9/17- Glomerular Diseases I & II: Anatomy, Function, and Clinical Syndromes Flashcards
Define:
- Glomerular diseases
- Glomerulonephritis
- Primary glomerular diseases
- Secondary glomerular diseases
- Glomerular diseases: diseases involving glomeruli primarily
- Glomerulonephritis: glomerular diseases in which glomerular inflammation is an important component
- Primary glomerular diseases: involves the kidneys only (e.g. membranous glomerulonephritis)
- Secondary glomerular diseases: involves the glomeruli as a component of a systemic disease (e.g. diabetic nephropathy, lupus nephritis)
What is seen here?
Glomerulus- filtering units of the kidney
How many glomeruli per kidney?
1-1.2 million
What are the involved cells in the glomerulus?
- Mesangial cell
- Endothelial cell (lines inner side of GBM)
- Podocyte (epithelial cell, lines outside of GBM)
What are mesangial cells?
- Function
- Properties
- Synthesis of mesangial matrix which acts as a structural support to the glomerulus
Properties
- Smooth muscle-like (contractile) properties: influences capillary surface area and filtration
- Macrophage-like properties: phagocytosis of immune complexes; secretion of cytokines, growth factors, proteases and oxidants
Describe the structure of the podocytes?
- Aka visceral epithelial cells
- Lines outside of GBM
- Interdigitates with the GBM via long “foot processes” which are separated by thin slit-diaphragms
What is the function of the glomerulus?
Filter (highly selective)
- Permeable to salt, water, and metabolic waste products (like creatinine, urea) Barrier to large molecules and proteins
- “Size” barrier (gap between endothelial cells 70-100 nm and between podocyte foot processes 30-40 nm)
- “Charge” barrier: negatively charged proteins coat the GBM (heparan sulfates) and podocytes (glycocalyx)
What are clinical manifestations/syndromes of glomerular diseases? What causes them?
Abnormal protein excretion
- Isolated proteinuria
- Nephrotic syndrome
- Nephritic syndrome
Loss of filtration and reduction in the glomerular filtration rate (GFR) (losing ability of kidney to excrete things like urea, creatinine…)
- Acute kidney injury (AKI)
- Chronic kidney disease (CKD)
What is normal protein excretion? Abnormal?
< 20 mg/day is normal
- Abnormal is > 30 mg/day
What is microabluminuria?
- Suggestive of what?
Microalbuminuria = 30-300 mg/day
- Not detectable by routine urinalysis (have to test for albumin specifically)
- Suggests early glomerular damage
- Clinically used to predict development of diabetic nephropathy
What is subnephrotic-range proteinuria?
- Suggests what?
Subnephrotic range = 300 mg - 3.5 g/day
- May be due to glomerular or tubular diseases
What is nephrotic range proteinuria?
Nephrotic range = > 3.5 g/day
- Due to defect in glomerular filtration barrier
- Usually results in decreased serum albumin -> development of edema -> NEPHROTIC SYNDROME
What is the definition of nephrotic syndrome?
- Proteinuria (>3.5 g/day or >40 mg/hr/m2 in children)
- Hypoalbuminemia (under 3.0 g/dl)
- Edema
- Hyperlipidemia (elevated serum cholesterol)
- Lipiduria (fat globules in the urine)
What is the pathogenesis of nephrotic syndrome?
Major glomerular abnormality is an excessive leak of protein through the glomerular capillary wall into the urinary space due to disruption of the slit diaphragm
- Podocyte injury
- Specific defect of the slit diaphragm (e.g., nephrin mutation)
What are the main processes of pathophysiology involved in nephrotic syndrome?
- Low serum albumin
- Edema/Anasarca
- Hyperlipidemia
- Lipiduria
- Increased risk for infections
- Increased risk for thrombosis
- Poor growth in children and osteomalacia
What causes low serum albumin in nephrotic syndrome?
- How does the body respond?
Low serum albumin
- Loss of albumin into the urine
- Increased reabsorption and degradation of protein by the proximal tubule
- Increased protein synthesis by the liver, but cannot compensate completely for the urinary losses
(even though urine loss only shows ~3.5 g and liver can make more, much more is lost in urine that has already been degraded by proximal tubule)
What causes edema/anasarca in nephrotic syndrome? - How does the body respond?
- Decreased plasma oncotic pressure -> filtration of fluid from the vascular compartment into the interstitial space
- Decrease in intravascular volume -> stimulation of renin-angiotension-aldosterone and vasopressin -> salt and water retention -> worsened edema
What causes hyperlipidemia in nephrotic syndrome?
- Results/risks?
- Increased lipoprotein synthesis by the liver mediated by a decrease in plasma oncotic pressure
- Increased risk for coronary artery disease/atherosclerosis
What is lipiduria?
- How is it observed?
- Fat in the urine (appearance of “maltese cross” under polarized light)
- Due to higher synthesis of lipid by liver (with protein production) and more loss in urine since glomerular disease
What causes the icnreased risk for infection in nephrotic syndrome?
Urinary loss of IgG and complement
What causes increased risk for thrombosis in nephrotic syndrome?
Increased synthesis of coagulation factors by the liver and urinary loss of anti-thrombin III
- Protein C/S, and AT III are smaller molecules; more likely to be lost (these inhibit clotting)
What causes poor growth in children and osteomalacia?
Urinary loss of Vitamin D
What are frequent causes of nephrotic syndrome?
Primary
- Minimal Change Disease
- Membranous Nephropathy
- Focal Segmental Glomerulosclerosis
- Membranoproliferative Glomerulonephritis
Secondary
- Diabetic Nephropathy
- Amyloidosis
- Lupus nephritis
What is the definition of nephritic syndrome?
- Non-nephrotic range proteinuria (> 500mg and under 3.5 g/day)
- Reduced glomerular filtration rate (GFR): seen as increase in serum urea nitrogen and serum creatinine
- Active urine sediment (RBCs, WBCs, casts)
- Edema
- Hypertension
What is the pathogenesis of nephritic syndrome?
Characterized by active inflammation and injury within the glomerulus -> glomerular damage and loss of capillary surface area -> loss of filtration and blood flow to the glomeruli
- Mesangial cell proliferation
- Endothelial cell proliferation and injury
- Podocyte injury
What are the main processes of pathophysiology involved in nephritic syndrome?
- Active urine sediment
- Reduction in glomerular filtrate rate (GFR)
- Proteinuria (usually under 3 g/day)
- Edema
- Hypertension
What causes active urine sediment in nephritic syndrome?
- Excretion of RBCs and WBCs into urine due to glomerular inflammation and disruption of GBM
- Hematuria with dysmorphic RBCs (projections; not nice and round; had to squeeze through GBM)
What causes the reduction in glomerular filtrate in nephritic syndrome?
- Acute inflammation within the glomeruli -> Glomerular vasoconstriction, occlusion and thrombosis -> Reduced renal blood flow and filtrating surface area
- Increased serum creatinine, nitrogen, urea…
What causes the proteinuria in nephritic syndrome?
(Proteinuria usually under 3 g/day)
- Glomerular capillary wall injury focal vs. nephrotic syndrome where the entire capillary wall has increased permeability
- In other words, less protein loss in nephritic syndrome because etiology (e.g. inflammation due to Ig deposition) is not evenly spread; not all nephrons are compromised
- Decreased GFR -> less filtered protein
What causes the edema in nephritic syndrome?
Salt and water retention
What causes the hypertension in nephritic syndrome?
- Salt and water retention
- Vasoconstriction
What is Rapidly Progressive Glomerulonephritis (RPGN)?
- Severe glomerular injury often with presence of crescents (proliferation of cells in Bowman’s space)
- Presents with rapid deterioration of renal function (over days to weeks)
- Low urine output, hematuria, hypertension and edema (in addition to other Sx of nephritic syndrome)
- Losing fibrin and GFs in urine that cause tubular cells to overproliferate and block off tubule system
- Crescent sign (proliferation of parietal (?) epithelial cell)