Learn more about blood cells and the lymphatic system
This two-sided color chart includes information about blood cells and the lymphatic system.
Understanding your child’s diagnosis will help you make informed decisions about their treatment. It will also give you greater insight into the scientific advances in blood cancer treatment and improvements in quality of life for survivors. Having a general understanding of how blood, bone marrow, and the lymphatic system function in your body can help you better understand your child’s diagnosis and test results.
Understanding blood and blood cells
Blood is the liquid that flows through a person’s arteries and veins. It is the main transport system in the body, carrying oxygen and nutrients to the lungs and tissue. It also carries away waste products to the kidneys and liver, which clean the blood.
Our blood contains red cells, platelets, and white cells suspended in plasma, the liquid part of our blood. Plasma is largely water with many chemicals also present, including:
- Proteins (such as erythropoietin, made in the kidneys, and albumin and blood-clotting proteins, made in the liver)
- Hormones (such as thyroid hormone and cortisol)
- Minerals (such as iron and magnesium)
- Vitamins (such as folate and vitamin B12)
- Electrolytes (such as calcium, potassium, and sodium)
- Antibodies, which are made by plasma cells
Learn about the types of cells that are found in the blood. Open each section below to learn more.
Red cells make up a little less than half of the blood's volume. They're filled with the red-colored protein hemoglobin, which picks up oxygen in the lungs and delivers it to the cells around the body. Hemoglobin then picks up carbon dioxide from the body's cells and delivers it back to the lungs, where it's removed when we exhale.
Platelets are small cells (one-tenth the size of red cells) that help stop bleeding at the site of an injury. For example, when a person has a cut, their blood vessels are torn open. Platelets stick to the vessel's torn surface, clump together, and plug up the bleeding site with the help of blood-clotting proteins (such as fibrin) and electrolytes (such as calcium). Later, a clot forms. The blood vessel wall, healed at the clot site, then returns to its normal state. Platelets also release growth factors that stimulate wound repair and new blood vessel formation.
There are several varieties of white blood cells:
- Neutrophils and monocytes: These white blood cells are called "phagocytes" (eating cells) because they can ingest and kill bacteria or fungi. Unlike red cells and platelets, phagocytes can leave the blood and enter the tissues, where they can attack invading organisms and help combat infection.
- Eosinophils and basophils: These white cells respond to allergens or parasites
- Lymphocytes: These white cells reside in the lymph nodes, the spleen, and the lymphatic channels, but some enter the blood
- Learn more about the role lymphocytes play in the lymphatic system
Bone marrow
Marrow is the spongy tissue in the central cavity of bones where blood cells are made. In newborns, all bones contain active marrow. By the time we reach young adulthood, the bones of our hands, feet, arms, and legs no longer have functioning bone marrow. The spine (vertebrae), hip bones, shoulder bones, ribs, breastbone, and skull contain the marrow that makes blood cells in adults. The process of blood cell formation is called “hematopoiesis.” A small group of cells called stem cells develop into all the blood cells in the marrow—a process called “differentiation.”
Stem cells
Healthy individuals have enough stem cells to keep producing new blood cells continuously. Blood passes through the marrow and picks up fully developed and functional red cells, white cells, and platelets for circulation in the body.
Some stem cells also enter the blood and circulate. They're present in such small numbers that they can't be counted or identified by standard blood count tests. Their presence in the blood is important because they can be collected by a special technique and used for stem cell transplantation. Doctors use certain methods to induce more stem cells to leave their home in the marrow and circulate in the blood, allowing for greater stem cell collection. If enough stem cells are harvested from a compatible donor, they can be transplanted to the patient.
Stem cells also circulate, from marrow to blood and back, in a developing fetus. After birth, placental, and umbilical cord blood can be collected, stored, and used as a source of stem cells for transplantation.
View a 3D model of blood cell development. Click or tap the "Interact in 3D" button to begin.
The lymphatic system
The lymphatic system is part of our immune system, which helps protect against disease and infection. Parts of our lymphatic system include:
- Lymph nodes
- Plasma cells
- Lymphatic vessels
- The spleen (the organ just above the stomach's left side that filters our blood)
- Lymphokines (a chemical made from white cells)
- Gastrointestinal (stomach and intestines) lymph areas
- Bone marrow (the spongy center of the bones)
- Immunoglobulins (proteins that help the body fight infection)
View a 3D model of the lymphatic system. Click or tap the "Interact in 3D" button to begin.
The lymphatic system is closely related to the blood cell-forming system. Lymphocytes, a type of white blood cell, are found in the lymph nodes (small oval-shaped organs found throughout the body that help trap and kill disease and infection that invade our bodies). Lymphocytes are also found in other parts of the lymphatic system, such as the skin, spleen, tonsils and adenoids, intestinal lining, and thymus (an organ in the chest area that produces lymphocytes until young adulthood).
Lymphocytes move around the body in lymphatic vessels that contain a milky white fluid, called “lymph.” Lymphatic vessels connect lymph nodes throughout our bodies and collect into large ducts, which empty into blood vessels. Lymphocytes enter the blood stream through these ducts.
There are three main types of lymphocytes:
- B lymphocytes (B cells) make antibodies in response to invading bacteria, viruses, or other microbes. B lymphocytes are present in the marrow.
- T lymphocytes (T cells) have several functions, including helping B lymphocytes make antibodies against invading microbes. An antibody works by attaching itself to an invading microbe. The white cell recognizes the antibody and pulls it into the cell with the attached microbe. The white cell can then kill the microbe.
- Natural killer (NK) cells attack virus-infected cells without requiring an antibody or other assistance
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