Acid-Base Balance Flashcards
pH
- measurement of a solutions H+ concentration
Normal pH of the body
- 4
- slightly alkaline
1 pH unit = ?
a 10-fold change in H+ concentration
pH changes can _______ proteins… why?
denature
- intracellular proteins are sensitive to pH changes
Changes in [H+] results in..?
- disruptions in hydrogen bonds
- alters the structure
Acidosis
- caused by a very low pH (excess H+)
- CNS depression, confusion, coma
Alkalosis
- caused by a high pH (low H+)
- hyper excitability in sensory neurons and muscles
- sustained respiratory muscle contraction
Acid Input
- result of diet and acids produced during metabolism
Largest daily source of acid?
CO2 from aerobic metabolism
pH Homeostasis Mechanisms
- buffers (first lie of defence)
- ventilations (handles 75% of
disturbances) - renal regulation of H+ and HCO3- (slowest)
Buffer Systems
- includes proteins, phosphate ions, HCO3-
Buffer Molecule
- moderates, but doesn’t prevent changes in pH by combining with or releasing H+
No buffer
- adding acid to a solution causes a sharp change in pH
Solution + Buffer
- H+ added is bound and pH change is slightly moderated or unnoticeable
HCO3-
- large amounts present
- the most important extracellular buffer system
- can buffer H+ from non-respiratory sources
Plasma [HCO3-]
- approx. 600,000x concentrated as plasma H+ (bound to Hb)
Relationship Btwn CO2, HCO3-, H+ in Plasma
CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-
Law of Mass Action
- any change in amount of CO2, HCO3-, H+ in solution causes reaction shift until new equilibrium is reached
Increase in CO2
- shifts equation to right creating 1 H+ and 1 HCO3-
Adding H+
- added through metabolic source (latic acid)
- shifts equation to the left
- HCO3- acts as a buffer
How does ventilation compensate for pH disturbances?
- peripheral and central chemoreceptors sense changes in plasma PCO2 and/or H+ and signals to respiratory control centre to adjust ventilation accordingly
- can correct disturbances or cause them
Hypoventilation
- right shift
- increase CO2 so increase in H+ and HCO3-
Hperventilation
- left shift
- decrease CO2 so decrease in H+ and HCO3-
What kind of buffers do the kidneys use?
ammonia and phosphate buffers
kidneys handle the remaining ____ of pH disturbances through two mechanisms:
25%
mechanisms: Directly and Indirectly
Directly
- by altering the rates of excretion of reabsorption of H+
Indirectly
- by changing the rate at which HCO3- .buffer is reabsorbed or excreted
Ammonia Buffer
- within tubule cells
Phosphate Buffer
- in the lumen of kidneys
What happens to excess H+ during Acidosis?
- excess H+ is buffered by ammonia within tubule cells or enters lumen and is buffered by phosphate ions
H+ is not _____, enters _____ via _____ only.
- filtered
- tubule
- secretion
Proximal Tubule
- secretes H+ and reabsorbs HCO3-
_____ amounts of HCO3- filtered
- high amounts
How is HCO3- filtered?
- indirectly because no apical transporter
Process of Proximal Tubule
- NHE secretes H+
- H+ in filtrate combines with filtered HCO3- to form CO2
- CO2 diffuses into cell
- CO2 combines with water to form H+ and HCO3-
- H+ is secreted again
- HCO3- is reabsorbed with Na+
- Glutamine is metabolized to ammonium ion and HCO3-
- NH4+ is secreted and excreted
Role of the Distal Nephron
- controls acid excretion
Role of the Collecting Duct
- plays a significant role in the fine regulation of acid-base balance
Type A Intercalated Cells
- acidosis
- function to increase H+ secretion and HCO3- reabsorption
- usually accompanied by increase K+ reabsorption (hyperkalemia)
Type B Intercalated Cells
- alkalosis
- function to increase H+ reabsorption and HCO3- secretion
- usually accompanied by increase K+ secretion (hypokalemia)
Three Compensatory Mechanisms
- buffers
- ventilation
- renal excretion
- take care of most variations in plasma pH
Acid-Base Disturbances
- classified by direction of pH change and by underlying cause
Underlying Causes of Acid-Base Disturbances
- metabolic
2. respiratory
Changes in Plasma pH due to Acid-Base Disturbances
- body buffers are ineffective at this point
- respiratory and renal compensation alleviate the change in pH
Respiratory induced changes in pH must be resolved via ______ mechanisms
RENAL
- excrete H+ and reabsorb HCO3-
Respiratory Acidosis
- occurs when alveolar hypoventilation results in CO2 retention and elevated plasma CO2
- pulmonary fibrosis and skeletal muscle disorders (muscular dystrophy)
Respiratory Alkalosis
- less common
- occurs as a result of hyperventilation in the absence of increased metabolic CO2 production
- in clinic: caused by excessive artificial respiration
- physiological: anxiety induced hyperventilation
- compensation: renal HCO3- excretion, H+ reabsorption
Metabolic Acidosis
- occurs when dietary and metabolic input of H+ exceeds H+ excretion
- lactic acidosis (anaerobic metabolism)
- ketoacidosis (excessive breakdown of fats and some amino acids)
- can also occur from excessive HCO3- loss (diarrhea)
Metabolic Acidosis Solution
- resolved by respiratory (increased ventilation) and slow renal compensation (HCO3- reabsorbed, H+ excreted)
Metabolic Alkalosis Causes
- excessive vomiting of acidic stomach contents
2. excessive ingestion of bicarbonate-containing antacids
Metabolic Alkalosis Solutions
- usually resolved rapidly by a decrease in ventilation, but effectiveness is limited because it can because hypoxia
- renal response: HCO3- excreted, H+ reabsorbed
