2024 October Acid Base Balance PDF

Acid-Base Balance 2024 By  pH pH is defined as the negative logarithm of hydrogen ion concentration to base 10. pH = ̶ Log [H+] = ̶ Log 10-7= ̶ ( ̶ 7) = 7 Low pH values correspond to high concentration of H+ and high pH values correspond to low concentrati...

Acid-Base Balance 2024 By  pH pH is defined as the negative logarithm of hydrogen ion concentration to base 10. pH = ̶ Log [H+] = ̶ Log 10-7= ̶ ( ̶ 7) = 7 Low pH values correspond to high concentration of H+ and high pH values correspond to low concentrations of H+. Maintenance of the extracellular fluid between pH 7.35 and 7.45 is essential for health Thus, a) A neutral solution has pH = 7 b) An acidic solution has pH less than 7 c) An alkaline solution has pH more than 7  Acid-Base Balance Definition:  Acid-base balance is the human homeostasis that keeps the pH in the normal range (7.35 to 7.45)  An excess of acid is called Acidosis (pH less than 7.35)  An excess of base is called Alkalosis (pH greater than 7.45). Importance of maintaining pH level: The body is very sensitive to any change outside the acceptable range of pH because: 1. Proteins are denatured and digested 2. Enzymes lose their ability to function 3. Brain dysfunction and death may occur Acid-base imbalance:  It occurs when there is a significant changes of the normal blood pH range (7.35 to 7.45).  Acid-base imbalance may occur due to respiratory or metabolic disturbances. Mechanisms of acid-base balance There are 3 mechanisms to maintain acid-base balance: A. Buffer Systems B. Lungs C. Kidneys A. Buffer Systems The body's acid-base balance is tightly regulated by several buffering agents that reversibly bind hydrogen ions and resist any change in blood pH The buffer system is of 2 types: I. Extracellular buffers include: Bicarbonate and Ammonia II. Intracellular buffers include: Proteins and Phosphate 1. The bicarbonate buffering system It is an important buffer system in the acid-base homeostasis of humans. In this system, carbon dioxide (CO2) combines with water to form carbonic acid (H2CO3) catalyzed by the enzyme carbonic anhydrase, which in turn rapidly dissociates to form hydrogen ion and bicarbonate (HCO3- ) In acidosis, excess hydrogen ions will associate with bicarbonate, forming carbonic acid and then CO2 + H2O i.e. the reaction shifts to left. In alkalosis, carbonic acid will dissociate into bicarbonate and hydrogen ions i.e. the reaction shifts to right. 2. Ammonia buffering system  Ammonia is important for normal acid-base balance.  Ammonia is formed from hydrolysis of glutamine amino acid Glutamine ============ α-ketoglutarate + NH3 (Ammonia) NH3 + H+ ============== NH4 (Ammonium)  Ammonium is excreted in the urine, resulting in net acid loss.  Ammonia may itself diffuse across the renal tubules, combine with hydrogen ions, and thus allow for further acid excretion 3. Proteins buffering system They are the most important buffers in the body. They work mainly intracellular and include Hemoglobin. Protein molecules possess basic and acidic groups which act as H+ Acceptors or Donors respectively if H+ is added or removed. 4. Phosphate buffering system This buffer (H2PO4- : HPO42-) is mainly intracellular. HPO42- acts as H+ acceptor while H2PO4- acts as H+ donors B. Role of lungs in acid-base balance: Acid-base imbalances that overcome the buffer systems can be compensated in the short term by changing the rate of ventilation C. Role of kidneys in acid-base balance: The kidneys have a slower role to compensate acid-base balance  Acidosis Acidosis results from increasing hydrogen ion concentration of arterial blood plasma Generally acidosis occurs when pH of the blood decreases below 7.35 Acidosis is either due to respiratory or metabolic causes A. Respiratory acidosis It results from any condition decreasing the rate of respiration = Hypoventilation. In respiratory acidosis, the CO2 is increased while the bicarbonate is either normal or increased Causes of respiratory acidosis: 1. Pulmonary problems e.g.: Pneumothorax, emphysema, chronic bronchitis, asthma, severe pneumonia, and aspiration 2. Head injuries 3. Drugs (especially anaesthetics and sedatives) 4. Brain tumors The lungs response to acidosis as follows: By increasing breathing, the lungs expell more CO2 This will shift the above reaction to the Left decreasing hydrogen ions concentration and pH will rise back to normal.  B. Metabolic acidosis  Metabolic acidosis results from the increased production of metabolic acids  In metabolic acidosis, the CO2 is Normal while the bicarbonate is Decreased Causes of metabolic acidosis: 1. Renal acidosis is due to renal failure in which, there is decrease in the ability of kidneys to excrete acid with an accumulation of urea and creatinine. 2. Lactic acidosis may occur from: a. Hypoxemia causing a fall in the rate of oxygen diffusion from arterial blood to tissues b. Hypoperfusion (e.g. hypovolemic shock) causing an inadequate blood delivery of oxygen to tissues. 1. Starvation and diabetic ketoacidosis is due to the accumulation of ketoacids (ketosis) The kidneys response to acidosis as follows: Tubular cells reabsorb more bicarbonate from the tubular fluid to the blood Collecting duct cells excrete more hydrogen and generate more bicarbonate, and increase formation of the NH3. Symptoms acidosis: Accelerated heartbeat (tachycardia). Feeling very tired (fatigue). Rapid breathing or long, deep breathing.  Alkalosis  Alkalosis results from reducing hydrogen ion concentration of arterial blood plasma.  Generally alkalosis occurs when pH of the blood exceeds 7.45  Alkalosis is either due to respiratory or metabolic causes A. Respiratory alkalosis It results from any condition increasing the rate of respiration = Hyperventilation In respiratory alkalosis, the CO2 is Decreased There are two types of respiratory alkalosis: acute and chronic. 1. Acute respiratory alkalosis occurs rapidly and the person may lose consciousness 2. Chronic respiratory alkalosis is a more long-standing condition Causes of respiratory alkalosis: 1. Excessive mechanical ventilation 2. Psychiatric causes: anxiety, hysteria and stress 3. CNS causes: stroke, meningitis 4. Drug use: aspirin, caffeine 5. High altitude areas, where the low oxygen stimulates increased ventilation 6. Fever 7. Pregnancy 8. Sexual activity The lungs response to alkalosis as follows: By decreasing breathing, expelling less CO2 This will shift the above reaction to the right increasing hydrogen ions concentration and pH will decrease back to normal. B. Metabolic Alkalosis Causes of metabolic alkalosis 1. Prolonged vomiting, resulting in a loss of hydrochloric acid 2. Severe dehydration 3. Consumption of alkali 4. Administration of diuretics 5. Endocrine disorders such as Cushing's syndrome The kidneys response to alkalosis by: 1. Excreting more bicarbonate in urine 2. Decreasing hydrogen ion excretion from the tubular epithelial cells 3. Increasing glutamine synthesis Symptoms of alkalosis 1. Decreased blood carbon dioxide levels 2. Peripheral paraesthesiae 3. Alkalosis may disrupt calcium ion balance, and cause the symptoms of hypocalcaemia (such as tetany and fainting) with no fall in total serum calcium levels.  Water Balance  WATER accounts for about 50 – 60% of an average person’s weight.  Fat tissue has lower percentage of water and women tend to have more fat, so the percentage of water in the average woman is lower (50 to 55%) than it is in the average man (60%).  The percentage of water is also lower in older and obese people.  A 70 kilogram man has about 45 liters of water in his body: 1. Intracellular fluid (2/3 of body water) = 30 L 2. Extracellular fluid (1/3 of body water) = 15 L  Interstitial fluid (4/5 of extracellular fluid) = 12 L  Plasma (1/5 of extracellular fluid) = 3 L How can the body regulates water? 1. The body obtains water primarily by absorbing it from the digestive tract in addition to the small amount of water produced during metabolism 2. Water intake must balance water loss to maintain water balance – and -- to protect against dehydration, the development of kidney stones, and other medical problems 3. Healthy adults should drink at least 1.5 - 2.0 liters/day 4. Drinking too much is better than drinking too little, because excreting excess water is much easier for the body than conserving water 5. The body regulates the amount of water in each of intracellular and extracellular compartments by moving water between these areas to keep the amount in each area relatively constant Causes of water lose: 1. The body loses water primarily by excreting it in urine from the kidneys depending on the body’s needs, the kidneys may excrete less than 500 ml up to several liters of urine a day. 2. Normally, little water is lost from the digestive tract. However, prolonged vomiting or severe diarrhea can result in the loss of 4.5 liters or more a day. 3. About one liter of water is lost daily by evaporated skin sweat and H2O breathed out by the lungs. 4. Profuse sweating which may be caused by vigorous exercise, hot weather, or a fever can dramatically increase the amount of water lost through evaporation. 5. Unable to drink enough fluids to compensate for water loss caused by prolonged vomiting or severe diarrhea, confusion, restricted mobility, or loss of consciousness Maintaining Water Volume The kidneys have the ability to conserve or waste water by decrease or increase urine volume by two mechanisms: 1. By the structure and transport properties of the loop of Henle in the nephron. 2. By the Anti-Diuretic Hormone (ADH), also called vasopressin Anti-diuretic hormone (ADH) = Vasopressin 1. Specialized nerve cells, called osmoreceptors, in the hypothalamus of the brain sense the Na ions concentration of the blood. 2. The nerve endings of these osmoreceptors are located in the posterior pituitary gland and secrete ADH. 3. ADH controls the ability of water to pass through the cells in the walls of the collecting ducts. 4. If no ADH is present, then no water can be reabsorbed by the walls of collecting ducts and urine volume increases to about 20 – 30 liters. 5. Increased Na ions concentration of the blood stimulates osmoreceptors to secrete ADH. 6. Decreased Na ions concentration of the blood inhibits osmoreceptors to secrete ADH.