ABSTRACT
The kidneys are a pair of bean-shaped organs lying in the retroperitoneal space. The upper pole of each kidney is found opposite the 12th thoracic vertebra, while the lower pole lies opposite the 3rd lumbar vertebra. In humans, the kidneys weigh 150-170 g each and are about 11-13 cm in length. Approximately 180 1 of glomerular filtrate is produced each day, 99% of which is reabsorbed. The nephron, the functional unit of the kidney consists of a glomerular capillary and tubular network, which empties into the collecting duct. There are approximately 1.2 million nephrons per kidney At rest, only one-tenth of these are required to maintain homeostasis. The nephrons enable the kidneys to regulate body water and ionic composition, and to excrete waste products and foreign chemicals (e.g. drugs). The nephrons also secrete hormones that participate in the regulation of systemic and renal haemodynamics (renin, angiotensin II, and prostaglandins), haematopoiesis (erythropoietin), and bone metabolism (calcitriol). Moreover, in the fasting state, they are capable of producing glucose (gluconeogenesis) and participate in the catabolism of peptide hormones.
