49.下列血液顏色的相關敘述何者正確 ？①急性氰化物中毒（cyanide poisoning）導致靜脈血的顏色類似動脈血 ②一氧化碳中毒 產生碳氧血紅蛋白（carboxyhemoglobin），導致血液顏色呈現鮮紅色（bright cherry red） ③亞硝酸鹽的中毒會產生變性血 紅素（methemoglobin），導致血液顏色呈現棕紅色（reddish-brown）或巧克力棕色（chocolate brown）
(A)僅①②
(B)僅①③
(C)僅②③
(D)①②③

  （六）其他血紅素相關疾病

1. 變性血紅素（Methemoglobin）：

Ø 血紅素內的Fe^2＋被氧化成Fe^3＋，而失去攜氧能力。

Ø 血液呈褐色。

Ø 亞硝酸鹽（Nitrites）、氯酸鹽（Chlorate）、硫酸鹽（Sulfate）氧化能力強。

2. 一氧化碳中毒：血紅素與CO親合力大於O₂形成碳氧血紅蛋白(HbCO)，血液呈鮮櫻桃紅色血

3. 氰化物中毒：氰化物抑制身體細胞行呼吸作用(中的電子傳遞鏈)，使氧氣無法被利用，不影響紅血球與氧的結合效率，使靜脈血的顏色似動脈血。

Cyanide.

Cyanide (CN-) is a toxic compound that, when ingested, blocks oxidative phosphorylation in mitochondria by  binding cytochrome oxidase. As a result, cells cannot use the oxygen in hemoglobin, so venous blood in cases of cyanide poisoning tends to be as red as arterial blood. Cyanide poisoning in herbivores is usually the result of consumption of plants that contain cyanogenic glycosides.  

Carbon Monoxide.

Hemoglobin has a much higher affnity for CO than for oxygen, so even a small amount of CO reduces oxygen transport capacity. When hemoglobin binds CO, it forms carboxyhemoglobin, which colors the blood bright cherry red and imparts a bright pink color to the tissues even in fatal cases of CO poisoning 

Nitrite Poisoning.

Nitrite poisoning can be associated with consumption of nitrate-accumulating plants by livestock, usually ruminants, or from a water source contaminated with nitrate runoff from fertilized felds. Nitrate is converted in the rumen to nitrite, which can oxidize the iron in the heme group of the hemoglobin molecule to the Fe+3 (ferric) state, converting hemoglobin to methemoglobin, which has low affnity for oxygen. Methemoglobin turns the color of blood to a chocolate brown (Fig. 1-49).  

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