Urinary: Ion Regulation Flashcards
Describe the pH of the filtrate as it flows through the tubules?
- 7.4 when filtered
- 6.7 at the end of the PCT
- 4.5 - 8 at the collecting duct
What is the minimum urine pH?
4.5
What are the buffers of the urine that helps to control the H+ (pH) ?
(HPO4)2-
NH4+
Excess H+ removed by ammonia system as phosphate is only secreted at 25-30 mmol/d
What is the difference in acid-base status between vomitig and diarrhoea?
Vomiting
- Loss of H+
- Loss of K+
- Result in metabolic alkalosis
Diarhoea
- Loss of K+
- Loss of bicarbonate
- Results in metabolic acidosis
What are the side effects of furosemide?
- Contirbutes to chloride loss
- Also contribute to potassium, salt and water loss
What is the distribution of potassium in the body?
-Mostly intracellular
How does the body prevent excess potassium in the ECf?
- Quick K+ uptake into cells
- K+ excretion in urine
What increases 3Na+/2K+ ATPase activity?
- K+ concentration in plasma
- Insulin
- Noradrenaline effect on B2 arenoreceptors
What increases potassium movement out of the cell?
- High osmolality
- Acidosis
- Cell damage
- Exercise
What reduces potassium moving out of the cell?
Alkalosis
What increase potassium movement into the cell? 3Na+/2K+
- ECF (K+)
- Insulin
- B2 receptor agonists
- NA/Salbutamol
- Aldosterone
What inhibits potassium movement into cells?
- Digitalis
- Chronic disease
How is potassium excreted?
Under normal circumstance
- Small amounts of potassium are lost in faeces and sweat
- Kidney predominantly responsible for excretion in urine. 15 mmol/day
- Potassium is regulated by excretion not absorption
How is variable potassium excretion controlled?
- If plasma potassium concentration is low, less excretion in DCT and CD
- If plasma potassium concentration is high, more excretion occurs in DCT and CD
What causes increases potassium secretion?
- Increased intracellular K+
- Electronegative lumen
- Permeability of luminal membrane
- Decreased luminal K+
Explain the aldosterone paradox in volume depletion
- Aldosterone stimulates the ENaC channels
- Ang 2 inhibits ROMK
- Ang 2 stimulate NaCL channel
Explain the aldosterone paradox after consuming a big K+ load in a meal.
- Aldosterone stimulate ROMK and ENaC
- Decreased Ang2 so inhibits of NaCl
What is the effect of hypokalaemia on membrane potential?
- Low serum K+ leads to bigger K+ gradient between intracellular and extracellular compartment
- Depolarisation lead to increased excitability
- Risk of arrhythmia
What is the effect of hyperkalaemia on membrane potential?
- High serum K+ leads to smaller K+ gradient
- Decreased membrane excitability
- Risk of cardiac arrhythmias
What are the symptoms of hypokalaemia?
- Weakness
- Polyuria (low potassium causes ADH resistance)
- Constipation
- Arrhythmias
What are the causes of hypokalaemia?
- Reduced dietary intake
- Increased entry into cells
- Increased GI loss
- Increased urine loss
How is a patient with hypokalaemia assessed?
- History
- Fluid balance
- Acid base status
- If K+ loss unclear from the above then urine K+ excretion
How is hypokalaemia treated?
- Oral K+ supplement
- Slow IV potassium
What are the issues with calcium?
- Difficult to keep in solution
- Crystalization would occur without inhibitors at usual concentrations
- High calcium in urine can lead to kidney stones
What is the distribution of calcium in the body?
Mostly intracellular
Extracellular calcium is
- Protein bound (50%)
- Free ionised
- Complexed
What are the symptoms of hypocalcaemia?
Muscular
- Fatigue
- Muscle weakness
- Paraesthesia
- Tetany
- Laryngospasm
Neurological
- Irritabiliy
- Memory loss
- Confusion
- Hallucination
- Paranoia
- Long QT
What are causes of hypocealcaemia?
- Vit D deficiency
- Lack of PTH
- Reduced intake
- Malabsorption
- Pancreatitis
- Chronic diarrhoea
- Hypercalciuria
- Hyperphosphateamia
- Hypomagnesaemia
- ECF expansion
- Acidosis
- Loop diuretics
What is the function of magnesium in the body?
- Intracellular signalling
- Co factor for protein and DNA synthesis
- Control of neuronal activity in the brain
- Cardiac excitability
- Neuromuscular transmission
- Osteoblast proliferation and bone strength
How is the intake of magnesium controlled?
- Magnesium in diet absorbed by gut (30-50% absorbed)
- Some magenisu in gut secretions
- Some magnesia is lost in faeces
- If dietary intake or serum magnesium is low, Gut can increase absoroption to 80% of the daily intake
What are symptoms of hypomagnesaemia?
- Fatigue
- Muscle spasm
- Anxiety or Headache
- Headache
less than 0.4
- Cardiac dysrhtmias
- Hyperreflexia
- Tetany
- Seizures
- Hypokalaemia
- Hypocalcaemia
What are causes of hypomagnesaemia?
- Decreased intake
- Drugs (loop diuretic, thiazide diuretics)
- GI loss
- Renal loss (diuretics, polyuria)
- Miscellaneous (alcoholism)
What is the treatment for hypomagnesaemia?
- Oral magnesium salts
- Intravenous magnesium sulfate
When does hypermagnesaemia occur?
- Renal impairment
- Adrenal insufficiency
- Usually iatrogenic (IV magnesium, purgatives, babies born to mother given IV magnesium)