Hematopoiesis Flashcards
What is hematopoiesis?
Process of blood cell formation
What is the classical marker of hematopoietic stem cells?
CD 34
When does hematopoiesis start in embryonic development?
Around the nineteenth day of embryonic development
What are the two related theories on the origin of hematopoietic progenitor cells?
Polyphyletic Theory, Monophyletic Theory
Which theory is most widely accepted among experimental hematologists?
Monophyletic Theory
What is the name of the pluripotential stem cell suggested by the Monophyletic Theory?
Pluripotential stem cell
What are the three phases of hematopoiesis?
Mesoblastic/Megaloblastic, Hepatic stage, Intramedullary/Myeloid
What is the chief site of hematopoiesis during the Mesoblastic phase?
Yolk sac
What is the chief site of hematopoiesis during the Hepatic stage?
Fetal liver, with contributions from spleen, thymus, lymph nodes
What is the chief site of hematopoiesis during the Intramedullary/Myeloid phase?
Bone marrow
What is the first blood cell formed during the Mesoblastic phase?
Primitive erythroblast
What hemoglobins are produced by Primitive Erythroblasts?
Gower-1, Gower-2, and Portland
How does yolk sac hematopoiesis differ from fetal and adult hematopoiesis?
Yolk sac hematopoiesis occurs intravascularly (within developing blood vessels)
What is the predominant hemoglobin during the Hepatic stage?
Hb F (Fetal hemoglobin)
Which organ is the first to develop in the fetus?
Thymus
What is the role of the thymus during the Hepatic stage?
Major site of T cell production
Which organs produce B cells during the Hepatic stage?
Kidneys and spleen
When does hematopoiesis start in the bone marrow?
Before the 5th month of fetal development
When does bone marrow become the chief site of hematopoiesis?
By the end of 24 weeks’ gestation
Where are hematopoietic tissues located in adults?
Bone marrow, lymph nodes, spleen, thymus, liver
What is produced by the bone marrow in adults?
Developing erythroid, myeloid, lymphoid, and megakaryocytic cells
What function does bone marrow have in adults?
Acts as a primary lymphoid organ
How many RBCs are generated per kilogram of body weight daily by the bone marrow?
2.5 billion RBCs
How many granulocytes are generated per kilogram of body weight daily by the bone marrow?
1 billion granulocytes
How many platelets are generated per kilogram of body weight daily by the bone marrow?
2.5 billion platelets
What is retrogression in the context of hematopoiesis?
The process of replacing red marrow with yellow marrow during development
When does retrogression occur in humans?
Between 5 and 7 years of age
What is the result of retrogression in adults? (RSVP)
Red marrow is restricted to the ribs, sternum, skull, shoulder blades, vertebrae, and proximal ends of long bones
What is yellow marrow made of?
Adipocytes
How does yellow marrow respond to increased demand on the bone marrow?
It can revert back to active marrow
What are the proportions of red and yellow marrow in adults?
Approximately equal amounts, 50% red marrow and 50% yellow marrow
What is the function of red marrow?
Hematopoietic activity, producing RBCs, WBCs, and platelets
What is the function of yellow marrow?
Inactive hematopoietic activity, made up of adipocytes
When does yellow marrow replace red marrow in childhood?
Between 5 to 7 years old
Where does lymphoid development occur?
Primary lymphoid organs (bone marrow and thymus), secondary lymphoid organs (spleen and lymph nodes)
What are primary lymphoid organs?
Bone marrow and thymus
Function of primary lymphoid organs?
Derivation of T and B lymphocytes
Location of B cell differentiation?
Bone marrow
Thymus during fetal development?
Increases in size until puberty, then atrophies with aging
Major secondary lymphoid organs?
Spleen and lymph nodes
Functions of secondary lymphoid organs?
Trapping foreign substances, antibody production, T lymphocyte induction
Largest secondary lymphoid organ?
Spleen
Lymph node shape and size?
Small, ovoid, bean-shaped, < 1 cm in diameter
Role of spleen in immunity?
Synthesis and release of antibodies
What is lymphoma?
Solid tumor of lymphoid tissue
Effects of splenectomy in children?
Increased bacterial sepsis (S. pneumoniae, N. meningitidis, H. influenzae)
Effects of splenectomy in adults?
Increased blood-borne bacterial infections
What is splenomegaly?
Enlargement of the spleen
Minor secondary lymphoid organs?
Tonsils, appendix, Peyer’s patches, MALT
Function of Peyer’s patches?
Detect substances in the small intestine lining
What is MALT?
Unencapsulated lymphoid tissues in mucosal areas
What is extramedullary hematopoiesis?
Hematopoiesis in the liver in response to infection or myelofibrosis
Role of liver in hematopoiesis?
Maintains hematopoietic stem cells for blood cell generation