Blood formation in the bone marrow and lymphatic organs is called, respectively, lymphoid and myeloid hemopoiesis.
True.
False.
Partially true.
Undetermined.
The Correct Answer is B
Choice A rationale
Hemopoiesis is the general term for blood cell formation. Myeloid hemopoiesis refers to the formation of red blood cells, granulocytes, monocytes, and platelets, which primarily occurs in the red bone marrow. Lymphoid hemopoiesis refers to the formation of lymphocytes, which occurs in lymphatic organs such as the lymph nodes, thymus, and spleen, but also significantly in the bone marrow for B-cell maturation and T-cell precursors. The statement incorrectly implies that lymphoid hemopoiesis occurs *only* in lymphatic organs and myeloid *only* in bone marrow, and the phrasing reverses their typical associations.
Choice B rationale
The statement is false. Hemopoiesis is indeed the formation of blood cells. Myeloid hemopoiesis, the formation of most blood cell types (erythrocytes, granulocytes, monocytes, platelets), predominantly occurs in the red bone marrow. Lymphoid hemopoiesis, the formation of lymphocytes, occurs in lymphoid tissues (lymph nodes, thymus, spleen) but also originates from stem cells in the bone marrow, with B cells maturing there and T cell precursors migrating to the thymus. The original statement incorrectly defines the primary sites and the relationship between lymphoid and myeloid hemopoiesis.
Choice C rationale
The statement contains fundamental inaccuracies regarding the primary sites of lymphoid and myeloid hemopoiesis. While there are overlaps and precursor origins in bone marrow for both lineages, the generalized and exclusive assignments made in the statement are incorrect, making it fully false rather than partially true.
Choice D rationale
The processes of lymphoid and myeloid hemopoiesis and their respective sites of formation are well-established scientific facts. There is no ambiguity or lack of information to render the statement "undetermined.”. The current understanding of hematopoiesis clearly refutes the claim. .
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
Choice A rationale
Fibrin is a crucial protein in the coagulation cascade. It is formed from fibrinogen by the enzyme thrombin. Fibrin polymerizes to form a mesh-like network that traps red blood cells and platelets, creating the structural framework of a stable blood clot, effectively sealing off damaged blood vessels and preventing further blood loss.
Choice B rationale
While platelets are involved in coagulation, fibrin itself is not released from platelets to attract other platelets. Platelets release various factors like ADP and thromboxane A2 to aggregate. Fibrin's role is structural, forming the clot framework after platelet plug formation.
Choice C rationale
Fibrin does not directly stimulate cell division. Its primary role is in hemostasis and clot formation. Cell division, or mitosis, is regulated by growth factors and signaling pathways independent of fibrin's direct action, although clot removal is part of wound healing.
Choice D rationale
Fibrin is a product of prothrombin activation, not an activator of prothrombin. Prothrombin is converted into thrombin by prothrombinase, and thrombin then acts on fibrinogen to produce fibrin, which then forms the clot. The sequence is critical for proper coagulation.
Choice E rationale
Fibrin is the main component of a blood clot and needs to be dissolved for tissue repair to be complete. However, fibrin itself does not dissolve blood clots. Fibrinolysis, the process of clot dissolution, is mediated by plasmin, an enzyme that degrades fibrin.
Correct Answer is D
Explanation
Choice D rationale
Venous pooling, particularly in the lower extremities, commonly occurs when standing still for prolonged periods due to the effects of gravity and reduced skeletal muscle pump activity. This pooling decreases venous return to the heart, leading to reduced cardiac output and consequently a drop in cerebral blood flow, which can result in syncope (fainting).
Choice A rationale
Increased respiratory rate (hyperventilation) typically leads to a decrease in carbon dioxide levels, causing respiratory alkalosis. While severe hyperventilation can lead to cerebral vasoconstriction and lightheadedness, it is not the primary physiological mechanism for syncope after prolonged standing.
Choice B rationale
Vasoconstriction, particularly systemic arteriolar vasoconstriction, would generally help maintain blood pressure by increasing total peripheral resistance, counteracting a drop in blood pressure. Therefore, it would typically prevent rather than cause syncope in this scenario, unless it was a compensatory, insufficient response.
Choice C rationale
An increased heart rate is a compensatory mechanism to maintain cardiac output when venous return or stroke volume is reduced, such as during orthostatic stress. While the heart rate does increase, it is often insufficient to prevent the fall in blood pressure that leads to syncope if venous pooling is severe.
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