A 59-year-old man with a history of poor dentition presents with fever, new-onset heart murmur, and positive blood cultures for Streptococcus species. The provider suspects infective endocarditis involving a native heart valve. Which pathophysiologic characteristic of cardiac valves most explains why bacteria are able to adhere and proliferate in this location?
Valves are mostly acellular with limited blood supply, reducing the local inflammatory response and allowing bacterial growth
Valves are highly vascularized, promoting rapid bacterial dissemination
Valves contain abundant immune cells that trigger excessive inflammation
Valves experience turbulent flow that mechanically damages leukocytes
The Correct Answer is A
A. Valves are mostly acellular with limited blood supply, reducing the local inflammatory response and allowing bacterial growth: Native heart valves are composed primarily of connective tissue with very few cells and minimal vascularization. This acellularity and poor blood supply limit delivery of immune cells and antibodies, creating a site where circulating bacteria can adhere to damaged endothelium or preexisting vegetations and proliferate.
B. Valves are highly vascularized, promoting rapid bacterial dissemination: Heart valves are actually avascular. High vascularization would improve immune surveillance, making it less likely for bacteria to establish infection, which is the opposite of what occurs in infective endocarditis.
C. Valves contain abundant immune cells that trigger excessive inflammation: Valves contain very few resident immune cells. The lack of immune surveillance, rather than excessive inflammation, is the key factor that allows bacterial colonization in endocarditis.
D. Valves experience turbulent flow that mechanically damages leukocytes: Turbulent flow can cause endothelial damage, creating a nidus for bacterial adhesion, but it does not directly impair leukocyte function. The main reason bacteria proliferate is the acellular, poorly vascularized nature of valve tissue, not mechanical leukocyte damage.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is E
Explanation
A. Bronchial asthma:Bronchial asthma is primarily an inflammatory airway disorder associated with atopy, allergens, and genetic predisposition. Alcoholism is not a recognized major risk factor for the development of asthma, which involves reversible bronchoconstriction rather than infectious or aspiration-related pathology.
B. Chronic bronchitis:Chronic bronchitis is most strongly associated with long-term cigarette smoking and environmental irritants. While alcohol use may coexist with smoking, alcoholism itself is not the primary predisposing factor for chronic bronchial inflammation and mucus hypersecretion.
C. Diffuse alveolar damage:Diffuse alveolar damage, the histologic basis of ARDS, is typically triggered by severe systemic insults such as sepsis, trauma, or aspiration. Although alcohol abuse may increase susceptibility to infections, it is not the most common direct cause of diffuse alveolar damage.
D. Emphysema:Emphysema results from destruction of alveolar walls, most commonly due to cigarette smoking or alpha-1 antitrypsin deficiency. Alcoholism does not directly cause the protease-antiprotease imbalance responsible for alveolar destruction seen in emphysema.
E. Pulmonary abscess:Alcoholism predisposes individuals to aspiration due to impaired consciousness and depressed cough reflex. Aspiration of oropharyngeal contents introduces anaerobic bacteria into the lungs, leading to localized suppurative infection and cavitation, which characterizes a pulmonary abscess.
Correct Answer is C
Explanation
A. B cell lymphoma:B cell lymphomas are hematologic malignancies affecting lymphoid tissues. Exposure to mineral fibers like asbestos does not specifically increase the risk for B cell lymphomas.
B. Carcinoid tumor:Carcinoid tumors are neuroendocrine tumors that can occur in the lungs or gastrointestinal tract. There is no direct link between asbestos exposure and carcinoid tumor development.
C. Mesothelioma:The presence of needle-like mineral fibers in the sputum is characteristic of asbestos exposure. Asbestos is a well-established risk factor for malignant mesothelioma, a cancer of the pleura or peritoneum. Chronic inhalation of asbestos fibers leads to inflammation, fibrosis, and eventual malignant transformation of mesothelial cells.
D. Teratocarcinoma:Teratocarcinomas are germ cell tumors that arise in the testes, ovaries, or midline structures. Asbestos exposure does not increase the risk for this type of malignancy.
E. Transitional cell carcinoma:Transitional cell carcinoma primarily arises in the urinary tract (bladder, ureters, renal pelvis). While chemical exposures like aromatic amines can increase risk, asbestos fibers are not a causative factor for this tumor type.
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