Which of the following is the least filtered in glomerules? (Which substance is least lost in urine)
**Core Concept**
The glomeruli in the kidneys act as selective filters, allowing certain substances to pass into the urine while retaining others. The glomerular filtration barrier consists of the endothelial cells of the capillaries, the basement membrane, and the podocytes with their foot processes. The size, charge, and lipid solubility of the substances determine their filtration through this barrier.
**Why the Correct Answer is Right**
Haemoglobin is the least filtered in the glomeruli due to its large size and negative charge. The glomerular basement membrane has a negative charge that repels negatively charged molecules like haemoglobin, preventing its passage into the urine. Additionally, haemoglobin is a large protein molecule that does not easily pass through the pores of the glomerular filtration barrier. As a result, only a very small amount of haemoglobin is lost in the urine, making it the least filtered among the given options.
**Why Each Wrong Option is Incorrect**
**Option B:** Albumin is normally filtered in small amounts in the glomeruli. However, under pathological conditions such as nephrotic syndrome, the glomerular filtration barrier becomes compromised, and large amounts of albumin are lost in the urine. In normal physiology, albumin is not the least filtered substance.
**Option C:** Myoglobin is a small protein that can be filtered in the glomeruli, especially in conditions of muscle damage or rhabdomyolysis. It is not the least filtered substance in the glomeruli.
**Option D:** Inulin is a polysaccharide that is completely filtered in the glomeruli and neither reabsorbed nor secreted by the renal tubules. It is often used as a marker of glomerular filtration rate (GFR). Inulin is not the least filtered substance in the glomeruli.
**Clinical Pearl / High-Yield Fact**
In conditions of glomerular damage, such as nephrotic syndrome, the loss of large proteins like albumin in the urine can lead to hypoalbuminemia, edema, and hyperlipidemia.
✓ Correct Answer: A. Haemoglobin