Which enzyme primarily converts angiotensin I to angiotensin II in the renin-angiotensin-aldosterone system (RAAS)?

Rationale:

A. Producing antibodies for immune response is incorrect. Antibody production is the function of B lymphocytes (a type of white blood cell), not erythrocytes. Red blood cells do not participate in the immune response.

B. Regulating body temperature is incorrect. While blood circulation helps distribute heat throughout the body, erythrocytes themselves do not directly regulate body temperature. Thermoregulation is a systemic process involving the hypothalamus, blood vessels, and sweat glands.

C. Forming blood clots to stop bleeding is incorrect. Blood clotting is primarily the role of platelets (thrombocytes) and clotting factors in plasma. Erythrocytes do not actively participate in coagulation.

D. Transporting oxygen from the lungs to the tissues is correct. Erythrocytes contain hemoglobin, a protein that binds oxygen in the lungs and carries it to tissues throughout the body. Hemoglobin also assists in transporting a portion of carbon dioxide from the tissues back to the lungs for exhalation. This oxygen delivery function is the primary responsibility of red blood cells and is critical for maintaining cellular metabolism and energy production.

Rationale:

A. Inhalation injury is a serious complication of severe burns, especially those involving the face, neck, or upper torso, or occurring in a fire with smoke or toxic fumes. Thermal or chemical injury to the respiratory tract can cause airway edema, bronchospasm, and impaired gas exchange, which can be life-threatening if not promptly managed.

B. Contractures can develop during the healing process of deep partial-thickness or full-thickness burns. Scar tissue and skin grafts can limit joint mobility, leading to permanent deformities if proper positioning, physical therapy, and splinting are not implemented.

C. Hypovolemic shock is a common early complication of severe burns. Extensive burn injuries cause massive fluid loss through damaged skin and increased capillary permeability, leading to decreased circulating blood volume, hypotension, and organ hypoperfusion. Immediate fluid resuscitation is critical to prevent shock and organ failure.

D. Hearing loss is not a recognized complication of burn injuries. Burns typically do not affect the auditory system unless there is a direct traumatic injury to the ears, which is rare.

E. Increased muscle mass is incorrect. Severe burns are associated with catabolism, muscle wasting, and negative nitrogen balance due to hypermetabolic stress, not increased muscle mass.

F. Infection is a major risk in burn patients because the skin barrier is destroyed, providing a portal for bacteria, fungi, and viruses. Burn wounds are highly susceptible to local infections and sepsis, which is a leading cause of morbidity and mortality in severe burn injuries.