What is the lifespan of platelets?
- 10 days
What is the lifespan of red blood cells?
- 120 days
What is the lifespan of white blood cells (neutrophils and lymphocytes)?
- Neutrophils: 2-4 days
- Lymphocytes: 1 day-years
Where are red blood cells, platelets and most white blood cells produced?
- Bone marrow
- Extensive throughout the skeleton in infants
- More limited distribution in adults, mainly in: pelvis, sternum, skull, ribs, vertebrae
What controls haemopoiesis?
- Cytokines (hormones)
~ erythropoietin (production of RBCs)
~ thrombopoeitin (production of platelets)
What is haemopoiesis?
- Formation of blood cellular components
What are blood cellular components derived from?
- Multipotent haemopoietic stem cell (haemoblast)
What are the stages of haemopoiesis?
- Proliferation
- Differentiation
Describe proliferation in haemopoiesis
- Stem cell divides in two
- One replaces original stem cell (self-renewal) and the other is used in differentiation
Describe differentiation in haemopoiesis
- Stem cell will first differentiate to form a myeloid blast or a lymphoid blast
- Type of cell that is differentiated into depends of the influence of a particular cytokine
What are the functions of red blood cells?
- Deliver oxygen to tissues and remove carbon dioxide
- Carry haemoglobin and maintain it in its reduced state
- Maintain osmotic equilibrium
- Generate ATP
How does the structure of RBCs suit its functions?
- Biconcave flexible disc 8um diameter: can pass through microcirculation that has a minimum diameter of 3.5um
- 4 globin chains: each has a haem molecule that can bind to 1 molecule of O2 each
- Exist in 2 conformations: variation in oxygen affinity
What metabolic pathways take place in RBCs?
- Glucose -> Lactate (generation of ATP)
- Glucose-6-phosphate metabolised (generation of NADPH)
What controls erythropoiesis?
- Reduced pO2 detected in kidneys
- Increased production of erythropoietin
- Stimulates maturation and release of red cells from marrow
- Haemoglobin rises
- pO2 rises; erythropoietin falls; RBC production falls
Where are white blood cells formed?
- Bone marrow by multipotent haemopoietic stem cells
- May mature elsewhere eg T-cells in thymus
What do WBCs do?
- Circulate in the blood and lymphatic system until signalled by damaged tissue (by injury/infection)
What types of white blood cells are there?
- Neutrophils
- Basophils
- Eosinophils
- Monocytes
- Lymphocytes
What is the function of neutrophils and what is their nucleus like?
- Phagocytosis
- Migrate out of circulation to site of infection
- Increased production by G-CSF (granulocyte colony stimulating factor)
- Multi-lobed nucleus and granular cytoplasm
What is the function of eosinophils and what is their nucleus like?
- Capable of phagocytosis
- Release cytotoxic particle to damage larger particles
- Bi-lobed nucleus
What is the function of basophils and what is their nucleus like?
- Mediate acute inflammatory reactions using heparin and histamine
- Bi- or Tri-lobed nucleus
What is the function of monocytes and what is their nucleus like?
- Migrate to become macrophages in many organs of the body
- Capable of phagocytosis and interact with T cells
- Kidney shaped nucleus
What is the function of lymphocytes and what is their nucleus like?
- B cell: humoral immunity; stimulated by antigens to transform into plasma cells which secrete immunoglobulins (antibodies); antigen presenting cells
- T cell: express CD4 on surface (helper cells); can be killer cells; permit the transformation of B cells into plasma cells
- Deep staining nucleus
What is the structure and function of erythrocytes?
- Structure:
~ Biconcave disc
~ 4 globin chains (2xa, 2xB)
~ each molecule carries a haem
- Function:
~ Carries O2 from lungs to tissues
~ Carries CO2 from tissues to lungsWhat is the structure and function of reticular cells?
- Structure:
~ Synthesise reticular fibres and surround them with cytoplasm - Function:
~ Direct T and B lymphocytes to specific regions with the lymphatic tissues
