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In renal disease albumin is first to appear in urine because:

A Of its high concentration in plasma

B Has molecular weight slightly greater than the molecules normally getting filtered

C High albumin: globulin ratio

D Tubular epithelial cells are sensitive to albumin

Ans. B Has molecular weight slightly greater than the molecules normally getting filtered

a. Functionally, the glomerular membrane permits the free passage of neutral substances upto 4 nm in diameter and almost totally excludes those with diameter greater than 8 nm. Glomerular wall is negatively charged with sialoproteins and Heparan sulfate, therefore, due to electrostatic force of repulsion, negatively charged substance as albumin (69 kD, 7 nm dia) not filtered.

b. Both charge and size (i.e. mol. wt.) selectively normally prevent virtually all plasma albumin, globulin (mol wt. 90 kD) and other larger weight proteins from crossing the glomerular wall.

c. Smaller' proteins (<20 kDa) are freely filtered but are readily reabsorbed by the proximal tubules.

d. Normal individual excrete < 150 mg/d of total protein and only about 30 mg/dL of albumin. the remainder of the protein in the Urine is secreted by tubules (Tamm-Horsfall, IgA, and Urokinase) or represents small amounts of filtered α2- micro - globulin, apoproteins, enzymes and peptide hormones".

Glomerular proteiuria: any disease 'damage the Glomerular filtration barrer 1st -ve charges are dissipated Albumin filtered' not reabsorbed in proximal tubules due to its larger mol. wt (size) appear in urine. Q

Tubular proteinuria: In the healthy, large amount of proteins of low mol. wt. than albumin are filtered by the glomerulus and reabsorbed in the PT. Injury to PT may result in decreased reabsorptive capacity and the loss of these low mol. wt. proteins in urine. Q

In tubular proteinuria, little or no albumin is detected, whereas in glomerular proteinuria the major protein is albumin Q

· Conclusion: Normally proteins upto size and mol. wt. of in albumin'are not filtered; and proteins with mol. wt. <20 kD are easily filtered but totally reabsorbed in PT. Albumin with mol. wt. 69 kD and larger mol. wt. proteins, they gets filtered in renal disease that disturbed size and-­ve charges of glomerular filteration barrier due to their larger mol. wt. they are not reabsorbed in PT and excreted in urine. There fore answer is (b) i.e. Albumin is first to appear in urine because, it has mol. wt. slightly>the molecules normally getting filtered.