tailieunhanh - Essential Guide to Acute Care - part 3

Acid như một sản phẩm phụ của quá trình trao đổi chất Cơ thể con người liên tục sản xuất axit như một sản phẩm phụ của quá trình trao đổi chất. Nhưng nó cũng phải duy trì một khoảng pH hẹp, cần thiết cho hoạt động enzyme | CHAPTER 3 Acid-base balance By the end of this chapter you will be able to Understand how the body maintains a narrow pH Know the meaning of common terms used in arterial blood gas analysis Know the causes of acid-base abnormalities Use a simple system to interpret arterial blood gases Understand why arterial blood gases are an important test in critical illness Apply this to your clinical practice Acid as a by-product of metabolism The human body is continually producing acid as a by-product of metabolism. But it must also maintain a narrow pH range necessary for normal enzyme activity and the millions of chemical reactions that take place in the body each day. Normal blood pH is and this is maintained by Intracellular buffers . proteins and phosphate Extracellular buffers . plasma proteins haemoglobin and carbonic acid bicarbonate Finally the excretory functions of the kidneys and lungs. A buffer is a substance that resists pH change by absorbing or releasing hydrogen ions H when acid or base is added to it. The intracellular and extracellular buffers absorb H ions and transport them to the kidneys for elimination. The carbonic acid bicarbonate system allows H ions to react with bicarbonate to produce carbon dioxide CO2 and water and the CO2 is eliminated by the lungs H HCO3 H2CO3 CO2 H2O carbonic anhydrase enzyme Carbonic acid H2CO3 continually breaks down to form CO2 and water hence this system always tends to move in a rightward direction and unlike other buffer systems never gets saturated. But it is easy to see how for example a problem with ventilation would quickly lead to a build-up of CO2 a respiratory acidosis. Uniquely the components of the carbonic acid bicarbonate system can be adjusted independently of one another. The kidneys can regulate H ions excretion in the urine and CO2 levels can be adjusted by changing ventilation. The excretory functions of the lungs and kidneys are connected by carbonic acid so that if one organ becomes .