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Blood Cells and Bone Marrow
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To work correctly, your body needs healthy blood cells. It makes new ones every day. All blood cells start in your bone marrow as stem cells.
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Blood cells
Blood cells are the most common type of cell in your body. They help:
- Carry oxygen throughout your body
- Defend against infection
- Control bleeding by helping your blood clot
Each type of blood cell does its job and then dies off. Because of this, your body needs to make new blood cells every day. Most blood cells are made in your bone marrow through a process called hematopoiesis.
Bone marrow
Bone marrow is the soft, squishy inner part of some bones, including your hips, legs, ribs, pelvis, and spine. It is the place in your body where blood stem cells divide and mature to make new blood cells.
Bone marrow is made up of:
- Blood stem cells
- Blast cells (partially mature blood-forming cells)
- Fat cells
- Supporting tissues that help cells grow
Blood stem cells
Stem cells are immature cells that can turn into any type of cell your body needs.
Blood stem cells live in your bone marrow. They are pluripotent. This means they can mature into any type of blood cell.
Types of blood cells
There are three types of blood cells:
- Red blood cells (RBCs) carry oxygen throughout your body.
- White blood cells (WBCs) fight infections.
- Platelets help control bleeding by clotting your blood.
Red blood cells (RBCs)
RBCs carry oxygen from your lungs throughout your body and take carbon dioxide (a waste gas) back to your lungs to be removed.
White blood cells (WBCs)
White blood cells (WBCs) are also called leukocytes. Many types of mature WBCs help your body fight infections caused by invading bacteria, viruses, fungi, and other germs.
Types of WBCs
There are 3 main types of WBCs:
- Lymphocytes
- Granulocytes
- Monocytes
Each type has its own work to do.
Lymphocytes
Lymphocytes are the main infection-fighting WBCs in your lymphoid tissue. They are also scattered throughout your bone marrow, digestive tract, and respiratory system.
- B lymphocytes (B cells) protect your body by becoming specialized cells called plasma cells. There are 2 main types of B cells: plasma B cells and memory B cells.
- T lymphocytes (T cells) can recognize otherwise “normal” cells that have been invaded by germs and other foreign substances. The types of T cells are: helper T cells, cytotoxic T cells, regulatory T cells, and memory T cells.
- Natural killer (NK) cells are lymphocytes that have a natural instinct to quickly attack and destroy infected cells.
Granulocytes
When your body senses an infection, granulocytes are sent to attack and destroy the invader. Granulocytes also help with inflammation (swelling) and wound healing after an injury.
There are 3 types of granulocytes:
- Neutrophils can directly destroy invading cells, especially bacteria and fungi.
- Eosinophils help attack and destroy parasites.
- Basophils help eosinophils attack parasites.
Monocytes
Monocytes act like a cleanup crew. Their job is to absorb and destroy bacteria, dead cells, and waste products from your body tissues.
Platelets
Platelets (also known as thrombocytes) are actually small pieces of large bone marrow cells called megakaryocytes. Their main role is to help control bleeding. They find and stick to an injured area, clumping together to form a clot or scab.
- Written by
The P站视频 medical and editorial content team
Our team is made up of doctors and?oncology certified nurses with deep knowledge of cancer care as well as editors and translators with extensive experience in medical writing.
Last Revised: July 16, 2025
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