system (Nephrology)

system (Nephrology)

Introduction:
Each normal person has 2 kidneys one on each side. The main function of kidneys is excretion. They must rid the body of certain substances that have been taken in excess of body requirements and substances that end products of protein metabolism such as urea and creatinine.
Although there are two kidneys anatomically, but physiologically they function as 1 unit. Each kidney is located retroperitoneally between L4 and L5.
The upper pole of right kidney rest on the 12th rib, while the upper pole of the left kidney rest on the 11th and 12th ribs.
A longitudinal section in the kidney shows an outer most layer finely granular known as cortex, followed by medulla which is characterized by pyramid like structures..
The apex of these pyramids is known as papillae. These pyramid-like structures have separated from each other by (columns of Berti).
The pyramid usually envelope the pelvis where urine is excreted from holes in the papillae to be taken away later by the ureter to the urinary bladder.
Normally, there are about 8-10 of these pyramid-like structures each of which has on its papillae about 15-20 orifices. So, there are totally about 250 of these orifices which are connected to the ducts of Bellini (collecting ducts).
The kidney usually receive about 1/5 of the cardiac output passes through the kidney, and 1/4 of plasma passing is filtered (250 ml/min.). this means that in each 24 hr. about 180 liters of fluid are usually filtered, however, only 1.5-2 L of urine are excreted each 24 hr. and the remainder 178-178.5 L are reabsorbed, so, the main function of kidney include filtration, reabsorption and secretion.
The ratio between cortex and medulla is about 1:3, however, in certain animals living in the desert this ratio may reach 1:11 where water is not available. The distribution of blood is not equal between the cortex and the medulla where are 90% of blood supply usually flows in the cortex, outer medulla receives 8% and inner medulla receives only 2%.