Pacemaker, by Chris Carr
The human kidney is an essential organ, playing vital roles in both the urinary and endocrine system. The kidney maintains the chemical and water balance of the body with the help of nephrons, which are the functioning units that remove waste from the blood. Nephrons accomplish this through filtration and both active and passive transport; each kidney has approximately 1 million nephrons. Figure 1 shows a nephron and the processes that occur .
It is important to note that the blood enters the nephron at the glomerulus, which filtrates solutes up to 60,000 Da. The glomerular filtration rate (GFR) for an average person is roughly 125 mL/min, or 180 liters/day. The resulting fluid and solutes then enter the renal tubes, where different types of transport occurs .
In the proximal tube (first part of the renal tube), water is reabsorbed back in the blood stream: around 178 liters/day. Other substances are also reabsorbed, such as sodium and glucose. Glucose is always fully recovered while sodium is regulated; depending on the salt concentration within the body, sodium is either reabsorbed or secreted .
The substances that were not filtered out in the glomerulus, like hydrogen and potassium ions, ammonia, and certain drugs, enter the peritubular capillaries. These components are then secreted into the distal tubule (second part of the renal tube). The toxins are then sent to the bladder with the ~1% of water that wasn't reabsorbed .
The kidney also has other important functions by sensing the composition of the blood and secreting substances that aid in bone metabolism, red blood cell production, and blood pressure regulation. When kidneys are no longer able to function as intended, renal failure occurs and can be classified as acute or chronic. Both can be treated with dialysis if there is not a donor organ available .
1854 - Thomas Graham developed an apparatus that held urine and water separated with a membrane. After several hours, sodium chloride and urea were found to have transported across the membrane. Set the basis for dialysis. 
1924 - Georg Haas performed first human hemodialysis on a uremic patient. 
1937 - First flat hemodialysis membrane made of cellophane produced. 
1940 - Willem Kolff takes interest in acute renal failure. 
1943 - Kolff created dialysis machine using sausage casings, washing machine, and orange juice cans. Treated 15 patients with little to no success. 
1945 - Kolff treated a 67 year old woman with longer dialysis time and she survived for another seven more years. 
1947 - Kolff donates his dialysis machines to other hospitals, allowing other doctors to learn the design of the machine and improve upon it. 
1948 - First hermodialysis machine constructed in the US to be used at Peter Bent Brigham Hospital. 
1954 - First kidney transplant. 
1960 - Belding Hibbard Scribner invented the Scribner shunt, preventing the numerous incisions required for dialysis. 
1962 - Scribner opened the first outpatient dialysis facility.