(kidney)
In humans the kideneys are situated below the diaphragm in the retroperitoneal space.
The kidneys are paired bean shaped organs whose main function it is to produce urine (filtration, reabsoption, concentration).
Through secretion and reabsorption the kidneys are important for systemic regulation of:
They are also an endocrine organ that synthesizes renin and erythropoetin and thus influences blood pressure and production of red blood cells.
The kidneys produce primary urine, an ultrafiltrate of the blood. Inside the tubule system further substances are secreted or reabsorbed and at the end of the process the actual urine (seconday urine) forms.
About 120 ml blood are filtered per minute (GFR, glomerular filtration rate) and about 180 liters of primary urine are produced per day but only about 1,8 liters of urine are excreted.
In humans the kidneys are situated under the diaphragm in the retroperetoneal space. They are between 10-12 cm lond and 5-6 cm wide. Their weight varies between about 120-200 g. On the outside, the kidney is surrounded by a coarse, non-stretchy connective tissue capsule (renal capsule) that is embedded in fatty tissue, the perirenal fat capsure or fatty capsule of the kidney. The whole package is covered in a coarse fascia sack, the renal fascia, Gerota's fascia.
The single kidney consists of 6-9 similar renal lobes that are divided into medulla and cortex. The shape of the medulla is similar to a cone or pyramid, which is why it can also be called renal pyramid. The tip of each renal papilla sits inside a renal calyx. On top of the renal papillas papillary ducts, fine pores that secrete urin are visible. All renal calyxes together form the renal pelvis.
The renal cortex forms an about 1 cm wide layer above the medullar pyramids and fills, in the form of renal columns, the spaces between the pyramids.
Roughly, the straight parts of the nephron and the collecting ducts are inside the medulla and the convuluted parts of the nephron and the glomeruli inside the cortex.
