Renal Physiology III b Flashcards
(35 cards)
- Understand the factors that affect renal handling of potassium and secretion.
A
*Understand the renal handling of other ions (Ca, Mg, and Phosphate)
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*Understand the renal handling of cations, anions and peptides
A
Describe the regulation of potassium distribution. Where is K+ mostly found and why? How much of K is contained in ECF/
About 98% total body K+ is found INTRACELLULARLY due to Na/K+ ATPASE pump
K+ found within cells as this pump actively transports potassium into cell.
Because the amount of K+ in ECF is so SMALL, even small changes into or out of cells can produce Large changes in extracellular potassium concentration.
Explain why it is important to maintain extracellular concentration of potassium relatively constant? What are the main variables for extracellular potassium?
It is important to maintain extracellular concentration of potassium relatively constant because of Role of K+ in Nerve and Muscle excitability.
Extracellular potassium is a function of variables:
1. Total amount of K+ in the body
2. Distribution of K+ between the extracellular and intracellular fluid compartments
1st variable: function of amount of K+ ingested and excreted.
What is the range of extracellular potassium concentration in the blood?
range Extracellular K+ concentration in blood: 3.5 to 5.7 millimolar (small amount)
Define how sodium concentration and K+ concentration are regulated.
Sodium is regulated by reabsorptive process,
the amount of K+ in body is regulated by a Net SECRETORY process.
Most of the potassium is reabsorbed in proximal tubule, 20% reabsorbed in thick ascending limb via Na/K+ 2 Cl- co transporter.
Where is K+ mostly reabsorbed? What is another location potassium is reabsorbed and how? What occurs when there is increasesd K+ in blood?
Most of Potaassium is reabsorbed in the proximal tubule
20% K+ is reabsorbed in THICK ASCENDING limb via Na/K+ 2 Cl- co-transporter. Variability of how potassium is handled in nephron is through secretion
increased K+ potassium in blood, increase aldosterone, which increases potassium secretion. Increase dietary K+, increase K+ secretion.
What process occurs with K+ in thick ascending loop of henle and distal tubule/collecting duct? Which cells are more prevalent (alpha-intercalating disk or principle cells)?
K+ reabsorption is reabsorbed in Thick ascending loop of Henle as well as in alpha-Intercalated disk (distal convoluted tubule)
Principle cells- where K+ SECRETION occurs in collecting duct, where MOST REGULATION of K+ occurs.
Principle cells are MORE PREVALENT than alpha-intercalated cells.
Where is K+ most regulated?
K+ is most regulated in PRINCIPLE cells of Collecting duct.
What are the factors that affect regulation of K+ secertion?
Factors affecting Regulation of K+ secretion:
- plasma K+ concentration
- Aldosterone
- Flow of Tubular fluid
- Diuretics
- Acid-base Balance
Explain how plasma K+ concentration regulates K+ secretion?
Plasma K+ concentration:
When there is a high potassium diet ingested, it causes plasma potassium to increase which drives the uptake of potassium (from blood to inside cell) via Na-K-ATPase which drives potassium into tubular lumen (pee out K+)
How does K+ intake affect aldosterone release?
High Potassium INCREASES Aldosterone release from adrenal cortex.
High potassium intake (diet) will increase plasma K+ concentration which increases aldosterone plasma aldosterone and INCREASES K+ SECRETION by principal cells of cortical collecting ducts.
Due to high K+ secretion you will have HIGHER K+ EXCRETION.
Anything that increases aldosterone release, will have impact on increasing K+ secretion and excretion.
What will have a great impact on K+ secretion and excretion?
Anything that INCREASES Aldosterone release, will have impact on increasing K+ secretion and excretion.
so, HIGH levels of Angiotensin II, you will get hypokalemia, due to high Ang II leading to high Aldosterone and high level of K+ secretion (so less K+ in bloodstream)
What is hypokalemia?
Hypokalemia- occurs when there is a decrease in K+ in body due to having high Aldosterone and high level of K+ secretion/excretion.
heart failure can lead to this also, as an increase renin, lead to increase in ang II, aldosterone- lead to hypokalemia (decrease in potassium) as well
What occurs when you decrease plasma volume?
Decrease plasma volume, increase renin secretion, increase plasma renin, increase plasma Ang II and cause increase in Aldosterone, which increases tubular reabsorption of sodium and hence decreasing sodium excretion.
At the same time, when you increase plasma K you increase plasma aldosterone and increase Tubular Secretion of K+ leading to Increase in Potassium excretion.
What happens when you increase flow rate to cortical collecting duct?
When you increase flow rate to cortical collecting duct INCREASES K+ secretion in cortical collecting tubule. This is because flow rate ( more fluid moving per unit time) , tends to dilute the K+ concentration in luminal fluid and so enhances K+ gradient for secretion.
you’ll have more time to dilute K+ and have more K+ secretion.
INCREASE Flow Rate ALWAYS increases K+ Secretion, leading to high K+ Excretion
What can cause in increase in flow rate?
DIURETICS cause an INCREASE in flow rate.
Diuretics will cause increase fluid flow through nephron tubule, which will increase potassium secretion and excretion. This can often cause Hypokalemia (loss of K in body)
Can also think; As you increase flow rate, more Na+ is reabsorbed, so more K+ can be secreted).
how are Na, K+ and flow rate connected?
Increase flow rate, Increase Na+ that can be reabsorbed, so more K+ can be secreted)
What happens when you are given a Thiazide diuretic
If a loop of Henle diuretic or Thiazide diuretic (works on distal convoluted tubule) is given, it cause increased fluid delivery or increased flow to cortical collecting duct, which increase potassium secretion and hence excretion.
This Thiazide diuretic will cause a Decreased Na+ reabsorption. which will increase Na Delivery to collecting duct principal cells. This will cause enhanced Na reabsorption, but still increased K+ secretion.
Describe effect of acid-base changes on K+ secretion
Alkalosis (decrease in H+ ion in blood) will INCREASE potassium concentration in Principal cells of cortical collecting duct (alkalosis can increase activity of Na+/K ATPASE pump) which INCREASES K+ SECRETION and K+ Excretion. This later leads to K+ Depletion.
How does alkalosis increase K+ concentration in cortical collecting duct?
Alkalosis will increase the activity of Na+/K+ ATPASE pump, driving more K+ into the cell, ultimately driving more K+ secretion and excretion
What causes increase in flow rate, and what occurs as a result?
Diuretics increase flow rate. Increase in flow rate ALWAYS increases K+ secretion and excretion.
What happens when you eat a High Sodium diet?
Eating a High sodium diet, you will have High sodium will increase Extracellular fluid volume, which increases GFR. Increase GFR will increase Fluid delivery to macula densa, which will decrease Renin, which decreases Aldosterone. Decrease in Aldosterone will Decrease K+ secretion by cortical collecting ducts and leads to Unchanged K+ secretion and excretion.
In another scenario: High sodium diet can increase GFR and lead to increase in Fluid delivery to the cortical collecting ducts, which increases K+ secretion, and these factors balance to form unchanged K+ Secretion and excretion.
