In the context of erythrocytes and hemoglobin, cyanosis is most directly caused by an increased blood concentration of which form of hemoglobin?

• A. Oxyhemoglobin
• B. Carboxyhemoglobin
• C. Methemoglobin
• D. Deoxygenated (reduced) hemoglobin

Answer: (D)

Verified step by step guidance

1. Understand the definition of cyanosis: it is a bluish discoloration of the skin and mucous membranes caused by an increased concentration of a specific form of hemoglobin in the blood.
2. Recall the different forms of hemoglobin: oxyhemoglobin (oxygen-bound), carboxyhemoglobin (carbon monoxide-bound), methemoglobin (oxidized form), and deoxygenated (reduced) hemoglobin (not bound to oxygen).
3. Recognize that cyanosis occurs when there is an increased amount of deoxygenated hemoglobin in the blood, which has a darker color and imparts a bluish tint to tissues.
4. Eliminate other forms: oxyhemoglobin is bright red and does not cause cyanosis; carboxyhemoglobin binds carbon monoxide and causes hypoxia but not cyanosis; methemoglobin is abnormal but not the primary cause of cyanosis.
5. Conclude that the form of hemoglobin most directly responsible for cyanosis is deoxygenated (reduced) hemoglobin due to its color and concentration in the blood.