Primaarivirtsan

Primaarivirtsan is a term used in Estonian-language nephrology and physiology texts to refer to the primary urine, also known as the glomerular ultrafiltrate. This filtrate is produced by the renal glomeruli as blood is filtered across the filtration barrier into Bowman's capsule. In English-language physiology, the corresponding term is “primary urine” or “glomerular ultrafiltrate.”

The concept encompasses the initial filtrate that is similar in composition to plasma but lacking plasma proteins and large solutes, with water, ions, glucose, amino acids, and small metabolites present in plasma at similar concentrations, and with an osmolarity close to that of plasma.

Formation and composition: The primary urine is formed by hydraulic filtration driven by the glomerular capillary pressure, with selective permeability of the glomerular basement membrane and podocyte slit diaphragms. Its volume depends on the glomerular filtration rate and renal perfusion. Most constituents are subsequently modified along the renal tubules by reabsorption and secretion to form final urine.

Usage and significance: In teaching and some regional medical literature, primaarivirtsan is used to illustrate the starting composition of filtrate before tubular processing. It is not a separate clinical specimen; rather, it represents the initial product of renal filtration. In English-language practice, the term “primary urine” is more common.

See also: Kidney, Nephron, Glomerulus, Glomerular filtration rate, Urine, Renal physiology.