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The normal range of GFR, adjusted for body surface area, is 100–130 average 125 (mL/min)/(1.73 m 2) in men and 90–120 (mL/min)/(1.73 m 2) in women younger than the age of 40. In children, GFR measured by inulin clearance is 110 (mL/min)/(1.73 m 2 ) until 2 years of age in both sexes, and then it progressively decreases.
In humans, about 20,000 protein coding genes are expressed in human cells and almost 70% of these genes are expressed in normal, adult kidneys. [ 26 ] [ 27 ] Just over 300 genes are more specifically expressed in the kidney, with only some 50 genes being highly specific for the kidney.
The kidney is divided into parenchyma and renal sinus. The renal sinus is hyperechoic and is composed of calyces, the renal pelvis, fat and the major intrarenal vessels. In the normal kidney, the urinary collecting system in the renal sinus is not visible, but it creates a heteroechoic appearance with the interposed fat and vessels.
In a typical mammal, a normal average pH level is around 7.4. [147] As in the case of other vertebrates in mammals, the acid-base balance is maintained mainly by the bicarbonate buffer system (HCO 3-/CO 2), which allows maintaining a constant pH level of the blood and extracellular fluid. [148]
The Glomerular filtration rate, an estimate of normal kidney function, is usually normalized to body surface area (S). S and V differ markedly between small vs. large people and between men and women. A man and a woman of the same S will have similar levels of GFR, but their values for V may differ by 15-20%.
The typical human reference ranges for serum creatinine are 0.5 mg/dL to 1.0 mg/dL (about 45 μmol/L to 90 μmol/L) for women and 0.7 mg/dL to 1.2 mg/dL (60 μmol/L to 110 μmol/L) for men. The significance of a single creatinine value must be interpreted in light of the patient's muscle mass.
The first step in urine formation is the filtration of blood in the kidneys. In a healthy human, the kidney receives between 12 and 30% of cardiac output, but it averages about 20% or about 1.25 L/min. The basic structural and functional unit of the kidney is the nephron.
This illustration demonstrates the normal kidney physiology, including the Proximal Convoluted Tubule (PCT), Loop of Henle, and Distal Convoluted Tubule (DCT). It also includes illustrations showing where some types of diuretics act, and what they do. Renal physiology (Latin renes, "kidneys") is the study of the physiology of the kidney.