Where and How does the body produce the blood cells?

Formed Elements.png - Wikimedia Commons. (2013, November 6).

Blood cell production, also called hematopoiesis or hemopoiesis, is a constant process that makes sure the biological parts of blood are always made when they are needed. Red blood cells, also known as erythrocytes; white blood cells, also known as leukocytes; and blood platelets are the three categories into which blood cells can be categorized (thrombocytes). Granulocytes, lymphocytes, and monocytes are the three primary subsets that are found within the white blood cell population.

Blood cells don't come from the bloodstream itself. Instead, they come from certain tissues that are in charge of making blood, especially the marrow in some bones. In a mature person, the bone marrow is responsible for the production of one hundred percent of the platelets, sixty to seventy percent of the white blood cells (also known as granulocytes), and one hundred percent of the red blood cells. Lymphatic structures, such as the thymus, the spleen, and the lymph glands, which make up 20–30% of the white blood cells, make lymphocytes. Monocytes are made by the reticuloendothelial tissues of the spleen, liver, lymph glands, and other organs. They make up about 4–8% of the white blood cells. Platelets are made from small pieces of the cytoplasm of the large cells (megakaryocytes) in the bone marrow. This means that platelets are not whole cells, but rather small pieces of cells. Platelets play an important role in blood clotting.

When a human zygote is first formed, the cells that will become blood cells start to form in the yolk sac. In the later stages of embryonic development, the liver takes over as the most important organ for making red blood cells. But this role is quickly taken over by the bone marrow, which is the only place where red blood cells and granulocytes come from in adults. Primitive stem cells are the cells that have the potential to develop into any of the progenitors of a blood cell. These cells are the starting point for the development of both red and white blood cells and go through a series of transformations that are intricate, gradual, and consecutive. Stem cells that have reached the point in their development where they are dedicated to the formation of a specific type of new blood cell are known as precursor cells.

File:1902 Hemopoiesis.jpg - Wikimedia Commons. (n.d.).

The bone marrow of a healthy adult produces the red blood cells needed to fill approximately a half liter (almost one pint) of blood each and every week. About 1% of the body's red blood cells are made every day, and the delicate balance between making new red blood cells and getting rid of old ones is carefully watched and controlled. The pace at which new blood cells are produced differs from person to person, but a typical production might be somewhere in the neighborhood of 200 billion red cells per day, 10 billion white cells per day, and 400 billion platelets per day.

The Structure and Function of Lymphoid Organs

Lymphoid tissue includes white blood cells (leukocytes), bone marrow, and organs like the thymus, spleen, and lymph glands. The lymphatic system is also known as the immune system of the body.

Because each type of lymphoid tissue has a specific role in the immune response, it can be organized in a number of different ways. The lymphoid tissues with the most complex structures are found in the thymus and lymph nodes, which are both well-defined, encased organs with clear architectural structures. The lymphoid tissue of the spleen is in the shape of a cylinder, and the small arteries are surrounded by cells that are not organized in a certain way. The spleen is a soft, purple organ that is located high in the abdomen. This tissue is found in the bone marrow, where it is mixed in with the cells that make blood. There is no clear structure to this tissue.

Most lymphoid tissue is found in the loose connective tissue right under the wet epithelial membranes that line the digestive tract and respiratory system. Many of the cells that make up the lymphatic system are free-floating in these regions, putting them at risk of being colonized by microorganisms and other external material. In response to these invasions, they can build centers for making new cells that are close to where the invaders are. These are called nodules, and you must not mistake them with nodes, which have a completely different structure. Nodes are an entirely different structure. Some nodules grow into structures that stay in place for a long time, like the tonsils, appendix, and Peyer's patches, which are in the small intestine. Other nodules are more transient. Most nodules form and disappear in response to needs in the area.

The lymphatic system is made up of many different types of cells, including but not limited to reticular cells, macrophages, lymphocytes, and other white blood cells. Most lymphoid organs are held together by narrow networks of fibers. These networks are made and kept in good shape by reticular cells, which are also a source of structural support. Macrophages are important for getting rid of invaders because they eat foreign substances and start the immune response. These cells can stay in one place, like lymph nodes, or they can move around freely in areas with flexible connective tissue.

In lymphoid tissue, lymphocytes are by far the most common type of cell. In the same way that macrophages are created from stem cells in the bone marrow, lymphocytes are transported through the circulation to the lymphoid tissue after their formation. T lymphocytes first go through the maturation process in the thymus before moving on to other lymphoid tissues like the spleen. B lymphocytes finish developing in the bone marrow and then move to lymphatic tissues all over the body. Both types are critically important to the immune system's ability to fight off pathogenic microorganisms.

Metastasis is the process by which cancer cells spread to tissues that are not near the place where the tumor started. Lymphoid tissue plays an important part in this process. The main reason for this is that lymph arteries are often close to tumors in organs or other body tissues. Lymph nodes can quickly collect cancer cells and could become the site of a second tumor.

References

• How are blood cells formed? (n.d.). Aplastic Anemia & MDS International Foundation. https://www.aamds.org/questions/how-are-blood-cells-formed
• Red blood cell production - Health Video: MedlinePlus Medical Encyclopedia. (n.d.). Red Blood Cell Production - Health Video: MedlinePlus Medical Encyclopedia. https://medlineplus.gov/ency/anatomyvideos/000104.htm
• Lymphoid tissue | Definition, Components, & Function. (n.d.). Encyclopedia Britannica. https://www.britannica.com/science/lymphoid-tissue
• Blood cell formation | Description, Process, & Types of Blood Cells. (n.d.). Encyclopedia Britannica. https://www.britannica.com/science/blood-cell-formation
• Moras, M., Lefevre, S. D., & Ostuni, M. A. (2017, December 6). From Erythroblasts to Mature Red Blood Cells: Organelle Clearance in Mammals. Frontiers. https://doi.org/10.3389/fphys.2017.01076
• The bone marrow and blood formation - Leukaemia Foundation. (n.d.). Leukaemia Foundation. https://www.leukaemia.org.au/blood-cancer/understanding-your-blood/bone-marrow-and-blood-formation/