1. The rapid change in the resting membrane potential to initiate an action potential is primarily caused by the opening of sodium gates and the influx of sodium into the cell. Option b, “Sodium gates open, and sodium rushes into the cell, changing the membrane potential from negative to positive,” is the correct answer. When the membrane potential reaches a certain threshold, voltage-gated sodium channels open, allowing sodium ions to flow into the cell. This influx of positive ions depolarizes the cell membrane, shifting the membrane potential from negative to positive and initiating an action potential.
2. The leakage of lysosomal enzymes during chemical injury can have various consequences. Option a, “Enzymatic digestion of the nucleus and nucleolus occurs, halting DNA synthesis,” is one of the consequences. Lysosomal enzymes, when released into the cytoplasm due to cell damage, can cause damage to various intracellular structures. If the nucleus and nucleolus are enzymatically digested, it can lead to the halt of DNA synthesis and interfere with cellular functions.
3. In hypoxic injury, the entry of sodium into the cell and subsequent swelling are primarily due to the insufficient ATP to maintain the sodium-potassium pump. Option b, “ATP is insufficient to maintain the pump that keeps sodium out of the cell,” is the correct answer. The sodium-potassium pump is responsible for maintaining the balance of sodium and potassium ions across the cell membrane. In hypoxic conditions, when ATP production is compromised, the pump fails to function effectively, leading to an accumulation of sodium inside the cell and subsequent swelling.
4. Lipid accumulation in liver cells can lead to various changes and disruptions in cellular processes. Option b, “Increased synthesis of triglycerides from fatty acids and decreased synthesis of apoproteins,” describes one of the mechanisms that occur. Lipid accumulation can result in increased synthesis of triglycerides from fatty acids, while the synthesis of apoproteins, which are essential for the formation of lipoproteins, is decreased. These changes contribute to the build-up of lipids within the liver cells.
5. During an IgE-mediated hypersensitivity reaction, the degranulation of mast cells is primarily a result of cross-linking of IgE antibodies bound to high-affinity Fc receptors on mast cells. Option d, “Acetylcholine bound to mast cells,” is not the correct answer. When an allergen binds to the IgE antibodies on mast cells, it triggers the degranulation process and the release of various inflammatory mediators, such as histamine, leukotrienes, and cytokines. These mediators contribute to the symptoms of an allergic reaction.
