13 Parts of the Human Kidney & its Functions

Kidneys are vital organs for our body. To live, we need at least one of us. The kidneys are essential to ensure good general health because they are responsible for filtering the blood and purifying it by discarding the toxic substances through the urine produced in these kidneys for further elimination.

It only takes 30 minutes to filter all the blood flowing through our body, which is possible thanks to the coordinated action of different structures that make up these organs. Thanks to one million nephrons, blood-filtering cells, and other functional parts, the kidneys have many health implications.

Eliminate toxic substances from the blood, regulate the amount of fluid in the body, balance water and mineral concentrations, control blood pressure, produce hormones, incite red blood cell production, collaborate on bone health… The kidneys have countless functions in the body.

And to comply with all these, all its structures must be healthy and work correctly. In today’s article, we will review these kidney structures that make up the kidneys, analyzing their individual functions.


What’s the anatomy of the kidneys like?

The kidneys are part of the urinary tract and consist of two organs located below the ribs, one on each side of the spine and a fist’s size.

Blood reaches “dirty” through the renal artery, where all blood flows from the body that must be filtered through the kidneys to remove toxic substances. Once inside, the different structures that we will see below purify the blood (or help make this happen correctly) so that, in the end, the substances conform to the urine and the blood will come out “clean” through the renal vein. Next, we will see each of the structures that make up the kidneys.

Renal artery

The renal artery is a blood vessel that causes “dirty” blood to reach the kidneys. Each of these organs connects to a renal artery, the pathway of blood inlet for further filtration and purification.



Nephrons are the functional units of the kidneys, that is, the function of filtering blood is achieved thanks to these nephrons, cells specialized in removing toxic substances from the blood. The inside of the kidneys is each made up of more than a million nephrons. These nephrons have a tubule that collects the blood, already clean, and returns it to circulation.

But the important thing is that they also have those known as Bowman capsules, which are the parts of nephrons that come into contact with the glomerules, a network of blood capillaries that carry blood to these nephrons to purify and filter it. From the renal artery, blood vessels branch to these glamorous, which come into contact with Bowman’s capsule to filter out the blood they carry.


Bowman capsule

Bowman capsule is the structure of nephrons that fulfils the function of blood filtration. It is a tiny sphere inside the glomer Nile, which is the network of capillaries that come into contact with nephrons. In this capsule, the blood is purified because it acts as a filter that let’s pass any molecule whose size is less than 30 kilodaltons (the measure to determine the size of the molecules) blood has “free way” to return to circulation.

Proteins and other molecules in our body have no problem crossing the membrane of Bowman’s capsule. However, those of drugs and other toxic substances, being larger, cannot pass through this structure, being retained. In this way it is possible, on the one hand, to obtain “clean” blood and, on the other hand, to retain the toxics so that they are collected and eliminated later thanks to the production of urine, which will be responsible for structures that we will see later.



The ureter is a tube that leaves the kidneys in the direction of the bladder. Waste substances collected by nephrons end up forming urine, which leaves the kidneys into the urinary bladder for further urination through these thin tubes born from the renal pelvis. Every few seconds, ureters send urine generated in the kidneys into the bladder.


Kidney vein

The kidney vein is the blood vessel that collects “clean” blood after the nephrons have performed their function, so there are no more toxins present in it. Subsequently, this blood, which, despite being free of harmful substances, has no oxygen or nutrients, connects to the vena cava, which carries blood from the lower body to the heart to oxygenate.


Renal cortex

As the name suggests, the renal cortex is the outer part of the kidney. It is about 1 centimetre thick and is an area of reddish tissue as it is in this outer layer that approximately 90% of blood flow arrives.

Most nephrons are in this outer layer of the kidneys, which also has the function of absorbing shocks to prevent kidney damage, which, in case the trauma is strong, can be life-threatening. It also protects the kidney from possible infections.


Adipose capsule

The adipose capsule is a layer of fat that, although it does not have nephrons and is therefore not involved in blood filtration, this lipid nature is beneficial to protect the kidneys, as it absorbs shocks to prevent kidney damage. This layer of adipose tissue (fat) makes the kidneys keep their position in the abdominal cavity stable and not to move.


Kidney marrow

Kidney marrow is an interesting part of the kidneys. In this marrow, after the nephrons in the renal cortex have worked and the waste substances have been collected, urine forms. Unlike the outer part, it only receives 10% of the blood supply, so it has a much paler colouration.

In this marrow, the blood is not filtered, but the cells thmakeeup produceces the substances necessath to concentrate ato dilute urine according to the circumstances. Through this marrow, urine is collected until it reaches the ureters for further elimination through urination.


Kidney pyramid

Kidney pyramids are the units in which the renal marrow is divided. They are comical-looking structures, and there are between 12 and 18 for each kidney. They are the kidney marrow where urine is actually produced to be subsequently conducted to the ureters.

These renal pyramids, also known as Malpighi pyramids, are separated from the others by a renal column and has a characteristic rounded vertex called the renal papilla.


Renal papilla

Renal papillae are located at the apex of each of the renal pyramids and where urine produced by the renal marrow is collected and discharged. Through these kidney papillae, urine reaches the lower chalice, a structure of the kidneys that we will see below.


Lower Chalice

Kidney calyxes are the cavities that urine from the kidney papillae reaches. First, urine reaches the minor calyxes, which are at the base of each renal papilla, and where urine flows to the following structure: the larger calyxes.


Major Chalice

Approximately every 3 smaller calyxes come together to form a larger chalice, which is the cavity through which urine continues to flow to collect it all and take it to the ureters. Minor calyxes converge to form them, and urine flows thanks to peristaltic movements (movements of the walls in a particular direction) that occur in these calyxes and prevent fluid reflux, something that would be very harmful to the kidneys.


Renal pelvis

The renal pelvis is the point of exit of urine from the kidneys, that is, the structure by which toxic substances are removed from the kidney. The major calyxes of each kidney converge in the form of a funnel until it results in a single cavity: the renal pelvis.

The urine of each kidney is collected in this cavity. Extensions come out, the ureters, which, as we have seen, lead the urine to the bladder for further elimination through urination. This closes the cycle, having, on the one hand, “clean” blood and, on the other hand, a correct elimination of the toxics.



  • Rayner, H.C., Thomas, M.A.B., Milford, D.V. (2016) “Kidney Anatomy and Physiology”.
  • Restrepo Valencia, C.A. (2018) “Anatomy and Renal Physiology”.
  • National Institute of Health. (2009) “Kidneys and how they work”.
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Dr. Med. Raoul Hasert is a specialist in dermatology and venereology. He is a senior physician in Praxisklinik Dr. Hasert.

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