L01 - Structure and function of the haematopoietic system Flashcards
2 major divisions of blood.
1) Blood plasma
2) Formed elements: RBC, WBC, Platelets
List the sequential sites of haematopoeisis from embryo to adult.
3rd week-3 months of gestation: yolk sac (mostly RBC)
1 month of gestation-birth: fetal liver
3-6 months of gestation: spleen
4 months of gestation-birth: red bone marrow, lymphatic tissue- Lymph nodes
Adult: Bone marrow of skull, ribs, sternum, vertebral column, pelvis, proximal ends of femurs
List the sequential lineage of haemotopoiesis.
Haematopoietic stem cells
Myeloid and lymphoid stem cells
Progenitor cells (colony-forming units)
Precursor cells (blasts)
Formed elements of blood
How is the differentiation of progenitor cells regulated?
Erythropoietin – (red blood cells)
Thrombopoietin – (platelets)
Colony-stimulating factors and interleukins (white blood cells)
Location of bone marrow in bone? Rate of blood cell formation and type of marrow change with age?
• Connective tissue found in the medullary space of bones (surrounded by spongy bone)
Rate of blood cell formation decreases as an individual ages
• Red marrow replaced by yellow marrow
• Yellow marrow is mainly adipose cells: retain hematopoietic potential during severe blood loss
Location of bone marrow in the skeleton? Where to extract bone marrow for examination?
Present chiefly in axial skeleton and some long bones
Samples are usually taken from the iliac crest of the hip bone
2 major cellular components and subdivisions of bone marrow?
1) Parenchymal cells
- haematopoietic stem cells/ progenitor cells
2) Stromal cells
- Reticular cells, endothelial cells, adipose cells, macrophages
- Provide microenvironment for haematopoiesis
Describe the organization of parenchymal cells in BM.
Hematopoietic stem cells (HSCs): densely packed cords and islands between meshwork of vascular sinusoids
Sinuses: full of mature RBCs
Cords: immature blood cells and megakaryocytes
Clusters of mature granulocytes may accumulate at margins of cords
How do mature blood cells in the marrow reach the blood circulation?
Mature blood cells and platelets in BM sinuses
> > drain in the central sinus
emissary vein
general circulation
Epithelium type of bone marrow sinuses?
Discontinuous endothelium
Allow blood cells to leak out into circulation
Define bone marrow cellularity and its trend with age?
Ratio of haematopoietic cells to stromal cells (adipocytes)
Decreases with age
Difference in cellularity between leukaemia and aplastic anaemia?
Leukaemia = Hypercellular: increased haematopoeitic cells
Aplastic anaemia = Hypocellular, increased adipocyte/ stromal cells
Shape, structural features, function of erythrocytes?
- Function in transporting O2 and CO2
- Biconcave shaped
- Non-nucleated and devoid of other organelles
- cytoplasm contains haemoglobin
- Cytoskeletal proteins (spectrin, actin) provide resilience, durability
Differentiation lineage and timeline in erythropoiesis?
Differentiation phase (~5 days) Maturation phase (~ 2 days)
Myeloid stem cell >> Hemocytoblast (Day 1) >> Proerythroblast >> Early/ Late erythroblast (Day 2-3) >> Normoblast (Day 4) >> Reticulocyte (Day 5-7) >> Erythrocyte (Day 7)
Changes to RBC during differentiation ineage?
- Cell size decreases, organelles disappear
- Cytoplasm volume increases
- Nucleus diminishes in size and eventually vanishes
How does RBC generate ATP?
devoid of organelles
> > uses anaerobic fermentation to produce ATP
What metric is Used to measure rate of erythropoiesis ?
Reticulocyte count
Mature into red blood cells within 1 to 2 days
Account for 0.5-1.5% of all RBCs
What determines blood type?
- Glycoproteins and glycolipids on the surface of RBCs determine blood types
- Genetically determined by antigens (that react against incompatible antigens on foreign RBCs)
List the blood groups.
4 different types: A, B, AB, O:
AB+ = universal recipient
O- = universal donor
Rh blood group
» Rh +/ -
Pathogenesis of Hemolytic disease of the newborn (HDN)?
Rh incompatibility, Arise during pregnancy
Normally no anti-Rh antibodies in Rh -ve mother blood plasma
If first fetus is Rh+, then mother’s immune system generates antibodies against Rh+ blood
If second fetus is also RH+, mother’s anti-Rh Ab attack fetal blood
Define chromic and cytic in relation to RBCs.
Chromic = colour: normochromic, hypochromic, hyperchromic
Cytic = size: normocytic, macrocytic, microcytic
Mechanism of erythropoietin?
Liver, kidneys sense hypoxemia (inadequate O2 transport)
> > secrete erythropoietin (EPO): stimulates red bone marrow
> > erythropoiesis accelerates
> > Increase RBC count to increase O2 transport
Mechanism of degrading RBC and recycling Hb?
Erythrocytes circulate for 120 days
Expired erythrocytes break up in liver, spleen:
Hb degradation
- Heme > Biliverdin > bilirubin > bile > feces
- Iron > stored for reuse
- Globin > hydrolyzed to free amino acids
Which nutrients are essential for erythropoiesis?
Folic acid
Vit B12
Amino acids
Iron
