renal lecture 5 potassiumm regulation and hydrogen ion regulation? Flashcards
What is the most abundant intracellular ion?
Potassium (K) is the most abundant intracellular ion.
98% Intracellular fluid
2% Extracellular fluid
Why is concentarion of K concentration important in extracellular fluid?
What is the resting potential of membranes related to?
-The K concentration in the extracellular fluid is extremely important for the function of excitable tissues (nerve and muscle)
-the resting membrane potentials of these tissues are directly related to the relative intracellular and extracellular K concentrations
What is hyper vs hypokalemia?
What do they both cause?
Hyperkalemia: high concentration of K in the extracellular fluid (>5 mEq/L)
Hypokalemia: low concentration of K in the extracellular fluid (<3.5 mEq/L)
-Both cause abnormal rhythms of the heart and abnormalities of skeletal muscle contraction.
What are the effects of hyperkalemia on the electrocardiogram?
-it can cause the heart to stop if K is equal to 8 or larger
How much potassium os excreted into urine vs feces and sweat?
When would we need to restrict sodium input?
-90% excreted into urine (adjusted via input)
-10% excreted into feces/sweat
-need to restrict the input if you have a kidney defiency?
Where is K freely filtered?
What do the tubules reabsorb most of?
-freely filtered at glomerulus
-tubules reabsorb most of this filtered K so that very little of the filtered K appear in the urine
What can K do unlike sodium or water?
What are changes in K excretion mainly due to?
-unlike sodium or water, K can be secreted at the cortical collecting ducts
- due mainly to changes in K secretion in the CCD (some in the
DCT)
What is normally the net reabsorption for K?
normally 86%
What is Na+ reabsorption coupled with?
-Na+ reabsorption coupled with K+ secretion
What is potassium secretion regulated by?
- Dietary intake of potassium
- Aldosterone
How is K+ regulated by dietary intake and aldosterone?
How does this affect pasma secretion and potassium excretion?
-high potassium increases aldosterone secretion
How does K+ secretion occur when the renin-aldosterone system is actiavted by other causes?
What occurs to plasma volume and Ag2 levels?
How does this affect aldosterone secretion, Na+ reabsorption and K+ secretion?
-
What is hyperaldosteronism?
What is its common cause?
-The conditions in which the adrenal hormone aldosterone is released in excess.
common cause: adenoma of the adrenal gland that produces aldosterone autonomously.
What are the symptoms of hyper aldosteronism?
Increased fluid volume, hypertension, hypokalemia.
Renin is suppressed. Metabolic alkalosis is often seen.
What are metabolic rxns highly sensitive to?
What concentration of extracellular fluid tightly regulated?
What is its pH?
-hydrogen ion concentration of the environment
-hydrogen ion concentraion
-pH: ~7.4 ([H+]: ~40 nmol/L
What is the equivalent of a bicarbonate ion being lost from the body?
What is the equivalent when a body gains a bicarbonate ion?
When bicarbonate ion is lost from the body, it is the same as if the body had gained a hydrogen ion
-when the body gains a bicarbonate ion, it is the same as if the body had lost a hydrogen iron
What are the sources of hydrogen ion gain and their equivalent loss?
- generation of H ion from Co2=hyperventilation (loss of Co2)
2.production of nonvolatile acids from the metabolism=using H ions in the metabolism
3.gain of H ions due to bicarbonate loss in diarrhea or other nongastric GI fluids=loss of H ions in vomit - gain of H ions due to bicarbonate in the urine= loss of H+ in urine
What are the 3 nonvolatile acids?
What is the average net production
Phosphoric acid (phosphate)
Sulfuric acid (sulfate)
Lactic acid (lactate)
-Average net production: 40-80 mmol of H+ per day
What is the defintion of a buffer?
What are most H ions buffered by?
What is pH equal to (formula)?
-Any substance that can reversibly bind hydrogen ions is
called a buffer.
- Most hydrogen ions are buffered by extracellular and intracellular buffers.
-pH=-log(H+)
What is normal ECF and what does it correspond to?
What happens to H+ concentrarion without buffering?
Normal ECF pH 7.4 corresponds to 40 nanomoles/L of H+
-Without buffering, hydrogen ion concentrations changes a
lot.
What is major extracellular vs intracellular buffer?
What does buffering not eliminate?
-Major extracellular buffer is the CO2/HCO3-system.
-Major intracellular buffers are phosphates and proteins
-Buffering does not eliminate hydrogen ions from the body. It only keeps them “locked up”
What is ultimate balance of H+ ion controlled by (what systems/part of body)?
What do the systems work together to do?
Respiratory system (by controlling CO2)
Kidneys (by controlling HCO3-)
-work together to minimize the change of hydrogen ion concentration (pH)
What are the renal mechanisms for H+ control for low H+ conc. vs high H+ conc.
-Low H+ concentration (high pH: alkalosis)—-> Kidneys excrete HCO3 (same as adding H+ to system)
-High H+ concentration (low pH: acidosis)—-> Kidneys produce new HCO3- and add to the plasma
What ratio gives you H+ concentration?
-ratio of bicarbonate and Co2 determines H+ conc.
What does H3O- excretion formula?
What do kidneys normally do for filtered HCO3-, when is there an exception?
Where is the transporter for HCo3-?
HCO3-excretion =HCO3- filtered (+ HCO3- secreted) - HCO3 -reabsorbed)
Normally, the kidneys reabsorb all filtered HCO3-
Exception: alkalosis
-on basolateral side
Where is the main HCO3- reabsorption?
80% in the proximal tubules
How do we add new HCO3- to plasma?
What can both processes be viewed as?
- by H+ secretion and excretion on nonbicarbonate buffers (such as phosphate).
- by glutamine metabolism with NH4+ excretion.
-Both processes could be viewed as H+ excretion by the kidney
What do kidneys normally contribute enough new HCO3- to the plasma to compensate for?
-to compensate for the hydrogen ions from nonvolatile acids generated in the body (40-80 mmol/day)
When does the first method of adding HCO3- to plasma only happen?
This happens only after all the HCO3- has been reabsorbedand is no longer available in the lumen
What is the 2nd method of adding HCO- to the plasma mainly take place?
What is this process also called?
-mainly in proximal tubule
-process is also called H+ excretion bound to NH3
