles and by breathing movements
- Right lymphatic ductthe smaller duct, draining lymph from the upper right quadrant of the body
- Thoracic ductthe larger duct, draining the rest of the body; it begins at a sac called the cisterna chyli
Lymph Nodes
Lymph nodes are the filters of the system. Hundreds of them lie along the lymphatic vessels, cleaning the lymph before it returns to the blood.
- Lymph nodea small, bean-shaped organ that filters lymph and houses immune cells
- Capsulethe dense connective tissue covering of a node
- Cortexthe outer region of a node, packed with lymphocytes in rounded clusters
- Medullathe inner region of a node
- Afferent vesselsthe lymphatic vessels that carry lymph into a node
- Efferent vesselsthe lymphatic vessels that carry filtered lymph out of a node, leaving at the hilum
- Node clustersnodes are especially concentrated in the cervical, axillary, and inguinal regions
The Lymphatic Organs
The lymphatic organs are sorted into primary organs, where lymphocytes form and mature, and secondary organs, where lymphocytes meet and respond to invaders. Compare them.
| Organ | Group | Location | Role |
|---|---|---|---|
| Red bone marrow | primary | the spongy bone of the axial skeleton and limb girdles | where all lymphocytes form, and where B cells mature |
| Thymus | primary | the mediastinum, behind the sternum | where T cells mature |
| Lymph nodes | secondary | clustered along the lymphatic vessels | filter the lymph |
| Spleen | secondary | the upper left abdomen, behind the stomach | filters the blood |
| Tonsils | secondary | a ring around the entrance to the throat | guard against inhaled and swallowed pathogens |
| MALT | secondary | the mucous membranes of the digestive, respiratory, and other tracts | guards the body's mucosal surfaces |
The Spleen, Thymus, and Tonsils
Three of the lymphatic organs are worth a closer look at their structure.
The spleen
- Spleenthe largest lymphatic organ, in the upper left abdomen behind the stomach
- White pulpthe lymphocyte-rich tissue of the spleen that carries out its immune functions
- Red pulpthe tissue of the spleen that filters the blood and removes worn-out erythrocytes
The thymus and tonsils
- Thymusthe primary organ where T cells mature; large in childhood and shrinking after puberty
- Tonsilsa ring of lymphatic tissue guarding the throat, including the palatine, lingual, and pharyngeal tonsils
- Pharyngeal tonsilthe single tonsil on the posterior wall of the nasopharynx, also called the adenoid
Disorders of the Lymphatic System
When drainage fails or the lymphatic tissue is diseased, the problems show up as swelling or as changes in the nodes and organs. Compare the common ones.
| Disorder | Structure affected | What it is |
|---|---|---|
| Edema | the interstitial space | swelling from excess interstitial fluid when lymphatic drainage cannot keep up |
| Lymphedema | the lymphatic vessels | long-term tissue swelling from blocked or missing lymphatic vessels, sometimes after lymph node removal |
| Lymphadenopathy | the lymph nodes | enlarged lymph nodes, often a sign the nodes are fighting an infection |
| Lymphoma | lymphatic tissue | a cancer arising in lymphatic tissue, including Hodgkin and non-Hodgkin lymphoma |
| Splenomegaly | the spleen | an enlarged spleen, which can follow an infection or a blood disorder |
| Tonsillitis | the tonsils | inflammation of the tonsils, common in childhood |
See also: Blood for the lymphocytes the system houses, and Blood Vessels, Structure and Types for the blood capillaries that lymph drains from.
Study questions
Work on answering these in writing, in your own words. They are the questions to bring to class, and good practice for the reasoning the exams ask for.
- Trace the path of lymph from a tissue back to the bloodstream, naming the major vessels.
- Compare a lymph node and the spleen by structure and the job each one does.
- Explain why the lymphatic system has no central pump, and how lymph still moves.
- Name the primary and secondary lymphoid organs and what happens at each.
Step 2 . Retrieval check
Now explain it back, in your own words.
In 60 words or more, pull together what the video just taught you. Include the key concepts. This is the point where the learning actually sticks. After you submit, your spaced-recall cards for this topic unlock.