Page 112 - Color Atlas Of Pathophysiology (S Silbernagl Et Al, Thieme 2000)

Abnormalities of Glomerular Function
The function of the glomeruli is to produce an the glomeruli and, via complement activation,
adequate GFR, i.e., the volume of plasma water produce local inflammation (→ p. 48ff.). This
that is controlled by the renal epithelium. The results in obstruction of the glomerular capil-
selective permeability of this filter (→ p.104) laries and destroys the filtering function (im-
ensures the formation of a nearly protein-free mune complex nephritis). Numerous drugs, al-
filtrate. As all of the blood flowing through the lergens, and pathogens can act as antigens.
kidney must pass through the glomerular ves- Streptococci (group A, type 12) are very often
sels, the resistance of these vessels also deter- responsible. Antibodies include IgG, IgM, and
Kidney, Salt and Water Balance ity (K f ), and the filtering surface (F): GFR = much less common than immune complex ne-
mines RPF.
commonly IgA (IgA nephritis).
Masugi’s nephritis, caused by autoanti-
The GFR is determined by the effective fil-
bodies against the basement membrane, is
tration pressure (P eff ), the hydraulic conductiv-
phritis. The local inflammation initially results
K f · F · P eff . The effective filtration pressure is
made up of the hydrostatic (∆P) and the oncot-
in hyperemia, accumulation of neutrophils
(exudative phase), and damage to the often
ic (∆π) pressure gradients across the filter
markedly thickened basement membrane. It
(→ A): P eff = ∆P – ∆π. Even if the filter is defec-
is common for endothelial, mesangial, or cap-
tive, π within the capsular space of the glomer-
the plasma oncotic pressure (π cap ). As a result
mately for excess mesangial matrix to form
of glomerular filtration, the protein concentra-
(sclerosing).
tion in plasma is increased and π cap as a rule
The glomeruli may also be damaged with-
5 ulus can be ignored, i.e., ∆π practically equals sular epithelial cells to proliferate and ulti-
comes close to the hydrostatic pressure gradi- out any local inflammation, for example, by
ent toward the end of the glomerular capillary deposition of amyloid in amyloidosis, by a
loops (filtration equilibrium). high concentration of filtrable proteins in plas-
Reduced hydraulic conductivity (→ A2) or a ma (e.g., in multiple myeloma), by high pres-
reduced filtration surface decreases the GFR. sure in the glomerular capillaries (e.g., in arte-
No filtration equilibrium can be achieved; as a rial hypertension, renal vein thrombosis, ve-
result of the reduced increase in π cap , P eff ulti- nous back pressure in right heart failure, or hy-
mately rises. But this does not compensate for perfiltration in diabetic nephropathy) as well
the reduced conductivity. as by reduced perfusion (e.g., in atherosclero-
Constriction of the vas afferens (→ A3) sis, arteriosclerosis).
when systemic blood pressure remains con- In glomerulonephritis, resistance in the
stant reduces the filtration pressure and thus vasa afferentia and efferentia is increased and
the proportion of filtered plasma water (filtra- the RPF is reduced despite filtration pressure
tion fraction = GFR/RPF). At the same time the usually being high. The reduced hydraulic con-
renal blood flow and the GFR fall because of ductivity prevents filtration equilibrium being
the increased resistance. achieved and lowers GFR. The reduced renal
Constriction of the vas efferens (→ A4) perfusion stimulates the release of renin
raises the effective filtration pressure and which, via angiotensin and aldosterone, raises
thus also GFR/RPF. Simultaneously it reduces blood pressure. In addition, the development
glomerular perfusion and thus GFR at any giv- of hypertension is aided by reduced excretion
en filtration fraction. The constriction of the of NaCl and H 2 O, brought about by the de-
vas efferens (e.g., on infusion of angiotensin II) crease in GFR (→ p.114).
or obstruction of venous flow (e.g., by renal Selective permeability is lost by damage to
vein thrombosis) can thus ultimately reduce the glomerular filter, thus leading to protein-
GFR. uria and edema (→ p.104).
The glomeruli can be damaged by inflam- Damage to the kidney can, for example, de-
matory disease (glomerulonephritis; → B). stroy erythropoietin-producing cells and thus
102 Among possible causes are soluble antigen– result in the development of anemia.
antibody complexes that become entangled in
Silbernagl/Lang, Color Atlas of Pathophysiology © 2000 Thieme
All rights reserved. Usage subject to terms and conditions of license.