Hardest CNN Practice Questions — Can You Answer These?

Nephrin. The NPHS1 gene encodes nephrin, a structural protein essential for the integrity of the podocyte slit diaphragm. Other key proteins include podocin (NPHS2). Dysfunction leads to massive proteinuria due to the loss of the final filtration barrier. Clinical Pearl: Podocytes are post-mitotic cells; their loss or effacement often leads to irreversible glomerulosclerosis (FSGS).

The JGA consists of the Macula Densa (distal tubule), Juxtaglomerular cells (afferent arteriole), and Extraglomerular Mesangial cells. Mechanism: High NaCl at the macula densa (indicating high GFR) triggers adenosine release, causing afferent arteriole vasoconstriction. This lowers glomerular hydrostatic pressure and GFR. Exam Strategy: Distinguish TGF from the systemic RAAS trigger.

Type IV Collagen (specifically the alpha-3, 4, or 5 chains). This is the hallmark of Alport Syndrome. The GBM provides the structural framework of the GFB and charge selectivity. Exam Strategy: NNCC often links structural anatomy to genetic conditions. Type IV collagen is the primary structural protein of the basement membrane; defects lead to thinning, splitting, and eventual sclerosis.

The vasa recta are specialized capillaries surrounding juxtamedullary nephrons. They maintain the medullary osmotic gradient via countercurrent exchange (slow blood flow prevents washing out solutes). Clinical Significance: The renal medulla is naturally hypoxic and hypertonic. In Sickle Cell Disease, these conditions promote RBC sickling in the vasa recta, leading to papillary necrosis.

Efferent arteriolar constriction increases glomerular hydrostatic pressure ($P_{gc}$) by creating back pressure in the capillary. This increases the net filtration pressure and GFR. Clinical Correlation: ACE inhibitors and ARBs dilate the efferent arteriole, lowering $P_{gc}$. This reduces hyperfiltration injury and is the basis for their nephroprotective effect in chronic kidney disease.