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20 CASE 20


A 5-year-old boy presents to the urgent care clinic because his mother noticed that the child is not going to the bathroom and his feet are swollen.


Two weeks earlier the child was treated for strep throat with penicillin. The mother admits to ceasing administering the medication to the child after a couple of days because she thought the child was better.



PHYSICAL EXAMINATION



VS: T 37°C, P 78/min, R 15/min, BP 120/90 mm Hg

PE: The patient is oliguric and has a slight fluid accumulation in the lower extremities and periorbital region. There is palpable peripheral edema in both feet.


LABORATORY STUDIES



Urinalysis: Very dark urine, presence of red blood cells, red blood cell casts, and protein (>3 g/day)

Serum complement C3, C4, CH50 levels: Low

ASO titer: 250 Todd units/mL (normal: <160 units/mL)

Anti DNase-B level: >60 units

BUN: 32 mg/dL (normal: 7-18 mg/dL)

Creatinine: 2.0 mg/dL (normal: 0.6-1.2 mg/dL)


DIAGNOSIS


Poststreptococcal glomerulonephritis



PATHOPHYSIOLOGY OF KEY SYMPTOMS


The first step in urine formation is the ultrafiltration of plasma in the glomerular capillaries. Filtration across the glomerular capillaries depends on the balance of hydrostatic pressure (blood pressure) and colloid osmotic pressure (oncotic) pressure. Blood pressure within the glomerular capillaries is around 55 mm Hg, much higher than any other capillary bed in the body. This hydrostatic pressure is the major force driving filtration in the renal glomerulus. Albumin and other plasma proteins normally do not cross the glomerular barrier. Consequently, they provide an osmotic (oncotic) pressure in the capillary, a reabsorptive pressure that diminishes glomerular filtration. The net filtration pressure is about 10 mm Hg favoring filtration, accounting for glomerular capillary blood pressure, Bowman’s capsule hydrostatic pressure, and the capillary oncotic pressure (Fig. 20-1).


image

FIGURE 20–1 Hydrostatic and oncotic pressures determine filtration across the glomerular capillary (GC). Glomerular capillary filtration depends on the balance of the hydrostatic and the oncotic pressures. Hydrostatic pressure at the afferent end of the glomerular capillaries is high and decreases slightly along the length of the glomerular capillary. Plasma oncotic pressure in the glomerular capillary increases along the length of the glomerular capillary as plasma is filtered, but the large proteins remain within the capillary. The net balance of pressures ensures that only filtration occurs in the glomerular capillaries.

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Jul 4, 2016 | Posted by in PHYSIOLOGY | Comments Off on 20

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