Renal tubular and glomerular diseases Flashcards
What percent of the ultra filtrate is reabsorbed in the proximal tubule?
60-65%
What percent of NaCl is absorbed in the loop of Henle?
30%
After passing through the loop of Henle, what is the osmolarity of the ultra filtrate compared to the plasma?
Hypoosmolar
What causes cystinuria?
Inherited proximal tubular defects, in which resorption of particular non-essential amino acids fails. Of the amino acids that are not resorbed, cystine is the most insoluble, resulting in the formation of cystic calculi in acidic urine
What dog breeds develop cystinuria due to an autosomal recessive mutation in the Slc3a1 gene?
Newfoundlands and Labrador Retrievers
What dogs breeds develop cystinuria due to an autosomal dominant mutation in Slc7a9?
Australian Cattle dogs
What is the mean age of calculus formation in dogs with cysteine stones?
Labs and Newfoundlands: can be as early as 4-6 months
All other breeds: 5 years
What other non-essential amino acid can be lost in the urine along with cysteine, and what are the clinical consequences?
Carnitine - chronic, excessive deficiency can lead to cardiomyopathy, especially DCM
What is hyperuricosuria?
Excessive secretion of uric acid, an intermediate product of protein metabolism, in the urine
Describe the normal breakdown of purines
Purine portions of nucleic acids are broken down into hypoxanthine and xanthine => oxidized to uric acid by xanthine oxidase
Uric acid => metabolized to allantoin (more soluble) by hepatic uricase
What breeds are affected with hyperuricosuria?
Dalmatians, English Bulldogs, Black Russian Terriers
Where is uric acid converted to allantoin?
Within the heptatocytes - uricase is stored in hepatic peroxisomes, so uric acid must be transported into hepatocytes before conversion to allantoin can occur
Why are Dalmatians unable to convert uric acid to allantoin?
Have abnormal uric acid transport across hepatic membranes. They express normal amounts of uricase, but can’t transport the uric acid into cells to access the enzyme
Apart from increased serum levels of uric acid, why do Dalmatians secrete more of it in the urine? What gene is responsible and how is it inherited?
Have less proximal tubular resorption that other breeds
Also have active distal tubular secretion of urates as a result of a membrane transport defect - mutation in Slc2a9 (gene that encodes for a transporter of uric acid) - autosomal recessive
What percent of male Dalmatians are clinically affected by Slc2a9 mutations?
25%
What gene mutation is responsible for hyperuricosuria in English Bulldogs and Black Russian Terriers?
Same as Dalmatians - mutations in Slc2a9
Why do dogs with hepatic disease develop hyperuricosuria?
Reduced conversion of uric acid to allantoin
Primary renal glucosuria has been reported in what breeds?
Scottish Terriers, Norwegian Elkhounds
What drug can rarely cause acquired Fanconi’s syndrome in cats?
Chlorambucil
The renal tubules regulate acid-base status through what two processes?
- Resorption of 80-90% of filtered HCO3- in the proximal renal tubule
- Excretion of acids by means of titration of urinary budders and excretion of ammonium in the distal renal tubule
Renal tubular acidosis leads to what form of acidosis?
Hyperchloremic metabolic acidosis
What occurs in type II renal tubular acidosis? What are the clinicopathologic changes and urinalysis changes?
Damage to the proximal tubule results in an inability of the proximal tubule to resorb HCO3-
- Moderate reductions in plasma HCO3-
- Urine pH during acidemia <6.0
- Mild hypokalemia
- Other defects of proximal tubule dysfunction noted
What occurs in type I renal tubular acidosis? What are the clinicopathologic changes and urinalysis changes?
Damage to the distal tubule results in an inability of the distal tubule to excrete H+
- Variable reductions in plasma HCO3-
- Urine pH during acidemia >6.0
- No other proximal tubule defects
- Mild to severe hypokalemia
What occurs in type IV renal tubular acidosis?
A type of distal RTA and hyperkalemia secondary to hypoaldosteronism or aldosterone deficiency
Why is metabolic acidosis less severe with proximal RTAs?
The distal tubule can still excrete acid to compensate
Why does the administration of sodium bicarbonate worsen potassium wasting in proximal RTAs?
The amount of HCO3- presented to the distal tubule increases, resulting in increased H+ secretion (and loss of potassium) - eventually the distal buffering system is overwhelmed, resulting in marked bicarbonaturia (>15% FE)
What is a better way to correct metabolic acidosis in proximal RTAs than using sodium bicarbonate?
Potassium citrate
How does the distal tubule secrete H+ ions?
Through a H+ ATPase pump
Also generates ammonia, which captures H+ ions in the tubule, leading to ammonium excretion
Why does hypoaldosteronism cause a distal RTA?
Aldosterone stimulates the H+ ATPase pump
What test can be used to confirm a distal RTA?
Ammonium chloride challenge test - give oral ammonium chloride and monitor urine pH hourly for 6 hours. Normal dogs should acidify their urine to a pH of 5.0
What is nephrogenic diabetes insipidus?
Any disorder in which the urinary concentrating mechanism is unable to respond to ADH to produce concentrated urine
Where is ADH produced, stored and why is it released?
Produced in the hypothalamus, stored in the posterior pituitary
Released in response to hyperosmolarity or hypovolemia
Name 5 causes of nephrogenic diabetes insipidus
- Toxins: E coli endotoxin
- Drugs: glucocorticoids, chemotherapeutics
- Metabolic conditions: hypokalemia, hypercalcemia
- Tubular injury or loss: renal cystic disease, pyelonephritis
- Alterations in the medullary concentration gradient: medullary washout
What is congenital nephrogenic diabetes insipidus?
Rare, inherited disease caused by a deficiency of ADH receptors in the tubules
What are the 3 layers of the filtration barrier in the glomerulus?
Fenestrated endothelium, glomerular basement membrane, and visceral epithelial cells (podocytes)
What are slit diaphragms?
Specialized cell junctions between podocytes and bridge the filtration slits
What size molecules freely pass through the glomerulus? What is the maximum size that can pass?
<5000 Daltons = freely filtered
Substances are retained with increasing efficiency as they increase in size to ~60,000 to 70,000 Daltons
How does ionic change influence filtration? Why?
- Negatively changed proteins are retained in the blood to a greater extent that would be predicted by size alone
- The podocyte foot processes, basement membrane, and endothelium all contain negative charged glycoproteins - creating a charge barrier
Renal azotemia with an intact concentrating ability in a dog should raise concerns for what disease process?
Glomerular disease - tubules are still intact to concentrate the urine
How are hyaline casts formed and why are they common with glomerular disease?
Proteinuria promotes the precipitation of Tamm-Horsfall mucoprotein, which envelops the protein in the tubular lumen into a hyaline cast. The purpose is to protect the renal tubular epithelium from damage due to protein
What glomerular disease is associated with the most severe clinical abnormalities (highest UPC, lowest albumin, higher incidence of nephrotic syndrome and hypertension)?
Membranoproliferative glomerulonephritis
What dog breed develops a familial form of membranoproliferative glomerulonephritis?
Bernese Mountain Dogs
What infection causes a rapidly progressive form of membranoproliferative glomerulonephritis along with tubular necrosis and interstitial inflammation?
Borrelia burgdorferi
What are the histologic findings with membranoproliferative glomerulonephritis?
- Immune complex deposition on the sub endothelial side of the GBM
- Thickened capillary loops
- Mesangial hypercellularity with interposition of the mesangial cells between the basement membrane, causing a “railroad” appearance of the GBM
What is the pathogenesis of membranoproliferative glomerulonephritis
Deposition of immune complexes leads to cytokine-mediated complement activation, expansion of the mesangium, and inflow of leukocytes
Name 4 other infectious diseases that can cause membranoproliferative glomerulonephritis in dogs
- Leishmaniasis
- Babesiosis
- Dirofilariasis
- Heterobilharzia
What does immunofluorescence of TEM reveal with membranoproliferative glomerulonephritis?
Granular deposits of C3 combined with IgG, IgA, or IgM
How is membranoproliferative glomerulonephritis or membranous nephropathy treated?
- Manage underlying infectious/inflammatory/neoplastic diseases that are causing immune complex formation
- Immunosuppression for severe, persistent, or progressive disease
- Antiplatelet drugs
- Treat proteinuria
What is the most common glomerular disease in cats?
Membranous nephropathy
Describe the pathogenesis of membranous nephropathy
- Immune complexes are deposited on the subepithelial side of the glomerulus
- Causes less complement activation, less cytokines response, and less inflammation (away from circulation)
What are the histopathologic findings with membranous nephropathy?
- Uniform thickening and increased rigidity of the basement membrane
- Immune deposits look like “spikes” or “beads” on the outside of the basement membrane using silver staining
Describe the pathogenesis of proliferative glomerulonephritis
- Endocapillary or mesangial proliferation occurs due to a type III hypersensitivity
- IgG/IgM antibodies bind to antigens and the immune complexes are deposited within the glomerular basement membrane
- Activates the complement system and the membrane attack complex forms, damaging the podocytes and mesangial cells
- Inflammatory cells are then recruited
What are 3 known causes of proliferative glomerulonephritis in dogs?
- Leishmaniasis
- Canine adenovirus type 1
- Systemic lupus erythematosus
What is the pathogenesis of immunoglobulin A nephropathy?
Immune deposits consisting of IgA are trapped in the mesangium, leading to mesangial proliferation