Renal Physiology Flashcards
What are the three layers of the glomerular filtration barrier?
Endothelium
GBM
Podocytes
What is the function of the arterioles bordering the glomerulus?
Vaso-constriction and dilation = control blood flow, intraglomerular pressure and filtration
What factors affect the afferent arteriole of the glomerulus?
Dilate - prostaglandins, dopamine, ANP?BNP, NO
Constriction - Angiotensin 2 (very high conc), adrenaline (note more alpha 1 than efferent)
What factors affect the efferent arteriole of the glomerulus?
Dilate - prostaglandins, dopamine, NO
Constrict - angiotensin 2 (preferentially), adrenaline (note more alpha 1 receptors on afferent), ANP/BNP
Why is the combination of ACEi and NSAIDs considered nephrotoxic?
ACEi - reduces levels of angiotensin 2 - prevents constriction of the afferent/efferent arteriole -> preferential has a greater relative vasodilation of the efferent arteriole
NSAIDs - reduce prostaglandins -> inhibits dilation of the afferent/efferent arteriole
Leads to a reduced eGFR
Where in the nephron do different diuretics have an effect?
Osmotic - PCT and desc LOH
Loop - ascending LOH
THiazide - DCT
Potassium sparing - CT/DCT
What is the main role of the PCT in the nephron?
Reabsorbs 60% filtrate
Mostly passive
By channels - glucose, phosphate and amino acids
Without a channel - Bicarb
What is the main reabsorption at the LOH?
NKCC channel - counter current system
Absorbed Na2+, K+ and 2Cl-
What ions are absorbed paracellularly in the LOH?
Sodium
Calcium
Magnesium
What are the different steps in the counter current mechanism of the LOH?
- Ascending limb = NKCC2 -> reabsorbs Na, K, Cl -> inc conc of interstitium, dec conc of filtrate, is impermeable to water
- Descending limb is surrounded by the same interstitium
- Establishes an osmotic pressure gradient for water to move out of desc into the interstitium - inc conc of filtrate, interstitium decrease conc
Note overall affect is filtrate and interstitium remain the same concentration at the start and the beginning
What is the urine osmolarity in the LOH?
300 mosm/kg
What process in the collecting ducts contribute the interstitial osmolarity?
Urea reabsoprtion
What are the common causes of hypercalcaemia?
Cancer - multiple myeloma
Hyperparathyroidism
Iatrogenic - thiazides, calcium supplements
What are the key symptoms of hypercalcemia?
Polyuria, polydipsia, dehydration
Stones - kidney
Bones - pain and fracture
Graons - constipation and abdo pain
Moans - psychiatric and depression
How does hypercalcemia lead to dehydration?
High calcium activates the CaSR which inhibits the ROMK channels in the DCT
Reduced NKCC2 activity
Leads to increased conc Na+ in the filtrate -> higher filtrate osmolarity
Reduces paracellular absorption of H2O and water movement in the LOH (as medullary concentration gradient is diminished)
Leads to larger volume of more dilute urine = poluria -> dehdyration
What is the purpose of the anion gap equation?
Calculate the type of metabolic acidosis by finding the difference between the positive and negative ions
(Na+K) - (Cl+HCO3) = gap in mmol/L
What are the potential causes of a high anion gap metabolic alkalosis?
Renal - uraemia
Toxins - paracetamol, ethylene glycol
Lactate - ischaemia, sepsis, metformin
Ketones - alcohol, diabetic, starvation
What are the indications for dialysis?
Acidosis
Electrolyte imbalance - refractory hyperkalaemia
Intoxicants - lithium, salicylates
Oedema - refractory to diuretics
Uraemia - encephalopathy, pericarditis
What medications typically cause hyperkalaemia?
ACEi
MRAs (spiro)
What are the signs of hyperkalaemia on ECG?
Tall tented T waves
QRS widening
PR prolongation
P wave widening/flattening
Bundle branch/fasicular block
What are the potential treatments for hyperkalaemia?
Salbutamol nebs - symptomatic,
Calcium gluconate - cardiac membrane stabiliser - save life
Insulin/dextrose infusion
What second line treatments may be needed in hyperkalemia?
IV fluids - rehydration
Potassium binders - patiromer, Lokelma
IV bicarbonate -
What are some pre-renal causes of AKI?
Hypotension
Hypovolemia
Medications - ACEi, diuretics, genatamicin, NSAIDs, immunotherpay
What are some renal causes of AKI?
Glomerulonephritis
INterstitisl nephritis
What are some post renal causes of an AKI?
Prostate enlargement
External compression e.g cancer around ureter
VUJ obstruction
How to manage a patient with AKI and hyperkalemia?
Catheterise
Hold ACEi
IV fluids
Full round hyperK+ treatment
Antibiotics at renal dose
What is the key difference between crystalloids and colloids?
Crystalloids - solutes of electrolytes and water - saline, hartman, glucose
Colloids - human plasma derviates - human albumin solution - inc oncotic pressure, stop third spacing of fluids
