Hematopoiesis is the process by which the body creates new blood cells to replace aging or dead cells. Stem cells are the building blocks of this process, forming precursor cells that eventually become specific types of blood cells, each with a specific function. The bone marrow is the primary site of blood cell formation in adulthood, and the body maintains a reserve of stem cells that can be activated in times of illness. The goal of hematopoiesis is to keep everything stabilized and replenish certain cell types as needed.
Hematopoiesis is a biological process that the body uses to make new blood cells to replace those that are aging or have died. It is continuously ongoing in all healthy humans and most animals. The process is somewhat complex from a scientific point of view, but in general it involves the development and conversion of immature cells, known as precursor cells, into functional blood cells. These new cells help the body fight infection, prevent excess bleeding, and carry oxygen to the tissues. There are several types of blood cells, each with a specific purpose and function; the body follows specific paths to create each type. There are nuanced differences depending on the end goal, but the process follows the same basic framework no matter what. In most cases the process starts with a stem cell as a base and growth takes place from there.
Basics of creating blood cells
Blood flows through nearly every part of the body, and cells die and age fairly regularly, even in people and animals considered young by most other measures. This cyclical creation and recreation is a normal part of blood health and is one of the ways cells stay active and able to transport nutrients and other particles efficiently and effectively.
The body creates new blood cells in various places depending on a person’s age. During fetal development, hematopoiesis occurs in the liver, spleen, and bone marrow. After birth and through development, the bone marrow assumes the role of major site of blood cell formation and, in adulthood, the process is mostly simplified to several major sites. These include the skull, sternum, vertebrae of the spine, pelvis, and upper thigh bones.
Importance and significance of stem cells
In almost all cases the creation of blood cells begins with stem cells. Stem cells are also called pluripotent cells and are often considered one of the “building blocks” of life due to how essential they are in determining future growth and development. Each pluripotent cell functions to form new stem cells or precursor cells that will eventually form specific types of blood cells.
Cell types
When a pluripotent stem cell forms a precursor cell, which is the beginning of the process of making blood cells, it typically takes one of five forms. In particular, blood cells are generally classified as erythrocytes, monocytes, lymphocytes, granulocytes or platelets. Granulocytes are further divided into three types of blood cells namely neutrophils, basophils and eosinophils. Each type of blood cell has a specific function that protects the body and helps it work more smoothly.
Erythrocytes, for example, are red blood cells responsible for carrying oxygen to body tissues from the heart and lungs. Monocytes and lymphocytes are important for protection against invading viruses and bacteria. Granulocytes are also important to the immune system, as they travel to a site of infection to consume toxins and foreign cells. Platelets are needed for blood to clot and collect at bleeding sites to clump together.
Keep things in balance
Healthy people usually have processes in place to make sure they have adequate numbers of each cell type, and also to make sure the cells are proportionately balanced against each other. When an infection occurs, for example, or in the event of an injury or trauma, some cells need to be elevated, but checks also need to be done to get things back to normal once the threat has passed. Unusually low or high levels of some types of blood cells can have a harmful effect on the body. One of the main goals of hematopoiesis from this perspective is to keep everything stabilized and to replenish certain cell types as needed.
In the bone marrow
The bone marrow also contains a collection of stem cells that can work to make more blood cells when needed, particularly if the body is in crisis. This reserve acts as a storehouse of more or less “neutral” cells that can be recalled and activated when necessary. The cells stored in the marrow can typically become almost any type of blood cell, depending on what is needed and where. Part of the process of hematopoiesis is for the body to continuously create new stem and precursor cells. In this way, the body sets up its own defense mechanism to react in times of illness.
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