The urinary system is responsible for the formation, conduction and storage of urine, a yellowish fluid known to all that is obtained as a result of the purification and filtration of an individual’s blood.
this mechanism is essential for the maintenance of balance in body fluids as well as for the elimination of toxic substances and even maintain blood pressure. Therefore, it’s no surprise that anyone knows that humans excrete an average of 1.5 liters of urine per day, depending on the food and fluids ingested.
We cannot talk about the urinary system without putting the eyes and the mind in the kidneys as they are one of the only two components that make up this apparatus along with the urinary tract. While every human has an overview of this interesting pair of organs, the kidneys hold a lot more secrets than they seem at first glance. That is why we are talking to you today about parts of the kidney and their functions.
Parts of the kidney and its functions: beyond urine formation
If one thinks of the urinary system, the first thing that comes to mind is the production of urine (logical, since this word is included in the first term). Despite this, kidneys do not limit their functionality to purifying blood. Therefore, first of all, we show you all the activities carried out by the kidneys for the physiological and metabolic balance of the human being:
- Regulation of volume and osmolarity (particle concentration) of body fluids. This is achieved by balancing the concentration of ions and water.
- Excretion of wastes, either as a product of normal cell function or by entry of foreign agents into the body.
- Synthesis of glucose from amino acids and other precursors. It represents 10% of the production of this monosaccharide in the body.
- Regulation of erythropoiesis (production of red blood cells) by secretion of the hormone erythropoietin.
- Regulation of blood pressure by the secretion of vasoactive factors such as renin (involved in the formation of angiotensin II)
- Regulation of the acid-base balance, mainly by the excretion of acidic substances. This is essential to maintain the internal pH balance.
- Production of 1,25-dihydroxyvitamin D3 (activated vitamin D), essential for maintaining adequate calcium levels in the bones.
As can be seen, we are dealing with multidisciplinary bodies, as they are not only responsible for the elimination of substances, but also they are also responsible for the synthesis of sugars such as glucose and hormones such as renin, erythropoietin or kallikrein, All with different functions on the body.
It’s amazing to think that a pair of organs that make up no more than 1% of a person’s body weight can become so essential to their survival, right? All of this is put more into perspective when we discovered that, for example, renal irrigation accounts for about 22% of cardiac output. The volume of blood passing through these structures at a given time is therefore a non-negligible value at all.
Once we anchor the functionality of these incredible structures, we dive into their characteristic morphology.
1. External protective fabrics
Let’s start with the outside and gradually dissect the kidney paste. First of all, it should be noted that each of these two organs is surrounded by three different layers of tissue:
- The outermost is known as the kidney capsule, a transparent, fibrous, continuous membrane that serves to protect the kidney from possible infections.
- A fat capsule, that is, a layer of fat of varying thickness that protects the kidney from blows and trauma and holds it in place in the abdominal cavity.
- The renal fascia, a layer of connective tissue that separates the fat capsule from adrenal fat.
It is especially important to remind readers that this system, by not being in direct contact with the environment, it does not have a microbiome or associated bacterial agents beneficial to its functions. To do this, we have these protective tissues, so that pathogens do not infiltrate and generate the dreaded urinary tract infections.
2. Renal cortex
This layer meets the outermost part of the kidney. It is one centimeter thick and has an earthy red coloration. this zone contains 75% of glomeruli, which are a network of small blood capillaries whereby purification and filtration of blood plasma takes place, as the first part of the urine formation process.
Therefore, the renal cortex receives 90% of the blood flow that enters these organs and has a function of filtration, reabsorption and secretion. It should be noted that this outermost layer is not separated longitudinally from the renal marrow, as a series of protrusions called renal columns occurs towards them.
3. Renal marrow
The renal medulla, in turn, it is located in a deeper point of the kidney and presents a greater morphological complexity, Since it is composed of units of conical appearance (with the base directed towards the crust) called renal pyramids. These are distributed among themselves by renal columns and their number varies between 12 and 18. We can therefore say that the human kidney is a multilobed organ.
The top of each renal pyramid leads to a smaller chalice, and the union of several of them give rise to the large calyxes, which join together to generate the renal pelvis. We must imagine this structure as if it were a tree: the renal pelvis is the trunk, and the calyxes each of the branches which lead to large leaves (the renal pyramids).
Finally, it should be noted that the renal pelvis corresponds to the section of the ureterTherefore, urine will travel here to the bladder, where it will accumulate until it is emptied by the process of urination known to all.
4. The nephron
It seemed that this moment would not come, but we cannot let the inkwell in the nephron: the basic structural and functional unit of the kidney, where blood is filtered and purified. To put it in perspective, we’ll say that there are an average of 1.2 billion nephrons in each kidney, which filter no more or less than 1.1 liters of blood per minute.
As difficult as it may be to form a mental picture of this complex structure, we will briefly describe its parts:
- Renal glomerulus / corpuscle: already named above, is the set of capillaries where the clearance and filtration of blood plasma takes place.
- Bowman’s capsule: Empty sphere in which the filtrate of the substances to be excreted is filtered. It wraps around the glomerulus.
- Proximal convoluted tubule: Its function is to increase the reabsorption and secretion surface of substances.
- Handle Henle: A fork-shaped tube that leads from the proximal profiled tubule to the distal profiled tubule.
- Contoured Distal Tubule: An ion-permeable tube that collects waste that was not initially filtered into the Bowman capsule.
As wrapped up as all this conglomerate of terminology may seem, the idea that should be clear is that the nephron is a highly specialized functional unit for performing the filtration of blood. This is summed up in four simple steps: filtration, tubular secretion, tubular reabsorption (recycling of nutrients and substances such as glucose, amino acids, 60-70% potassium and 80% bicarbonate) and excretionIn other words, the emptying of the nephron.
It should be noted that from the age of 40, on average 10% of nephrons are lost every 10 years. This happens because the kidneys are not able to regenerate them. However, the remaining nephrons have been shown to adapt to maintain proper kidney function within normal limits.
As we have seen, not only the parts of the kidney and their functions are very complex, but each of these organs is made up of millions of small, individual filtering machines: the nephrons.
We have to see the process of filtering and producing urine as a tree-shaped machine: From the small capillaries called glomeruli, where the filtration of blood occurs in as microscopically as possible to the renal pelvis (the place where the kidneys collect in the bladder), urine undergoes a series of changes and reabsorption that lead to the expulsion of the yellowish liquid.
- Rodrigues, CFS, Olave, E., Gabrielli, C., and Sousa, LMC (1997). Anatomical considerations in renal fusion: a case report. Chilean Journal of Anatomy, 15 (1), 51-55.
- Cachofeiro, V., Lahera, V. and Tresguerres, JA (1999). Anatomo-functional aspects of the kidney. HUMAN, 374.
- Anatomy of the Urinary Tract, stanfordchildrens.org. Retrieved September 9 from https://www.stanfordchildrens.org/es/topic/default?id=anatomyoftheurinarysystem-85-P04568
- Urinary system, Laboratory of physical anthropology and human anatomy. Retrieved September 9 from http://www.anatomiahumana.ucv.cl/morfo2/ren.html