URINARY STONES

R.A.S HEMAT, MB;BCh, FRCSI, DUL.

Urinary tract stones are a common painful, and costly medical condition. Retention of microcrystals by the urothelium is a critical event in stone maturation. Membrane phospholipids appear to be involved in the attachment of stone crystals to kidney epithelium.

15-20% of all urinary calculi are associated with infection.

Factors affect crystal retention

1-Adherence of particles to the urothelium.

2-Anatomical abnormalities.

3-Foreign bodies.

4-Residual urine.

Factors determine urinary saturation

1-Nature of the solvent, urine.

2-Nature of solute ions.

3-pH.

4-Temperature.

5-Crystalization inhibitors.

Urinary stones are polycrystalline aggregates composed of varying amounts of crystalloid and organic matrix.

Urinary calcium excretion is increased in hypertensives (HT), the hypercalciuria is regarded as the pathogenic link between HT and urolithiasis.

Morphologically, the matrix is composed of fibers of different colors. The matrix is remarkably stable against chemical degradation. Carbon dioxide, oxygen, nitrogen, hydrogen, titanium, chromium and sulfur are present.

Tamm-Horsfall glycoproteins is produced by the kidneys and has been localized in the thick ascending limb of Henle and the early distal, convoluted tubule segments of the nephron.

About 80% of the all renal stones contain calcium oxalate and/or calcium phosphate as their main crystalline components. The endogenous production of oxalate derived from the metabolism of glyoxylate and ascorbate, contributes importantly to the amount of oxalate that is excreted in the urine. Epithelial cells respond to hyperoxaluria and the presence of CaOx crystals in the kidneys by increased enzymuria and internalization of crystals. Crystal-cell interaction results in movement of crystals from the luminal to the basolateral side between the cells and the basement membrane.

Causes of hyperuricosuria

1-Adminstration of uricosuric agents, e.g probanecid.

2-Increased dietary intake of purine.

3-Primary or secondary gout.

4-Cancer, lymphoma and leukaemia.

Fundamentals of shock wave production in lithotripsy

1-spallation, occurs when a wave traveling in a brittle material such as stone is internally reflected.

2-cavitation, involves the nucleation, enlargement and collapse of bubble in a fluid.

Obstructive uropathy

Obsruction exists in a fluid-transporting system if the fluid pressure proximal to a relative narrowing must be raised to transmit the usual rate of flow through this area.

There are two phases of obstructive injury:

1-during obstruction.

2-immediately following its release.

Pathobiological renal changes that can be produced by ureteric obstruction:

1-the alteration in renal blood flow, has a major influence.

2-backpressure, initially but it is not a sustained stimulus.

3-neurogenic reflexes, but are shortlived.

4-chemical and hormonal changes.

5-immunological changes.

6-release of free radicals.

June, 2001

Note: The information in this article has been excerpted from the following books: urotext-ebook simplifying urology, Principles of modern urology, by Dr. R.A.S HEMAT. Permission is granted to copy and redistribute this document electronically as long as it is unmodified. This article may not be sold in any medium, including electronic, CD-ROM, or database, or published in print, without the explicit, written permission of Dr. R. A. S. Hemat.

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Dr. R.A.S HEMAT declares no conflicts of interest or financial interests in any product or service mentioned in this article, including grants, employment, stock holdings, gifts, or honoraria.