The nurse observes bilateral 3+ pitting edema on a client diagnosed with severe malnutrition. Which explanation is the best explanation for the edema?

Choice A reason: Ischemia of the motor and sensory neurons in the brain is not the cause of multiple sclerosis, but a possible consequence of it. Ischemia is a lack of blood supply to the tissues, which may result from inflammation, thrombosis, or embolism. It may cause neuronal death, stroke, or dementia.

Choice B reason: Damage and scarring of the white matter in the brain is the best description of the cause of multiple sclerosis. Multiple sclerosis is an autoimmune disorder that causes the immune system to attack the myelin sheath, which is a protective layer that covers the nerve fibers. The damage and scarring of the myelin sheath, also called demyelination, disrupts the transmission of nerve impulses and causes various neurological symptoms.

Choice C reason: Infection of the parietal and temporal lobes of the brain is not the cause of multiple sclerosis, but a rare complication of it. Infection of the brain, also called encephalitis, may occur due to viral, bacterial, or fungal agents. It may cause fever, headache, confusion, seizures, or coma.

Choice D reason: Increased amounts of epinephrine and acetylcholine in the brain are not the cause of multiple sclerosis, but a possible effect of it. Epinephrine and acetylcholine are neurotransmitters that regulate the sympathetic and parasympathetic nervous systems, respectively. They may be affected by the demyelination of the nerve fibers, which may alter the autonomic functions such as heart rate, blood pressure, digestion, or bladder control.

Choice A reason: Macrophages, monocytes, and bradykinin are involved in the inflammatory response, but they do not directly cause the symptoms of asthma. They may activate other cells and mediators that contribute to bronchoconstriction and mucus production.

Choice B reason: B lymphocytes, serotonin, and immunoglobulin D are not major players in the pathophysiology of asthma. B lymphocytes produce immunoglobulins, but immunoglobulin E (IgE) is the main antibody involved in allergic asthma. Serotonin is a neurotransmitter that may affect mood and sleep, but it does not cause bronchospasm. Immunoglobulin D is a rare antibody that has no known role in asthma.

Choice C reason: Histamine, leukotrienes, and prostaglandins are the main inflammatory mediators that cause the clinical manifestations of asthma. They are released by mast cells and other cells in response to allergens or irritants. They cause bronchial smooth muscle contraction, increased vascular permeability, edema, mucus secretion, and airway inflammation.

Choice D reason: Helper T lymphocytes, natural killer cells, and interleukin-1 are involved in the immune response, but they do not directly cause the symptoms of asthma. They may modulate the activation and differentiation of other cells and mediators that contribute to airway hyperresponsiveness and inflammation.