Which of the following is FALSE regarding biochemical pathology of urine?
Answer A
Tamm-Horsfall protein, which is the most abundant urinary protein, is secreted by renal epithelial cells in the thick ascending limb and the distal convoluted tubule as a membraneanchored protein. It is a potent inhibitor of calcium oxalate monohydrate crystal aggregation, but not growth. Nephrocalcin, an acidic glycoprotein, is synthesised in the proximal renal tubules and the thick ascending limb. Osteopontin, or uropontin, is an acidic phosphorylated glycoprotein expressed in bone matrix and renal epithelial cells of the ascending limb of the loop of Henle and the distal tubule. Glycosaminoglycans, acid mucopolysaccharides, and RNA are examples of polyanions that have been shown to inhibit crystal nucleation and growth. The inhibitory activity of magnesium is derived from its complexation with oxalate, which reduces ionic oxalate concentration and calcium oxalate supersaturation. Among the glycosaminoglycans, heparin sulfate interacts most strongly with calcium oxalate monohydrate crystals.
Which of the following is FALSE regarding renal tubular acidosis (RTA)?
Answer C
RTA type I, also called ‘classic RTA’ or ‘distal RTA’ is the most common form in which the underlying problem is failure of H+ secretion in the distal nephron. The acquired causes are listed above. The hallmark of the condition is a hyperchloremic metabolic acidosis with a high urinary pH (>5.5) in the face of persistently low serum HCO3. Patients can also get hypokalemia associated with secondary hyperaldosteronism. These patients are recurrent stone formers mainly composed of calcium phosphate. While sodium bicarbonate corrects the sodium deficit, potassium citrate can increase the citrate levels and prevent stone formation.
Which of the following agents do NOT have a vasoconstrictor effect on renal artery?
Answer E
Substances like nitric oxide, carbon monoxide, acetylcholine and glucocorticoids decrease the renal artery tone. Vascular tone of the renal blood vessels is the net balance of all these substances and is crucial to the maintenance of GFR, tubular renal function and systemic blood pressure.
Which of the following factors do NOT stimulate the release of ADH?
Ethanol ingestion and phenytoin inhibit the release of ADH while nicotine and morphine stimulate the release. ADH is released in response to stimulation of osmoreceptor and/or baroreceptors in the carotid sinus and aortic arch. Osmoreceptor stimulation is involved in maintaining tonicity of body fluids. Baroreceptor stimulation leads to renal water retention though increased permeability of the collecting ducts, leading to concentrated urine.
The following are common causes of hyperkalemia EXCEPT for:
Answer D
Hyperkalemia could result due to primary renal tubular potassium secretory defect as in sicklecell disease, systemic lupus erythematosus, postrenal transplantation, obstructive uropathy, tubulointerstitial renal disease and pseudohypoaldosteronism. It can also occur due to inhibition of tubular secretion caused by drugs such as diuretics (amiloride, spironolactone and triamterene), cyclosporine and lithium. Impairment of renin-aldosterone axis can also result in hyperkalemia. Examples of this situation include Addison disease, primary hypoaldosteronism and could be drug induced (heparin, prostaglandin inhibitors, ACE inhibitors, pentamidine and beta blockers) (Leyendecker et al. 2004).
Click to expand