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© Dirk Biddle
Inflammation of the kidney (nephritis), marked by inflammation of the capillary loops of the renal glomeruli (the networks of tiny blood vessels in the kidneys where the blood is filtered and waste products are removed), is termed glomerulonephritis.
Glomerulonephritis is confined to small-vessel vasculitis (thus its presence provides a concrete criterion for separating small-vessel vasculitis from the large- and medium- vessel vasculitides) and the hallmarks of the condition are hematuria and proteinuria. Glomerular proteinuria results from increased permeability of the glomerular wall, allowing proteins of greater than usual molecular weight to escape from the blood into the urine. Further, due to loss of immunoglobulins in the urine, most nephrotic patients show a decreased level of serum IgG and an elevated level of IgM. Also the loss of hormone binding proteins in the urine may lead to endocrine abnormalities such as vitamin D deficiency.
Furthermore, loss of blood proteins like albumin in the urine can result in a fall in their level in the bloodstream. In normal blood, albumin acts like a sponge, drawing extra fluid from the body into the bloodstream, where it remains until the kidneys remove it. But when albumin leaks into the urine, the blood loses its capacity to absorb extra fluid from the body. Fluid can accumulate outside the circulatory system in the face, hands, feet, or ankles and cause swelling (oedema).
The pathogenesis of glomerulonephritis involves three phases of injury. The first is usually an antigen-antibody (immune complex) reaction that secondarily activates one or more chemical mediators and stimulates resident cells to proliferate and/or transform metabolically. At this point the glomerulus is not irreversibly damaged and can heal. The third phase is progression to chronic disease due to buildup of glomerular basement membrane (GBM) material resulting in sclerosis and obliteration of surface area of ultrafiltration (410).
Deposits once formed activate complement which in the subendothelial space can attract circulating polymorphonuclear leukocytes which appear to strip away the overlying endothelium to gain access to the deposit. Endothelial damage may result in platelet-aggregation and induction of coagulation. Leukocytes can produce proteolytic enzymes, toxic oxygen metabolites, and along with platelets release cationic proteins that can affect glomerular permeability. Mesangial and subendothelial deposits are associated with glomerular hypercellularity and at times crescent formation. Crescents are accumulations of macrophages, fibroblasts and fibrin within Bowmans' space which indicate active and usually severe glomerular injury. Thus subepithelial deposits activate complement along the membrane of the epithelial cell producing injury to the podocytes. This results in increased glomerular permeability and a buildup of GBM (spile formation) around the deposits as seen in membranous nephropathy. In some glomerular diseases immune deposits may be formed by a single mechanism, whereas in lupus glomerulonephritis, where deposits are found in all portions of the glomerulus, several mechanisms may be involved. There is also experimental evidence that lymphocytes sensitized to a glomerular antigen can produce acute proliferative injury by direct invasion of the glomerulus in the absence of immune complex formation (410).
Glomerulonephritis is one of the most frequent manifestations of Polyarteritis nodosa or Wegener’s granulomatosis. The most common form of mesangial proliferative glomerulonephritis is IgA-associated glomerulonephritis (Berger’s disease), named because of the finding of IgA and C3 deposits within the mesangium. Occasionally IgM is the principal immunoglobulin along with C3 and it is called IgM nephropathy. IgA associated glomerulonephritis and Henoch-Schönlein purpura are considered to be part of the same disorder having similar IgA glomerular deposits and with some patients having elevated serum IgA levels and IgA deposits in skin.
Large-vessel vasculitis also causes renal dysfunction but in a different way by injuring the renal arteries and the aorta adjacent to the renal artery ostia. These injuries result in reduced renal blood flow and lead to renovascular hypertension.
Medium-vessel vasculitis most often affects lobar, arcuate, and interlobular arteries in and around the kidney, and may result in infarction and haemorrhage.
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Nephritis: Inflammation of the kidney, a focal or diffuse proliferative or destructive process which may involve the glomerulus , tubule or interstitial renal tissue. (OMD),
Capillary: Any of the smallest blood vessels connecting arterioles with venules and forming networks throughout the body. (M+),
Glomerulus: One of the structures which comprise the nephron (functional unit) in the kidney. The glomerulus is composed of capillary blood vessels which are actively involved in the filtration of the blood. (OMD),
Glomerulonephritis: A variety of nephritis characterised by inflammation of the capillary loops in the glomeruli of the kidney. It occurs in acute, subacute and chronic forms and may be secondary to haemolytic streptococcal infection . Evidence also supports possible immune or autoimmune mechanisms. (OMD),
Hematuria: The finding of blood in the urine. (OMD),
Proteinuria: Too much protein in the urine. This may be a sign of kidney damage. (OMD),
Mesangial: Referring to the mesangium: A central part of the renal glomerulus between capillaries; mesangial cells are phagocytic and for the most part separated from capillary lumina by endothelial cells.
Extraglomerular mesangium, mesangial cells that fill the triangular space between the macula densa and the afferent and efferent arterioles of the juxtaglomerular apparatus. (OMD)
A thin membrane that gives support to the capillaries surrounding the tubule of a nephron. (M+),
Hypercellularity: The presence of an abnormal excess of cells (as in bone marrow). (M+),
Bowmans' space: (Capsular space; Filtration space) The slitlike space between the visceral and parietal layers of the capsule of the renal corpuscle; it opens into the proximal tubule of the nephron at the neck of the tubule. (OMD),
Podocytes: Cells of the visceral epithelium that closely invest the network of glomerular capillaries in the kidney.
Most of the cell body is not in contact with the basal lamina, but is separated from it by trabeculae that branch to give rise to club shaped protrusions, known as pedicels, interdigitating with similar processes on adjacent cells.
The complex interdigitation of these cells produces thin filtration slits that seem to be bridged by a layer of material (of unknown composition), that acts as a filter for large macromolecules. (OMD),
Spile: 1. A small plug or wooden pin, used to stop a vent, as in a cask.
2. A small tube or spout inserted in a tree for conducting sap, as from a sugar maple.
3. A large stake driven into the ground as a support for some superstructure; a pile. Spile hole, a small air hole in a cask; a vent. (OMD),
OstiumAn opening; a passage,
Hypertension: Abnormally high arterial blood pressure. (M+),
Lobar: Having to do with a lobe. For example, lobar pneumonia. (OMD),
Arcuate: Curved like a bow,
Interlobular: Between lobules; as, the interlobular branches of the portal vein. (OMD)