Solute Homeostasis Flashcards
What percentage of sodium filtered by the kidneys is reabsorbed?
99%
What would be done to counteract an increase in ECF sodium concentration?
ADH secretion and water retention
What would be done to counteract a decrease in ECF sodium concentration?
Water excretion
What stimulates release of renin?
Decrease in blood pressure which decreases the stimulation of stretch receptors
Sympathetic stimulation to granular cells
Decrease in salt delivery to macula densa which results in paracrine release
Describe the renin angiotensin aldosterone pathway
Renin stimulates conversion of angiotensinogen into angiotensin I
Angiotensin I is converted into angiotensin II
Angiotensin II stimulates aldosterone release
What are the systemic effects of the RAA system?
Vasoconstriction to increase blood pressure
ADH release
Increased thirst and salt appetite
What are the renal effects of the RAA system?
Decreased glomerular filtration
Increased tubular reabsorption
What causes decreased glomerular filtration in response to RAA?
Efferent vasoconstriction
Mesangial cell contraction decreases filtration area
What causes increased tubular reabsorption of sodium in response to RAA?
Increase Na/K/ATPase activity
What stimulates release of aldosterone?
Angiotensin II
Hyperkalaemia
What is the role of aldosterone?
Increased transcription of ENaC and ROMK channels to increase sodium reabsorption and decrease potassium secretion
What is the role of serum glucocorticoid kinase? How is it stimulated?
Stimulated by aldosterone
Increases ENaC and ROMK activity
Increases sodium reabsorption
Decreases potassium secretion
Increases hydrogen ion secretion in collecting duct
Increases sodium reabsorption in gut and sweat glands
Where is atrial natriuretic peptide released from?
Right atrium
What stimulates atrial natriuretic peptide release?
Increased pressure in right atrium
What are the effects of atrial natriuretic peptide?
Closure of ENaC channels Inhibition of Na/K/ATPase Inhibition of aldosterone secretion Inhibition of renin secretion Afferent arteriole vasodilation Inhibits Na/H exchanger
How does potassium transport differ between the PCT & loop and DCT & duct?
Potassium transport in the PCT and loop is constitutive
It can be altered in the DCT and duct
What causes hypokalaemia?
Diarrhoea
Vomiting
Hyperinsulinemia
Fluid replacement without potassium
What causer hyperkalaemia?
Acidosis
Renal failure
Insulin deficit
Tissue death
What are the symptoms of hypokalaemia?
Muscle weakness
Dysrhythmia
Polyuria
Thirst
What are the symptoms of hyperkalaemia?
Muscle weakness
Dysrhythmia
What causes muscle weakness in hyperkalaemia?
The membrane has a higher resting potential which decreases the threshold, so the cell cannot return to true rest
What causes muscle weakness in hypokalemia?
A lower resting potential increases the threshold
How is potassium concentration regulated?
High potassium stimulates secretion of aldosterone which decreases potassium secretion
How does increased tubular flow increase potassium excretion?
Increase flow bends the cilia which allows a calcium influx by PKD1/2
Calcium influx activates ROMK channels so more potassium is secreted
How are pH and potassium levels linked?
Proton secretion in intercalated cells is tied to potassium reabsorption
What hormones regulate calcium and phosphate levels?
Parathyroid hormone
Calcitonin
Vitamin D
What stimulates release of parathyroid hormone?
Increasing serum phosphate
Decreasing serum calcium
What stimulates release of calcitonin?
Increasing serum calcium
What is the role of parathyroid hormone?
Stimulates vitamin D synthesis
Increases calcium resorption from bone
Increases renal calcium reabsorption by increasing TRPV5/6 activity
Decreases renal phosphate reabsorption by decreasing abundance of NPT2
What is the benefit of increasing renal calcium reabsorption while decreasing renal phosphate reabsorption?
Calcium phosphate is near the solubility limit, therefore if your add more calcium into the tubule then phosphate should be removed to prevent precipitation
What is the role of calcitonin?
Decreases renal phosphate reabsorption
Increases bone formation
Inhibits calcium resorption from bone
What is the role of vitamin D?
Increases renal calcium reabsorption by increasing TRPV5/6 abundance
Increases calbindin abundance
Decreases renal phosphate reabsorption
Describe calcium reabsorption in the collecting duct
Calcium diffuses into the cell from the tubule via TRPV5/6 channels
Some calcium is absorbed by calbindin
Calcium is then transported out of the cell by PMCa ATPase and Sodium Calcium exchanger
Describe potassium reabsorption in the proximal tubule
Na/K/ATPase sets up a sodium gradient
Phosphate is brought into the cell via cotransport with sodium
Phosphate is then exchanged on the basolateral membrane by an anion exchanger
How is magnesium reabsorbed?
Mostly paracellularly
