Kidney Function and Fluid and Electrolyte Balance Flashcards
List the functions of the kidney?
Remove metabolic waste from extracellular fluid (urea, acids)
Control the volume of extracellular fluid (link to BP)
Maintaining optimal concentrations of vital solutes in the extracellular fluid (Na, K, H, Ca, Mg, Cl, Phos)
Vitamin D metabolism as its involved in the 2nd hydroxylation step to convert it to active vitamin D
Erythropoitein secretion from interstitial cells of the kidney
What is the composition of the extracellular fluid dependant on?
Salt intake
Water intake
Salt and water loss (sweat, gut)
Name and briefly describe the 3 processes of the nephron?
Glomerular filtration: Filtering of blood into tubule forming the glomerular primary filtrate.
Tubular Reabsorption: Selective absorption of substances from the tubule to blood.
Tubular secretion: Secretion of substances from blood to tubular fluid.
Describe the structure of the Glomerulus?
Mesangium supports capillaries.
Glomerular filtration barrier has unique endothelium, collagen BM and podocytes.
Endothelial cells have fenestration.
Podocytes had foot processes to provide a large surface area and gaps for filtrate to come through.
The filtration barrier is a size selective sieve.
What is the normal glomerular filtration rate?
100ml/min = 144L per day
Describe the Countercurrent Exchange Multiplier?
As the filtrate reaches the descending loop, the concentration increases as water exits to the interstitium as it is freely permeable.
Tubular concentration then decreases as sodium is transported out the ascending loop via the Na/K/2Cl pump to the interstitum.
This movement of sodium makes the interstatium highly concentrated, creating the osmotic gradient for water exit in the descending.
The vasa recta uses countercurrent exchange so it doesn’t wash away the gradient.
How is glomerular filtration measured?
By eGFR as actual GFR is cumbersome to measure.
Creatinine is freely filtered at the glomerulus and is not reabsorbed. It is a waste product of muscle metabolism and is constant in individuals.
Creatine clearance = urine vol X urine [creatinine] / Plasma [creatinine]
What are the limitations of eGFR?
- Only an estimate and extreme/unusual body compositions can skew results, e.g. body builders, those with muscle wasting.
- GFR is lower in the older population.
- Creatinine has an exponential relationship with GFR, so creatinine may not initially be changed, but there may be kidney damage and it will later drop quickly.
- Only a good measure in constant conditions where GFR is not changing much.
List causes of chronic obstruction to bladder outflow?
BPH
Bladder stones
Kidney stones
Bladder tumours
What is hydronephrosis?
Dilation of the renal pelvis and calyces due to urine build up. It also causes the ureters to be backed up and lose their peristaltic function.
Untreated it leads to progressive atrophy and renal impairment.
Can be graded 1-4 depending on severity.
Describe the role of the kidney in Vitamin D metabolism?
Vitamin D goes through 2 hydroxylation steps to become active. This first is in the liver, and the second is in the kidney, which is influenced by PTH.
What role does vitamin D have in the body?
1,25 DHCC stimulated calcium absorption in the intestine.
Describe the role of the kidney in EPo production?
EPo is produced by the kidney under hypoxic conditions by fibroblast-like cells in the renal interstitium.
Loss of renal function can lead to decreased EPo function and therefore lead to anaemia.
Recominant human EPo can by biosynthesised and can be used in patients with CKD.
List some complications of kidney failure?
If cant excrete fluid then fluid build up e.g. pulmonary oedema or peripheral oedema.
Can affect heart function. On ECG get bizarre QRS complex and loss of P wave.
What can constrict the afferent arteriole of the golmerulus?
Sympathetic NS and prostaglandins (hence why NSAID’s can affect kidney function through impaired prostaglandins).
