Physiology Module 12
Where do the H+ come from (that's being pumped by ATP powered hydrogen ion pump)?
Reaction in which CO2 combined with H2O inside cell to form bicarbonate and H+ Note: CO2 did not come from filtrate, came from cell or interstitial fluid
What are the 2 types of acidosis?
Respiratory acidosis and metabolic acidosis
What are the 2 types of alkalosis?
Respiratory alkalosis and metabolic alkalosis
What is alkalosis?
Term to describe body fluids when pH is above 7.4 Too much bicarbonate or too little acid
What is acidosis?
Term to describe body fluids when pH is below 7.4 Too much H+ or too little bicarbonate
What is the pH of lemon juice?
2.5
What is a volatile acid?
Term to describe carbonic acid when it reforms into CO2, which is REMOVED BYLUNGS
What is the neutral pH value?
7
What is the pH of venous blood?
7.35
What is the normal pH of body fluids?
7.35-7.45, average 7.4 (slightly basic)
What is the pH scale?
The negative logarithm (to base of 10) of H+ concentration (b/c it's negative logarithm, the more free H+, the lower the pH and vice versa) - way of quantifying the concentration of H+ in any solution
What is the result of metabolic acidosis?
Decrease in extracellular bicarbonate ions
What is the function of CO2?
(with help of enzyme carbonic anhydrase) combines with water in RBC to produce H2CO3 --> dissociate into free H+ and HCO3. In lungs, reaction will reverse - H2CO3 reforms, converts to CO2 (removed and exhaled) + H2O. RESULT: no NET increase in free H+ in plasma.
What is the interval of the pH scale? Interpret this.
0-14 (0-6.99 is acidic; 7.01-14 is basic)
What are the 3 mechanisms used to regulate free H+ concentrations?
1. Buffers 2. Respiratory sytem 3. Kidneys
What are the causes of metabolic alkalosis?
1. Buildup of bicarbonate ions 2. Loss of HCl from stomach from vomiting 3. Ingestion of alkaline drugs (sodium bicarbonate for treating ulcers)
Why is acid-base balance important?
1. Chemical reactions are sensitive to presence of H+ 2. H+ alters shape of enzymes (proteins) that speed up chemical reactions Thus, change in concentration of H+ will affect activity of most cells
What are the causes of metabolic acidosis?
1. Kidney failure resulting in inability to reabsorb bicarbonate from filtrate 2. Formation of excess metabolic fluids in body 3. Ingestion of acids (common: aspirin and methyl alcohol) 4. Loss of bicarbonate in diarrhea (most common cause)
What is the pH of arterial blood?
7.45
What is the pH of baking soda?
8.5
What percentage of bicarbonate ions filtered at glomerulus is reabsorbed in proximal tubule?
90%
What is a strong acid?
Acid that dissociates rapidly and release large amounts of H+ (the more H+, the more acidic) ex. HCl
What are examples of nonvolatile acids?
Acids produced by metabolic breakdown of proteins; HCl in stomach
What is a nonvolatile acid?
Acids that cannot be removed by lungs; significant source of free H+; constantly produced throughout body, thus must be dealt with to maintain constant pH
What is a strong base?
Base that attaches to MORE H+, resulting in less free H+, thus decreasing acidity of solution --> more basic/alkaline
What is an example of a base?
Bicarbonate ions (HCO3-, the most important base in body) will bind with H+ to form carbonic acid (H2CO3). Base lowers concentration of free H+ in solution by combining with them.
Explain reabsorption of bicarbonate ions in kidneys
Bicarbonates are filtered freely at glomerulus into filtrate, cannot be directly reabsorbed by tubule cells. Must first be converted to CO2 which is then reabsorbed. Once in tubule cells, CO2 combines with H2O (+ carbonic anhydrase) to produce bicarbonate and H+. Bicarbonate leave tubule cells by simple diffusion and reabsorbed back into circulation. Remaining H+ in cell secreted into lumen by Na+/H+ exchanger Note: for ever bicarbonate reabsorbed, H+ secreted
How does hemoglobin minimize pH change?
Binds to CO2 to reduce the POTENTIAL acidity should CO2 combine with H2O to form H2CO3
What buffers can free H+ bind to?
Buffers in intracellular fluid and extracellular fluid
How is respiratory acidosis counteracted?
By buffers in blood and by excretion of excess H+ by kidney?
How can the respiratory system guard against changes in free H+?
CO2 detection of central and peripheral chemoreceptors. When CO2 levels increase, both receptors detect change and cause ventilation increase --> more CO2 removed at lungs --> blood CO2 normal
What is the byproduct of ATP producing process?
Carbon dioxide
What is respiratory alkalosis?
Caused by increased ventilation and decreased PCO2. Although infrequent, can be caused by stress or emotionally induced hyperventilation. Hyperventilation will result in increased removal of CO2 from blood causing decrease in PCO2. Caused by high altitudes when O2 levels are low, causing low PO2 levels of blood which stimulates hyperventilation.
What is respiratory acidosis?
Caused by increased ventilation and increased PCO2. This can occur if respiratory centers in brain stem are damaged or from lung damage resulting in decreased ability to remove CO2 from blood
What is the ATP powered H+ pump important for?
Creating extremely acidic urine
How is respiratory alkalosis counteracted?
Excretion of bicarbonate ions from kidney
How do the kidneys regulate H+ concentration?
Function: excrete/buffer nonvolatile acids to maintain pH 7.4 1. excrete H+ from nonvolatile acids 2. reabsorb bicarbonate ions filtered at glomerulus (to help buffer blood) 3. create new bicarbonate ions which get absorbed into circulation
What is an example of an extracellular buffer?
HCO3- (the most powerful)
What is an example of an acid?
HCl will dissociate into free H+ and Cl- (presence of H+ makes it solution acidic)
What does a hydrogen ion consist of?
Hydrogen atom that lost its electron (thus, positively charged) - sometimes called proton
How do the kidneys regulate pH by reabsorbing, secreting, or excreting substances?
If amount of H+ in urine exceeds amount of bicarbonate reabsorbed --> net loss of acid from body, thus pH in body will increase, more basic If amount of bicarbonate excreted in urine exceeds amount of H+ excreted --> net loss of base from body leaving H+ behind --> pH decrease, more acidic
What does metabolic acidosis not involve?
Increased CO2 levels in blood
Where are H+ secreted in kidneys?
Into filtrate in proximal tubule by Na+/H+ exchanger, then in distal tubule and collecting duct by H+-ATP pump
What is the ATP powered hydrogen ion pump?
Located on luminal side of tubule cells, secretes one H+ (responsible for 5% of H+ secretion) for every ATP molecule consumed (when single H+ secreted, new bicarbonate ion is absorbed into circulation)
What is the most common cause of metabolic alkalosis?
Loss of HCl from stomach from vomiting
What is a buffer?
Molecule that can reversibly bind (or release) free H+, reducing amount of free H+ in solution, stabilizing pH Note: buffers do not prevent pH from changing, they only help to minimize pH change until free H+ removed from body by the lungs or kidneys
What is a base?
Molecule that will ACCEPT a H+
What is an acid?
Molecule that will RELEASE hydrogen atoms when put into solution
What does a high H+ concentration mean?
More acidic, lower pH
What does a low H+ concentration mean?
More basic/alkaline, higher pH
What are examples of intracellular buffers?
Phosphates Intracellular proteins (hemoglobin)
What does a hydrogen atom consist of?
Single proton and single electron (thus, electrically neutral)
What will the metabolic breakdown of various proteins produce?
Sulphuric acid, phosphoric acid, lactic acid, other organic acids (non-volatile acids)
What is the relationship between pH, H+ concentration, and the acidity of solution?
The more free H+ in solution, the more acidic, the lower the pH
When will death occur with regards to acid-base balance?
When pH is below 6.8 or above 7.8 for a long period of time
What is the respiratory system's principle function?
To remove CO2, keeping levels of gas constant, thus helping to keep pH of blood constant
What is the general reaction between buffer and free H+?
X + H+ <--> XH