Renal

Question 1

The filtration fraction (FF)

Answer 1

FF = GFR/RPF

RPF = RBF * (1 - Hematocrit)

RPF = CLERANCE OF PAH
GFR = CLERANCE OF Creatinine OR INULIN

he clearance (C) of any given substance S can be calculated as:
Cs = ([Urine concentration of S] x [Urine flow rate]) / (Plasma concentration of S)

Question 2

renal acid excretion

Answer 2

The kidneys can normally compensate somewhat for metabolic acidosis by increasing renal acid excretion. The major mechanisms of increased renal acid excretion include:

Increased H+ secretion: Intracellular acidosis leads to a direct increase in H+ secretion via increased activity of the apical Na+/H+ exchanger.

Increased HCO3− reabsorption: Carbonic anhydrase in the proximal tubular lumen facilitates reabsorption of filtered HCO3−. Each reabsorbed HCO3− is equivalent to the secretion of one H+. In metabolic acidosis, HCO3- is completely reabsorbed from the tubular fluid.

Increased acid buffer excretion: Urinary acid buffers, hydrogen phosphate (HPO42−) and ammonia (NH3), are used to trap H+ in the lumen in the form of H2PO4- and NH4+, vastly increasing the amount of acid that can be excreted in the urine. With chronic acidosis, proximal tubular cells greatly increase NH3 production to increase acid excretion capacity.

Question 3

Pregnancy and GFR

Answer 3

Pregnancy results in significant plasma expansion and widespread vasodilation, leading to increased renal plasma flow and glomerular filtration rates.

Serum creatinine is reduced by approximately 0.4 mg/dL in this population; therefore, a rise in serum creatinine, even to levels that are normal in nonpregnant patients, represents significant renal dysfunction.

Question 4

CKD can cause hyperphosphatemia AND LOW EPO

Answer 4

due to impaired renal excretion of phosphorus.

Elevated blood phosphate triggers the release of fibroblast growth factor 23, which lowers calcitriol (1,25-dihydroxyvitamin )production and intestinal calcium absorption.

Chronic kidney disease usually causes hyperphosphatemia (binds serum Ca2+) and low 1,25-dihydroxyvitamin D (decreases intestinal Ca2+ absorption and Ca2+ release from bone). The resulting hypocalcemia stimulates release of parathyroid hormone, causing secondary hyperparathyroidism.. IMPORTANTTTT

Osteitis fibrosa cystica is a form of renal osteodystrophy characterized by abnormally high bone turnover caused by chronic parathyroid hormone stimulation of osteoclasts to a greater degree than that of osteoblasts. Bone biopsy would show an increased number of both osteoclasts and osteoblasts.

Fibroblast growth factor 23 (FGF23) is secreted ( by osteocytes) in response to hyperphosphatemia and lowers plasma phosphate by 1)reducing intestinal absorption(vit d) and 2)renal reabsorption of phosphate. FGF23 levels are useful as an early marker of abnormal phosphate metabolism in patients with CKD.

Question 5

Renal excretion of a drug is dependent on:

Answer 5

Glomerular filtration (reduced with low renal blood flow, kidney disease, and high drug protein binding)
Renal tubular secretion (reduced by coadministration of drugs with overlapping substrate specificity)
Tubular reabsorption (may be altered by changes in urine p

Question 6

Erythropoietin

Answer 6

Erythropoietin (EPO) is produced primarily by peritubular fibroblast cells in the renal cortex (Peritubular interstitial cells) in response to decreased renal oxygen delivery

LOW IN CKD NORMAL WITH AGING

side effect : venous thrombosis and HTN

Question 7

Glomerular filtration rate (GFR)

Answer 7

can be assessed using an ideal filtration marker that is freely filtered across the glomerulus and is not metabolized, secreted, or reabsorbed by the kidney tubules. In common practice, GFR is estimated using creatinine clearance. However, creatinine is actively secreted by the proximal tubules, so uncorrected creatinine clearance overestimates the GFR by approximately 10%-20%

Question 8

AFFERANT VS EFFERANT CONSTRICTION

Answer 8

Angiotensin II preferentially constricts the efferent arteriole, resulting in an increased hydrostatic pressure gradient and increased net filtration pressure.

Alpha-1 receptors are located mainly in the afferent arteriole; alpha agonists (eg, epinephrine, norepinephrine) result in constriction of the afferent arteriole, which reduces hydrostatic pressure and leads to lower net filtration pressures.

Prostaglandins (eg, prostaglandin E2) are responsible for dilation of the afferent arteriole.

NSAIDs Inhibition of prostaglandin synthesis,, results in constriction of the afferent arteriole, leading to reduced hydrostatic pressure and a lower net filtration pressure.

Albumin is not filtered across the glomerular capillary and would increase the oncotic pressure gradient, resulting in a lower net filtration pressure.

Question 9

Refeeding syndrome

Answer 9

occurs after the reintroduction of carbohydrates in patients with chronic malnourishment, which stimulates insulin secretion and drives phosphorus intracellularly in an effort to maintain cellular energy metabolism (eg, ATP production); this redistribution of phosphorus can result in severe hypophosphatemia

Question 10

ADH

Answer 10

Antidiuretic hormone acts on the medullary segment of the collecting duct (principal cells) to increase urea and water reabsorption, allowing for the production of maximally concentrated urine

he medullary interstitium is the region of highest osmolarity in the kidney

This hormone stimulates V2 receptors causing translocation of aquaporin 2 channels into the apical cell membrane

fluid in the distal tubules is the most dilute (lowest osmolarity, approaching 100 mOsm/L).

Question 11

DIABETES INSIPIDUS DI

Answer 11

1))CENTRAL DI

2)) Nephrogenic DI is characterized by polyuria, dilute urine (low urine specific gravity), hypernatremia, and high antidiuretic hormone.

Treatment includes thiazide diuretics and replacement of water losses.

Question 12

SIADH

Answer 12

manifests with low serum osmolality, hyponatremia, high urine osmolality, and high urine sodium.

IN CONTRAST WITH DI

Causes

CNS disturbances (stroke, hemorrhage, trauma)
Medications (eg, carbamazepine, SSRIs, NSAIDs)
Lung disease (eg, pneumonia)
Malignancy (eg, small-cell lung cancer)

Clinical findings

Nausea, forgetfulness (mild hyponatremia)
Seizures, coma (severe hyponatremia)
Euvolemia (eg, moist mucous membranes, no edema, no JVD)

Question 13

obstruction WITH FGR AN FF

Answer 13

Acute ureteral constriction or obstruction decreases the glomerular filtration rate and filtration fraction.

BY increased renal tubular hydrostatic pressure. As the intraglomerular capillary hydrostatic pressure is unchanged, this results in a decreased hydrostatic pressure gradient leading to a reduction in glomerular filtration

Consequences of VUR:

↑ Risk of chronic pyelonephritis

Renal inflammation from infection & ↑ hydrostatic pressure

Scarring pattern:
Most severe at upper & lower poles (compound papillae always open → more susceptible)
Mid-kidney papillae less affected (simple papillae closed at baseline).

Long-term: Reflux nephropathy → secondary hypertension

Question 14

osteoblasts and PTH

Answer 14

PTH receptors activation causes osteoblasts to increase production of receptor activator of (RANK-L) and monocyte colony-stimulating factor. These factors stimulate osteoclastic precursors to differentiate into bone-resorbing osteoclasts.

PTH also decreases the release of (OPG), a decoy receptor for RANK-L; therefore, lower levels of OPG allow for more interaction between RANK-L and the osteoclastic receptor, increasing bone resorption and releasing calcium and phosphate into circulation

intermittent administration of recombinant PTH analogs induces a greater increase in osteoblast activity in proportion to osteoclast activity and a net increase in new bone formation. Teriparatide is a recombinant PTH analog used to treat osteoporosis.

PTH decreases proximal (note) tubular reabsorption of phosphate
and increases calcium reabsorption in the distal convoluted tubule and collecting duct.(note)

Question 15

vascular calcifications (VCs)

Answer 15

VCs occur when metabolic insults (eg, electrolyte abnormalities, dyslipidemia, oxidative stress, uremia) cause smooth muscle cells in the arterial media to differentiate into osteoblast-like cells (ie, osteogenic differentiation), resulting in active deposition of calcium salts within the vessels

CKD : Electrolyte abnormalities: Hyperphosphatemia and/or hypercalcemia promote calcification by stimulating osteogenic differentiation

Question 16

Salicylate poisoning ASPIRIN

Answer 16

mixed primary respiratory alkalosis and primary anion gap metabolic acidosis
by
increased respiratory rate
increased production of lactic acid (uncouples oxidative phosphorylation)

Symptoms include tinnitus, tachypnea, hyperthermia, vomiting, and altered mental status.

Question 17

Hypokalemia

Answer 17

1. Decreased intake
2. Intracellular translocation (shift into cells)
   *Insulin (eg, DKA treatment, refeeding syndrome)

*β-adrenergic activity
Pharmacologic: albuterol, dobutamine
Stress-induced: alcohol withdrawal, acute MI

*Alkalosis (respiratory or metabolic)

*↑ Cell reproduction (eg, acute myeloid leukemia, GM-CSF therapy)

3. Gastrointestinal loss
4. Urinary loss

Hyperaldosteronism
Diuretics (loop, thiazide)
Renal tubular acidosis (type 1 and type 2)
Hypomagnesemia (induces renal K⁺ wasting)

5. Sweat loss

Question 18

potassium (K⁺)

Answer 18

Fixed handling (not regulated by K⁺ load):

Bowman’s capsule → freely filtered (100%)
Proximal tubule → reabsorbs ~65%
Thick ascending limb (Na⁺/K⁺/2Cl⁻ cotransporter) → reabsorbs 25–30% → ~5–10% remains

Regulated handling (site of control):

Late distal & cortical collecting tubules
Principal cells → secrete K⁺ (stimulated by ↑ dietary K⁺ & aldosterone)
α-intercalated cells → reabsorb K⁺ (via H⁺/K⁺-ATPase; stimulated by hypokalemia)

Question 19

hemodialysis. What factors determine the rate of molecular diffusion?

Answer 19

Concentration gradient (ΔC)
Membrane surface area (A)
Solubility of the substance

Membrane thickness (Δx)
Molecular weight (√MW)

Question 20

SGLT-2 inhibitors e.g Canagliflozin

Answer 20

Glucose is reabsorbed from the proximal tubule by sodium-glucose cotransporter-2 (SGLT-2). Normally, nearly all filtered glucose is reabsorbed.

SGLT-2 inhibitors lower the threshold at which filtered glucose can be fully reabsorbed; this increases urinary glucose losses and lowers blood glucose levels. RISK OF HYPOGLYCEMIA

Question 21

transport maximum (Tmax) AND GLUCOSE

Answer 21

At normal plasma concentrations of glucose, the renal tubules reabsorb the entire filtered load of glucose because it is below the maximum tubular reabsorption ability (transport maximum of glucose).
At higher plasma concentrations, glucose is excreted when the filtered amount exceeds the transport maximum.
The serum concentration at which glucosuria begins, called the threshold of glucose, is approximately 200 mg/dL.

Question 22

DM effect

Answer 22

1))Type 4 Renal Tubular Acidosis (RTA)

Cause: ↓ Aldosterone effect (deficiency or resistance)
Hyperkalemia → impaired K⁺ excretion
Non–anion gap metabolic acidosis → impaired H⁺ excretion (↓ ammonium)
↓ Na⁺ reabsorption → mild total body sodium loss (but serum Na⁺ often normal due to ADH)

2)) diabetic nephropath

Progression:

1.Hyperfiltration
INCREASE GFR ,Glomerular hypertrophy

2.incpint DN
Basement membrane thickening, mesangial expansion, podocyte injury
HTN
Microalbuminuria → Macroalbuminuria (>300 mg/day)

4.Overt DN
DECREASE GFR
Overt Proteinuria (Nephrotic)
KW lesion
mesangial sclerosis (Glomerulosclerosis) → ↓ GFR → ESRD

Homogeneous deposition of eosinophilic hyaline material in the intima and media of small arteries and arterioles characterizes hyaline arteriolosclerosis.
This is typically produced by untreated or poorly controlled hypertension and/or diabetes.

Glycosuria is seen at blood glucose levels >200-300 mg/dL due to saturation of renal glucose transporters. Glycosuria reflects poor glycemic control but does not correlate with the degree of renal damage in DN.

Question 23

primary nocturnal enuresis

Answer 23

Definition: Bed-wetting in a child ≥5 years who has never achieved sustained nighttime continence.

Pathogenesis:

1)Maturational delay in bladder control:

↓ Awareness of bladder filling
↓ Cortical suppression of bladder contractions
Poor coordination of sphincter & detrusor (pontine micturition center)

2) ↑ Overnight urine production (↓ ADH activity, excessive evening fluids)

3)Reduced functional bladder capacity

Question 24

AKI :: Acute interstitial nephritis

Answer 24

Causes

Antibiotics (eg, beta-lactam, sulfonamide, rifampin)
Proton pump inhibitors
NSAIDs
Diuretics
Other: Autoimmune diseases, Mycoplasma, Legionella

Clinical features

Rash, fever, or asymptomatic
New drug exposure IMPORTANT

Laboratory findings

Acute kidney injury
Pyuria, hematuria, WBC casts IMPORTANT
Eosinophilia, urinary eosinophils IMPORTANT

Renal biopsy: Inflammatory interstitial infiltrate and edema

Symptoms typically resolve with withdrawal of the offending agent.

Microscopy: patchy interstitial inflammation, tubular atrophy, fibrosis

Gross: shrunken kidneys, irregular contours, distorted calyces, papillary necrosis

Question 25

AKI:: ATN AND ischemia

Answer 25

Loss of epithelial cell polarity is an early change that occurs in renal tubular cells in response to ischemia (ie, acute tubular necrosis). Depletion of ATP causes rapid cytoskeletal disruption; this leads to 1) a loss of cell-cell adhesion and causes 2) redistribution of integrins and Na-K-ATPases from the basolateral membrane to the apical membrane. Acute tubular necrosis can be caused by renal ischemia and is characterized by oliguria, increased serum creatinine, and muddy brown casts. SAME AS ANY INTERSTIAL AKI (NEXT CARD) Ischemic injury predominantly affects the renal medulla (IMPORTANT), which has a relatively low blood supply. The proximal tubules and the thick ascending limb of the loop of Henle are the most commonly involved portions of the nephron. Scleroderma renal crisis (SRC) is a life-threatening complication of systemic sclerosis characterized by acute renal failure and severe hypertension. SRC is caused by immune-mediated injury to small renal vessels that leads to reduced renal perfusion due to vascular narrowing and obliteration.

Question 26

AKI :: ATN due to nephrotoxins

Answer 26

Common nephrotoxins Antibiotics: aminoglycosides (eg, gentamicin), vancomycin Antivirals: cidofovir, foscarnet Other: radiographic contrast, cisplatin, heavy metals, heme pigment Histology Tubular epithelial cell necrosis with cell detachment, cast formation & tubular lumen obstruction Proximal tubules (IMPORTAAAAANTTT) primarily affected Presentation IMPORTANTTT BUN/creatinine ratio <20:1, FENa >2% Muddy brown (granular) or epithelial cell casts, low urine osmolality ~300 mOsm/kg Oliguria or polyuria, ± electrolyte abnormalities Stages of acute tubular necrosis 1))Initiation stage (24-36 hours) Tubular injury resulting from: Ischemia (eg, hemorrhage, sepsis) Cytotoxins (eg, aminoglycosides, myoglobin) 2))Maintenance stage (days to weeks) Oliguric renal failure (↓ GFR, ↓ urine output, volume overload) ↑ Creatinine & BUN, ↑ serum K & PO4, metabolic acidosis 3))Recovery stage (weeks to months) Gradual increase in urine output, high-volume diuresis Impairment of tubular resorptive function (electrolyte wasting) Tubular epithelial regeneration occurs from surviving tubular cells Normal architecture restored if the basement membrane is intact

Question 27

AKI :: Prerenal

Answer 27

Etiology Decreased renal perfusion : True volume depletion: Decreased EABV (eg, heart failure, cirrhosis) Displacement of intravascular fluid (eg, sepsis, pancreatitis) Bilateral renal artery stenosis with ACE inhibition Afferent arteriole vasoconstriction (eg, NSAIDs) Clinical features: Increase in serum creatinine (eg, 50% from baseline) Decreased urine output IMOPRTANTTT: Blood urea nitrogen/creatinine ratio >20:1 Fractional excretion of sodium <1% High urine osmolality (>450 mOsm/kg) and specific gravity (>1.015) Unremarkable urinalysis (eg, no protein, cells, or casts) Hyaline casts IMPORTANTTTT Invasive vascular procedures can be complicated by atheroembolic disease, which may involve the kidneys, gastrointestinal tract, CNS, and the skin. Light microscopy shows a partially or completely obstructed arterial lumen with needle-shaped cholesterol clefts within the atheromatous embolus. Renal infarctions are most commonly caused by cardioembolic disease; atrial fibrillation is the greatest risk factor. Clinical features include flank pain, nausea, vomiting, low-grade fever, and hypertension (due to renin release from hypoxic tissue). Gross pathology demonstrates sharply demarcated, yellow-white, wedge-shaped areas with surrounding hyperemia.

Question 28

renal artery stenosis

Answer 28

hypoperfusion and activation of the RAAS system. Angiotensin II causes arteriolar vasoconstriction and increases aldosterone and ADH synthesis. This leads to increased renin release by modified smooth muscle (juxtaglomerular) cells in the walls of afferent glomerular arterioles. Chronic renal hypoperfusion can cause hyperplasia of the juxtaglomerular apparatus. IMPORTANT :The resultant hypertension helps reduce the decline in glomerular filtration rate in the affected kidney, but causes a pressure natriuresis with increased sodium excretion in the unaffected kidney. Marked unilateral kidney atrophy is suggestive of renal artery stenosis COULD ASSOCIATED WITH : 1-Chronic mesenteric ischemia: postprandial pain + weight loss in patients with atherosclerotic risk factors ++ Atherosclerotic RAS: unilateral kidney atrophy, refractory hypertension, abdominal/bruit clues 2-Fibromuscular dysplasia

Question 29

Fibromuscular dysplasia: RAS +ANAURYSM (CVA)

Answer 29

Manifestations Fibromuscular webs (luminal stenosis) alternating with areas of aneurysmal dilation Loss of the internal elastic lamina Most common in women, age <55 Presentation Resistant hypertension (RAS) CNS involvement: Headache, TIA, stroke, ruptured aneurysm Diagnosis Angiography (CT, MRI, percutaneous) String-of-beads appearance (multifocal disease) IMPORTANTTT

Question 30

HTN

Answer 30

Hypertensive Nephrosclerosis (HN) Pathology: Arterioles: Medial hypertrophy Fibrointimal proliferation Hyaline arteriolosclerosis (plasma protein & BM deposition) Severe HTN → fibrinoid necrosis + onion-skin arterioles → acute renal failure Result → lumen narrowing → ischemia → RAAS activation → vicious cycle of HTN Glomeruli: Ischemia & fibrosis (glomerulosclerosis) Collapse of capillary loops Thickened Bowman capsule Gross kidney: Bilateral mild atrophy Finely granular surface Clinical: Usually elderly Slowly progressive Advanced disease: more common in African Americans, severe HTN, diabetes Urine: bland sediment (± mild proteinuria) CKD complications: anemia (↓ EPO), renal insufficiency (late)

Question 31

tubuloglomerular autoregulation system

Answer 31

decreased sodium and fluid delivery to the macula densa and subsequent activation of the tubuloglomerular autoregulation system. Subsequent dilation of the afferent arterioles and constriction of the efferent arterioles increases intraglomerular capillary pressure, resulting in an increased glomerular filtration rate (hyperfiltration) and glomerular hypertrophy

Question 32

urinary incontinence AND MS

Answer 32

1))Stress ↓ Urethral sphincter tone Urethral hypermobility Leakage with coughing, sneezing, lifting 2))Urge Detrusor overactivity Sudden, overwhelming urge to urinate 3))Overflow Impaired detrusor contractility Bladder outlet obstruction Incomplete emptying & persistent involuntary dribbling MS develop urge incontinence due to loss of central nervous system inhibition of detrusor contraction in the bladder( spastic bladder=HYPERTONIA) . As the disease progresses, the bladder can become atonic and dilated, leading to overflow incontinence.

Question 33

osteoporosis

Answer 33

HyperPTH → cortical bone loss + subperiosteal erosions, “salt & pepper” skull, osteitis fibrosa cystica (brown tumors, cystic bone lesions) Aging osteoporosis → trabecular bone loss

Question 34

Hypercalcemia of Malignancy

Answer 34

1)) PTHrP ↑ → squamous, renal, breast, ovarian Diagnostic: ↓ PTH, ↑ PTHrP ⚡ Note: Unlike PTH, PTHrP does not ↑ 1,25-dihydroxyvitamin D 2)) Bone mets / myeloma → osteolysis, Diagnostic: ↓ PTH, ↓ PTHrP, ↓ vitamin D 3)) Lymphoma → ↑ vitamin D ,↓ PTH

Question 35

pathophysiology of metabolic alkalosis

Answer 35

Total body chloride depletion (VOMITING) is often important in the pathophysiology of metabolic alkalosis. Measurement of urine chloride (IMPORTANT) can be helpful in determining the underlying etiology.

Question 36

Renal Changes in Normal Aging

Answer 36

low GFR, normal serum creatinine (due to ↓ muscle mass), normal EPO production HOW ? 1)) ↓ Renal mass & functional glomeruli Cortical atrophy, fibrosis ↓ GFR & Cr clearance ↓ Urine concentrating ability → risk of hypovolemia 2)) ↓ Renal blood flow (RBF) Microvascular loss → ischemic susceptibility RBF becomes prostaglandin-dependent → NSAIDs ↑ risk of AKI 3)) ↓ Hormonal responsiveness ↓ Renin secretion → blunted RAAS ↓ 1α-hydroxylation of vitamin D → ↓ Ca²⁺ regulation Erythropoietin preserved (unlike CKD) 4)) Cellular changes ↑ Apoptosis after insults (ischemia, toxins) ↓ Regeneration capacity

Question 37

Hyperparathyroidism & hypoparathyroidism

Answer 37

Hyperparathyroidism (↑ PTH) ↑ Calcium, ↓ phosphate Osteoporosis Nephrolithiasis Polydipsia, polyuria Constipation Bone pain Muscle pain Hypoparathyroidism (↓ PTH) ↓ Calcium, ↑ phosphate Tingling, numbness Trousseau & Chvostek signs Muscle spasms Seizures Injury to the parathyroid glands during thyroid surgery is a common cause of hypoparathyroidism and acute hypocalcemia.

Question 38

kidney stones

Answer 38

1))CALCIUM PHOSPHATE,OXALATE : Normocalcemia, hypercalciuria Hypercalciuria is the most common risk factor for calcium (calcium oxalate and calcium phosphate) kidney stones in adults; contributing factors may include increased gastrointestinal absorption, increased mobilization of calcium from bone, or decreased renal tubular calcium reabsorption. However, most patients remain normocalcemic due to regulation of plasma calcium levels by vitamin D and parathyroid hormone. Normal calcium intake → dietary calcium binds oxalate in gut → excreted in stool. Low calcium diet → ↓ binding → ↑ free oxalate absorbed → hyperoxaluria → ↑ risk of calcium oxalate stones. SO Restricting calcium increases stone risk. Normally, citrate excreted by the kidneys binds to ionized calcium in the urine, preventing the formation of insoluble calcium-oxalate complexes. When urinary citrate is low (hypocitraturia), increased calcium availability leads to formation of calcium-oxalate complexes that can precipitate and form calcium oxalate stones. IMPORTANTTT Hypocitraturia often occurs in the setting of chronic metabolic acidosis (eg, distal renal tubular acidosis, chronic diarrhea) due to enhanced renal citrate reabsorption. Supplemental oral potassium citrate is often prescribed to prevent recurrent calcium stones. 2))STRUVITE Risk factors Recurrent upper urinary tract infection Urease-producing organisms (eg, Klebsiella, Proteus E.COLI) Pathogenesis Hydrolysis of urea to yield ammonia: Urea → 2 NH3 + CO2 NH3 + H2O → NH4+ + OH− Increased urine pH IMPORTANTTTTT Precipitation of magnesium ammonium phosphate salts Clinical features: Large staghorn calculi IMPORTANTTTT Fever, mild flank pain due to infection Obstruction of collecting system & atrophy of renal parenchyma 3))URIC ACID Cystinuria is an autosomal recessive disorder caused by defective transportation of cystine, ornithine, arginine, and lysine across the intestinal and renal tubular epithelium. Recurrent nephrolithiasis is the only clinical manifestation. Urinalysis shows pathognomonic hexagonal cystine crystals. 4))cystine stones Recurrent nephrolithiasis in a young patient Pathophysiology: Autosomal recessive defect in proximal tubule & intestinal transporter Defective reabsorption of COLA amino acids: Cystine (forms stones) Ornithine Lysine Arginine Only cystine is poorly soluble → hexagonal crystals Diagnosis: Urinalysis: hexagonal cystine crystals (pathognomonic) Screening: Sodium cyanide–nitroprusside test → red-purple color Confirm: ↑ urinary cystine (aminoaciduria) IMPORTANTTTTT (We don’t call it simply “cystinuria” in the lab test result because the transporter defect affects all 4 dibasic amino acids:) Treatment: ↑ Fluids (dilution) Urinary alkalinization (acetazolamide, potassium citrate) ##Ethylene glycol ingestion causes acute tubular necrosis with vacuolar degeneration and ballooning of the proximal tubular cells. Typical clinical findings include altered mentation, renal failure, high anion gap metabolic acidosis, increased osmolar gap, and calcium oxalate crystals in the urine. IMPORTANT

Question 39

RTA

Answer 39

Type 2 RTA (Fanconi Syndrome) Proximal tubule dysfunction → impaired reabsorption Normal PCT Functions Reabsorbs: HCO₃⁻, glucose, phosphate, potassium, water, amino acids ↓ HCO₃⁻ reabsorption → Normal anion gap metabolic acidosis ↓ HCO₃⁻, compensated by ↑ Cl⁻ (hyperchloremia) Glycosuria (with normal serum glucose) → Osmotic diuresis → polyuria, dehydration Hypophosphatemia → Rickets (widened wrists, frontal bossing, bowed legs) Hypokalemia → Muscle weakness Aminoaciduria / proteinuria (low MW proteins) → Marker of proximal tubule dysfunction (minimal clinical effect)

Question 40

Rhabdomyolysis (myoglobinuria).

Answer 40

Muscle breakdown → release of myoglobin, K⁺, PO₄³⁻, uric acid,↑ CK (very high) Urine dipstick reacts to heme pigment (myoglobin/hemoglobin), not just RBCs → "blood positive, no RBCs." Causes tubular damage → pigmented granular casts. (muddy brown casts) Myoglobin causes acute tubular necrosis via: Direct tubular cytotoxicity. Renal vasoconstriction. Possible hypocalcemia (early, due to Ca²⁺ deposition in damaged muscle) IMPORTANT ALSO Contrast-induced nephropathy is characterized by an acute rise in creatinine and blood urea nitrogen after radiologic contrast administration, followed by a gradual return to baseline. It is characterized histologically by diffuse necrosis of the proximal tubular cells (acute tubular necrosis). Urinalysis usually demonstrates muddy brown casts.

Question 41

Hemolytic uremic syndrome

Answer 41

triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury Etiology Shiga toxin–producing bacteria Escherichia coli O157:H7 Shigella Clinical features 1)Antecedent diarrheal illness (often bloody) 2)Hemolytic anemia with schistocytes (e.g. conjunctival pallor) 3)Thrombocytopenia 4)Acute kidney injury (eg, oliguria/anuria, hematuria, increased creatinine). Primary thrombotic microangiopathy (TMA) syndromes share common clinical and pathologic features and result in platelet activation and diffuse microthrombosis in arterioles and capillaries. They present with hemolytic anemia, schistocytes, thrombocytopenia, and organ injury (eg, brain, kidneys). Unlike disseminated intravascular coagulation, in which coagulation cascade activation leads to prolongation of coagulation studies (PT and activated PTT), TTP is almost always characterized by normal PT and activated PTT. The diagnosis can be confirmed with histopathology, which typically shows thrombi in small blood vessels (eg, glomerular capillaries, arterioles).

Question 42

nephrotic syndrome IMPORTANT

Answer 42

reduces plasma oncotic pressure, which causes a fluid shift into the interstitial space, resulting in edema. Low oncotic pressure also triggers increased lipoprotein production in the liver (ie, hyperlipidemia). IMPORTANTT 1))Minimal change disease is the most common cause of nephrotic syndrome in children. Systemic T-cell dysfunction leads to the production of glomerular permeability factor, which causes podocyte foot process fusion and decreases the anionic properties of the glomerular basement membrane. The loss of negative charge leads to selective albuminuria.(IMPORTANT) 1))Minimal Change Disease (MCD) Kids, recent infection, Hodgkin lymphoma LM: normal EM: diffuse foot process effacement Steroid responsive 2))Focal Segmental Glomerulosclerosis (FSGS) MC in adults (esp. African American, HIV, heroin, obesity) LM: segmental sclerosis & hyalinosis EM: foot process effacement Poor steroid response 3))Membranous Nephropathy (MN) MC in Caucasian adults Primary: anti-PLA2R Abs Secondary: SLE, HBV/HCV, solid tumors LM: diffuse capillary wall thickening Silver stain: “spike & dome” IF: granular IgG & C3 (IgG4 antibodies to the phospholipase A2 receptor PLA2R, which might play a role in development of the disease. Antibody titers are useful for diagnosis and correlate with disease activity.) 4))Diabetic Nephropathy Mesangial expansion, GBM thickening Nodular glomerulosclerosis (Kimmelstiel-Wilson) 5))Amyloidosis Congo red (+), apple-green birefringence LM: amorphous pink material Associated with chronic inflammatory diseases

Question 43

Amyloidosis

Answer 43

Differentials: 1)) AL (Ig light chain, plasma cell dyscrasia, MM): Kidney, heart, liver, neuropathy 2))AA (serum amyloid A, chronic inflammation): Kidney, liver, spleen 3))ATTR (transthyretin, age/hereditary): Cardiac 4))Dialysis-Related Amyloidosis (DRA) Precursor protein: β2-microglobulin (MHC I component) Cause: Inadequate clearance in ESRD despite dialysis → deposition as amyloid Target tissues: Osteoarticular structures (stabilized by GAGs & type I collagen) Dx : serum protein electrophoresis would be helpful to look for a monoclonal protein produced by an undiagnosed plasma cell dyscrasia (eg, multiple myeloma, Waldenstrom macroglobulinemia) causing AL amyloidosis. Manifestations: Scapulohumeral periarthritis (rotator cuff pain/hypertrophy) Carpal tunnel syndrome (median neuropathy) Flexor tenosynovitis (contractures) Bone cysts (pathologic fractures) Risk: ↑ prevalence with age & duration of dialysis

Question 44

NIPHRITIC SYNDROME

Answer 44

General features: Hematuria, RBC casts, oliguria, HTN, mild proteinuria 1))Post-streptococcal GN (PSGN): After GAS infection (pharyngitis/skin) Immune complex (IgG, C3) → “lumpy-bumpy” ↓ C3, kids > adults IF: C3 granular staining along GBM EM: subepithelial humps Increased age (ADULT), conversely, is the most important poor prognostic factor; 2))IgA Nephropathy (Berger disease): Recurrent hematuria (often post-URI or GI infection) LM: mesangial hypercellularity IF: IgA in mesangium 3))Henoch-Schönlein Purpura (IgA vasculitis): Triad: palpable purpura (legs/buttocks), arthralgia, abdominal pain IgA nephropathy + systemic small-vessel vasculitis Treatment: Supportive (hydration, NSAIDs), steroids for severe renal/GI involvement 4))Membranoproliferative GN (MPGN): Type I: Subendothelial immune complexes, “tram-track” Type II (dense deposit disease): C3 nephritic factor Associated with Hep B/C 5))RPGN (Crescentic GN): Pauci-immune Rapid renal failure, crescents (fibrin + macrophages) SILVER STAIN Subtypes: 1.Goodpasture: anti-GBM, hematuria + hemoptysis ((autoantibodies against the alpha 3 chain of type IV collagen in glomerular and alveolar basement membranes (anti-GBM antibodies))) 2.Granulomatosis w/ polyangiitis (Wegener): c-ANCA, resp + renal 3.Microscopic polyangiitis: p-ANCA LM: glomerular crescents IF: fibrin in crescents IF: linear staining (IgG) along GBM without immunoglobulin or complement deposits 6))Alport Syndrome Cause: Mutation in type IV collagen (X-linked most common) Features: Nephritic syndrome + hearing loss + ocular defects EM: lamellated appearance of GBM 7))Diffuse Proliferative GN (often SLE) Cause: Immune complex deposition (DNA/anti-DNA) Histology: Wire-loop lesions, subendothelial deposits type III hypersensitivity), leading to glomerular injury and reduced renal function. infective endocarditis (IE)

Question 45

Immune mechanisms of glomerular injury

Answer 45

1)) Immune complex formation within the glomerulus 1)) INTRINSIC (fixed) glomerular antigens Type IV collagen: anti-GBM disease (GN) PLA2R: membranous nephropathy (NS) 1))Deposited ("planted") glomerular antigens Bacterial antigens: poststreptococcal GN Tumor antigens: membranous nephropathy (NS) 2))Preformed immune complex deposition from the circulation 2))Endogenous antigens Galactose-deficient IgA: IgA nephropathy (GN) dsDNA: lupus nephritis (GN, sometimes NS) 2))Exogenous antigens Viral hepatitis C or B, HIV: immune complex MPGN Bacterial antigens: endocarditis-associated GN 3))Neutrophil activation: minimal (pauci-) immune complex deposition 3))Neutrophil cytoplasmic antigens MPO/PR3 (ANCA-associated GN) NOTE *Clinical picture determined by site of glomerular immune injury: NS: Injury to podocytes → isolated from inflammatory mediators in Bowman space/urinary side of GBM → proteinuria without inflammation GN: Injury to GBM, mesangial cells, or endothelial cell

Question 46

polycystic kidney disease

Answer 46

1))Autosomal dominant ADPKD Genetics Autosomal dominant mutation in PKD1 or PKD2 Presentation: IMPORTANTTTT Microscopic cysts present at birth but undetectable on imaging Become symptomatic later (age 40–50) Symptoms: Flank pain, hematuria, hypertension, progressive CKD Gross: Enlarged kidneys with numerous cysts in cortex & medulla Extrarenal manifestations Liver cysts Cerebral aneurysms IMPORTANTTTTT 2))Autosomal Recessive (ARPKD) Inheritance: Autosomal recessive (PKHD1 mutation) Presentation: Neonates/infants (birth or 1st year of life) IMPORTANTTT Bilateral flank masses, renal failure, pulmonary hypoplasia (Potter sequence in severe cases) Hypertension early in life Pathology: Cysts from collecting ducts & distal tubules Ultrasound: Enlarged echogenic kidneys at birth; cysts seen if >1 cm Associations: Congenital hepatic fibrosis → portal hypertension

Question 47

Renal Cell Carcinoma (RCC) with IVC obstruction and erythrocytosis.

Answer 47

90% of renal malignancies. Risk factor: Smoking (also obesity, HTN, von Hippel–Lindau). Classic triad (rare but high-yield): Flank pain Palpable mass Hematuria IVC Obstruction Mechanism: RCC invades renal vein → IVC (up to 25% of cases). Causes intraluminal tumor thrombus, not just compression. Manifestations: Bilateral leg edema Prominent tortuous abdominal wall veins (collateral circulation). Paraneoplastic Syndromes in RCC: ↑ Erythropoietin → Erythrocytosis (polycythemia) ↑ PTHrP → Hypercalcemia ↑ Renin → Hypertension ↑ ACTH → Cushing syndrome Histology (Clear cell) ORGINATED FROM PROXIMAL TUBULES IMPORTANTT Cuboidal or polygonal cells with abundant, clear cytoplasm Branching, "chicken-wire" vasculature Gross pathology typically demonstrates a sphere-like mass composed of golden-yellow cells (due to high lipid content) with areas of necrosis and hemorrhage. METZ RCC most commonly metastasizes to the lungs (IMPORTANTT), where it often presents as large, rounded, well-circumscribed "cannonball" metastases. Osteolytic bone lesions and liver metastases also occur frequently.

Question 48

🧬 VHL Gene & Renal Cell Carcinoma

Answer 48

Associated RCC Types: Sporadic Hereditary (von Hippel-Lindau disease) Genetics: Gene: VHL (tumor suppressor) Location: Chromosome 3p Mechanism: VHL normally inhibits hypoxia-inducible factors (HIFs) Mutation → constitutive HIF activation → ↑ transcription of angiogenic & tumorigenic factors (e.g., VEGF, PDGF)

Question 49

Urothelial (transitional cell) carcinoma of the bladder

Answer 49

rises from transitional epithelium (urothelium) ((rises from the epithelium of the renal pelvis, ureters, or bladder)) Risk factor: Smoking (strongest), also occupational exposures (aromatic amines, Rubber, plastics) Prognosis: Tumor stage = depth of invasion (IMPORTANT) Lamina propria invasion: T1 Muscularis propria invasion: T2 or higher → worse prognosis

Question 50

BPH

Answer 50

BPH INCRESE THE RISK OF UTI HOW? increase resistance to urine flow in the urethra and lead to incomplete bladder emptying during micturition. The residual urine can act as a growth medium for pathogenic bacteria (STASISI) and increase the risk for urinary tract infection. BPH DOSNT INCREASE THE RESIK FOR Prostatic adenocarcinoma (cancer) SO, WHAT IS INCREASE THE RISK OF CANCER ?? ↑ Age (most important) African American race Positive family history Pathology: Epithelial + stromal hyperplasia Predominantly in transition & periurethral zones Rubbery prostate on DRE (vs. nodular, firm in cancer) Complications: IMPORTANTT Overflow incontinence (dribbling due to retention) Bladder wall hypertrophy Hydroureter + hydronephrosis → pressure atrophy of kidney parenchyma → CKD Fibrosis and strictures are late effects of radiation therapy. Radiotherapy for prostate cancer may lead to urethral fibrosis and result in obstructive uropathy.

Question 51

Renal oncocytomas

Answer 51

are rare tumors that originate from collecting duct cells. Gross pathology often demonstrates a homogenous brown tumor with a central stellate scar that is often visible on imaging;

Question 52

Angiomyolipomas

Answer 52

are rare tumors that arise from perivascular epithelioid cells. Gross pathology demonstrates a well-circumscribed tumor composed of variable amounts of 3 different tissue types: yellow adipose tissue, red vascular components, and grayish smooth muscle. Angiomyolipomas are benign neoplasms often associated with tuberous sclerosis.

Question 53

Wilms Tumor (Nephroblastoma)

Answer 53

Definition: Most common renal malignancy in children (ages 2–5). 🔹 Origin: Derived from embryonic renal blastema. 🔹 Genetics: Associated with mutations on chromosome 11. WT1 / WT2 genes. 🔹Classic Presentation (Triad): 1)Large, unilateral flank mass (often smooth, palpable) 2)Hematuria (gross or microscopic) 3)Hypertension (due to ↑ renin secretion) 🔹Key Syndromes Associated: 1-WAGR syndrome (WT1 deletion): Wilms tumor Aniridia (absence of iris) Genitourinary malformations Retardation (intellectual disability) 2-Denys–Drash syndrome (WT1 mutation): Wilms tumor Early-onset nephrotic syndrome (diffuse mesangial sclerosis) Male pseudohermaphroditism 3-Beckwith–Wiedemann syndrome (WT2 mutation, IGF-2 overexpression): Wilms tumor Neonatal hypoglycemia Muscular hemihypertrophy Organomegaly (esp. tongue, liver, kidney, pancreas)

Question 54

Multiple myeloma

Answer 54

Pathophysiology Plasma cell neoplasm produces monoclonal paraprotein (immunoglobulin) Manifestations Bone pain, fractures Constitutional symptoms (weight loss, fatigue) Recurrent infections Laboratory Normocytic anemia Renal insufficiency Hypercalcemia (constipation, muscle weakness) Monoclonal paraproteinemia (M-spike) (Elevated gamma gap: ≥ 4 g/dL → suggests excess non-albumin proteins (mainly immunoglobulins).) Radiology Osteolytic lesions/osteopenia (osteoclast activation)

Question 55

Renal Papillary Necrosis (RPN)

Answer 55

Clue: Abrupt-onset gross hematuria + family history of sickle cell disease/trait. Causes (think "SAAD papa"): Sickle cell disease/trait → sickling → ischemia Analgesic nephropathy (NSAIDs) → ↓ prostaglandins → afferent vasoconstriction Acute pyelonephritis → edema → medullary ischemia Diabetes mellitus → vascular changes → hypoperfusion Papa = papillary necrosis Pathology: Gross: gray-white/yellow necrosis of distal 2/3 renal pyramids Microscopy: coagulative necrosis with preserved tubule outlines Later: cortical scars from fibrosis Symptoms: Gross hematuria (± papillary tissue flecks in urine) Flank pain/colicky pain (sloughed papilla → obstruction

Question 56

Renal Ammonia genesis (NH4) in Metabolic Acidosis

Answer 56

importanttttt : Glutamine → NH₄⁺ Clinical Context: Acute ischemic colitis → tissue hypoperfusion → anaerobic metabolism → lactate accumulation → anion gap metabolic acidosis Renal Response: Acidosis stimulates renal ammoniagenesis in proximal tubular cells Glutamine metabolism → generates NH₄⁺ + HCO₃⁻ NH₄⁺ → excreted in urine HCO₃⁻ → returned to blood → buffers acids

Question 57

FOR EMBRYO CHEACK THE BOOK

Question 58

Congenital Urachal Anomalies

Answer 58

Embryology: IMPORTANN Allantois: tubular outpouching from caudal yolk sac → bladder → umbilicus Normally obliterated by 12 weeks gestation → becomes fibrous urachus Types of Patent Urachus: 1))Complete patent urachus Connection from bladder → umbilicus Neonatal urinary drainage from umbilicus 2))Partial patency: Urachal sinus: open only at umbilicus Urachal diverticulum: open only at bladder → can cause urinary stasis & recurrent UTIs IMPORTANTT Urachal cyst: central portion remains patent

Question 59

Fetal Hydronephrosis & UPJ Obstruction

Answer 59

Embryology & Pathogenesis: UPJ = last segment of ureter to canalize Failure of canalization → stenosis → proximal ureter obstruction Results in hydronephrosis with renal pelvic/calyceal dilation Usually unilateral, no ureteral dilation IMPORTANTTTTTTTTTTTTTTT Differential (why unilateral UPJ obstruction is most likely): 1))Vesicoureteral junction abnormalities / VUR: rare, usually with ureteral dilation IMPORTANTTT 2))Neurogenic bladder / spinal cord defects: usually bilateral + hydroureter 3))Urethral or meatal obstruction: usually bilateral + ureteral dilation (eg, posterior urethral valves) The most common cause in newborn boys is posterior urethral valves due to a persistent urogenital membrane. IMPORTANT

Question 60

Horseshoe Kidney

Answer 60

Abnormal migration/fusion of right & left metanephric blastema → fusion at inferior poles → U-shaped (horseshoe) kidney IMA IMPORTANTTT: Isthmus (fused central portion) trapped by inferior mesenteric artery → kidney lies lower than normal Clinical Consequences: Often asymptomatic; incidental finding Abnormal ureter orientation → intermittent ureteropelvic junction obstruction Urinary stasis → ↑ risk for: Nephrolithiasis Recurrent UTIs / vesicoureteral reflux

Question 61

Embryonic Kidney Development

Answer 61

Origin: Intermediate mesoderm → nephrogenic cord (urogenital ridge) Sequential nephric systems: 1))Pronephros Forms first, rudimentary Completely regresses 2))Mesonephros Forms from mid-nephrogenic cord Females: regresses Males: persists as Wolffian ducts → epididymis, ductus deferens 3))Metanephros (permanent kidney) Forms from caudal nephrogenic cord Requires reciprocal induction between: IMPORTANTT: 1.Metanephric blastema → nephron structures: Glomeruli Bowman space Proximal tubules Loop of Henle Distal convoluted tubules 2.Metanephric diverticulum (ureteric bud) → collecting system: Collecting tubules & ducts Major & minor calyces Renal pelvis Ureters

Question 62

Terminology Distinctions:

Answer 62

Sequence: anomalies caused by a single primary event (Potter sequence) Syndrome: multiple anomalies with known genetic cause, independent development (e.g., Down syndrome) Association: ≥2 anomalies occurring more often than by chance, unknown cause (e.g., VACTERL) Dysplasia: abnormal tissue/organ growth (e.g., congenital hip dysplasia) Mosaicism: 2+ genetically distinct cell lines in one patient Polymorphism: normal phenotypic variation in a population (e.g., eye color)