Excretory System

Introduction into the Excretory System

The system that gets the least amount of credit.

Why need an Excretory System?

Think about your rooms' kiddos. Is your room completely clean right now? More than likely not; however, if you mom/dad comes in to tell you to clean up your room you get to cleaning right?

Well this same idea of keeping a clean house is the exact reason why we have an excretory system. In fact excretion means to separate and eliminate or discharge (waste) from the blood, tissues, or organs. Therefore we need the excretory system in order to eliminate and or get rid of waste build up in the body.

Recall one of the "Chracteristics of Life": Living Things produce waste. However we also need to be able to get rid of it as well.

Introducing the Excretory System

Pictured here what we call the "Urinary system" however the excretory system involves auxiliary organs that have secondary functions related to the excretion of wastes.

However, we will start with introducing the "urinary system" and get into the other organs in the excretory system.

Excretory System Organs and Auxiliary Organs

• The Kidneys (Excretory Organ)

• Ureter (Excretory Organ)

• Bladder (Excretory Organ)

• Urethra (Excretory Organ)

• Lungs (Auxiliary Organ)

• Liver (Auxiliary Organ)

• Skin (Auxiliary Organ)

The Kid Knees

Arguably one of the most important organs in our bodies due to the role they serve. These organs are responsible for being one of the most important filters in the body.

The kidneys serve the role of filtering the blood by removing nitrogenous waste, salts, excess water, and urea. This waste is removed in the form of urine. This is the first step in our urinary journey through the excretory system.

Nephrons: How the Kid Knees filter the blood

Each of your kidneys has a collection of tubules called Nephrons. These Nephrons number at about 1 million per kidney and they serve the job of filtering the blood coming in through the arteries.

You can think of the nephron as being split into two parts.

1. The Bowman's Capsule

2. Renal Tubing that connects to a collection duct

These nephrons filter blood in 2 distinct stages that we will get into in the next slide.

Stage 1 of Urine Formation

1. Blood will flow into the cluster of capillaries (The Glomerulus) in the thin walled hollow nephron capsule (Bowman's Capsule).

2. Urea, glucose, and some water are filtered out of the blood and into the Bowman's capsule.

3. These materials then pass into the nephron tube which includes the proximal tubule and the Loop of Henle.

Stage 2 of Urine Formation

1. As the material flows through the Loop of Henle, most of the needed glucose and water is reabsorbed back into the blood through the capillary bed.

2. Most of the urea and some water remain in the nephron tube and continue into the distal tubule that connects to the collecting duct.

3. These collecting ducts then collect the urine and filter it through into the ureters.

Urea

A very important waste product in the body; this molecule is made up of nitrogen, hydrogen, and oxygen. This chemical comes from the breakdown of proteins in the body. Without the kidneys this urea would build up in the body; this can cause a host of renal issues which we will get into later.

This waste product is mixed with excess water and other wastes in the urine of most animals and excreted through the ureters in most animals.

Ureters

Once the kidneys are done filtering the blood of wastes it is turned into a substance we are all familiar with, urine. This urine flows through the tubes show in the diagram to the right. These tubes are known as the ureters.

Their main function is to carry this urine from the kidneys to the urinary bladder, which will be our next step in the urinary process of the excretory system.

Multiple Choice

These specialized filtering units give the kidney it's ability to filter the blood.

• Nephrons

• Cilia

• Villi

• Capillaries

Multiple Choice

This waste product is mixed with water and other waste products in order to produce Urine.

• Urea

• Nitrogen

• Salts

• Carbon Dioxide

The Bladder

The primary function of the bladder is similar to that of the gallbladder; and that is storage of materials. In this case, the material being stored is the waste product Urine.

There are also sphincter muscles in the bladder that are similar to the sphincter muscles in our rectum/anus that allow for more precise control in excreting the waste. Once the bladder is filled, there is a signal sent from the brain to these muscles that trigger a desire to "pee".

The Urethra, not to be confused with the Ureters

Once the bladder muscles contract this triggers urine to be pushed from the bladder cavity to the only exit site, that being the Urethra.

So while it has a simple function, it is incredibly important because it is the only outlet for urine in the human body.

Auxiliary Organs to the Excretory System

Aside from the Kidneys and other excretory organs, there are other organs that work to supplement this system. These organs are the Liver, the Lungs, and the Skin.

The Lungs (Respiratory Organ) plays a role in eliminating Carbon Dioxide and some water from the body.

The Skin (Integumentary Organ) contains sweat glands that produce perspiration. This perspiration is a waste product that contains mostly water, salt, and a small amount of urea.

The Liver (Digestive Organ) make urea from the breakdown of proteins, however, it also serves the role of breaking down wastes and recyling old cells.

Consequences of Waste Buildup

There are many painful and sometimes life threatening consequences of waste build up. Pictured to the right is a fairly common example of waste build up in the body, Kidney Stones!

These literal stones in the kidney and bladder are a result of the urine containing more crystal forming substances such as calcium, uric acid, and oxalate.

Consequences of Waste Buildup P2

Another common side effect of waste buildup in the body is kidney failure. The kidneys are meant to filter blood, however, when this filtration does not occur the kidneys could be subjected to a buildup of toxins that can cause cellular death.

Kidney Failure can be the result of an injury, the loss of a lot of blood, or the result of medicines and or toxins. However, if the kidneys are seriously damaged they may recover. UTI's are also another common consequences of waste buildup.

Multiple Select

The primary function of the bladder is to store urine. True or False?

• True

• False

Multiple Select

Please check all of the organs that serve a supporting role to the excretory organs

• Lungs

• Gallbladder

• Liver

• Skin

• Urethra