The kidneys

The main organ of the urinary system is the kidney which is covered by a capsule of dense collagenous connective tissue known as nephrotic capsule , and its medial border lies a notch called renal hilum where we see the output of vital structures such as the artery and renal vein and ureter.
If the kidney is cut parallel to its two faces , one can observe that the parenchyma ( serving cell ) is comprised of two areas of different color , which has been called medullary , or internal , and cortical , or external . In bone striations are organized in a pyramid . These pyramids are the pyramids of Malpighi called ( or kidney ) having a vertex oriented chalices (papillae ) .
Cortex or bark : Located on the outside and light red . The cortical , more yellow color , has in its outermost small spots that correspond to the Malpighian corpuscles . The cortical substance covering the spinal cord and also fills the spaces left between the pyramids of Malpighi .
Medulla : Occupies the inside , the medullary substance , dark red , composed of 8-18 triangular formations ( renal pyramids of Malpighi ) . Its base is in contact with the cortical substance and its apex , which has small holes 15 and 20 , is in communication with a renal calyx , which carries the urine to the renal pelvis .
In a longitudinal section of a kidney, three parts can be recognized :
The renal cortex , presents a dark reddish granules and completely surrounds the renal medulla sending extensions called renal columns are grafted core throughout the depth .
Renal medulla , have twice the crust thickness and structures clear reddish pyramid shaped , termed renal pyramids , which are separated by renal columns .
The renal papillae are distributed each into a minor calyx funnel-shaped , bearing in mind that each human kidney has 8-18 renal pyramids , and there is also 8-18 minor calyces , and major calyces 2-3 .
The nephron is the functional unit delparénquima kidney . In humans, each kidney contains about 1,000,000 to 2,000,000 nephrons. Nephron structure is complex and consists of uncorpúsculo untúbulo communicating with renal impairment. The renal corpuscle is Malpighian spherical , consisting of Bowman's capsule and glomerular capillary oglomérulo contained therein . The capsule, internally lined by a flattened epithelium , has two openings : the vascular pole , through which penetrates the afferent arteriole and the efferent arteriole emerges , and urinary pole , which communicates with the renal tubule.