Renal Regulation of Ion Concentrations Flashcards
What is the normal extracellular level of potassium?
4.2 mEq/L
What happens when there is elevated potassium in the body?
Slightly elevated to 3 or 4 will lead to cardiac arrhythmia
higher concentrations can lead to cardiac arrest or fibrillation
What percent of extracellular fluid does potassium make up?
2%
What is the normal intracellular concentration of potassium ions?
140 mEQ
What are the total amounts of potassium in the body compartments?
Extracellular= 4.2 mEQ/L x 14 L= 59 mEq
Intracellular=140 mEQ/L x 28L = 3920 mEq
What are the major factors that are responsible for potassium excretion?
- increased potassium concentration in the distal renal tubules and the collecting ducts
- aldosterone secretion
Describe the relationship between potassium and aldosterone.
Increased extracellular potassium stimulates increase in aldosterone secretion
Where are the sites of potassium reabsorption?
proximal tubule
ascending limb of Henle
Where are the sites for potassium secretion?
Late tubule and collecting duct
What is in charge of potassium secretion and sodium reabsorption and secretion?
Principal cells; stimulated by potassium concentration and aldosterone
Describe the relationship between the potassium concentration and the aldosterone secretion levels
A small change in the potassium concentration will cause large changes in the aldosterone secretion by the adrenals
Describe the process of the high potassium levels leading to potassium excretion
Increased potassium intake leads to increased plasma concentration
This leads to an increase in aldosterone and an increased potassium section in the cortical collecting tubules
Leads to increased potassium secretion
Which two channels allow the sodium to leave the cell?
BK (big potassium channel) and ROMK (renal medullary potassium channel)
What happens to the regulation of potassium concentration if the aldosterone system is blocked?
It impairs the regulation and the plasma potassium concentration sky rockets
What are conditions that cause an increase in tubular flow rate ?
- volume expansion
- high sodium intake
- some diuretics
Describe the relationship between a high potassium diet and tubular flow
a high potassium diet greatly enhances the effects of increased tubular flow rate in order to increase the K+ secretion
Describe the relationship between a high sodium intake and the renal excretion of potassium
- increased sodium intake leads to a decrease in aldosterone which leads to decreased potassium secretion in the cortical collecting ducts which leaves to an unchanged potassium excretion
- increased sodium leads to an increased GFR which increases distal tubular flow rate which leads to increased potassium secretion in the cortical ducts which will lead to potassium secretion but will have little effect on the potassium excretion
- increased sodium intake will lead to a decreased reabsorption of sodium in the proximal tubule. This will lead to an increased distal tubular flow rate which will increase the K+ secretion in the collecting ducts but will have little effect on the potassium secretion
Describe the relationship bettie a high sodium/low potassium diet and a low sodium/high potassium diet
???
Describe the role of PTH in the renal system
Helps to maintain an extracellular concentration of calcium
What percent of the total plasma calcium is in the ionized form?
50%; ionized form gives it biological activity at the cell membranes
Describe calcium binding in acidosis and alkalosis
in acidosis less calcium is bound to the plasma proteins
in alkalosis, more calcium is bound to the plasma proteins
Describe the calcium in the body. Where is it stored? Where is it excreted?
It is stored in the bone and excreted in the GI tract
When are the parathyroid glands stimulated?
low calcium levels, increased PTH secretion
Describe the effects of PTH on the body
stimulates bone reabsorption
stimulates the activation of vitamin D
increases the tubular calcium reabsorption
Describe the reabsorption of calcium in the proximal tubule
- 99% of filtered calcium is reabsorbed
- 65% via paracellular and 20% via the trans cellular route
Describe the reabsorption of calcium in the loop of henle
-restricted to the ascending limb
50% of the reabsorption occurs in the paracellular route via passive diffusion
50% via the transcelluar route that is stimulated by the PTH
Describe the reabsorption of calcium in the distal tubule
-active transport via the calcium ATPase pump in the basolateral membrane and is stimulated by PTH
What are the factors that will increase the reabsorption of calcium which in turn decreases the calcium excretion?
Increased PTH levels
Increased plasma concentration of phosphate
Increased metabolic alkalosis
What is the transport maximum for phosphate?
0.1 mM/min
Describe phosphate reabsorption in the renal system
75-80% is reabsorbed in the proximal tubule (trans cellular)
10% is reabsorbed in the distal tubule
What is the role of PTH in reabsorption of phosphate
increased phosphate in the extracellular fluid
greater loss of phosphate in the urine
What is in charge of regulating extracellular potassium?
- insulin
- aldosterone
- catecholamines
- metabolic acidosis and alkalosis
- cell lysis
- strenuous exercise
- increased extracellular fluid osmolarity
Describe the role of insulin in regulating potassium
stimulates potassium uptake in the cells
Describe the role of aldosterone in potassium regulation
increases the potassium uptake by the cells, stimulates the reabsorption of Na+ via the NA/K ATPase, increases permeability of luminal K+ and increases the extracellular potassium concentrations
Describe the role of catecholamines in regulating potassium
B-adrenergic stimulation(epinephrine); stimulates the potassium uptake by cells
or B adrenergic blockers which leads to hyperkalemia
Describe the effects of metabolic alkalosis and acidosis on the extracellular potassium concentrations
- In metabolic acidosis, there will be an increase in extracellular potassium because there will be an increase of H+ ions which will lead to a reduction int he NA/K ATPase pump which will lead to a decreased cellular uptake of K+
- metabolic alkalosis will lead to a decreased extracellular potassium concentration
Describe hypokalemia
excess secretion of aldosterone (Conns syndrome)
Describe hyperkalemia
deficiency in aldosterone secretion (addison’s disease)
What is the rate of the potassium filtration?
180L/day x 4.2 mEq/L= 756 mEq/day
What is the rate of potassium reabsorption?
65% in the proximal tubule and 25-30% in the loop of Henle
What are the 3 processes that determine the renal potassium excretion?
- rate of potassium filtration
- rate of potassium reabsorption
- rate of potassium secretion
Where are principal cells found?
in the late distal tubule and the cortical collecting ducts; 90% in these regions
Describe the secretion of potassium from the principal cells including the control of potassium secretion and the act of secretion.
Controlled by the activity of the NaK pump, electrochemical gradients, and the permeability of the membrane
secretion is acheieved via the pump and the diffusion of potassium into the lumen
What are the factors that stimulate secretion of K+?
- increased extracellular K+ concentration (stimulates the pump, increases the potassium gradient, and stimulate aldosterone secretion)
- increased aldosterone
- increased tubular flow rate
Describe intercalated cells
Reabsorb K+ during K+ depletion via the HK ATPase pump
secrete H+ into the lumen
Describe what happens with lower than normal and a higher than normal level of extracellular fluid volume
Lower- death
higher- edema
What happens to arterial pressure with the angiotensin is blocked?
Arterial pressure will decrease BUT it will still increase with an increased sodium intake and output
