MODULE 2 UNIT 1 INTRO TO HEMATOPOIESIS Flashcards
the process of cellular formation, proliferation, differentiation and maturation of blood cells.
Hematopoiesis
is generally categorized as primitive or definitive.
Hematopoiesis
occurs in the embryo during the first two weeks and lasts up to the eighth week of gestation. It is the time when the blood cells produced are mostly primitive erythrocytes.
Primitive hematopoiesis
occurs on the eighth week until adulthood. In this stage, different blood cells are produced which can be distinguished morphologically and functionally thus the term definitive.
Definitive hematopoiesis
• “Yolk sac phase”
Mesoblastic Phase
• Begins around 19th day of embryologic development
Mesoblastic Phase
Mesoblastic Phase
• PRIMARY SITE OF HEMATOPOIESIS: [?] (Hematopoiesis occurs intravascularly)
Blood islands of the YOLK SAC
i. Cells of the yolk sac
- Mesodermal cells
- Angioblasts
Develop to primitive erythroblasts
- Mesodermal cells
Forms the future blood vessels
- Angioblasts:
BLOOD CELL/S FORMED in MESOBLASTIC PHASE
(1st month of embryonic development)
Erythroblasts
BLOOD CELL/S FORMED: Mesoblastic Phase
Erythroblasts (1st month of embryonic development)
Embryogenic hemoglobins are formed:
i. [?] (2 zeta chains & 2 epsilon chains)
ii. [?] (2 zeta chains & 2 gamma chains)
iii. -?] (2 alpha chains & 2 epsilon chains)
- Gower I
- Portland
- Gower II
▪ Begins at around 5-7 gestational weeks
Hepatic Phase
▪ PRIMARY SITE/S OF HEMATOPOIESIS: FETAL LIVER
Hepatic Phase
• Becomes the primary site of hematopoiesis during the 3rd month of fetal development
• Retains minimal activity up to 1-2 weeks after birth
Liver
• First fully developed organ in the fetus
• Becomes the major site of T cell production
Thymus
• Production of B lymphocytes
Spleen & Kidneys
gradually decreases granulocytic production and involves itself solely in lymphopoiesis
Spleen
BLOOD CELL/S FORMED: Hepatic Phase
• Erythrocytes still in production
• Granulocytes & Megakaryocytes (3rd month of gestation)
• Lymphocytes (4th month of gestation)
• Monocytes (5th month of gestation)
FETAL HEMOGLOBIN (4th month of gestation) is the PREDOMINANT HEMOGLOBIN but detectable levels of adult hemoglobin may be present
i. HbF: 2 alpha & 2 gamma chains
• Begins prior to the 5th month of development
Myeloid Phase
• PRIMARY SITE/S OF HEMATOPOIESIS: BONE MARROW (end of 6th month)
Myeloid Phase
Hematopoiesis occurs inside the medulla of the bone (where the bone marrow is located)
“Medullary hematopoiesis”
At birth, [?] becomes the ONLY SITE FOR PRODUCTION of erythrocytes, granulocytes, monocytes, platelets, and B lymphocytes
bone marrow
Myeloid-to-erythroid ratio gradually approaches
3:1 (adult levels)
Measurable levels of Hemoglobins F and A
i. HbA :
ii. HbA2:
i. HbA : 2 alpha chains & 2 beta chains
ii. HbA2: 2 alpha chains & 2 delta chains
Adult hematopoietic tissues can be classified according to their roles in
lymphocyte development
function for the production and maturation of T and B lymphocytes. These include the bone marrow and the thymus.
primary lymphoid tissues
Consists primarily of adipocytes
Adult
Yellow marrow
Hematopoietically active
Fetal
Flat bones
Epiphysis of long bones
Red marrow
all bones in the body contain the red marrow.
during infancy and early childhood
By age 5 to 7, retrogression occurs. This is the process of replacing the haematopoietically active red marrow with yellow marrow. The yellow marrow is consisting of adipocytes that is capable of reverting back to active marrow in cases of increased demand for blood cell production in the body.
By age 5 to 7, [?] occurs. This is the process of replacing the haematopoietically active red marrow with yellow marrow.
retrogression
is consisting of adipocytes that is capable of reverting back to active marrow in cases of increased demand for blood cell production in the body.
yellow marrow
is consisting of adipocytes that is capable of reverting back to active marrow in cases of increased demand for blood cell production in the body.
yellow marrow
Structure of the BM
A. Vascular region: Vascular sinuses
B. Hematopoietic cords
C. Trilaminar sinus wall
specialized blood vessels
Vascular sinuses
These are extravascular cords that are composed of hematopoietic cells and macrophages. They are located in spaces between the vascular sinuses and are supported by trabeculae of spongy bone.
Hematopoietic cords
It is noted that hematopoietic cells develop in specific [?] within the cords.
niches
separates the extravascular cords from the vascular sinuses
trilaminar sinus wall
Components (From the extravascular cords to the vascular sinus)
a. (Reticular) Adventitial cells
b. Basement membrane
c. Endothelial cells
Incomplete layer of cells on the abluminal surface of the vascular sinus (facing the extravascular cords)
(Reticular) Adventitial cells
Form a single, continuous layer along the luminal (inner) surface of vascular sinuses
Endothelial cells
play a very important role in nurturing and protecting hematopoietic stem cells
Niches/ Hematopoietic Microenvironment (within the cord)
Develop in small clusters; More mature forms located in outer surfaces of the vascular sinuses
Erythroblast
Found surrounding ironladen macrophages
Erythroblast
Adjacent to the walls of vascular sinuses
o Largest bone marrow cell
o Production of PLATELETS - Cytoplasmic fragments of megakaryocytes
Megakaryocytes
Deep within the cords (as the mature, they move closer to the vascular sinuses)
Immature myeloid cells (up to metamyelocyte stage)
ENTRY OF MATURE BLOOD CELLS FROM THE BONE MARROW TO PERIPHERAL CIRCULATION
Mature blood cell → Adventitial cell layer (contracts) →
Basement membrane → Endothelial cell layer →
Receptor-mediated process → Mature cells bind to the surface of endothelial cells →
Cells pass through pores in the endothelial cytoplasm → Vascular sinus →
Peripheral circulation
Bone Marrow Specimens: Collection
- Trephine/ Core biopsy
- Aspiration
▪ Utilizes Trephine biopsy needle ([?] needle)
Jamshidi needle
▪ Aspiration needle (?)
University of Illinois sternal needle
Collection is oftentimes carried out to observe the patient’s
myeloid to-erythroid ratio
Myeloid-to-Erythroid ratio:
Normal:
Infection:
Leukemia:
2:1 to 4:1 (Average of 3:1)
6:1
25:1
Normal marrow cells
a. All developing hematopoietic cells
b. Macrophages
c. Mast cells
d. Osteoblasts
e. Osteoclasts
▪ Misidentified as megakaryocytes
▪ Waterbug or comet appearance
▪ Confused with plasma cells
d. Osteoblasts
▪ Misidentified as megakaryocytes
e. Osteoclasts
a small, flat bilobed organ (Fig. 2-8, left) found in the thorax that has an average 30g weight at birth, 35 g weight at puberty and gradually atrophies. It is where T-cell maturation happens.
thymus
separates the two lobes of the thymus. It has extensions known as Trabeculae that penetrate the thymus and divides the two lobes into lobules
Capsule
It is the outer part of the thymic lobule and consists of a large amount of pre-T cells and scattered dendritic cells, epithelial cells, and macrophages.
Cortex in the Lobules
It is the outer part of the thymic lobule and consists of a large amount of pre-T cells and scattered dendritic cells, epithelial cells, and macrophages.
Cortex in the Lobules
are immature T cells that migrate from the red marrow to the thymic cortex and proliferate and start to mature at the cortex.
Pre-T cells
are derived from the monocytes. They exhibit long dendrite-like projections and assist the maturation process of the pre-T cells.
Dendritic cells
are specialized to carry out the positive selection process of pre-T cells. They have long processes that serves as a framework for the T cells and produce thymic hormones that are thought to aid in the maturation of T cells
Epithelial cells
help clear out the debris of dead and dying cells.
thymic macrophages
help clear out the debris of dead and dying cells.
thymic macrophages
is the inner part of the thymic lobule. It consists of more mature T cells, dendritic cells, and epithelial cells, and macrophages.
Medulla
is the inner part of the thymic lobule. It consists of more mature T cells, dendritic cells, and epithelial cells, and macrophages.
Medulla
In the medulla are* [?] which are clusters of epithelial cells that become arranged into concentric layers of flat cells that degenerate & become filled with keratohyalin granules and keratin.
Thymic (Hassall’s) corpuscles
These tissues are where lymphoid cells become competent (where lymphoid cells respond to foreign antigens). These consist of the spleen, lymph nodes, and lymphatic nodules.
Secondary lymphoid tissues
are bean-shaped structures found along lymphatic vessels which are specialized to filter lymph flowing through the lymphatic vessels.
Lymph Nodes
The [?] contains the primary and secondary follicles.
cortex
The [?] contain mature B cells, follicular dendritic cells, and macrophages. They are located are B cells that are not yet introduced and stimulated by any antigen thus become the site of antigen recognition of the mature B cells.
primary follicles