Diseases of the respiratory system.

(I) ANOXIA: Definition: It means failure of the tissues to receive an adequate supply of oxygen Types of anoxia: 1-Anoxic anoxia: Occurs when there is defective oxygenation of the blood in the pulmonary circulation. It is usually caused by primary disease of the respiratory tract. 2-Anemic Anoxia: Occurs when there is a deficiency of hemoglobin per unit volume of the blood. The percentage saturation of the available hemoglobin & oxygen tension are normal, but the oxygen carrying capacity of the blood is reduced. It is usually caused by anemia due to any cause.”e.g.”poisoning by nitrites or carbon monoxide . 3-Stagnant Anoxia: Occurs when the rate of blood flow through the capillaries is reduced. It usually occurs in cases of congestive heart failure, peripheral circulatory failure & venous obstruction. 4 –Histotoxic Anoxia: Occurs when the blood is fully oxygenated, but because of the failure of the “tissue oxidation system,” the tissues can not take up oxygen . It usually occurs as a result of cyanide poisoning. Special causes of Anoxic Anoxia: When the oxygen tension of the inspired air is too low, that it can not oxygenate the pulmonary blood. Any lesion or dysfunction of the respiratory tract reducing the supply of alveolar air such as : -Pneumonia. -Pulmonary atelectasis. -Pneumothorax. -Pulmonary edema &congestion. -Any decrease in the chest movement due to pain in the chest wall. -Obstruction of air passage by accumulation of the exudates. Depression of the respiratory center by drugs or toxins. Congenital defects of the heart & large blood vessels, when mixing of arterial & venous blood occurs through shunts between the two circulation . Paralysis of respiratory muscles. Botulism. Tetanus. Strychnine poisoning.