Kidneys are complex organs that perform many functions. In addition to filtering blood, they secrete hormones that regulate blood pressure and maturation of red blood cells. Many of the filtration functions also have secondary effects, such as maintaining bone health and controlling the acid-base balance in the body. Given these numerous functions, it is not surprising that kidneys are made up of many cell types. Listed below are the most common.
Structures in the kidney include the renal corpuscle (comprised of a glomerulus and bowman's capsule), which filters the blood, and various tubules, through which blood and urine pass. The renal corpuscle is made of parietal cells, podocytes and mesangial cells. The various tubules are made of columnar and cuboidal epithelial cells.
Mesangial cells make up the mesangium. "Dorland's Medical Dictionary" defines mesangium as "the thin membrane supporting the capillary loops in renal glomeruli." The terms "mesangium" and "mesangial matrix" are used interchangeably. They refer to the central part of the glomerulus in between capillaries. It is also called the mesangial matrix.
These cells are particularly important, because they are involved in many glomerular diseases, such as IgA nephropathy, MPGN, IgM nephropathy and others.
Podocytes are particularly fascinating, because many researchers, including Richard Ransom at the University of Michigan Health System and Marcello Camici at Pisa University, have recently shown that kidney patients lose these cells when they are shed into the urine. These cells look rather like a hairy creature with long appendages, called foot processes. Researcher Andrey Shaw at Washington University in St. Louis believes they help regulate filtration, as well as act as a filtration barrier.
The term "effaced foot processes" is used to describe the abnormal appearance of podocytes in kidney biopsies.
Other Glomerular Cells
Juxtaglomerular cells and parietal cells make up the bowman's capsule, which protects the glomeruli. Juxtaglomerular cells are involved in the release of renin, a hormone involved in the regulation of blood pressure. These cells can also be destroyed by kidney disease.
Loop of Henle
According to the "Encyclopedia Britannica," the loop of Henle is involved in recovering water and sodium chloride from urine. This has the effect of concentrating wastes in the urine in a minimal amount of fluid. Because water is recovered and recycled, less water intake is necessary to sustain life.
The loop of Henle is comprised of renal medullary tubular cells.
The loop of Henle is flanked by the distal and proximal convoluted tubules. The proximal convoluted tubule connects the renal corpuscle to the loop of Henle. The distal convoluted tubule is at the other end and connects the loop of Henle to the collecting duct system that passes urine to the ureters and, ultimately, the bladder.
Although the proximal and distal convoluted tubules are both made from columnar epithelial cells, they look different under the microscope. Cells in the distal tubule appear shorter, whereas cells in the proximal convoluted tubule have what is called a brush border appearance.
These cells can be damaged due to diabetes or advanced stages of the diseases described above.