MLT GlobePhysiology: Blood physiology
19 Physiology MCQs on Blood physiology with answers and explanations.
A neutrophil engulfs a bacterium by extending pseudopodia around it. This uptake of a large particle is:
Large particles enter cells by phagocytosis, an endocytic process that forms a membrane-bound phagosome. Diffusion processes move only small molecules or ions.
Total blood volume in a healthy adult is approximately:
Adult blood volume is about 65-75 mL/kg, about 5 L in a 70 kg person. This figure is used when calculating safe donation or transfusion volumes.
Which packed cell volume is closest to normal for a healthy adult man?
The adult male haematocrit is about 40-50% (females slightly lower). A value of 30% indicates anaemia, and 65% indicates polycythaemia.
A woman has tiredness, palpitations and breathlessness on exertion. Her haemoglobin is 8.5 g/dL. The most likely diagnosis is:
Low haemoglobin reduces oxygen delivery, causing fatigue, a compensatory rise in heart rate and dyspnoea on effort. These are the classic features of anaemia.
Lymph nodes, spleen, thymus and lymphatic vessels belong to which system, whose chief role includes immunity?
The lymphatic system returns tissue fluid to the blood and houses lymphocytes in lymphoid organs where immune responses happen.
Antibody-secreting plasma cells develop from which leucocyte?
Activated B lymphocytes differentiate into plasma cells that secrete immunoglobulins. Monocytes become macrophages.
Which statement about the lymphatic system is correct?
Lymph passes through nodes where macrophages and lymphocytes remove microbes and debris. Lymph capillaries are more permeable than blood capillaries, and adult erythropoiesis is in marrow.
Activated thrombin speeds up its own production until a clot forms. This is an example of:
Thrombin activates factors V, VIII and XI, amplifying its own generation; the loop ends when the clot forms. Childbirth contractions are another positive-feedback loop.
A person moves to a high-altitude city. Which stimulus mainly increases renal erythropoietin production?
Low oxygen delivery stabilises HIF in peritubular interstitial cells of the kidney, increasing erythropoietin and hence red cell production.
Platelets are formed by fragmentation of the cytoplasm of which bone marrow cell?
Large polyploid megakaryocytes shed cytoplasmic fragments into sinusoids as platelets. Megaloblasts are abnormal erythroid precursors in B12 or folate deficiency.
On a peripheral blood film, which normal leucocyte is the largest, with a kidney-shaped nucleus and grey-blue cytoplasm?
Monocytes measure about 15-20 um, the largest normal white cells, with folded or kidney-shaped nuclei. Small lymphocytes are about the size of a red cell.
A 9-year-old passes a roundworm in his stool. Which change in his differential leucocyte count is most expected?
Tissue-invading helminths trigger a Th2/IL-5 response that raises eosinophil counts. Neutrophilia is typical of acute bacterial infection.
For forensic DNA profiling from a blood stain, which blood component provides no nuclear DNA?
Mature red cells lose their nuclei, and platelets are anucleate fragments. Nuclear DNA in blood comes from leucocytes.
What is the main functional advantage of the red cell's biconcave disc shape?
The biconcave shape gives a high surface-to-volume ratio for O2 and CO2 diffusion and lets cells fold through capillaries. Central pallor results from the shape; it is not its purpose.
A patient has an isolated prolonged APTT with normal PT. Which factor is NOT involved in the extrinsic (PT) pathway?
The PT tests factor VII plus the common pathway (X, V, II, fibrinogen). Factor IX belongs to the intrinsic pathway, so its deficiency prolongs only the APTT.
In a bone marrow smear, haemoglobin first becomes visible, giving a mixed blue-pink cytoplasm, at which stage?
Earlier precursors have deeply basophilic cytoplasm full of ribosomes. Haemoglobin accumulating in the polychromatic stage adds pink, giving the grey-lilac colour.
After release from megakaryocytes, platelets survive in the circulation for about:
Platelet lifespan is roughly 7-10 days before removal by the spleen and liver. 120 days is the red cell lifespan.
Blood cell formation first begins in the human embryo in which site?
Haematopoiesis starts in yolk sac blood islands in week 3, shifts to the liver (main site in mid-gestation) and spleen, and finally to bone marrow.
Which circulating leucocyte carries high-affinity IgE receptors (FcεRI) and releases histamine when cross-linked by allergen?
Basophils and tissue mast cells bear high-affinity FcεRI; allergen bridging bound IgE causes degranulation. Eosinophils mainly use lower-affinity receptors.