Pre Clinical Medical Science SBAs
Pre Clin Haematology and Immunology: (34 questions)

Questions

• 1
  Where is tissue plasminogen activator produced?
  Difficulty: Medium     Topic: Thrombolysis
  a

  Endothelial cells

  b

  Kidney

  c

  Liver

  d

  Lungs

  e

  Platelets
  Explanation: Tissue plasminogen activator (tPA) is produced by intact endothelial cells in response to thrombin. This occurs on the venous side of a thrombus to help prevent clot propagation and increase breakdown. tPA acts on fibrin to cleave it into soluble fibrin degradation production and initial clot dissolution.
• 2
  What is present inside dense granules in platelets?
  Difficulty: Medium     Topic: Platelet granules
  a

  ADP, Ca2+, 5-HT

  b

  ATP, FVIII-vWF

  c

  FII, FX, FXII

  d

  FV, FVII, vWF

  e

  Glycogen
  Explanation: Platelets contain dense granules and alpha granules. The dense granules contain factors that cause platelet activation: ADP, calcium and 5-HT. Dense granules contain coagulation factors needed for the clotting cascade: FV, FVIII, vWF and fibrinogen. Platelets do also contain glycogen granules but these are separate to alpha and dense granules.
• 3
  Which receptor mediates a strong bond between platelets in a thrombus?
  Difficulty: Medium     Topic: Platelet adhesion
  a

  ADP-receptor

  b

  GpIb

  c

  GpIIb/IIIa

  d

  PPAR-gamma-receptor

  e

  vWF-receptor
  Explanation: Platelets have two main surface glycoprotein receptors. GpIb is constitutively present and binds to subendothelial collagen via vWF following an injury. This causes activation of platelets and GpIIb/IIIa is then expressed on platelet surface. GpIIb/IIIa mediates the main bond between platelets in a thrombus, linked together with fibrinogen. ADP-receptors are used in platelet activation. The PPAR-gamma receptor is involved in intracellular metabolic regulation. vWF does not have its own specialised receptor.
• 4
  Which factor that is released by endothelial cells causes platelet activation?
  Difficulty: Medium     Topic: Platelet activation
  a

  ADP

  b

  Fibrin

  c

  Histamine

  d

  Prostglandin E2

  e

  Thrombin
  Explanation: Platelets can be activated by a number of factors including: thromboxane, calcium, thrombin (from activation of the clotting cascade) and ADP, which is released by damaged endothelial cells. Fibrin is formed from clotting cascade activation. Histamine does not activate platelets. Prostaglandin are anti-aggregatory and reduce platelet activation.
• 5
  What is the first reaction in activation of the extrinsic pathway of the clotting cascade?
  Difficulty: Easy     Topic: Extrinsic clotting cascade
  a

  FVII binds FX

  b

  FVII binds vWF

  c

  Tissue factor binds FVII

  d

  Tissue factor binds FX

  e

  vWF binds tissue factor
  Explanation: The extrinsic pathway of the clotting cascade describes the process of clotting activation from exposure of tissue factor in subendothelial collagen. Tissue factor binds FVII, which becomes activated and causes the rest of the cascade to become activated. The final result is generation of active FX (with its co-factor FVa), which converts prothrombin to thrombin. Thrombin causes fibrinogen to turn into insoluble fibrin and form a clot. The intrinsic pathway refers to continued activation of the cascade after thrombin has initially been formed.
• 6
  What is the most important physiological mechanism for haemostasis in venous (low-pressure) vessels?
  Difficulty: Medium     Topic: Haemostasis
  a

  Anti-thrombin

  b

  Coagulation cascade

  c

  Platelet thrombus

  d

  Protein C cascade

  e

  Protein S cascade
  Explanation: The main physiological methods for haemostasis are platelet activation and the clotting cascade. Clotting factors are more important in low flow, low pressure vessels - the venous circulation. Whereas platelets are more important in the arterial circulation where flow is high. Both components will propagate the thrombus but they do have their respective more important roles. Protein C, protein S and anti-thrombin are all natural anti-coagulants.
• 7
  Which two factors are required for the activation of prothrombin?
  Difficulty: Medium     Topic: Clotting cascade
  a

  FV & FVII

  b

  FV & FX

  c

  FVII & FVIII

  d

  FVII & FX

  e

  FVIII & FX
  Explanation: The coagulation cascade all converges on generation of active factor X and its co-factor, active factor V. These together cleave prothrombin to thrombin, activating the enzyme. Thrombin is then able to break down soluble fibrinogen into fibrin that forms the clot.
• 8
  What is a common cause of sequestrative thrombocytopenia?
  Difficulty: Hard     Topic: Thrombocytopenia
  a

  Autoimmune destruction

  b

  Bone marrow failure

  c

  Glanzman's thrombasthenia

  d

  Hypersplenism

  e

  Uraemia
  Explanation: Platelets may be low (thrombocytopenia) for a number of reasons: reduced production, increased destruction or sequestration. In hypersplenism many platelets reside in the splenic sinusoids therefore circulating numbers of platelets are low though total body platelets may be normal. Autoimmune destruction causes platelets to be removed by macrophages. Bone marrow failure reduces production of platelets. Uraemia and Glanzman's thrombasthenia are qualitative platelet defects, not causing thrombocytopenia.
• 9
  Which of the following factors requires vitamin K for its synthesis?
  Difficulty: Medium     Topic: Vitamin K
  a

  FVIII

  b

  von Willebrand factor

  c

  FX

  d

  FXII

  e

  Thrombomodulin
  Explanation: Vitamin K is a fat soluble vitamin required for the synthesis of clotting factors II (prothrombin), VII, IX and X; plus protein C and protein S. Vitamin K is needed for post-translational modification of clotting factors. Vitamin K antagonists (e.g. warfarin) are used as oral anticoagulant agents.
  All of the other factors don't require vitamin K for their synthesis.
• 10
  Which two cells are the immediate precursors to red blood cells?
  Difficulty: Medium     Topic: Haematopoesis 2
  a

  Megakaryocytes and normoblasts

  b

  Normoblasts and reticuloblasts

  c

  Normoblast and reticulocytes

  d

  Normocytes and reticuloblasts

  e

  Reticulocytes and myeloblasts
  Explanation: Red blood cells are derived from reticulocytes, which are immature anucleated cells that are released into the circulation and mature into erythrocytes. Normoblasts are the precursors to reticulocytes, they are the last nucleated cell in erythropoesis and are normally only found in the bone marrow. A normocyte is a red blood cell of normal volume. Reticuloblasts do not exist. A myeloblast is an early myeloid progenitor.
• 11
  What is the role of activated protein C?
  Difficulty: Easy     Topic: Protein C
  a

  Activate the alternative pathway of complement

  b

  Activate the intrinsic pathway of coagulation

  c

  Activate plasminogen

  d

  Degrade FVa and FVIIIa

  e

  Inhibit activation of thrombin
  Explanation: Activated protein C is one of the body's most important natural anticoagulation systems. In the presence of thrombin, protein C becomes activated. It then associated with FV and protein S to cause degradation of FVa and FVIIIa, which are needed for the clotting cascade.
• 12
  What is the most common hereditary thrombophilia?
  Difficulty: Hard     Topic: Thrombophilia
  a

  Anti-thrombin deficiency

  b

  Factor V Leiden mutation

  c

  Familial hyperhomocystinaemia

  d

  Protein C deficiency

  e

  Protein S deficiency
  Explanation: There are many causes of thrombophilia and they are most commonly acquired however some people have inherited defects in antithrombin mechanisms. Factor V Leiden mutation causes FV to be less efficiency at associating with protein C for antithrombosis and causes FVa to be more resistant to activated protein C degradation. The other causes listed are much more rare.
• 13
  What characteristics of red blood cells would be expected in a patient with iron deficiency anaemia?
  Difficulty: Easy     Topic: Anaemia 1
  a

  Macrocytic

  b

  Macrocytic with megaloblastic neutrophils

  c

  Macrocytic with nuclei

  d

  Microcytic, hypochromic

  e

  Normocytic, hypochromic
  Explanation: Iron deficiency anaemia is one of the most common causes of anaemia. The red blood cells contain less haemoglobin (hypochromic) and are smaller than normal (microcytic). The iron deficiency may be dietary, due to increased requirements or from chronic blood loss.
• 14
  What does the direct Coombs’ test aim to identify?
  Difficulty: Hard     Topic: Coombs' test
  a

  Antibodies against donor RBC

  b

  Antibody bound to patient's RBC

  c

  Antibody circulating in patient's RBC

  d

  Antigens on donor's RBC

  e

  Antigens on patient's RBC
  Explanation: A direct Coombs' test looks for antibody already bound to patient's red blood cells, such that when they are put into recipient serum the red cells agglutinate - used to test for haemolysis. Conversely, an indirect Coombs' test looks for the presence of antibodies in a patient's serum, that then react with donor red blood cells - this is used to test for potential transfusion reactions.
• 15
  Which of the following typically causes a normocytic anaemia?
  Difficulty: Medium     Topic: Anaemia 2
  a

  Acute blood loss

  b

  Folate deficiency

  c

  Iron deficiency

  d

  Sickle cell disease

  e

  Thalassaemia
  Explanation: Normocytic anaemia occurs when there is a low concentration of haemoglobin in the blood (anaemia) but the red cells are of normal size. When whole blood is lost in one acute event then there is reabsorption of fluid into the circulation. This reduces the haematocrit and causes a normocytic anaemia. This is in contrast to chronic blood loss that causes iron deficiency and a microcytic anaemia. Sickle cell disease and thalassaemia also cause microcytosis. Folate deficiency causes a megaloblastic, macrocytic anaemia.
• 16
  Which is the underlying pathology in thalassaemia?
  Difficulty: Medium     Topic: Thalassaemia
  a

  Failure of red blood cell differentiation

  b

  Haemoglobin unable to bind oxygen

  c

  Inability to incorporate iron into globulin chains

  d

  Inappropriate agglutination of haemoglobin

  e

  Ineffective production of globulin chains
  Explanation: Thalassaemia is caused by ineffective production of one or more haemoglobin chains. The most common form is beta-thalassaemia minor, where one of the beta-chain loci contains a mutation but the other locus is normal. Therefore there is reduced, but not entirely absent, normal beta-chains for haemoglobin production. The effect is a chronic haemolysis with small red cells.
• 17
  Where does the spleen lie?
  Difficulty: Easy     Topic: Spleen
  a

  Anterior to the stomach

  b

  Anterolateral to the left kidney

  c

  In the retroperitoneal space

  d

  Posterior to the pancreas

  e

  Underneath ribs
  Explanation: The spleen lies in the abdomen, in the upper left quadrant. It is a small, fist-sized organ that is underneath ribs 9-11. It is within the peritoneal cavity and lies anterolateral to the left kidney, posterolateral to the stomach and anterolateral to the tip of the pancreas. The splenic artery is a branch of the coeliac axis and it runs posterior to the stomach along with the splenic vein.
• 18
  What is the name given to the process by which oxygen shifts the CO2-Hb dissociation curve to the right?
  Difficulty: Medium     Topic: CO2 carriage 2
  a

  Bohr effect

  b

  Graham's law

  c

  Haldane effect

  d

  Hering-Breuer reflex

  e

  Hill equation
  Explanation: The Haldane effect describes the relationship between the Hb-CO2 dissociation curve and the partial pressure of oxygen. CO2 may bind to amine groups on Hb and this is more likely to occur in the presence of deoxyhaemoglobin, therefore when oxygen tensions are lower i.e. venous blood, rather than arterial. Bohr effect is shift of the oxygen dissociation curve. Graham's law describes the factors for diffusion of a gas through other gases. The Hering-Breuer reflex is inhibition of inspiration due to stretch receptor activation. The Hill equation is a method of deriving the Hb-oxygen dissociation curve.
• 19
  What globin chains are present in HbF?
  Difficulty: Easy     Topic: Haemoglobin 2
  a

  2x alpha + 2x beta

  b

  2x alpha + 2x delta

  c

  2x alpha + 2x epsilon

  d

  2x alpha + 2x gamma

  e

  4x alpha
  Explanation: All forms of haemoglobin have 4 globin chains and normally these are in two pairs of which one pair are alpha chains. HbA is the most prevalent Hb in adults, comprising 95% of all. It contains 2 alpha and 2 beta chains. In adults there is also HbA2 (2 alpha + 2 delta). HbE is an embryonic form of haemoglobin and contains epsilon chains. HbF (foetal) is 2x alpha + 2x gamma.
• 20
  What is methaemaglobin?
  Difficulty: Hard     Topic: Haemoglobin 3
  a

  De-oxygenated Hb

  b

  Hb with carbon dioxide bound

  c

  Hb with carbon monoxide bound

  d

  Hb with oxidised iron

  e

  Hb with reduced iron
  Explanation: In order for the iron in each globin chain to bind oxygen it must be in the reduced (Fe2+) state. Methaemaglobin is the term given to haemoglobin when the iron is oxidised. Red cells contain the enzyme methaemoglobin reductase to convert iron back to Fe2+. Deoxyhaemoglobin is de-oxygenated haemoglobin. Carboxyhaemoglobin is with carbon monoxide bound.
• 21
  What is the role of 2,3-diphosphoglycerate?
  Difficulty: Medium     Topic: 2,3-diphosphoglycerate
  a

  Increases binding of CO2 to haemoglobin

  b

  Increases binding of oxygen to haemoglobin

  c

  Increases oxygen delivery to tissues

  d

  Prevents binding of nitrogen to haemoglobin

  e

  Shifts the Hb-dissociation cure to the left
  Explanation: 2,3-DPG is a by-product of anaerobic metabolism that increases oxygen delivery to tissues by reducing oxygen's affinity with Hb and shifting the oxygen-Hb dissociation curve to the right. Anaerobically respiring tissues will produce more 2,3-DPG so will have a greater delivery of oxygen from haemoglobin. It has no effect on nitrogen.
• 22
  What is the Bohr effect?
  Difficulty: Easy     Topic: Bohr effect
  a

  High CO2 reduces Hb's affinity for oxygen

  b

  High pH reduces Hb's affinity for oxygen

  c

  Low CO2 increases Hb's affinity for CO2

  d

  Low oxygen increases Hb's affinity for CO2

  e

  Low pH increases Hb's affinity for oxygen
  Explanation: The Bohr effect is the right shift of the Hb-oxygen dissociation curve in response to a rise in CO2 or a fall in pH. These indicate tissue hypoxia and cause a reduction in the affinity of Hb for oxygen so more is released to the tissues. Conversely, low CO2 and high pH cause a left shift of the dissociation curve. Though 2,3-DPG causes a right shift of the dissociation curve it is not technically part of the Bohr effect.
• 23
  Why is the dissociation curve of HbF a different shape to that of HBA?
  Difficulty: Easy     Topic: Foetal Hb
  a

  Beta-chains have more oxygen binding sites

  b

  Delta-chains have higher CO2 affinity

  c

  Gamma-chains cannot bind 2,3-DPG

  d

  HbF has no alpha-chains

  e

  There is a higher concentration of HbF
  Explanation: At the materno-foetal interface there is transfer of oxygen from HbA to HbF because HbF has a higher affinity for oxygen. This higher affinity is due to the inability of gamma chains to bind 2,3-DPG, which lowers the oxygen affinity of beta chains. There is no difference in number of binding sites. Delta chains are not in HbA or HbF. All forms of physiological haemoglobin contain two alpha chains. HbF is at a higher concentration than HbA, but the concentration does not affect its oxygen affinity or shape of the dissociation curve.
• 24
  What is the shape of the myoglobin-oxygen dissociation curve?
  Difficulty: Easy     Topic: Myoglobin
  a

  Asymptotic

  b

  Hyperbolic

  c

  Linear

  d

  Parabolic

  e

  Sigmoidal
  Explanation: Myoglobin is a globin molecule that can bind only 1 oxygen molecule. It resides in muscle and is used when the muscle becomes very hypoxic. Its curve is hyperbolic because there is only one molecule to bind and after that it becomes fully saturated. Whereas haemoglobin has a sigmoidal shape because there are 4 oxygen molecules to bind at they show co-operative binding. Such that binding of the 1st oxygen helps binding of the 2nd and 3rd, but the 4th becomes more difficult - giving the steep middle section to the sigmoid curve.
• 25
  How do oxygen saturations change in anaemia?
  Difficulty: Medium     Topic: Anaemia 1
  a

  Fall in capillary oxygen saturation

  b

  Fall in venous oxygen saturation

  c

  No change in oxygen saturations

  d

  Rise in arterial oxygen saturation

  e

  Rise in venous oxygen saturation
  Explanation: Anaemia is a reduction in the concentration of haemoglobin per volume of blood (often measured in g/dl). The oxygen carrying capacity of blood is reduced because there is less haemoglobin available, however the saturation - the percentage of all available binding sites filled with oxygen - will not be affected.
• 26
  In what form is most carbon dioxide transported in the blood?
  Difficulty: Easy     Topic: CO2 carriage 1
  a

  Bicarbonate ions

  b

  Bound to haemoglobin

  c

  Bound to other proteins

  d

  Carbonic acid

  e

  Dissolved in plasma
  Explanation: Most carbon dioxide is transported in the form of HCO3-, which is generated from dissociation of carbonic acid. Dissolved CO2 combines with H20 and is converted to H2CO3 (carbonic acid) under the action of carbonic anhydrase. A minority of CO2 may bind to amine groups on haemoglobin and other proteins. A very small amount is dissolved in plasma.
• 27
  What globin chains are present in HbA?
  Difficulty: Easy     Topic: Haemoglobin 1
  a

  2x alpha + 2x beta

  b

  2x alpha + 2x delta

  c

  2x alpha + 2x epsilon

  d

  2x alpha + 2x gamma

  e

  4x alpha
  Explanation: All forms of haemoglobin have 4 globin chains and normally these are in two pairs of which one pair are alpha chains. HbA is the most prevalent Hb in adults, comprising 95% of all. It contains 2 alpha and 2 beta chains. In adults there is also HbA2 (2 alpha + 2 delta). HbE is an embryonic form of haemoglobin and contains epsilon chains. HbF (foetal) is 2x alpha + 2x gamma.
• 28
  Approximately what percentage composition of whole blood is cells?
  Difficulty: Easy     Topic: Blood composition 1
  a

  35%

  b

  45%

  c

  55%

  d

  65%

  e

  75%
  Explanation: Blood is made of cells (45%) and plasma (55%). The haematocrit is the percentage of whole blood that is red blood cells, and RBC make up over 95% of the mass of all blood cells so haematocrit is normally 0.4-0.5. Plasma is composed of mostly water with salts, plus proteins.
• 29
  What is the most prevalent protein in plasma?
  Difficulty: Easy     Topic: Blood composition 2
  a

  Albumin

  b

  C-RP

  c

  Fibrinogen

  d

  Immunoglobulin

  e

  Peptide hormones
  Explanation: Albumin is the plasma protein with the highest serum concentration. It has two main functions: exerting oncotic pressure for maintenance of intravascular volume; and binding of substances to aid in their transport. The liver is the only site of albumin synthesis. C-RP is one of the acute phase proteins involved in activation of complement. Fibrinogen is precursor to fibrin, needed for clot formation. Immunglobulins are involved in immune responses but are present at a baseline concentration. There are many circulating hormones but their concentrations are comparatively low.
• 30
  What is blood serum?
  Difficulty: Medium     Topic: Blood composition 3
  a

  Whole blood with all cells and all proteins removed

  b

  Whole blood with all cells and clotting factors removed

  c

  Whole blood with all cells removed

  d

  Whole blood with red cells removed

  e

  Whole blood with white cells removed
  Explanation: Whole blood with all cells removed is known as plasma. Once the coagulation factors have been removed from plasma, blood serum is formed. The process of removing white cells is known as leucophoresis.
• 31
  What antibodies are present in the serum of a person whose blood group is A-positive?
  Difficulty: Medium     Topic: Blood groups 1
  a

  Anti-A

  b

  Anti-A, anti-Rhesus D

  c

  Anti-B

  d

  Anti-B, anti-A and anti-Rhesus D

  e

  Anti-B, anti-Rhesus D
  Explanation: The description of a patient's blood group refers to the antigens they have present on the surface of their red blood cells. There are naturally occurring (IgM) antibodies to all blood groups that are not present on the red cells. Rhesus D is a further blood antigen, most people are rhesus positive but those who are rhesus negative have potential to develop anti-Rhesus antibodies, if they are exposed to Rhesus positive blood.
• 32
  What blood group will a person be who has anti-B, anti-A and anti-Rhesus D antibodies?
  Difficulty: Easy     Topic: Blood groups 2
  a

  A+

  b

  AB+

  c

  AB-

  d

  O+

  e

  O-
  Explanation: If a patient has antibodies to A and B antigens then they will not have either on their red cells. In order to have antibodies to Rhesus D, a patient who has Rhesus negative red cells must be have been previously exposed to Rhesus D positive blood. Conversely, an AB+ patient will have none of these antibodies.
• 33
  Which blood may be transfused to a patient who is O+
  Difficulty: Easy     Topic: Blood groups 3
  a

  AB+ only

  b

  AB- only

  c

  AB+ or AB-

  d

  Any blood group

  e

  O+ or O-
  Explanation: A patient can be transfused blood that doesn't contain any antigens for which the patient has antibodies. An O+ patient will contain antibodies against A-antigen and B-antigens therefore cannot accept A, B or AB blood. Rhesus positive patients do not contain anti-Rhesus antibody therefore can accept positive or negative blood. So this patient may only have group O but positive or negative.
• 34
  How are platelets produced?
  Difficulty: Easy     Topic: Haematopoesis 1
  a

  Asymmetric division of myeloblasts

  b

  Budding off of megakaryocytes

  c

  Maturation of megakaryocytes

  d

  Maturation of normocytes

  e

  Maturation of reticulocytes
  Explanation: Platelets are nuclei deficient cells that bud off from very large, multinucleated cells called megakaryocytes. Megakaryocytes are derived from common myeloid progenitors, which also divide into erythrocytes, granulocytes and macrophages. Normoblasts and reticulocytes are red cell progenitors