Ch 26: Electrolytes Part 2 Flashcards
What is the importance of K+ balance?
- Affects RMP in neurons and muscle cells
What occurs if ECF of [K+] increases?
RMP decreases causing depolarization reducing excitability
What occurs if ECF of [K+] decrease?
Hyperpolarization and nonresponsiveness
What is too much K+?
Hyperkalemia
What is too little K+?
Hypokalemia
What controls K+ balance in cortical collecting ducts?
Regulating amount secreted into filtrate
What is the K+ ECF levels when acidodic?
Rise
What is the K+ ECF levels when alkalodic?
Fall
What in the most important factor of affecting K+ secretion?
Concentration in ECF
What occurs during a high K+ diet?
Increase K+ content of ECF → K+ entry into principal cells → K+ secretion
What occurs during a low K+diet?
Reduces it secretion
How does aldosterone influence K+ balance?
Stimulates K+ secretion (and Na+ reabsorption) by principal cells
What is ECF Ca2+ important for?
- Blood clotting
- Cell membrane permeability
- Secretory activities
- Neuromuscular excitability
How much of the calcium in body is in the bones?
99%
What is caused by hypocalcemia?
Increased excitability and muscle tetany
What occurs during hypercalcemia?
Inhibits neurons and muscle cells causing arryhthmias
What hormone controls calcium balance?
PTH
What are the targets of PTH?
- Bones: osteoclasts breaking down matrix
- Kidneys: increase calcium reabsorption
- Small intestine: increases calcium absorption
How much of calcium is reabsorbed due to PTH?
98%
What hormone affects phosphate reabsorption?
Insulin: increase
Glucagon: decrease
How much of Cl- is reabsorbed?
99%
What is the purpose of Cl-?
Helps maintain osmotic pressure of blood
What is the purpose of acid-base balance?
pH affects all functional proteins and biochemical reactions
What is the pH of the arterial blood?
7.4
What is the pH of the venous blood and IF fluid?
7.35
What is the pH of the ICF?
7
What is alkalosis?
pH > 7.45
What is acidosis?
pH < 7.35
What process produce H+?
- Phosphorus-containing protein breakdown releases phosphoric acid into ECF
- Lactic acid from anaerobic respiration of glucose
- Fatty acids and ketone bodies from fat metabolism
- H+ liberated when CO2 converted to HCO3– in blood
What systems regulate H+?
- Chemical buffer systems
- Brain stem respiratory centers
- Renal mechanisms
What is the chemical buffer system?
- Strong acids dissociate completely in water; can dramatically affect pH
- Weak acids dissociate partially in water; are efficient at preventing pH changes
- Strong bases dissociate easily in water; quickly tie up H+
- Weak bases accept H+ more slowly
What is a chemical buffer?
System of one or more compounds that act to resist pH changes when strong acid or base is added
What are examples of buffer systems?
- Bicarbonate buffer system
- Phosphate buffer system
- Protein buffer system
What is the bicarbonate buffer system?
- Mixture of H2CO3 (weak acid) and salts of HCO3– (e.g., NaHCO3, a weak base)
- Buffers ICF and ECF
- Only important ECF buffer
What happens in the bicarbonate buffer system when strong acid is added?
pH decreases only slightly, unless all available HCO3– (alkaline reserve) used up
What happens in the bicarbonate buffer system when strong base is added?
pH rises slightly, H2CO3 supply is almost limitless
What is the importance of the phosphate buffer system?
Effective buffer in urine and ICF when phosphate is high
What are sodium salts of the phosphate buffer system are created from?
- Dihydrogen phosphate (H2PO4–), a weak acid
- Monohydrogen phosphate (HPO42–), a weak base
What is amphoteric?
Both weak acid and base
What is the importance of intracellular proteins?
Most plentiful and powerful buffers
What is the importance of respiratory and renal systems?
- Regulate amount of acid or base in body
- Act more slowly than chemical buffer systems
- Have more capacity than chemical buffer systems
How does the body eliminate excess acids and bases?
- Lungs eliminate volatile carbonic acid by CO2
- Kidneys eliminate nonvolatile (fixed) acids
- Kidneys also regulate blood levels of alkaline substances; renew chemical buffers
What occurs during CO2 unloading?
Reaction shifts to left (and H+ incorporated into H2O)
What occurs during CO2 loading?
Reaction shift to right (and H+ buffered by proteins)
What occurs when hypercapnia activates medullary chemoreceptors?
Increased respiratory rate and depth
What occurs when there is a rise of plasma H+ activates peripheral chemoreceptors?
- Increased respiratory rate and depth
- More CO2 is removed from the blood
- H+ concentration is reduced
What occurs when alkalosis depresses the respiratory center?
- Respiratory rate and depth decrease
- H+ concentration increases
What is caused by hyperventilation?
Alkalosis
What is caused by hypoventilation?
acidosis
What is the paupers of Renal Mechanisms of Acid-Base Balance?
- Conserving (reabsorbing) or generating new HCO3–
- Excreting HCO3–
- Reabsorb bicarbonate
- To excrete excess bicarbonate
Where does H+ secretions occurs?
PCT and collecting duct type A intercalated cells
What does renal regulation depend on?
Kidney’s ability to secrete H+
What occurs when the rate of H+ secretion changes with ECF CO2 levels?
Increase CO2 in peritubular capillary blood leading to the increase rate of H+ secretion
How is alkaline reserves maintained?
- kidneys must replenish bicarbonate
- Tubule cells cannot reabsorb bicarbonate
- Must conserve filtered bicarbonate in roundabout way
What occurs during bicarbonate reabsorption?
- CO2 combines with H2O within the tubule cell forming H2CO3
- H2CO3 is quickly split forming H+ and HCO3-
- H+ secreted into the filtrate
- H+ secreted, HCO3 entered the peritubular capillary blood either support with Na+ or anti port with Cl-
- Secreted H+ combines with HCO3- in filtrate, forming carbonic acid.
- The H2CO3 formed in the filtrate dissociates to release CO2 and H2O
- CO2 diffuses into the tubule cell, where it triggers further H+ secretion
What is the most important urine buffer?
Phosphate buffer system
What occurs during the excretion of buffered H+?
- CO2 combines with water within the type A intercalated cell forming H2CO3
- H2CO3 is quickly split forming H+ and bicarbonate ion
- H+ is secreted into the filtrate by a H+ ATPase pump
- For each H+ secreted a HCO3- entered the peritubular capillary blood via an anti port carrier in a HCO3-, Cl- exchange process
- Secreted H+ combines with HPO42- in the tubular filtrate forming H2PO4-
- The H2PO4- is excreted in the urine
What occurs during ammonium ion excretion?
- PCT cells metabolize glutamine to NH4+ and HCO3-
- This weak acid NH4+ is secreted into the filtrate, taking the place of H+ on a Na+H+ anti port carrier
- For each NH4+ secreted a bicarbonate ion enters the peritubular capillary blood via a support carrier
- The NH4+ is excreted in the urine
What causes respiratory acidosis and alkalosis?
Caused by failure of respiratory system to perform pH-balancing role
Single most important indicator is blood PCO2
What causes metabolic acidosis and alkalosis?
All abnormalities other than those caused by PCO2 levels in blood; indicated by abnormal HCO3– levels
What occurs the if PCO2 above 45 mm Hg?
Respiratory acidosis
What occurs if PCO2 below 35 mm Hg?
Respiratory alkalosis
What causes metabolic acidosis?
- low blood pH and HCO3 for too much alcohol
- Excessive loss of HCO3-
- Accumulation of lactic acid, ketosis, starvation, and kidney failure
What causes metabolic alkalosis?
Rising blood pH and HCO3-
What occurs if blood pH is below 6.8?
Depression of CNS causing coma or death
What occurs if the blood pH is above 7.8?
Excitation of NS leading to muscle tetany, convulsions, or death
How is respiration affected by metabolic acidosis?
High H+ levels stimulate respiratory centers elevating breathing
How is respiration affected by metabolic alkalosis?
Shallows and slows breathing
How does the renal system compensate for respiratory acidosis?
Renal compensation indicated by high PCO2 (causes acidosis) and HCO3– levels (indicates kidneys compensating)
How does the renal system compensate for respiratory alkalosis?
Exhibits low PCO2 and high pH
Renal compensation is indicated by decreasing HCO3– levels
What occurs during acid-base imbalances?
- Respiratory system cannot compensate for respiratory acidosis or alkalosis
- Renal system cannot compensate for acid-base imbalances caused by renal problems
