Ch 26, L4

• Lecture focuses on chemical buffers and respiratory regulation which rapidly minimize pH changes

Important Sources of Acids in the Body

• Biochemical reactions are influenced by the pH of the encompassing fluid environment

• The acid-base balance of bodily fluids is closely regulated as a result

• Optimal pH is variable

• Arterial blood pH is normally 7.4, venous blood and interstitial fluid pH is 7.35, and intracellular fluid pH averaged 7.0

• Alkalosis or alkalemia occurs when arterial blood pH rises above 7.45

• Acidosis or acidemia refers to a drop in arterial pH below 7.35

• Most hydrogen ions (H+) originate as metabolic by-products or end products, though small amounts of acidic substances enter the body

• Protein - Phosphoric Acid is a source of acid in the body -Anaerobic respiration of glucose can cause Lactic Acid to be produced

• Fat Metabolism creates Fatty Acids

• Transport of CO2 as Bicarbonate - Release H+

Major Chemical Buffer Systems

• H+ concentration in blood is sequentially regulated

• Chemical buffers act within a fraction of a second to resist pH changes and are the first line of defense

• Brainstem respiratory centers regulate changes in respiratory rate and depth to compensate for acidosis or alkalosis and takes 1–3 minutes

• Renal mechanisms: The kidneys are the body's most potent regulatory system and take hours to a day or more to alter blood pH

• The respiratory and renal systems unite to form physiological buffering systems

• They control pH by regulating the amount of acid or base

• They are slower than chemical buffer systems

• The systems have the power of all the body's chemical buffers combined

• A chemical buffer is a system of one or more compounds

• It resists changes in pH when a strong acid or base is added

• It occurs by binding H+ ions whenever the pH drops and releasing them when pH rises

• The main buffer systems are Bicarbonate, Phosphate, and Protein

• Changes in H+ concentration in one fluid compartment lead to simultaneous changes in the others

• Buffer systems effectively buffer one another

• The entire buffer system resists pH drifts

• Bicarbonate Buffer System: Mixture of H2CO3 (a weak acid) and salts of HCO3 (a weak base); main extracellular fluid buffer that also operates in intracellular fluid

• Phosphate Buffer System: Salts of H2PO4 (a weak acid) and HPO4^2- (a weak base); buffer in urine and ICF

• Protein Buffer System: Some amino acid side chains act as either weak acids (-COOH) or weak bases (e.g., -NH2); mainly in ICF, but also in blood plasma

Impact of Respiratory System on Acid-Base Balance

• The respiratory system eliminates CO2 from the blood while replenishing its O2 supply

• Carbon dioxide produced by cellular respiration is converted to bicarbonate ions for transport in the plasma

  • Healthy individuals expel CO2 from the lungs at the same it is formed in the tissues
  • During carbon dioxide unloading, the reaction shifts to the left, and H+ generated from carbonic acid is reincorporated into water
  • H+ produced by CO2 transport is not allowed to accumulate because of the protein buffer system and has little or no effect on blood pH

• Elevate arterial PCO2 levels activate medullary chemoreceptors

  • This causes an increase in respiratory rate and depth
  • An increase in plasma H+ concentration similarly stimulates deeper, more rapid respiration
  • As ventilation increases, more CO2 is removed from the blood, reducing the H+ concentration

• Under high blood pH:

  • Respiratory centers are depressed
  • Respiratory rate drops becoming more shallow
  • Causing CO2 accumulates and H+ to increase
  • pH is then more normal and take minutes

• Respiratory impairments:

  • CO2 retention (hypoventilation) = Acidosis
  • Excessive elimination of CO2 (hyperventilation) = Alkalosis

• Impairments shift the pH either to Respiratory Acidosis or Respiratory Alkalosis

Renal Regulation

• Kidneys regulate the process for acid-base balance long-term

  • They adjust the volume of bicarbonate in the blood

• The kidneys conserve (regenerate) or generate new bicarbonate or excrete bicarbonate

  • Loss of Bicarbonate from the body = increases in H+ ions
  • Generating or Resorbing bicarbonate = decreases in H+ ions

Abnormalities

• Abnormalities change pH due to physiological distress

• Respiratory acidosis is a falling blood pH and PCO2 that occurs from shallow breathing or respiratory diseases

• Respiratory alkalosis is when CO2 is eliminated faster than it is produced

• Metabolic acidosis occurs when blood pH and bicarbonate levels are low from excessive loss of bicarbonate ions or high alcohol ingestion

• Metabolic alkalosis has a rising blood pH and bicarbonate levels from excessive vomiting or high base intake