Final answer:
A glomerular marker, such as inulin, is an external substance injected into the bloodstream to accurately measure the glomerular filtration rate (GFR). Unlike tumor markers, which are naturally produced by the body and may indicate cancer, inulin is not produced by the body and is solely utilized to assess kidney function.
Step-by-step explanation:
The term glomerular marker often refers to a compound used to measure renal function, particularly the glomerular filtration rate (GFR). An ideal marker is one that is completely filtered by the glomerulus but is neither secreted nor absorbed by the kidney, so that its concentration in the urine directly reflects its filtration rate. One such marker is inulin, a plant polysaccharide that is injected into the bloodstream. As inulin is not produced by the human body, it serves as an effective glomerular marker for determining GFR.
Another important concept related to renal function is the juxtaglomerular apparatus (JGA), which resides near the glomerulus and plays a critical role in the regulation of renal blood flow and GFR. The JGA includes juxtaglomerular cells that secrete renin in response to a fall in blood pressure. This is different from a tumor marker which is a substance found in the body that can be elevated in cancer, indicating the presence of the disease process. However, the distinction is clear as a tumor marker is produced by the body and can be a sign of cancer, whereas a glomerular marker like inulin is an external substance used to measure kidney function.