In this article we are going to discover what are the parts of a kidney and the different functions it performs (both in humans and in animals). Being this one of the main organs of the human body and of the urinary system, its evolution until today has been essential for the survival of all the species that carry it.
Performing basic functions and with unique characteristics, compared to other organs, it is one of the fundamental elements for the homeostasis of the body and its survival.

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What is a kidney
As everyone knows, the kidney is an organ of the urinary system . This system is responsible for generating urine, storing it and expelling it. In the human body, the kidneys are located in the posterior area of ​​the abdomen, since there are two. Specifically, on each side of the spine.
On the other hand, the kidneys are irrigated by the renal vein, the renal artery and connected to the central nervous system thanks to a nerve called the renal plexus.
Each kidney has on itself what are known as adrenal glands . These glands are responsible for regulating the response to stress, thanks to the synthesis of corticosteroids and catecholamines.
There are 5 fundamental parts of the kidney to understand its operation. Although there are others, we can mention these as the most remarkable and anatomically visible. In this image, the ones that we are going to explain and others are also indicated.
Major parts of the kidney. | Image: Courtesy. 1. Renal cortex
Makes up the outermost part of the kidney. It is approximately one centimeter thick (depending on the area) and is red-brown in color. Of all the blood that receives the kidney, 90% goes to the renal cortex.
Its main functions are: filter, reabsorb substances and secrete. 2. Renal medulla It is the deepest part, located after the renal cortex. Composed of about 8-18 renal pyramids (cone-shaped tissues also called Malpighian pyramids) among which are the columns of Bertin. 3. Nephron or Nephron
The nephron is composed of 4 components (corpuscle, proximal convoluted tubules, Loop of Henle, distal convoluted tubules). This is where blood filtration occurs to deposit useless elements in the urine.
It is the most “sensitive” part to diseases, since most of them affect this area in particular. 4. Juxtaglomerular apparatus
This structure can be found in each of the nephrons of the kidney. Being one of the smallest parts of the kidney, it is also one of the most significant. SpecificallyIt is located between the afferent and efferent arteriole , next to the distal convoluted tubule.
The structure of the apparatus is made up of the so-called juxtaglomerular cells, which secrete renin, an enzyme (protein) that serves to maintain the water and salt balance in the body. In addition , the cells of the macula densa and Goormaghtigh cells
also play an indispensable role in its structure. 5. Collecting duct system
They are also called papillary ducts or Bellini’s ducts. This is the part of the kidney where the glomerular filtrate arrives, via the distal convoluted tubule.
In other words, the collecting ducts are responsible for receiving secretions from the nephrons and draining the minor calyces (where the urine is) to the ureters. The final step will be to send the urine from each ureter to the urinary bladder , where it will be stored until its final expulsion, thanks to the urethra. Characteristics of the kidney
Continuing with the anatomical position in the human body, the right kidney rests behind the liver ; while the left kidney is just below the diaphragm and next to the spleen. The upper part of both kidneys (especially the left one, because it is higher) is partially protected by ribs 11 and 12 (the last ones).
One of the most significant characteristics of the kidneys is that they account for 22% of the cardiac output of the entire organism . That is, 22% of the work done by the heart is to make these organs work. In addition, the kidneys account for 1% of the total weight of a person (on average).

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Functions of the kidney
The kidney performs a large number of functions, the most varied. Below we discuss the most important. 1. Excretion
The most popularly known function is to expel disposable substances through urine . To do this, the kidney is responsible for creating urine where it places all those substances that the body does not need and that could be harmful, such as ammonia and urea. 2. Homeostasis Homeostasis consists of a state where the organic stability and self-regulation . The kidney has the function of getting the body (animal or human) to be in this state of balance. To achieve this, it uses several highly complex mechanisms. Among which we can find:

  • Regulation of the ionic composition of the blood.
  • Regulation of blood osmolarity .
  • Regulation of plasma volume .
  • Regulation of blood pressure .
  • Regulation of blood pH .

3. Secretion of hormones
One of the most remarkable functions of the kidney is the secretion of different hormones, with different purposes. Among them we have: erythropoietin, renin, vitamin D and kallikrein . 4. Metabolic function
Through a metabolic process called gluconeogenesis, the kidney creates glucose from amino acids present in the body. This is done in emergency cases when the body has not eaten for long periods. Anyway, this function is especially responsible for the liver .
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