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.

Gas Gangrene, also known as clostridial myonecrosis or anaerobic cellulitis, is a severe and rapidly progressing form of necrotizing soft tissue infection caused by the bacterial genus Clostridium. The condition is characterized by the production of gas within the tissues due to the fermentation of carbohydrates by the bacteria. The most common species implicated in gas gangrene is Clostridium perfringens.

1. Clostridium tetani: This bacterium is the causative agent of tetanus, which is a neurotoxic disease that leads to muscle spasms and rigidity. It is not directly associated with gas gangrene, although both are anaerobic infections that can occur in deep puncture wounds and both produce exotoxins. However, the primary symptom of tetanus is muscular rigidity and spasms due to the production of tetanospasmin, not the tissue destruction and gas production seen in gas gangrene.

2. Clostridium perfringens: This is the most common cause of gas gangrene. C. perfringens produces alpha toxin, which is a powerful enzyme that can break down tissue and release gas as a byproduct. The infection typically occurs in the deep layers of the skin and muscles following a severe trauma, surgery, or burns, where there is a lack of oxygen, allowing the anaerobic bacteria to thrive. The rapid spread of infection is due to the bacteria's ability to produce multiple exotoxins that cause tissue necrosis and vasoconstriction, leading to ischemia and further tissue damage.

3. Clostridium difficile: Although a member of the Clostridium genus, C. difficile is mainly associated with antibiotic-associated diarrhea and pseudomembranous colitis. It is a hospital-acquired infection that affects the intestinal tract and is not typically involved in causing gas gangrene. While it is an anaerobic bacterium, its pathogenicity is primarily due to the production of toxins that damage the colon's mucosal lining rather than invading tissues outside the gut.

4. Peptostreptococci: These are anaerobic bacteria that can be part of the normal skin and mucosal flora. They are involved in various infections, particularly in immunocompromised individuals or those with underlying medical conditions. Peptostreptococci are more commonly associated with mixed anaerobic infections such as abscesses, osteomyelitis, and other soft tissue infections, but they are not typically the sole cause of gas gangrene.

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.

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.

Diapedesis is a critical process in the body's immune response, particularly in the context of inflammation.