Week 7 Haematology Flashcards
Key components of blood
Plasma = liquid component of blood (water 92%) (makes up 55% of blood)
Red blood cells = needed for transporting oxygen
Buffy coat =
Key functions of the blood
Transportation
•Oxygen and carbon dioxide
•Nutrients
•Hormones
•Heat and waste products
Regulation
•pH
•Body temperature
Water content of cells
Protection
Clotting
Immune response
Blood proteins
Formation of blood cells
The process by which the formed elements of the blood develop: Haematopoiesis.
•Sites of haematopoiesis vary according to stage of the life cycle:
Haematopoietic stem cells
Approximately 0.05-0.1% of cells in the bone marrow are haematopoietic stem cells.
•These cells are able to reproduce themselves, proliferate and differentiate into cells that give rise to blood cells.
•This process is essential as the formed elements of blood have a short half-life.
•Some stem cells can also form osteoblasts, chondroblasts and muscle cells, and are therefore important as a source of bone, cartilage and muscle tissue.
Red Blood Cells (RBCs)
Biconcave discs with a diameter of 7-8um
•Plasma membrane is strong and flexible – allows cells to squeeze through narrow blood capillaries.
•Glycolipids present in plasma membrane, called antigens, which account for different blood groups.
•No nucleus or other organelles
•Cannot reproduce or carry out extensive metabolic activities
•To maintain normal levels of RBCs, new mature cells must enter the circulation at a rate of 2 million per second!
•Haemoglobin found in cytoplasm of RBCs and constitute approx. 33% of cell weight.
Physiology of RBCs
Highly specialised for oxygen transport:
•All internal space available for 02 transport as no nucleus
•Lack mitochondria and generate ATP anaerobically so do not use up 02
•Large surface area for diffusion of gas molecules
Little dimple
Other functions of RBCs
Transportation of carbon dioxide
•Hb carries approx. 23% of total carbon dioxide in the body
•Carbon dioxide binds to amino acids in the globin part of Hb as blood travels through capillaries
•A blood flows through the lungs, the carbon dioxide is released and then exhaled.
Regulation of blood flow and blood pressure
•Nitric Oxide (NO), produced by endothelial cells lining blood vessels, can bind to Hb.
•NO causes vasodilation which improves blood flow and enhances oxygen delivery
The role of carbonic anhydrase
•RBCs contain an enzyme called carbonic anhydrase.
•Carbonic anhydrase catalyses the conversion of carbon dioxide and water into carbonic acid, which then dissociates into H+ and HC03-
Co2 + water >-< carbonic acid <-> hydrogen ion + Bicarbonate ion
•This allows 70% of carbon dioxide to be transported in the plasma in the form of HC03-.
•Reaction also serves to act as a buffer in the extracellular fluid.
The life cycle of RBCs
RBCs survive for approx. 120 days due to damage to plasma membranes from moving through narrow capillaries.
•RBCs become increasingly fragile with age and more prone to rupture.
•RBCs cannot synthesise new components to repair damage due to a lack of nucleus and other organelles.
•RBC breakdown occurs in the liver and spleen, with breakdown products being recycled and reused in a number of other processes.
Normally formation and destruction of red blood cells occur at the same pace
Formation of RBCs: Erythropoiesis
1.Begins in the bone marrow with a precursor cell.
- Proerythroblast divides several times to become a reticulocyte, which ejects its nucleus.
- Reticulocytes leave the bone marrow and enter the bloodstream.
- Reticulocytes develop into red blood cells within 1-2 days of their release from the bone marrow.
Control of erythropoiesis
Stimulus is usually hypoxia e.g. high altitude, anaemia, circulatory problems.
•Hypoxia stimulates the kidneys to increase release of erythropoietin (EPO).
•Erythropoietin increases production of pro-erythroblasts in the bone marrow.
•Ultimately, production of RBCs increases, and increased oxygen is delivered to tissues.
Can you think of any examples of where we might manipulate this control mechanism?
Blood Doping 1
The use of certain techniques or substances to increase the number of circulating red blood cells and haemoglobin in the body.
•Considered one of the most well-known methods of doping in sport.
•May include the use of erythropoietin (EPO).
Blood Doping 2
Administration of erythropoietin mimics natural release from kidneys to stimulate increased RBC production.
•Increase in circulating RBCs allows increased oxygen carrying capacity and delivery to muscles.
•This improves aerobic capacity, endurance and performance.
•EPO has been demonstrated to increase performance parameters like V02max and time to exhaustion.
Blood doping 3
•EPO is prohibited at all times under the WADA Prohibited List.
•Such practices carry significant risks as they raise the viscosity of the blood, which contributes to increased risk of high blood pressure and stroke.
