Renal & Electrolytes UWorld Flashcards
Why are patients on thiazides more likely to become hyponatremic compared to those taking loop diuretics?
The loop diuretics prevent reabsorption of salt in the ascending loop of Henle and disrupt the normal corticomedullary gradient. This results in significant water and salt loss. Thiazides do not affect the corticomedullary gradient and patients respond more to increased vasopressin levels, retain more water and are at higher risk of hyponatremia.
Light microscopy, electron microscopy and immunofluorescence in patients with post-strep glomerulonephritis?
LM = hypercellularity EM = sub-epithelial humps IF = lumpy-bumpy IgG, IgM and C3 deposits
Layers of the anterior abdominal wall
Skin Camper's fascia Scarpa's fascia External oblique Internal oblique Transversus abdominis Transversalis fascia Extraperitoneal fat Peritoneum
A) Substances that are freely filtered by the glomerulus without absorption or secretion?
B) Substances with net reabsorption?
C) Substances with net secretion?
A) Manitol and inulin
B) Glucose, Na and BUN
C) PAH and creatinine
Where is BUN reabsorbed and secreted in the nephron?
Reabsorbed: PCT & medullary collecting duct
Secreted: thin loop of Henle
What is used to calculate renal plasma flow?
PAH. It is freely filtered, more is secreted than is filtered and not reabsorbed.
Congenital abnormalities that can result from failure of the urachus to obliterate?
Patent urachus = attachment of bladder to umbilical cord
Vesicourachal diverticulum = asymptomatic out pouching at the apex of the bladder
Urachal sinus = failure to close the distal urachus resulting in recurrent infections
Urachal cyst = fluid filled cyst between the two obliterated ends of the urachus between the navel and bladder
Baby with meconium coming from his belly button
Persistent vitelline duct (yolk sac). Partially obliterated vitelline duct results in a Meckel diverticulum.
Most common viral cause of acute hemorrhagic cystitis in children
Adenovirus
2nd most common cause of UTI in sexually active women
S. saprophyticus
Hyper acute, acute and chronic kidney transplant characteristics
Hyperacute: preformed antibodies, within minutes to hours
Acute: C4b deposition, PMNs, lymphs and vasculitis less than 6 months after transplant
Chronic: vascular wall thickening, fibrosis and atrophy months to years after transplant
Drugs for renal transplant patients that can cause renal arterial hyalinization, tubular vacuolization and reduced renal blood flow.
Calcineurin inhibitors: tacrolimus and cyclosporine
Embryonic kidney development
Pronephros: forms and completely regresses by 5 weeks
Mesonephros: gives rise to the vas deferens, epididymus and Gartner’s ducts in women.
Metanephric diverticulum: ureteric bud sprouts off mesonephros. It penetrates into the sacral intermediate mesoderm and induces surrounding tissue to differentiate into the metanephric mesoderm (blastema). The metanephric blastema then causes the ureteric bud to differentiate into the collecting system.
Metanephric blastema: gives rise to the glomerulus, PCT and DCT.
Content inside granules of eosinophils
Major basic protein
Causes of metabolic alkalosis that are saline responsive?
What types are not saline responsive?
Saline-responsive: vomiting/NG (low urine Cl) and prior diuretic use (high urine Cl) deplete the body of Cl-. This prevents HCO3- excretion and promotes H+ excretion.
Saline-non-responsive: Bartter, Gitleman and excess mineralocorticoid receptor stimuli
What enzyme is critical for DNA synthesis in bacteria and is involved in the incorporation of uracil into DNA?
Primase. It synthesizes the RNA primers at the replication fork that are necessary before DNA polymerase III can continue replication away from the replication fork.
Enzyme that repairs single-stranded breaks in DNA
Ligase
Enzyme that is primarily responsible for synthesis of the daughter strands in DNA replication
DNA polymerase III
Enzyme that is responsible for replacement of RNA primers with DNA bases
DNA polymerase I has 5’->3’ exonuclease activity that allows it to remove the RNA bases and replace them with DNA bases
What allows DNA polymerase I and III to repair mismatched bases in newly formed daughter strands?
3’->5’ exonuclease proofreading function
Enzymes involved in unwinding DNA during replication
Helicase unwinds it at the replication fork, topoisomerase II relieves the downstream tension secondary to unwinding the double helix
Why must you be cautious when prescribing ACE-I to patients with renal artery stenosis?
ATII is necessary to maintain renal perfusion pressure. When ATII is blocked, renal perfusion pressure can drop and the patient can develop acute kidney injury.
Mechanism of Henoch-Schoelin purpura
Post-infectious IgA immune complexes result in leukocytoclastic vasculitis and deposit in vessel walls (palpable purpura), GI tract (hematochezia), kidneys (IgA nephropathy) and joints (arthralgia).
Taking what class of drugs would decrease the response of your patient to loop diuretics?
NSAIDs. Loops also increase prostaglandin release, dilating blood vessels and increasing drug delivery to the target site. NSAIDs inhibit prostaglandin synthesis and limit this effect.
How does the tonicity of tubular fluid change as you progress through the nephron?
PCT: isotonic because water is passively reabsorbed
Descending loop of Henle: hypertonic due to its impermeability to Na+, but permeability to H2O and hypertonicity of medulla
Ascending loop of Henle: becomes hypotonic due to impermeability to H2O, but transport of Na, K and Cl out of tubule.
DCT: lower water permeability generally means hypotonic fluid, however, this region is dependent on vasopressin
CD: hypertonic in presence of ADH due to increased H2O permeability, hypotonic in absence of ADH due to decreased H2O permeability
Substances that can be used to calculate GFR and renal plasma flow (RPF)?
GFR = inulin and creatinine RPF = PAH
Clearance = [urine] x (flow rate/[plasma])
How to calculate filtration fraction. Normal value?
GFR/RPF. Normal value ~ 20%.
How does diabetic nephropathy occur?
1st morphologic changes = GBM thickening and mesangial matrix deposition
1st clinical changes = upregulation of heparinase, degradation of heparin sulfate in GBM, proteinuria and increased GFR
In later stages Kimmelstein-Wilson nodules form, GFR drops dramatically and patients develop nephrotic syndrome
Triggers of minimal change disease and characteristic EM findings?
Immunization, bee stings and allergies can cause. EM shows podocyte foot process effacement.
Membranoproliferative glomerulonephritis LM and EM findings
LM = hypercellularity EM = splitting of GBM due to sub endothelial immune complex deposition
Membranous nephropathy EM findings
Sub epithelial spikes
Post-strep GN LM, EM and IF findings
LM = diffuse hypercellularity. EM = Sub epithelial humps composed of IgG and C3 that luminesce on IF
Causes of secondary hyperaldosteronism
Anything that elevates renin: reninomas, renal artery stenosis, diuretics and malignant hypertension.
BPH treatment
alpha-1 blockers to relax smooth muscle in bladder neck
5-alpha-reductase inhibitors to prevent hormone-mediated hyperplasia by inhibiting conversion of testosterone to dihydrotestosterone
Why give thiazides to patients with recurrent Ca-based stones
Inhibition of the apical Na/Cl cotransporter in the DCT results in decreased intracellular Na, then activation of the basal 3Na/Ca transport, then Ca leaves the tubular cell and increased amounts of Ca are absorbed into the tubular cell from the tubular lumen, thus decreasing tubular [Ca].
Hypovolemia from diuretics increases Na and H2O reabsorption in the PCT. This also increases paracellular reabsorption of Ca.
Regions of the nephron particularly susceptible to ischemic injury?
PCT and ascending loop of Henle because the participate in high levels of active transport requiring ATP. The medulla is also susceptible due to low blood supply compared to the rest of the kidney.
Mechanism of calcineurin inhibitor toxicity
They cause dose dependent vasoconstriction and tubular damage, resulting in hypertension and acute kidney injury. This can be precipitated by patients drinking grapefruit juice because CYP3A is inhibited by grapefruit juice and calcineurin inhibitor levels rise.
Rule of thumb in predicting GFR from serum creatinine?
Every time the creatinine doubles, cut the GFR in half. Note however, that large GFR losses above 60% will result in a relatively unchanged creatinine.
