The underlying pathophysiology of sickle-cell anemia is:

A. A loss of red blood cells, white blood cells, and platelets is incorrect because sickle-cell anemia primarily affects red blood cells. White blood cells and platelets are usually unaffected in terms of production; the condition does not cause a pancytopenia like aplastic anemia.

B. Abnormally-shaped red blood cells that cause obstruction of small blood vessels is correct because sickle-cell anemia is caused by a mutation in the beta-globin gene, resulting in hemoglobin S. Under low oxygen conditions, hemoglobin S polymerizes, causing red blood cells to become rigid, crescent-shaped (sickle-shaped), and less flexible. These sickled cells block small blood vessels, leading to vaso-occlusion, ischemia, pain crises, and organ damage. Additionally, sickled cells are prone to hemolysis, resulting in chronic anemia.

C. Increased numbers of circulating red blood cells and hemoglobin is incorrect because sickle-cell anemia results in hemolytic anemia, meaning red blood cell counts and hemoglobin levels are reduced, not increased.

D. Decreased red blood cells due to a lack of intrinsic factor is incorrect because this describes pernicious anemia, not sickle-cell anemia. Sickle-cell anemia is a genetic hemoglobinopathy, not a vitamin B12 absorption issue.

A. Ringworm is incorrect because ringworm (tinea) is a superficial fungal infection of the skin characterized by circular, scaly, and often itchy lesions. It is caused by dermatophytes and is not primarily an inflammatory reaction to irritants.

B. Eczema is correct because eczema, also known as atopic dermatitis, is a chronic inflammatory skin condition that results in redness, itching, and increased sensitivity to environmental irritants such as soaps, detergents, certain fabrics, or changes in temperature and humidity. The skin barrier is compromised, making the skin more prone to irritation, dryness, and secondary infections. Eczema often follows a relapsing course with flare-ups triggered by allergens or irritants.

C. Psoriasis is incorrect because psoriasis is a chronic autoimmune condition characterized by rapid proliferation of skin cells, leading to thick, silvery, scaly plaques. It is not primarily caused by external irritants, although trauma or stress can exacerbate it.

D. Impetigo is incorrect because impetigo is a highly contagious bacterial infection of the skin, typically caused by Staphylococcus aureus or Streptococcus pyogenes. It presents as vesicles or pustules that rupture and form honey-colored crusts. It is an infectious condition, not a chronic inflammatory response to irritants.