Topic 6: Acid Base Balance Flashcards
Define physiological acidosis
when arterial pH drops below 7.35
Define physiological alkalosis
when arterial pH rises above 7.45
What is NET ACID LOAD
- The metabolism of food results in the formation of 15,000 mMoles of acid per day, form of CO2 & 40,000 mMoles per day of fixed acid in form of H2SO4 & H3PO4 (bicarbonates).
- The plasma concentration of H+ is only 0.00004 mmoles/L. Clearly for plasma H+ to remain in ablance, both Co2 and fixed acid has to be effectively eliminated. The lungs eliminate Co2 and the kidneys fixed acid
What is the difference between lung and kidney statistics in net acid load?
Lungs
- metabolism of 15,000 mmoles Co2/day and expired air 15,000 mmoles Co2/day
Kidneys
- metabolism H+ as non-volitile acids 40 mmole/day, ECF pH 7.4, which is 4320 mmole of HCO3-/day is filtered into kidneys. 70 mmole of H+ day in urine (Then 40 mmole NH4+/day and 30 mmole titratable acid/day goes into urine)
3 Types of biological buffers in the body that prevent acidification, their location and importance (1, 2, 3)
- Intracellular Buffers
- Protein Buffers
- Phosphate Buffer
3 Types of biological buffers in the body that prevent acidification, their location and importance (1, 2, 3 - EXPAND)
- Intracellular Buffers
- 57% todat body buffering capacity
- increasing ECF H+ or HCO3_ move across cell membranes
- CO2 is extremely rapid
- RBC’s move more quickly and Hb has crucial role in buffering pH changes in blood - Protein Buffers
- can accept/donate H+
- proteins are msot important of itnracellular buffers along with phosphates
- important role in plasma - Phospahte Buffer
- most important intracellularly
- dihydrogen phosphate ion acts as a weak acid, which buffers strong base
- monohydrogen phosphate acts as a weak base by buffering the H+ released by strong acid
- sodium salts of dihydrogen phosphate weak acid
- monohydrogen phosphate weak base
What is the formula for the Bicarbonate Buffer System
hint when pH = pka (1/2 acid:1/2 base)
pH = 6.1 + log (HCO3-) / 0.03 x pCO2
What is the Human Acid Base Control formula
when
pH = a constant + (kidneys / lungs)
Summarise the global control of acid-base offered by the lung and kidneys via exhalation of carbon dioxide, and kidney excretion of H+.
- Several minutes to exert effect
- relies on diffusion across gradients
- system is controlled by respiratory centre in medulla which stimulates increasing breathing reate when plasma CO2 rises (therefore H+ rises)
What does “blowing off Co2” mean?
The consequences of it and what Co2 retention results in?
The kidneys conserve and secrete HCO3- in order to get pH back to normal a patient can blow off CO2 by HYPERventilating this causing decrease acid levels and ALKALOSIS. Kidneys respond by excreting HCO3 to restore pH.
HYPERventilating will blow off more CO2 lowering pCO2 levels. Holding breath will retain CO2 increasing pCO2 levels.
Henderson-Hasselbalch equation to calculate pH, PCO2 and [HCO3-]. - EXPLAIN *
pH = 6.1 + log (HCO3- / 0.03 x pCO2)
Explain Hydrogen Ion control in kidneys
- H ions are removed from the blood by the process of tubular secretion, therefore acid loss (H ions) exit from the blood and enter the nephron (distal tubule + colelcting duct). The kidneys can oppose the process of acidosis and remove “non-volitaile”acids
- When H ions are removed (blood), HCO3- ions are reabsorbed by nephrons. Nephrons through blood of peritubular capillaries.
- Reabsorption of HCO3- ions into blood opposes acidosis. The HCO3- ions (neg) bind with H+ ions (Pos), removing the soruce of acidity (free H+ ions) from the blood
- Therefore, the bubular secretions of H+ ions and reabsoption of HCO3- ions works together to control pH of blood.
Describe the process of maintaining acid-base balance through respiraotry and renal compensation
- An attempt to correct the problem by respiraotry and renal compensation.
- A/B imbalance due to the inadequacy of a phsyiological buffer system is compensated for by the other system. The respiratory system will attempt to correct metabolic A/B imbalances and kidnets will work to correct imbalances caused by respiraotry disease
Describe the process of maintaining acid-base balance through respiratory compensation
- Metabolic acidosis rate and depth of breathing increase. Blood pH is below 7.35 + HCO3- level is low.
- As CO2- is eliminated by the respiraotry system, pCO2 fall below normal. In respiratory the respiratory rate is often depressed and is teh immediate cause of acidosis.
- Metabolic alkalosis, slow, shallow breathing, allowing CO2 to accumulate in the blood. Correction is revealed by high pH (>7.45), elevated HCO3- levels and increased pCO2
Describe the process of maintaining acid-base balance through renal compensation
- *** to correct respiratory A/B imbalance renal mechanisms are stepped up
- Acidosis has hgih pCO2 and high HCO3- levels. The high PCO2 is teh cause of acidosis. Increased HCO3- levels indicated the kidneys are retaining bicarbonate to offset the acidosis
- Alkalosis has decreased pCO2, increased pH. The kidneys elimate HCO3- from the body by failing to reclain it or by actively secreting it. H+ is therefore retained.
