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Questions and Answers
What percentage of body weight does Total Body Water approximate?
Which of the following components are part of the Extracellular Fluid compartment?
What is the primary role of Erythropoietin in blood physiology?
At what stage does red blood cell production predominantly occur in the bone marrow?
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Which vitamins are essential for the proper production of red blood cells?
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What shape does a mature erythrocyte primarily exhibit?
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What condition is indicated by a reduced amount of red blood cells or hemoglobin?
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Which of the following is a consequence of high altitude on red blood cell production?
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Where is the primary site of red blood cell production in adults?
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Synthetic Erythropoietin is used primarily for which medical condition?
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What is the primary function of hemoglobin in red blood cells?
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Which of the following statements about hemoglobin structure is accurate?
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What is a primary cause of anemia in patients with Sickle Cell Disease?
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During the breakdown of red blood cells, which of the following sequences correctly describes the breakdown of heme?
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Which blood group is considered a 'Universal Donor'?
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What happens to bilirubin in the body?
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Which of the following is NOT a function of red blood cells?
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How does foetal hemoglobin differ from adult hemoglobin?
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What condition is primarily caused by a high level of bilirubin in the blood?
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Which of the following statements about RBC lifespan is correct?
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Study Notes
Total Body Water
- Approximately 60% of body weight is water
- In a 70kg male, this equates to 40-45 litres of water
- Water is divided between intracellular fluid (ICF) and extracellular fluid (ECF)
- ECF consists of plasma and interstitial fluid (ISF)
Composition of Blood
- Plasma is a component of the ECF compartment
- Blood is composed of 55% plasma and 45% cellular components
Cellular Content of Blood
- Red blood cells (erythrocytes)
- White blood cells (leukocytes)
- Platelets (thrombocytes)
Red Blood Cells (Erythrocytes)
- Mature red blood cells are non-nucleated
- Cells are biconcave in shape
- Shape allows for increased surface area to volume ratio for efficient gas exchange
RBC/Erythrocyte Production
- Production begins in utero
- Bone marrow takes over production at 6-7 months
- All bone marrow involved in children
- In adults, production is mainly in the sternum, vertebrae, ribs, and pelvis
- Production requires adequate intake of:
- Protein
- Vitamins like B12 and folic acid
- Erythropoietin, a hormone released by the kidneys, plays a crucial role
- Anaemia is a condition where there is a lack of red blood cells or haemoglobin, leading to a reduced oxygen carrying capacity
- Erythropoietin production is stimulated by low oxygen levels in the blood.
Sequence of Events in RBC Production
- Committed stem cell differentiates into proerythroblast
- Proerythroblast undergoes several divisions and maturation stages
- Nucleus shrinks and is eventually expelled
- Reticulocyte is released into bloodstream and matures into erythrocyte
Role of Erythropoietin in RBC Production
- Erythropoietin stimulates erythropoiesis in the bone marrow
- Increased production can be triggered by altitude changes or chronic renal failure
- Synthetic erythropoietin is available for treatment of chronic renal failure
- Use of erythropoietin in athletes for blood doping is dangerous and can lead to:
- Polycythaemia
- Increased blood viscosity
- Heart failure or stroke
Functions of RBCs
- Contain haemoglobin
- Oxygen transport
- Carbon dioxide transport
- Blood buffering to maintain a normal blood pH of 7.4
Structure of Haemoglobin
- Consists of four polypeptide chains:
- Two alpha (α) and two beta (β) chains in adult HbA
- Two alpha (α) and two gamma (γ) chains in fetal HbF
- Each polypeptide chain is linked to a haem molecule
- Each haem molecule contains one iron atom for oxygen binding
- Haemoglobinopathies are caused by abnormal haemoglobin structure, such as sickle cell disease and thalassaemias
Anaemia
- Sickle cell disease is a genetic disorder
- Symptoms appear in childhood
- Sickled cells are fragile and become trapped in microcirculation
- Obstruction of blood flow leads to ischemia, pain, and potentially stroke, jaundice, and respiratory symptoms
Red Blood Cell Breakdown
- Lifespan of red blood cells is about 120 days
- Old cells become fragile
- They are trapped and destroyed in the spleen
- Haemoglobin breaks down into heme and globin
- Globin is recycled as amino acids
- Iron from heme is recycled
- Heme breakdown products yield biliverdin, which converts to bilirubin
- Bilirubin is a yellow pigment transported to the liver and excreted in bile
- Jaundice occurs when bilirubin levels in the blood are high, potentially due to liver disease
Blood Groups
- Determined by the antigen present on the red blood cell membrane
- Each blood group is either Rh positive or Rh negative
- Blood group O-negative is a "universal donor" as it lacks antigens that would react with antibodies in the recipient's plasma.
Blood Transfusions
- Patients' blood is typed and crossmatched with donor cells to determine compatibility
- If donor cells react with antibodies in the recipient's plasma, a transfusion reaction can occur.
Role of Platelets in Haemostasis
- Platelets (thrombocytes) are essential for haemostasis, the process of stopping bleeding.
- They adhere to the site of injury and form a platelet plug, which helps seal the damaged blood vessel.
Sequence of Events in Clotting
- The clotting cascade is a complex series of enzymatic reactions that lead to the formation of fibrin.
- Fibrin is a protein that forms a mesh-like structure over the platelet plug, trapping red blood cells and forming a clot.
- The cascade involves:
- Intrinsic pathway (activated by factors within the blood)
- Extrinsic pathway (activated by factors outside the blood)
- Both pathways converge to activate a common pathway, culminating in the formation of thrombin.
- Thrombin converts fibrinogen to fibrin, forming the clot.
- The cascade involves:
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