Flashcards in Potassium Disorders Deck (49)
Where is 60-65% of the filtered Na, CL, and H2O reabsorbed in the nephron?
in the proximal convoluted tubule
Where is the remainder 25-35% of NaCl reabsorbed besides in the PCT?
in the ascending loop of henle
What is the role of principle cells
Reabsorb Na+ and Cl- (remaining 5%) and secrete K+ under the control of aldosterone
What is the role of the intercalated cells?
Secrete H+, reabsorb H+, and in the case of metabolic alkalosis, secrete HCO3-
Antidiuretic hormone stimulates...
reabsorption of water in the collecting duct
Where is almost all the filtered glucose and amino acids reabsorbed in the nephron?
in the PCT
What is secreted in the PCT?
urea, uric acid, creatinine, and some drugs
What is the TOTAL list of things that are reabsorbed in the PCT from the filtrate? (10+ things)
- amino acids
- uric acid
Where are H+ and NH3+ secreted in the nephron?
in the PCT and the collecting duct
What is the normal serum potassium level?
Potassium is the most abundant _____ cation?
Why can both hypo and hyperkalemia cause muscle paralysis and cardiac arrhythmia?
because the balance of high ICF and low ECF is required for normal membrane potential
What is the average daily intake of K+ and how much is excreted?
50-150 mEq, allof which needs to be excreted
- 90% excreted in the urine and 10% in stool
Since renal excretion of K+ takes hours to adjust in situations of changing K+ levels, how does the body respond rapidly to dangerous levels of K+?
through the Na/K/ATPase which is present on all cells and can buffer small changes in ECF levels of K+
What two factors stimulate K+ uptake into cells following ingestion?
Insulin and ß-adrenergic catecholamines
What % of potassium is in the ECF? in the urine?
1-2% both in the ECF and urine given that it is freely excreted
Which process, secretion or reabsorption, controls excretion of K+?
- despite K+ levels, most of the filtered K+ is reabsorbed in the PCT and ALH
- principal cells in the CT control excretion
~65-75% of filtered K+ is reabsorbed in the.... by...
PCT by paracellular diffusion driven by high intratubular concentration gradients caused by H2O reabsorption following Na+
- basically solvent drag
How is K+ reabsorbed in the ascending loop of henle? (15-25%)
In the NaK2Cl co-transporter
What are the 4 main factors that impact K+ secretion?
- tubular flow rate
- luminal delivery of Na
- acid/base status
Where is the main site of K+ secretion?
In the cortical collecting duct
How does aldosterone impact K+ secretion?
High K and hypovolemia trigger aldosterone secretion from the adrenal glands
This causes an increase in Na reabsorption and K secretion by acting on the principal cells:
- increasing rate of Na/K/ATPase
- increasing the # and activity of ENaC channels on the luminal membrane
- stimulates ROMK K+ channels on the luminal membrane
How does tubular flow rate impact K+ secretion?
High urinary flow rate past functionally decreases the luminal [K+] in the distal tubule and therefore increases the ECF/ICF concentration gradient and facilitates excretion from the principal cells
How does the [Na+] in the distal tubule?
the more Na that reaches the DCT, the more that an be reabsorbed by the principal cells and exchanged for K
How does acid/base status impact K+ excretion?
in the case of metabolic alkalosis where there is low [H+], more H+ will be reabsorbed and exchanged for K+ at the basolateral side of the principal cell
In the case of acidosis, there will be increased H+ secretion and K+ reabsorption at the H/K ATPase on the intercalated cells
What is the serum potassium level considered to be hyperkalemic?
>6mEq/L is potentially dangerous
>6.5 mEq/L + symtoms is an emergency
what are the typical clinical manifestations of hyperkalemia?
weakness, nausea, paresthesias, palpitations, arrhythmias
What are the typical ECG findings associated with hyperkalemia?
- peaked T waves
- prolonged PR interval
- widened QRS
- loss of P wave
- sinewave pattern
Hyperkalemia is most often due to which causative process?
impaired renal autoregulation in the context of AKI (and CKD?)