Haematopoiesis Flashcards
What are the cellular components of blood?
Erythrocytes Leukocytes Plasma Platelets Water
What does blood plasma contain?
Water
Small organic compounds and electrolytes
Proteins (Albumins, Globulins + Fibrinogen)
What is blood made up of?
Cells + Plasma
What is haematopoiesis?
Production of all types of mature blood cells (RBCs, WBCs and platelets)
Where are haemopoietic stem cells found?
Bone marrow
What are the functions of the biconcave disc shape of erythrocytes?
Maximise surface area
Minimise distance from surface
Increases flexibility
What is folic acid used for?
DNA synthesis and cell proliferation
What is Cobalamin (B12) used for?
Recycling of folic acid
What causes megaloblastic anaemia?
Folic acid or B12 deficiency
Where is folic acid absorbed?
Duodenum
Jejunum
How does folic acid deficiency arise?
Inadequate intake
Malabsorption
Increased demand
Where is vitamin B12 absorbed?
Terminal ileum (requires Intrinsic Factor)
What is the usual cause of vitamin B12 deficiency?
Malabsorption (rarely due to inadequate intake)
What is pernicious anaemia?
Lack of Vit B12 or Folic Acid causes RBCs to not develop as normal leading to increased size of RBCs (macrocytic anaemia)
Caused by lack of intrinsic factor, low B vitamins in diet, decreased absorption of B vitamins
What is a totipotent stem cell?
The most potent form of stem cell that is able to differentiate into any cell type (inc. embryonic and extraembryonic)
What is a pluripotent stem cell?
A cell that can differentiate into any cell type of the embryo
What is a multipotent stem cell?
A cell that can differentiate into several different, but related, cell types
What is an oligopotent stem cell?
A cell that can differentiate into a small number of very closely related cell types
What is a unipotent stem cell?
A cell that can produce more cells of an identical cell type
What are the 2 lineages of haematopoiesis differentiation?
Myeloid (which produces thrombocytes, erythrocytes, granulocytes, mast cells and macrophages)
Lymphoid (which produces natural killer cells, T/B lymphocytes and plasma cells)
What are the stages of erythropoiesis?
- Differentiation (down myeloid lineage)
2. Maturation (from immature cells to mature cells - Proerythroblasts to Erythroblasts to Reticulocytes to Erythrocytes)
What is involved in the maturation process in erythropoiesis?
- Decrease in cell size
- Hb production
- Loss of organelles (even nucleus!)
- Acquisition of biconcave shape (inv. cytoskeleton)
What controls the maturation process of erythrocytes?
EPO (Erythropoietin) - released by fibroblasts in response to cellular hypoxia and stimulates erythropoiesis in the bone marrow.
Requires iron, folic acid and B12
What are the nutritional requirements for erythropoiesis to occur?
DNA synthesis requires Folic Acid, Vit B12 (+IF)
Hb synthesis requires Vit B6 and Iron (for haem)
What happens to absorbed iron in the body?
Majority transported to bone marrow to make haem
Rest stored in liver or spleen or used in enzymatic processes in other tissue cells
What is Hepcidin?
Hormone released by the liver in response to high iron levels.
Works by decreasing Ferroportin action (on basolateral membrane of intestinal epithelial cells thus reducing ability to absorb iron)
What are the different types of anaemia?
Iron deficiency Pernicious anaemia/ B12 deficiency Aplastic Haemolytic Anaemia of chronic diseases
What is iron deficiency anaemia?
Iron deficiency leading to low Hb which in turn decreases the production of RBCs
Caused by blood loss, low iron in diet or poor iron absorption
What is aplastic anaemia?
A life threatening condition in which the bone marrow is unable to produce enough blood cells
Caused by cancer therapies, exposure to toxic substances, autoimmune disorders and some viral infections
What is haemolytic anaemia?
RBCs are destroyed faster than the bone marrow can replace them.
Caused by inherited disorders such as sick cell anaemia or thalassemia
What is anaemia of chronic diseases?
Certain chronic illnesses (e.g. Rheumatoid, kidney disease, diabetes, TB or HIV) can reduce the production of RBCs
How can different types of anaemia be classified in terms of size of cell?
Macrocytic = large erythrocytes that are low in number (or have low Hb count per cell) Microcytic = small erythrocytes Normocytic = normal size erythrocytes but usually low in number
How is anaemia classified in terms of amount of Hb per RBC?
Hypochromic = pale in colour due to lack of Hb (and therefore less oxygen) Normochromic = normal colour, normal Hb
What is leukocytosis?
A white cell count disorder characterised by high level of white cells
What is leukopenia?
Low white cell count
What controls differentiation of platelets?
Thrombopoietin - produced in the liver and stimulates differentiation of megakaryocytes and thrombocytes (platelets)
Negative feedback loop so thrombocytes reduce thrombopoietin levels
