blood constituents, haematopoiesis and transfusion Flashcards
What is blood made of?
Plasma 55%
Buffy coat (leukocytes and platelets) <1%
Erythrocytes 45%
Adults have 5l of blood
Haematocrit- 0.45 (% RBCs)
If too high- stroke etc
1000x more than WBCs as have to transport O2
What is haematopoiesis?
The process by which blood cells are formed
Least mature- multipotential hematopoietic stem cell (pluripotent)- needed to make all blood cells, in bone marrow, needed for bone marrow transplants
Most mature- macrophage, plasma cell etc, more limited life span
What stems from common myeloid progenitors?
Erythrocytes (RBCs) Mast cells Myeloblasts Basophils Neutrophils Eosinophils Monocytes Macrophages Megakaryocytes Thrombocytes (platelets)
What stems from common lymphoid progenitors?
Natural killer cells (large granular lymphocytes)
Small lymphocytes
T and B lymphocytes
Plasma cells
What can be seen in a whole blood smear?
Small cell fragments- platelets
Many RBCs- anuclear
WBCs- lobed nucleus
Where does haematopoiesis take place?
Bone marrow
In children- all bones
In adults- axial skeleton and proximal ends of long bones (if not in bone marrow due to eg. Cancer or anaemia, can resume in liver/spleen)
~bone marrow in pelvis contains precursor cells (taken for transplants)
In embryo- waves of haematopoiesis come from yolk sac
What is the bone marrow niche?
Stem cells Endothelial cells Fibroblasts Stromal cells Fat cells
Cues to enable changes in haematopoiesis via cell surface receptors on stem cells that tell them how to divide
What are stem cells?
Pluripotent
Self replicating
Some progeny differentiate into mature cells
As stem cells taken out, they differentiate in vitro or in blood (why we need bone marrow transplants)
What is the lifespan of mature cells in blood?
RBCs- 120 days
WBCs- 6-24hrs (neutrophils), a day (monocytes)
Platelets- 7-10 days
Old/dying cells are removed by liver and spleen via reticuloendothelial system
How is haematopoiesis controlled?
Hormones (often glycoproteins) act via intracellular signalling cascades eg. phosphorylation to transmit signals from receptors to nucleus- changes transcription to differentiate into correct cell
Erythropoietin drives RBC production
Granulocyte colony stimulating factor is used to treat neutropenia (stimulates WBCs)- elevated after infection
Thrombopoietin used to treat thrombocytopenia (stimulates platelets)
What are RBCs?
No nucleus/mitochondria
Bags of Haemoglobin (if free Hb- renal failure)
Rely on glycolysis for ATP (lactose goes to liver)
Rely on pentose phosphate pathway to make reducing NADPH and prevent oxidative damage (ROS)
Biconcave disc, high SA:vol for gas transfer, flexible, 4 x 10^12/l RBCs, can’t cross endothelia
Stem cell-> early progenitor-> nucleated precursor-> reticulocyte (48hrs)-> RBC
Kidney- Hif- detects O2- can drive EPO
Reticulocytes- if high- haemorrhage, if low- deficiencies
What is haemoglobin?
4 chains- 2 beta, 2 alpha
Tetrameric structure
Each monomer has haem group containing Fe where O2 binds
Cooperative binding- 1 O2 binding facilitates other binding, release of O2 facilitates others
Low O2- H+, CO2, 2,3-diphosphoglycerate causes release of O2 to periphery
Mutations lead to eg. Sickle cell anaemia, thalassaemia
What is anaemia?
Not enough RBCs, not enough Hb Not many specific symptoms Acute- blood loss Chronic- insufficient haematinics eg. Vit B12, B6 and folate Genetic causes- mutations
What are symptoms of anaemia?
Fatigue Dizziness Pallor (mucous membrane esp) Headaches Increased cardiac output Tachycardia Systolic murmur
What is polycythaemia?
Increase in RBCs due to-
Raised EPO
Hypoxia
Polycythaemia vera- mutation of JAK2
Reduced plasma volume due to-
Dehydration, smoking, industrial working, hypoxic lung disease
Can lead to- high Hb-> more viscous blood-> thrombosis (arterial and venous)
