Sickle cell disease results from mutation, or change, of certain types of hemoglobin chains in red blood cells (the beta hemoglobin chains).

When the oxygen concentration in the blood is reduced, the red blood cell assumes the characteristic sickle shape. This causes the red blood cell to be stiff and rigid, and stops the smooth passage of the red blood cells through the narrow blood vessels.

All of the listed conditions (leukoplakia, solar keratosis, and margins of long-standing draining sinuses) are known precursors to squamous cell carcinoma.

Extensive cellulitis is most accurately described by the term "phlegmon

Phlegm is a thick, viscous substance produced by the respiratory tract, especially during a respiratory infection, which can be coughed up from the lungs or expelled from the nose. It is primarily composed of mucus, dead cells, and other substances.

Phlegmon is a term that is closely related to extensive cellulitis. It refers to a severe form of cellulitis where the infection has spread deeply into the subcutaneous tissues and is accompanied by significant inflammation, including the presence of pus and necrosis. Phlegmon is characterized by intense pain, swelling, redness, and warmth in the affected area. This condition often requires aggressive medical management, including intravenous antibiotics and surgical drainage if an abscess forms. It is an advanced and severe stage of cellulitis that can lead to systemic infection if not treated properly.

Enlargement of interendothelial junctions: This option refers to the widening of the spaces between endothelial cells, which can occur during inflammation. This enlargement allows leukocytes to pass through the endothelium more easily. This is a significant mechanism in the process of leukocyte transmigration.

Epitheloid cells are a hallmark of granulomatous inflammation, which occurs in response to certain chronic infections (like tuberculosis), autoimmune diseases, and foreign body reactions. In granulomas, epitheloid cells aggregate to form a protective wall around the irritant.