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What is Excretory System in Humans? Everything You Need to Know

by Sankalan Baidya
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Excretory System

The Excretory System in humans is one of the various systems that is tasked with a specific type of job. The human body has, what we like to call, a layered structure. At microscopic levels, it is made of cells. These cells combine to form various tissues. Specific types of tissues then combine to make organs. A set of organs make up a system. A system in turn has a specific type of job to perform. There are in total, 13 systems in a human body. They are mentioned in the table below:

SYSTEM NAME A QUICK OVERVIEW
Circulatory System It is involved in circulation of blood throughout the body.
Digestive System It is a system in which food is converted into basic nutrients and energy that our body requires to stay alive.
Excretory System It is a system that is designed to eliminating waste products from the body using a process known as homeostasis.
Endocrine System This system is designed for using hormones for providing chemical communication inside the body.
Integumentary System or Exocrine System It is a system responsible for production as well as secretion of certain substances either for protection or lubrication of the body. This system is made of glands.
Immune System It is a defensive system of our body that is responsible for defending our body from diseases that are caused by various microbes.
Lymphatic System It is actually a part of both the Circulatory System and the Immune System and is composed of network of tissues and organs designed for eliminating toxins from the body. This system also contains the White Blood Cells and hence, a support for the Immune System.
Muscular System This is a system that makes use of muscles for to help the body move.
Nervous System It is a system of nerves responsible for collecting information from various senses as well as brain and sends tells the muscles in the body to take physical actions.
Urinary System or Renal System One of the primary functions of this system is filtration of blood. The other important function is waste elimination and hence, the Renal System is also a part of the Excretory System.
Reproductive System It is a system of organs (sex organs) responsible for offspring production. Well, they are also used for simple pleasure.
Respiratory System It is a system of organs that are responsible for bringing air inside the body. The system involves lungs and trachea.
Skeletal System It is a system of bones that provides support to the body and all the organs inside the body.

One really important thing you need to understand about these systems is that they are interconnected with one another in some way or the other. They cannot work independently. A small example is that of Immune System and Lymphatic System. Another example is the Circulatory System and Reproductive System where penis cannot get erect if blood supply to penis (a sex organ) stops. While what we said is overly simplified, the truth is that each and every bodily system is way too complex.

So, it is now time to get back to the original topic – the Excretory System of human body. Let’s start…

What is Excretory System?

The Excretory System in human body is a passive biological system that is designed to remove the unnecessary biological wastes from our body fluids. One of the primary reasons for removing the wastes is to maintain chemical homeostasis. Chemical homeostasis is a property in which, the concentration of various substances (chemicals) in the body fluid is maintained in a particular concentration. If the concentration of those chemicals change, our body will be inflicted with internal damage. So, maintaining a constant concentration is important. This is what the excretory system does. It actively regulates the chemical concentration in our body by removing unnecessary biological wastes.

What waste products are removed by Excretory System?

As we mentioned earlier, our body has a number of systems that are dependent on each other. All these system generate a number of waste products or byproducts through various chemical process that take place in our body. These byproducts or waste products are essentially various chemicals that our body doesn’t need. Presence of those chemicals will only damage our body. So, removing them is mandatory and the Excretory System does the job. The question is, what are the waste products that are produced? A number of them actually. Here is a quick table to help you:

SYSTEM BYPRODUCTS OR WASTES
Respiratory System Carbon Dioxide, Water and various other gases.
Integumentary System Urea, Lactic Acid, Inorganic Salts.
Digestive System Water, Salts, Lipids, Cholesterol, Carbon Dioxide, Bile Pigments
Urinary System Hydrogen Ions, Hormones, Water, Salts, Drugs, Toxins, a wide range of metabolic wastes.

How does the Excretory System excrete wastes?

The whole Excretory System of humans can be considered as one big organism made of several organs throughout the body. The waste products that are produced inside the body are excreted by the system. The commonest way of doing so is through URINE. So yes, Urinary System is a major part of the Excretory System of our body. However, several wastes are also expelled through other means such as exhalation and sweating. So, this brings us to the question, ‘what are the organs involved in Excretory System?’

Organs that form the Excretory System

Here is something interesting. The Excretory System involves many organs. However, when spoken in the narrow sense, people use Excretory System and Urinary System synonymously. The truth is that Urinary System is the major part of the Excretory System and not the whole of the Excretory System. So, this brings us to the question – ‘what are the organs involved in Excretory System?’

Here is the answer: The organs and components that are involved in Excretory System include:

  • Kidneys
  • Liver
  • Lungs
  • Bile
  • Large Intestine
  • Skin
  • Ureters
  • Urinary Bladder
  • Urethra

Is Defecation not a part of the Excretory System?

You must be wondering why we asked this question. We will explain. In case you have noticed, we have not listed ‘Anus’ as part of Excretory System. Anus is the part from where we defecate (poop). So, why is it not on list.

The reason is simple. Defecation is actually a part of the Digestive System. The act of Defecation is also known as Elimination. It is not the same as Excretion. In Elimination, undigested food material is removed from the body via Anus in form of fecal matter. Defecation is the final act of digestion.

Fecal matter (what is, in common parlance, known as poop or slightly technically, stool) is not a byproduct of metabolism. It is not metabolic waste. Poop is the end product of digestion. We eat a variety of food but not everything can be digested by our Digestive System. What remains undigested composes the stool that can contain solid, semisolid or liquid waste from the process of digestion.

This is the reason why Defecation or Elimination is not a part of the Excretory System. Hopefully this clarifies why we asked the question in the first place.

Organs and Components of Excretory System and their functions

The heading is pretty self-explanatory. We will discuss about each organ and component of the Excretory System and their functions in this section. We don’t intend to explain everything is extreme details because we already have separate articles on them rounding up important facts about them. The relative links will be provided in due course.

Let’s begin…

Kidneys as part of Excretory System:

Sitting on either side of our vertebral column right in our abdominal cavity are two small organs that have the shape of a bean. They are the Kidneys. These Kidneys get their blood supply from Renal Artery. When blood enters into the Kidneys, they remove various nitrogenous wastes such as urea from the blood. In addition, they also remove various salts and unneeded excess water. All these unnecessary things like urea, salt, water etc. All these extracted byproducts are then removed from our body via Urine. The question is, ‘what happens to the blood?’

Excellent question. The blood (impure blood laden with waste products) that enter the Kidneys through the Renal Artery needs to leave the Kidneys. That is exactly what happens. The blood leaves the Kidneys but using the Renal Vein.

What about the wastes? The wastes that are collected by the Kidneys are passed into the Urinary Bladder in from of Urine. The waste products move into the Urinary Bladder through Ureters that connect the Kidneys and the Urinary Bladder. Eventually, the Urine then passes out of the body from another opening known as the Urethra.

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Liver as part of Excretory System:

Just like our Kidneys, our Liver is an extraordinary organ without which the Excretory System cannot work. What does this Liver do? Something really important. It is the organ which is designed for breaking down chemical, poisons and various toxins that enter into our body. For instance, our body is not designed for ammonia. When ammonia enters our body, the Liver converts it into urea so that it can be disposed off by the Kidneys. Also, Liver is responsible for production of Bile. Keep reading…

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Bile and Gall Bladder as part of Excretory System:

Liver produces Bile. It is a fluid substance that, once produced by Liver, moves into the Gall Bladder. From the Gall Bladder, the Bile is injected into the Small Intestine. Once in the Small Intestine, the Bile starts working on substances like ethanol, acidic wastes, fats etc. and breaks them down into harmless substances. Working on fats, the Bile will break down the fats into usable fats and unusable fats. Bile salts are wastes but in the stomach, they help in fat absorption. These Bile Salts are later excreted.

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Large Intestine as part of Excretory System:

We did say that defecation is not part of the Excretory System. Then, how come Large Intestine is a part of the system? It is so because, apart from transporting undigested food out of the body, it also collects various wastes, for example, bilirubin. Bilirubin is a by product of what we know as heme catabolism. The other wastes collected from the body by the Large Intestine include lipophilic substances (substances that dissolve or combine in fats and lipids), sterols, extra vitamins, some drugs etc.

These are all removed along with feces or poop. So, though stool is eliminated and not excreted, everything else that moves out of the Large Intestine along with poop are excretory wastes. This makes Large Intestine a part of the Excretory System (though just a secondary one). To be more precise, all those waste products that move out of the body along with stool are hydrophobic (that is, they don’t like water) and hence, cannot move out via urine (which contains water).

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Skin as part of Excretory System:

Our Skin is also a part of our Excretory System but excretion is not the primary function of the Skin. This makes Skin a secondary excretory organ. Skin has Sweat glands, which allows excretion of fluid waste in form of perspiration or sweat. Sweat or perspiration is basically excess water. Apart from excess water, Skin also helps to get rid of excess salt and helps to maintain salt concentration in the body.

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Ureters as part of Excretory System:

Ureters are very important because they connect Kidneys to the Urinary Bladder. The Urine from Kidneys reach the Urinary Bladder because of gravity as well as because of peristalsis (a wave-like motion that makes the urine move forward).

Urinary Bladder as part of Excretory System:

Urinary Bladder is where the Urine is stored. From the bladder, the urine passes out of the body through another opening called Urethra.

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Urethra as part of Excretory System:

Urethra is basically a tube that connects the Urinary Bladder with opening of the body from where the urine is passed. This tube is longer in males and shorter in females and has the same function – passing Urine.

Lungs as part of Excretory System:

Carbon Dioxide is produced in our body by cellular respiration. Our body cannot use Carbon Dioxide. This Carbon Dioxide is collected from all over the body by blood straight into the Lungs from where the gas is expelled out of the body through exhalation (the part of breathing where we send unnecessary gas out of our body through our nose). This means that Lungs are a vital part of our Excretory System.

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Primary and Secondary Organs or Excretory System

All the organs and components that we mentioned above can be broken down into Primary and Secondary Organs of Excretory System. The table below gives that separation:

PRIMARY EXCRETORY ORGANS SECONDARY OR ACCESSORY EXCRETORY ORGANS
Lungs Skin
Kidneys Large Intestine
Urethra
Ureters
Urinary Bladder
Bile/Gall Bladder
Liver

Conclusion

So, Excretory System in humans is a complex system that involves various organs. It works in tandem with other systems in our body. The Excretory System can get into serious troubles in many ways. Liver damage or Kidney damage are serious dangers. The damage of the Biliary drainage system (a system for draining Bile) can also cause serious problems. There are various diseases related to the Excretory System as a whole. We will exclude them from discussion.

Sources: 1, 2, 3, 4, 5, 6, 7, 8

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