As development progresses, blood formation occurs primarily in the spleen, liver, and lymph nodes. When bone marrow develops, it eventually assumes the task of forming most of the blood cells for the entire organism.
However, maturation, activation, and some proliferation of lymphoid cells occurs in lymphoid organs spleen, thymus, and lymph nodes. In children, haematopoiesis occurs in the marrow of the long bones such as the femur and tibia. In adults, it occurs mainly in the pelvis, cranium, vertebrae, and sternum.
In some cases, the liver, thymus, and spleen may resume their haematopoietic function if necessary. This is called extramedullary haematopoiesis. It may cause these organs to hypertrophy and increase in size substantially.
During fetal development, the liver functions as the main haematopoetic organ since bones and marrow develop later. Therefore, the liver is enlarged during development relative to its mature proportions. Privacy Policy. Skip to main content. Cardiovascular System: Blood. Search for:. White Blood Cells. Types of WBCs The different types of white blood cells leukocytes include neutrophils, basophils, eosinophils, lymphocytes, monocytes, and macrophages.
Learning Objectives Distinguish between the two major types of leukocytes white blood cells : granulocytes and agranulocytes. Key Takeaways Key Points The two main types of leukocytes are granulocytes and mononuclear leukocytes agranulocytes. Leukocytes arise from hemopoietic stem cells in the bone marrow. Leukocytes are involved in pathogen recognition, phagocytosis ingestion of particles , pathogen destruction, inflammation mediation, and antigen presentation. Granulocytes include neutrophils, basophils, eosinophils, and mast cells.
Their granules contain enzymes that damage or digest pathogens and release inflammatory mediators into the bloodstream. Mononuclear leukocytes include lymphocytes, monocytes, macrophages, and dendritic cells. This group is involved in both innate and adaptive immune system function. Key Terms endocytosed : Engulfed during the process by which the plasma membrane of a cell folds inwards to ingest material.
Examples include bacteria, viruses, protozoa, or fungi. Microorganisms are not considered pathogenic until the population has grown large enough to cause disease. Learning Objectives Describe the functions of leukocytes white blood cells. Key Takeaways Key Points Leukocyte functions often occur in the bloodstream and may represent either the innate or adaptive immune systems.
Innate immune system functions are non-specific and include phagocytosis, inflammation, and degranulation. Adaptive immune system functions are antigen -specific and involve antigen presentation as well as cell -mediated and humoral -mediated activities. Leukopenia occurs when the WBC falls below 4, Viral infections, overwhelming bacterial infections, and bone marrow disorders can all cause leukopenia.
Patients with severe leukopenia should be protected from anything that interrupts skin integrity, placing them at risk for an infection that they do not have enough white blood cells to fight. For example, leukopenic patients should not have intramuscular injections, rectal temperatures or enemas. Drugs that may produce leukopenia include:.
Leukocytes: critical low and high values. When a patient is receiving chemotherapy that suppresses bone marrow production of leukocytes, the point at which the count is lowest is referred to as the nadir.
It is important to consider both the relative and absolute values of various types of white blood cells when interpreting a WBC differential. True False. Corticosteroids can mask infection by suppressing the inflammatory response and the release of WBCs. Select personalised content. Create a personalised content profile. Measure ad performance. Select basic ads. Create a personalised ads profile. Select personalised ads. Apply market research to generate audience insights.
Measure content performance. Develop and improve products. List of Partners vendors. Share Flipboard Email. Regina Bailey. Biology Expert. Regina Bailey is a board-certified registered nurse, science writer and educator.
Updated October 09, Key Takeaways The primary purpose of white blood cells is to protect the body from infection.
White blood cells are produced by bone marrow and their levels of production are regulated by organs such as the spleen, liver, and kidneys. Granulocytes and agranulocytes are the two types of white blood cells or leukocytes. Granulocytes contain granules or sacs in their cytoplasm and agranulocytes do not.
0コメント