______ are secreted by cells infected with viruses, alerting neighboring cells and protecting them from becoming infected.
Complement system globulins
Interferons
Granzymes
Pyrogens
Perforins
The Correct Answer is B
A. Complement system globulins: These are a group of plasma proteins synthesized primarily by the liver that circulate in an inactive state. They are activated by a cascade mechanism to enhance phagocytosis, inflammation, and cytolysis of pathogens. They are not specifically secreted by virus-infected cells to alert neighboring cells.
B. Interferons: When a cell is compromised by a viral pathogen, it synthesizes and releases these signaling proteins as a paracrine defense. Interferons bind to receptors on adjacent healthy cells, triggering the production of antiviral proteins that inhibit viral replication. They act as a critical early warning system in the innate immune response.
C. Granzymes: These are proteolytic enzymes released by natural killer cells and cytotoxic T lymphocytes via exocytosis. They enter a target cell through pores to induce programmed cell death or apoptosis. Their function is the direct destruction of infected or neoplastic cells rather than the signaling of neighbors.
D. Pyrogens: These substances, such as interleukin 1, act on the hypothalamus to elevate the body's temperature set point, resulting in fever. While they are part of the systemic inflammatory response, they do not provide localized cellular protection against viral entry. They modulate systemic thermoregulation rather than cellular viral resistance.
E. Perforins: These are pore-forming proteins secreted by effector lymphocytes to compromise the structural integrity of a target cell's plasma membrane. By creating holes in the membrane, they allow granzymes to enter and facilitate rapid cytolysis. They are tools of direct cellular execution rather than prophylactic intercellular signaling.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
A. immediately before the P wave: The period before the P wave represents the end of the previous cardiac cycle or the quiescent period of diastole. During this time, the atria are filling but have not yet received the signal to contract. Electrical activity must be recorded before any mechanical action can take place.
B. During the P wave: The P wave on an electrocardiogram represents atrial depolarization, which is the electrical signal for the atria to contract. Atrial systole, the mechanical contraction, begins shortly after the start of this wave as the electrical signal spreads through the myocardium. This coordination ensures blood is pumped into the ventricles.
C. during the Q wave: The Q wave is the initial downward deflection of the QRS complex, signaling the start of ventricular depolarization. By this stage, atrial systole is concluding and the atrioventricular valves are beginning to close. The focus of the cardiac cycle has shifted from the atria to the ventricles.
D. during the S-T segment: This segment represents the plateau phase of ventricular action potentials, during which the ventricles are actively contracting. Atrial tissue is undergoing repolarization and is in a state of diastole during this period. The atria are filling with blood while the ventricles are in systole.
E. immediately after the T wave: The T wave represents ventricular repolarization, and the period immediately following it is part of early diastole for the entire heart. During this phase, both the atria and ventricles are relaxed and filling passively. There is no systolic activity occurring in any chamber at this time.
Correct Answer is A
Explanation
A. CO2 + H2O ⇌ H2CO3 ⇌ HCO3- + H+: This equation represents the primary equilibrium for maintaining physiological acid-base homeostasis. Carbon dioxide reacts with water to form carbonic acid, which subsequently dissociates into bicarbonate and hydrogen ions. It accurately depicts the reversible hydration of carbon dioxide catalyzed by carbonic anhydrase.
B. CO2 + H2O ⇌ HCO3- + H+ ⇌ H2CO3: This sequence incorrectly places the ionic dissociation products before the formation of the weak acid intermediate. Chemical equilibrium follows a specific pathway where the hydration of carbon dioxide must produce carbonic acid first. The arrangement does not reflect the standard biochemical progression of this buffer system.
C. H2CO3 ⇌ CO2 + H2O ⇌ HCO3- + H+: This arrangement suggests that carbonic acid is the primary precursor to both carbon dioxide and the dissociated ions simultaneously. While the reaction is reversible, the standard physiological representation starts with the respiratory gas component. This layout disrupts the logical flow of the carbon dioxide-bicarbonate equilibrium.
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