bone marrowThe bone filling in which every blood cell begins. There are two kinds. Red marrow is the working kind, and yellow marrow is mostly fat.
hematopoiesisThe body's nonstop production of new blood cells. All three kinds of blood cell, red cells, white cells and platelets, grow from stem cells in the red marrow.
immune responseThe body's fight against a germ it has detected. During one, lymphocytes multiply in the lymphatic organs and travel in the blood to where they are needed.
lymphFluid on its way from the tissues back to the blood. It is clear and watery. Lymph coming from the small intestine is milky with fat and is called chyle.
lymph nodeA small bean-shaped filter for lymph. Lymph enters through several vessels, trickles through the spaces inside and leaves by another vessel at a dent in one side.
lymphatic systemThe network of lymph vessels, nodes and organs. It has three jobs: it returns leaked fluid to the blood, takes up fats from food and defends the body.
Show all 36 terms (30 more)
Lymph, nodes and organs, continued
lymphatic vesselA thin-walled tube that carries lymph. Lymph moves through it in one direction only, out of the tissues. Small vessels merge into larger ones.
lymphocyteThe white blood cell type that packs the lymph nodes. Its large, dark nucleus nearly fills the cell. Its two main types are the T cell and the B cell.
spleenAn organ by the stomach that strains the blood. It is the largest lymphatic organ. It works on blood much as a lymph node works on lymph, and it holds a reserve of blood.
thymusA two-lobed chest organ that is largest in children. It lies behind the breastbone. In older adults the thymus is quite small.
tissue fluidThe fluid filling the gaps between body cells. Its other name is interstitial fluid. It brings oxygen and nutrients to the cells, and once it enters a lymph capillary it is called lymph.
tonsilsClumps of tissue that guard the throat's entrance. The best-known pair is the palatine tonsils, at the back of the mouth. The one behind the nose is the adenoid.
Lymph, blood and flow 12
backflowMovement of a fluid in the wrong direction. The stretch of vessel between two valves is called a lymphangion. It tightens to pass lymph forward.
blood capillaryA hair-thin blood vessel with a leaky wall. Fluid seeps out of it into the tissues, and most of that fluid goes straight back in. The lymphatic system collects the rest.
circulationThe endless looping journey of blood in the body. Blood travels in a closed loop. Lymph travels one way and joins the loop near the heart.
lymph capillaryA microscopic blind-ended tube where lymph begins. The cells of its wall overlap like tiny doors, so fluid can get in but not back out.
lymph heartAn organ that pumps lymph in frogs and reptiles. Mammals have none. In people the lymphatic vessels themselves tighten to push lymph along.
plasma proteinA protein dissolved in the liquid part of blood. Albumin is the most plentiful. Small proteins that leak out of the blood are carried back to it by lymph.
reabsorbTo soak a fluid back up after letting it out. Of about 20 liters of fluid filtered out of the blood each day, roughly 17 are reabsorbed. The other 3 liters go home by way of the lymph.
red blood cellThe oxygen-carrying cell that the spleen recycles. The spleen takes old and damaged ones out of the blood and saves their iron.
small intestineThe gut section where lymph vessels take up fats. Its lining is covered with tiny fingers called villi. A lymph capillary in each one, a lacteal, takes in fats and the vitamins that dissolve in fat.
smooth muscleInvoluntary muscle that squeezes a vessel narrower. Its squeezing is one of three things that move lymph. The others are the working of the skeletal muscles and the motion of breathing.
thoracic ductThe body's main lymph channel, running up the chest. It drains every part of the body except the upper right quarter. It empties into the blood where two large veins meet, at the base of the neck on the left.
valveA pair of flaps that keeps fluid from slipping back. Lymphatic vessels have valves along their length, as veins do.
Tissues and cells of defense 12
antibodyA Y-shaped protein that grips one kind of invader. Its other name is immunoglobulin. Each antibody fits a single target, as a key fits a lock.
antigen-presenting cellA cell that displays bits of an invader to T cells. Dendritic cells, macrophages and B cells can all do the job. Its short name is APC.
B cellA lymphocyte that matures in the bone marrow. Its B first stood for the bursa of Fabricius, the organ where these cells mature in birds. An activated B cell can become a plasma cell.
cell-mediated immunityDefense by cells directly, with no antibodies. Its T cells destroy body cells that a virus has already entered.
humoral immunityDefense carried by antibodies in the body's fluids. Humor is an old word for a body fluid. This is the branch of defense that B cells and plasma cells run.
lobuleA small compartment inside an organ. Walls of connective tissue divide the spleen into lobules. Each lobe of the thymus is divided into them too.
lymphoid organAn organ where lymphocytes are made or put to work. The bone marrow and the thymus are primary lymphoid organs. Lymph nodes, the spleen and the tonsils are secondary ones.
MALTLymphoid tissue under the linings of gut and airways. The letters stand for mucosa-associated lymphoid tissue. It makes up about half of the lymphoid tissue in the body.
plasma cellA cell that pours out one kind of antibody. One plasma cell can release several thousand antibodies a second.
T cellA white blood cell whose T stands for thymus. T cells begin in the bone marrow and move to the thymus to mature.
thymic involutionThe thymus growing smaller as the years go by. Fat slowly takes the place of the working tissue. It happens in almost all animals with a backbone.
trabeculaA tiny beam of tissue that braces an organ inside. The word is Latin for small beam. Trabeculae reach inward from the outer coat of a lymph node and of the spleen.
How this list was compiled: Term list chosen for this site on 2026-10-13. Each meaning is written in our own words and was checked that day against the Dictionary of Cancer Terms of the National Cancer Institute (https://www.cancer.gov/publications/dictionaries/cancer-terms), entries lymphatic system, lymph, lymph node, lymph vessel, spleen, thymus, tonsil, bone marrow, lymphocyte, T cell, B cell, plasma cell, antibody, immune response, lymphoid, interstitial fluid, capillary, small intestine, red blood cell and antigen-presenting cell; against the Lymphatic System pages of the SEER Training Modules of the National Cancer Institute (https://training.seer.cancer.gov/anatomy/lymphatic/): Introduction to the Lymphatic System, Components of the Lymphatic System, Lymph Nodes, Tonsils, Spleen, Thymus and Review; and against articles of the English Wikipedia (https://en.wikipedia.org/), whose text is under the Creative Commons Attribution-ShareAlike license: Lymphatic system, Lymph, Lymph node, Lymphatic vessel, Spleen, Thymus, Tonsil, Bone marrow, Lymphocyte, T cell, B cell, Antibody, Plasma cell, Thoracic duct, Plasma protein, Lymph heart, Mucosa-associated lymphoid tissue, Thymic involution, Antigen-presenting cell, Humoral immunity, Cell-mediated immunity and Trabecula. Valve, reabsorb, backflow, circulation, lobule, smooth muscle and humoral rest on their entries in Wiktionary, the free dictionary (https://en.wiktionary.org/). The fact after each meaning is from the same pages. The list names parts of the body and what they do: it is a study aid for a science class, not health advice. Licence: own work
How it works
This lymphatic system vocabulary worksheet lists lymph, lymph node, lymphatic vessel, spleen, thymus, tonsils, bone marrow, lymphocyte and four more terms beside their meanings in mixed order. The key prints last. It is a study aid, with no diagram.
Read the full guide
Lymph, blood and flow
Set opens on Lymph, nodes and organs. The second set has lymph capillary, valve, thoracic duct, blood capillary, plasma protein, smooth muscle, small intestine, lymph heart, reabsorb, backflow, red blood cell and circulation.
Tissues and cells of defense
The third set has T cell, B cell, antibody, plasma cell, lymphoid organ, MALT, thymic involution, antigen-presenting cell, humoral immunity, cell-mediated immunity, lobule and trabecula.
Lacteal, chyle, adenoid, macrophage and antigen are answers on the lymphatic system crossword, not terms here.
Questions and answers
Is the lymphatic system part of the immune system or the circulatory system?
It belongs to the immune system and works alongside the circulatory system. Its organs and lymphocytes defend the body, and its vessels hand leaked fluid back to the blood.
What is lymph made of?
A clear, watery fluid much like the blood plasma it comes from. It carries proteins, fats, debris from the cells and white blood cells, lymphocytes among them.
How many lymph nodes are in the human body?
Hundreds: about 450 in an adult by one count. They sit along the lymphatic vessels throughout the body and cluster in the neck, the armpits, the chest, the abdomen and the groin.
What is the difference between T cells and B cells?
B cells make antibodies, and T cells do not. Some T cells destroy body cells that are infected, and helper T cells direct other defenders. Both kinds are lymphocytes that start out in the bone marrow.