Which mechanism best explains weight gain in hypothyroidism?
Increased protein synthesis.
Decreased basal metabolic rate.
Increased glucose metabolism.
Increased catecholamine sensitivity.
The Correct Answer is B
Choice A rationale
Increased protein synthesis is typically an anabolic process that occurs under the influence of growth hormone or testosterone, and it is not a hallmark of hypothyroidism. In a hypothyroid state, there is actually a decrease in both protein synthesis and protein degradation. The lack of thyroid hormone leads to a general slowing of all cellular activities. Weight gain in this condition is not due to the accumulation of muscle mass or protein but rather metabolic slowdown.
Choice B rationale
Thyroid hormones, specifically thyroxine and triiodothyronine, are the primary regulators of the basal metabolic rate, which is the amount of energy the body expends at rest. In hypothyroidism, low levels of these hormones lead to a significant decrease in oxygen consumption and caloric burning by cells. Consequently, even with a normal or reduced caloric intake, the body stores more energy as fat and retains excess water and mucopolysaccharides, leading to the characteristic weight gain.
Choice C rationale
Increased glucose metabolism would typically lead to weight loss or increased energy expenditure, which is seen in hyperthyroidism, not hypothyroidism. In a hypothyroid state, the rate of glucose absorption from the gastrointestinal tract is decreased, and the peripheral uptake of glucose by cells is slowed down. The body's inability to efficiently process and burn glucose as fuel contributes to the overall sluggishness and weight gain associated with the deficiency of circulating thyroid hormones.
Choice D rationale
Thyroid hormones normally increase the sensitivity of cells to catecholamines like epinephrine and norepinephrine by upregulating beta-adrenergic receptors. In hypothyroidism, there is a decreased sensitivity to these catecholamines. This reduction in sympathetic nervous system responsiveness leads to a slower heart rate and decreased lipolysis, which is the breakdown of fats. The inability to effectively mobilize fat stores for energy due to this decreased sensitivity contributes directly to the accumulation of adipose tissue.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
Choice A rationale
Hypertrophy is an increase in the size of individual cells, which leads to an increase in the overall size of the organ. In chronic hypertension, the left ventricle must pump against increased systemic vascular resistance. To compensate for this increased workload, the cardiac myocytes synthesize more proteins and organelles, becoming larger to generate more force. This is a common adaptive response in non-dividing cells like those found in the heart and skeletal muscles when facing stress.
Choice B rationale
Hyperplasia is an increase in the number of cells in an organ or tissue resulting from increased cellular division. This occurs in tissues capable of mitosis, such as the liver or the glandular epithelium of the breast during pregnancy. Since cardiac muscle cells are largely post-mitotic and have a very limited capacity for regeneration or division, the heart cannot adapt to hypertension by making more cells; it must rely on increasing the size of existing cells.
Choice C rationale
Metaplasia is a reversible change in which one adult cell type is replaced by another adult cell type of the same germ line. This is usually a protective response to chronic irritation. An example is the change from ciliated columnar epithelium to squamous epithelium in the airways of chronic smokers. This adaptation is not seen in the heart in response to pressure overload, as the tissue remains muscular but simply becomes thicker and less compliant.
Choice D rationale
Dysplasia refers to abnormal changes in the size, shape, and organization of mature cells. It is often a precursor to cancerous changes and is characterized by a loss of cellular uniformity and architectural orientation. While it can occur in various epithelial tissues due to chronic irritation or inflammation, it is not the mechanism by which the heart adapts to the mechanical stress of high blood pressure, which is a physiological/pathological growth process. .
Correct Answer is A
Explanation
Choice A rationale
A seizure is defined by a sudden, paroxysmal, and uncontrolled electrical discharge from a group of neurons in the cerebral cortex. This hypersynchronous activity disrupts normal brain function and can manifest as changes in consciousness, motor movements, or sensory experiences. The pathophysiology involves an imbalance between excitatory neurotransmitters, like glutamate, and inhibitory neurotransmitters, like gamma-aminobutyric acid. When excitation overcomes inhibition, a feedback loop of rapid firing occurs, leading to the clinical manifestations observed during an active seizure event.
Choice B rationale
A disruption in blood flow causing permanent cell death describes an ischemic stroke or cerebral infarction. While a stroke can eventually become a trigger for seizures due to the resulting scar tissue or irritability of the surviving neurons, the stroke itself is a vascular event, not an electrical one. Seizures are functional disturbances of neuronal firing, whereas strokes are structural injuries caused by lack of oxygen and glucose. Seizures do not inherently cause cell death unless they are prolonged.
Choice C rationale
A decrease in neuronal activity would describe states of CNS depression, such as coma, anesthesia, or the effects of sedative medications. Seizures are the exact opposite; they represent a massive increase in neuronal signaling and metabolic demand. During a seizure, the brain's oxygen and glucose consumption can increase significantly because the neurons are firing at such high frequencies. Reducing brain signaling would actually be the goal of many anticonvulsant medications used to treat or prevent seizure activity.
Choice D rationale
A failure of neurotransmitters to bind at the synapse might describe the action of certain toxins or diseases like myasthenia gravis, but it does not characterize a seizure. In a seizure, neurotransmitters are often being released in excessive amounts, particularly excitatory ones. The issue is not a failure to bind, but rather an overstimulation of the postsynaptic membrane or a failure of inhibitory mechanisms to stop the signal. This leads to the characteristic electrical "storm" associated with clinical seizure activity.
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