14 - Haemopoiesis Flashcards
A haemopoietic stem cell can differentiate into what two common progenitor cells?
- Common myeloid progenitor
- Common lymphoid progenitor
What cell types are formed from the common myeloid progenitor?
- Megakaryocyte (platelets)
- Erythrocyte
- Mast cell
- Myeloblast:
> Basophil
> Neutrophil
> Eosinophil
> Monocyte –> Macrophage
What cell types are formed from the common lymphoid progenitor?
- Natural killer (large granular lymphocyte)
- Small lymphocytes (T cells and B cells)
Not all the cells in the bone marrow end up in the blood, what process removes the cells that aren’t required?
Apoptosis
What hormone is responsible for common myeloid progenitor differentiation into a megakaryocyte?
Thrombopoietin
What hormone is responsible for common myeloid progenitor differentiation into an erythrocyte?
Erythropoietin
What moelcules are responsible for common lymphoid progenitor differentiation into T cells and B cells?
Interleukins
What is the lifespan of an erythrocyte?
120 days
How are erythrocytes specialised for oxygen transport?
- Biconcave shape increases surface area
- Minimal organelles to maximise space
- No mitochondria so oxygen is not used up (only use anaerobic respiration)
- Haemoglobin to increase affinity of oxygen binding
Summarise the process of erythropoiesis.
- Proerythroblast formed in bone marrow
- Matures to erythroblast in bone marrow, intially have a large nucleus and lots of RNA but nucleus gradually shrinks and RNA is removed (except what is needed to make haemoglobin)
- Nucleus is removed to form a reticulocyte
- Enters peripheral blood and matures to an erythrocyte
What precursor to RBCs can be found in the blood in a high number during recovery from blood loss?
Reticulocytes (final step before RBC)
What is erythropoietin? When and where is it produced?
A glycoprotein that increases the levels of RBCs. Stops apoptosis of erythrocyte progenitors.
Produced by the kidneys in response to tissue hypoxia. Made in the liver during foetal life.
What factor is responsible for myeloblast maturation into neutrophils?
Granulocyte colony stimulating factor (G-CSF)
What are granulocytes?
A sub-group of white blood cells, named due to presence of granules in the cytoplasm
- Neutrophils
- Basophils
- Eosinophils
What is a neutrophil? What does it do?
- Multi-lobed nucleus
- 3 types of granules
- Most abundant of granulocytes
- First line of defence
- Kills bacteria in multiple ways
What granules does a neutrophil contain?
- Lysozomes
- Matrix metalloproteinases (MMPs)
- Gelatinase
Other than secretion of its granules, what other functions does a neutrophil have?
- Phagocytosis
- Antigen presentation
- Neutrophil Extracellular Traps (NETs)
- Respiratory burst (create free radicals and superoxide to destroy bacterial DNA)
Where does G-CSF come from and what does it do?
- Secreted by many immune cells and endothelial cells
- Released in response to inflammation
- Acts on bone marrow to increase number of neutrophils
- Also increases speed of maturation
What are basophils and what do they do?
Granulocyte with a bilobed nucleus. Granules contain histamine and heparin.
- Release histamine to trigger inflammation
- Mediate hypersensitivity reactions (e.g. asthma)
What are eosinophils and what do they do?
Granulocyte with a bilobed nucleus. Granules contain antihelminthic proteins (fight parasitic worms) and cell component destroying enzymes.
- Phagocytose pathogens
- Fight parasites
- Role in inflammation and allergy?
All lineages of granulocyte undergo which main steps in granulopoiesis?
- Nuclear condensation and lobulation
- Formation of granules
What is the difference between a monocyte and a macrophage?
Cell is a monocyte in the bloodstream but becomes a macrophage when it enters the tissue.
What is a macrophage and what does it do?
Largest blood cell with unilobular horseshoe-shaped nucleus. First line of defence.
- Phagocytose pathogens, cellular debris and senescent cells
- Antigen presentation (‘raise the alarm’)
What is the structure of a platelet (thrombocyte) and what does it do?
Very small biconcave cells. No nucleus, only cytoplasm. Contain vast amounts of protein and clotting factors. Specialised receptors on the surface for aggregation
- Stop bleeding and mediate haemostasis
What factor upregulates thrombopoiesis?
Thrombopoietin, produced by the liver
How are platelets formed?
- Common myeloid progenitor produces megakaryocytes (very large cells with multi-lobular nucleus) in bone marrow
- Megakaryocyte sends out extensions of its membrane (proplatelets) through the vessel wall
- These extensions break down into platelets in the blood
What are the three types of lymphocyte produced in lymphopoiesis?
- B lymphocyte
- T lymphocyte
- Natural killer cell
What are B lympocytes and what do they do?
Mature in the bone marrow and then in Peyers patches (intestine), spleen and lymph nodes.
- Each B cell is specific to an antigen
- Produce antibodies
- Can activate T cells
What are T lympocytes and what do they do?
Large nucleus with a small ring of cytoplasm, indistinguishable from B cells.
- Kill virus-infected and neoplastic cells and transplanted tissue
- Activate B cells (IL 4)
- Proliferate (IL 2)
Where do T cells mature?
- Start in bone marrow (or liver in foetus) and migrate to thymus to mature
- Then migrate to secondary lymphoid organs to await activation (spleen, lymph nodes, appendix, tonsils)
How does the site of haemopoiesis change during foetal development and after birth?
- Initially the yolk sac
- Then foetal liver and spleen
- Bone marrow takes over around 6 months into pregnancy
- Postnatally, only in bone marrow (most in the vertebra)
What is plasma and what is it made up of?
The supporting medium for blood cells that makes up the circulating volume.
- 92% water, 8% proteins
- Ions
- Proteins include: albumin, clotting factors, hormones, cytokines, antibodies etc.
What is the difference between plasma and serum?
Serum is plasma without the clotting factors
What is a low platelet count known as?
Thrombocytopenia
