Human Kidney Functions

The main functions of the human kidney are the formation and excretion of urine, and control of the composition of body fluids. Details of the structure and functions ofthe human kidney may be found in textbooks of physiology [1] or biomedical engineering [13]. Each ofthe two human kidneys contains approximately one million units of tubules (nephrons), each 20-30 pm in diameter, and with a total 

The total blood flow rate through the two kidneys is approximately 

The mechanisms of transfer of molecules and ions across the wall of tubules are more complicated than in the artificial apparatus. In addition to osmosis and simple passive transport viz., ordinary downhill mass transfer due to concentration gradients), renal mass transfer involves active transport viz., uphill mass transport against gradients). The mechanism of active transport, which often occurs in living systems, is beyond the scope of this text. Active transport requires a certain amount of energy, as can be seen from the fact that live kidneys require an efficient oxygen supply. 

As is evident from the major difference between the GFR and the rate of urine production, the majority of the water in the filtrate is reabsorbed into the blood in the capillaries, by osmosis through the wall of the tubule and the interstitial fluid. This reabsorption of water occurs mostly in the proximal tubule, although some is also reabsorbed in the distal tubule and collecting duct. 

At the proximal tubule, the concentrations of glucose, proteins, and amino acids decrease greatly due to reabsorption by active transport into the capillary blood. Na , K+, Cl , and HCOg are also reabsorbed by active transport, although their concentrations vary minimally due to the large decrease in the water flow rate. 

This reabsorption of water occurs mostly in the proximal tubule, though some is also reabsorbed in the distal tubule and collecting duct. 

In the distal tubule and collecting duct, some Na + is either actively transported out or exchanged for K +, H +, NH4 + and water moves out by osmosis. Thus, the ion concentrations and pH of the body fluids are maintained at appropriate levels. 

---

S. Ramamoorthy, W. Liu, Y. Y. Ma, T. L. Yang-Feng, V. Ganapathy, and F. H. Leibach. Proton/peptide cotransporter (PEPT 2) from human kidney functional characterization and chromosomal localization. Biochim Biophys Acta 1240 1-4 (1995). 

In the U.S., the central nervous system syndrome is usually more common among children, and the gastrointestinal syndrome is more prevalent in adults. Exposure to lead is also linked to decreased fertility in men. Lead is a probable human carcinogen, based on sufficient animal evidence. Populations at increased risk of toxicity from exposure to lead include developing fetuses and young children, individuals with decreased kidney function, and children with sickle-cell anemia. 

Wang, J., et al. Na(+)-dependent purine nucleoside transporter from human kidney cloning and functional... 

Hosoyamada M, Sekine T, Kanai Y, Endou H. Molecular cloning and functional expression of a multispecific organic anion transporter from human kidney. Am... 

S. Masuda, T. Terada, A. Yonezawa, Y. Tanihara, K. Kishimoto, T. Katsura, O. Ogawa, and K. Inui. Identification and functional characterization of a new human kidney-specific H+/organic cation antiporter, kidney-specific multidrug and toxin extrusion 2. J Am Soc Nephrol 17 2127-2135 (2006). 

A number of clinical tests are available to detect kidney damage. The clinician examining a patient or the toxicologist monitoring an animal toxicity stndy collects urine and blood samples. Indications of kidney damage (which, of course, for the human patient could be related to many factors other then chemical toxicity) include urinary excretion of excessive amonnts of proteins and glucose, and excessive levels in the blood of unexcreted waste products such as urea and creatine. A number of additional kidney function tests are available to help pin down the location of kidney dysfunction. 

The functional unit of the kidney is the nephron. It is made up of the Malpighian bodies or renal corpuscles (consisting of Bowman s capsules and the glomerulus), the proximal tubule, Henle s loop, and the distal tubule, which passes into a collecting duct. The human kidney contains around one million nephrons. The nephrons form urine in the following three phases. 

In general, a medical device is defined as follows a medical device is an implant and equipment to be used either to achieve disease diagnosis, medical treatment, or disease prevention for human and animals, or to influence the physical structure and function of human and animals. Medical devices for humans may also be classified based on whether and how long the device is in contact with tissue or cells and on the degree of disjunction induced by the device when in a disabling situation. The term covers various categories, such as scissors and tweezers, with small risk to human function, to central venous catheters, artificial dialysis (human kidney), and pacemakers, with high risk to human function. 

Adverse Effects. The primary adverse effect of systemic pentamidine administration is renal toxicity. Renal function may be markedly impaired in some patients, but kidney function usually returns to normal when the drug is withdrawn. Other adverse effects include hypotension, hypoglycemia, gastrointestinal distress, blood dyscrasias (leukopenia, thrombocytopenia), and local pain and tenderness at the site of injection. Adverse effects are reduced substantially when the drug is given by inhalation, and this method of administration is desirable when pentamidine is used to prevent pneumocystis pneumonia in patients with human immunodeficiency virus (HIV) disease. 

Blood is delivered to the human kidney by the renal artery. Blood flows to the kidneys of the adult human at a rate of roughly 1 L/min. The adult human kidney contains approximately 1 million functional units, called nephrons, to which the blood is delivered for removal of solutes. Collected materials are excreted from the body in the urine. 

Creatine is not recommended for use by individuals with kidney problems, or by anyone at risk for kidney disease (such as those with a family history of kidney problems or diabetes). Again, further controlled clinical studies are needed to determine the long-term impact and safety of creatine supplement use on human renal function. 

OATP4C1 is the isoform predominantly expressed in the human kidney, and its rat isoform is expressed in the lung and kidney (111). In the kidney, it is mainly expressed in the basolateral membrane of the proximal tubules, and functional analysis elucidated that it accepts digoxin and T3 as substrates (111). 

---