What is the primary pathophysiological mechanism underlying beta-thalassemia?
Impaired synthesis of globin chains
Abnormal iron absorption
Deficient production of red blood cell precursors
Increased production of erythropoietin
The Correct Answer is A
A. Beta-thalassemia is a hereditary disorder characterized by a mutation in the beta-globin gene, leading to reduced or absent synthesis of beta-globin chains. This results in an imbalance of globin subunits, where excess alpha chains precipitate and damage the red blood cell membrane. This mechanism causes premature hemolysis and ineffective erythropoiesis, leading to the severe anemia characteristic of the disease.
B. While abnormal iron absorption and subsequent iron overload are major clinical complications of thalassemia, they are not the primary cause of the disease. Iron accumulation occurs due to frequent blood transfusions and a compensatory increase in intestinal absorption driven by ineffective red cell production. The root pathology remains a genetic defect in hemoglobin synthesis rather than a primary disorder of iron metabolism.
C. In beta-thalassemia, the bone marrow actually exhibits massive hyperplasia of red blood cell precursors as it attempts to compensate for the anemia. The problem is not a lack of precursors, but rather that the cells produced are defective and die before or shortly after entering circulation. This "ineffective erythropoiesis" is the result of the globin chain imbalance, not a deficiency in the marrow's starting material.
D. Increased production of erythropoietin is a secondary physiological response to the chronic tissue hypoxia caused by severe anemia. The kidneys release more erythropoietin to stimulate the bone marrow to produce more red cells. While this hormone level is elevated in patients with thalassemia, it is a symptomatic effect of the underlying hemoglobin defect rather than the primary cause of the pathology.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is D
Explanation
A. Impaired relaxation of the left ventricle describes diastolic dysfunction, where the ventricle fails to fill properly due to decreased compliance or delayed lusitropy. While this can lead to heart failure symptoms, it is distinct from the primary systolic failure described in the context of chronic coronary artery disease. Diastolic failure involves preserved ejection fraction despite impaired filling.
B. Ineffective contraction of the left atrium is often observed during atrial fibrillation, where the "atrial kick" is lost, reducing ventricular filling by approximately 20%. While this can exacerbate existing cardiac conditions, it is not the fundamental primary mechanism of left-sided heart failure. The core issue of heart failure resides in the ventricular myocardium rather than atrial electrical disturbances.
C. Decreased afterload typically results in increased cardiac output because the resistance against which the left ventricle must pump is reduced. In heart failure, afterload is usually pathologically increased due to systemic vasoconstriction and the activation of the renin-angiotensin-aldosterone system. Reducing afterload is actually a primary therapeutic goal to improve ventricular stroke volume.
D. Inability of the left ventricle to adequately eject blood is the primary pathophysiological mechanism of systolic left-sided heart failure. This occurs when myocardial contractility is diminished due to ischemia or chronic pressure overload from hypertension. The result is a reduced stroke volume and an increase in left ventricular end-diastolic pressure, leading to pulmonary venous congestion.
Correct Answer is C
Explanation
A. While a decreased residual volume can occur in restrictive lung disease, it is not the defining diagnostic criterion used to differentiate it from obstructive patterns. The FVC and TLC reductions are the primary indicators of a loss of lung compliance or thoracic expansion. RV changes are variable and depend on the specific underlying etiology of the restriction.
B. A decreased FEV1/FVC ratio is the hallmark of obstructive lung diseases, such as asthma or chronic obstructive pulmonary disease. In these conditions, air trapping leads to a disproportionate reduction in expiratory flow compared to volume. This ratio indicates an increased resistance to airflow, which is the physiological opposite of pure restrictive lung disease.
C. In restrictive lung disease, the FEV1 and FVC both decrease proportionally, which results in a normal or even slightly elevated ratio. This occurs because the lung tissue is stiff or the chest wall movement is limited, but the airways remain patent. This pattern confirms that the primary pathology involves reduced lung volumes rather than airway obstruction.
D. Restrictive lung disease is fundamentally defined by a reduction in total lung capacity below the 80 percent predicted value. A normal TLC would effectively rule out a restrictive diagnosis, as it indicates the lungs can still achieve their full physiological volume. Identifying a normal TLC suggests that any reduction in FVC is likely due to other factors.
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