Haematopoietic System Flashcards
Name the components of blood
~55% plasma
~1% buffy coat
~45% erythrocytes/RBC (~42% for females)
What are the functions of blood?
- Transport nutrients and O2
- Transport waste to kidneys and liver
- Transport of WBCs and antibodies to fight infection
- Transport of platelets and clotting factors to form clot
- Regulation of body temperature
What is found in plasma?
- Nutrients
- Electrolytes
- Albumin proteins: transport lipid and steroid hormones + contribute to osmotic pressure
- Globulin proteins: haemoglobin, immunoglobin
- Regulatory proteins: hormones, enzymes
- Clotting factors
- Antibodies
What is found in buffy coat?
- Platelets/thrombocytes
- Leukocytes: monocytes/macrophages, neutrophils, eosinophils, basophils, lymphocytes
Describe the morphological features of white blood cells/leukocytes
Neutrophils: multilobated nucleus
Eosinophils: bilobed nucleus; red cytoplasmic granules
Basophils: bilobed nucleus; purplish-black cytoplasmic granules
Lymphocytes: large spherical nucleus, thin rim of pale blue cytoplasm
Monocytes: kidney-shaped nucleus, abundant pale blue cytoplasm
What is the function of erythrocytes?
O2/CO2 transport for metabolic requirements
Hb as an acid-base buffer
How should a blood sample be taken?
- Fill to the top, as too little blood alter the citrate:plasma ratio
- Add citrate to keep blood uncoagulated
Define haematocrit
Proportion of blood volume consisting of RBCs expressed as % (normal range: 40-54%)
Define haematopoiesis
Haematopoiesis is the process of formation and differentiation of different elements in blood
Briefly outline the process of haematopoiesis
- Haematopoietic stem cell (HSC) undergoes long-term self-renewal
- With the appropriate growth factors/cytokines + fibroblasts, HSCs differentiate into multipotent progenitor
- Multipotent progenitor differentiate into lymphoid and myeloid stem cell depending on the differentiation factors it is exposed to
- For the myeloid stem cell, it further divides at medullary/extramedullary sites
- Into leukocytes if granulocyte-colony stimulating factor is present
- Into megakaryocytes → platelets if thrombopoietin is present
- Into erythrocytes if erythropoietin is present - For the lymphoid stem cell, it further divides into T and B lymphocytes in the thymus and bone marrow respectively
Describe the location of haematopoiesis throughout the course of life
Yolk sac: 3-8 weeks
Liver: 6 weeks-birth
Spleen: 8-28 weeks
Bone marrow: 18 weeks-adult
Define the process of erythropoiesis
The process of formation and development of erythrocytes
Outline the 14-day process of erythropoiesis
- Myeloid stem cells stimulated to differentiate into pro-erythroblast in the presence of erythropoietin growth factor
- Pro-erythroblast undergoes DNA synthesis, becoming erythroblast
- Nucleus of erythroblast condenses and is extruded; cytoplasm of erythroblast turns from blue to pink
- Filling of Hb containing heme into erythroblast, forming reticulocyte
- Reticulocyte undergoes diapedesis to capillaries by squeezing through tiny pores
- Reticulocytes maturing into erythrocytes that are released into the bloodstream where it circulates for 120 days
Describe how the process of erythropoiesis is regulated
Hypoxic conditions → hypoxia-induced factor 1alpha (HIF-1a) produced at kidney released into bloodstream → stimulate transcription and translation of erythropoietin growth factor → increase rate of erythropoiesis
Neoplasms → angiogenesis → formation of new capillaries → increased reticulocyte diapedesis → increase rate of erythropoiesis
Define polycythaemia/ erythrocytosis
Increased levels of erythrocytes
What are the signs and symptoms of erythrocytosis?
- Plethoric appearance
- Hyperviscosity with hypoxia and/or clotting
Define lymphopenia
Decreased lymphocyte count → increased susceptibility to viral infections
Define neutropenia
Decreased neutrophil count → increased susceptibility to bacterial/fungal infections
Define haemolysis
Destruction of RBCs
Describe the process of haemolysis
RBCs age → lose membrane elasticity → cannot squeeze through tiny pores of spleen → get trapped and burst → macrophages engulf and destroy it → release Hb → release heme
How is heme, Hb and erythrocytes related?
Heme is a prosthetic group of proteins
Haemoglobins are tetrameric proteins consisting of 4 polypeptide chains (2 alpha 2 beta), each with a heme group
Erythrocytes are packed with Hb
Describe how Hb is encoded for by genes
Hb is made up of 2 alpha globins and 2 beta globins
Each alpha globin is encoded for by one ζ (zeta) and two α (alpha) genes found on chromosome 16
Each beta globin is encoded for by one ε (epsilon), one γ (gamma), one δ (delta) and β (beta) genes found on chromosome 11
Classify the forms of Hb and their inheritance pattern
Different combination of genes on the two chromosomes (one from each parent) give rise to different forms of Hb
Initial embryonic development
HbGower = ζ2ε2
Fetal development
HbF = α2γ2
Adult development
1. HbA = α2β2 (90%)
2. HbA2 = α2δ2 (2-5%)
3. HbF = α2γ2 (<2%)
Describe how oxygen binding to Hb is regulated
Regulated by diff binding affinities of diff forms of Hb
At tissues, deoxy-Hb is mostly present
1. Position of heme shifts
2. Tense state
3. Binding affinity to O2 low
4. Hb release O2
At lungs, oxy-Hb is mostly present
1. Position of heme shifts
2. Relaxed state
3. Binding affinity to O2 high
4. Hb binds O2