Excretory System
Kidneys

EXCRETION IS NOT ELIMINATION
The excretory system is very important to your body and only has a few parts.
In a similar way to removing solid waste from your body, you must also get rid of
fluids. You know the results of the excretory system as urine.
Urine is the result of the excretory system balancing the amount of water and salts in your body. Your kidneys are the core organs involved in the excretory system.
Related body parts include the ureters, bladder, and urethra.

As your body performs the many functions that it needs in order to keep itself alive, it produces wastes.
These wastes are chemicals that are toxic and that if left alone would seriously hurt or even kill you.
For example, as your cells break down amino acids, they produce a dangerous toxin known as urea. The cells of your body excrete this urea into your blood.

WHAT DOES THIS SYSTEM DO?
Kidneys do a regulation process of body fluids and salt levels, called osmoregulation.
• The kidneys act as a filter all of the blood in your body.
• The kidneys pull harmful molecules out of your bloodstream and leave the ones that are good for you.
• The kidneys are also key players in the
hydration (water) levels for your body.
Chemical signals are sent to your kidneys to reabsorb as much water as possible.
• A normal day has you creating about one and a half liters of fluid.

INTERACTING WITH OTHER SYSTEMS
The excretory system is a close partner with both the circulatory and endocrine system. The circulatory system connection is obvious. Blood that circulates through the body passes through one of the two kidneys. Urea, uric acid, and water are removed from the blood and most of the water is put back into the system.
The endocrine system is the major controller of the excretory system.
As levels of compounds and fluids are monitored, kidney function must be
constantly altered to provide the best internal environment for your cells.
If you drink too much water, hormones are released that allow for more urine production.
If you are dehydrated, less urine will be produced.
The kidneys are also tied to the endocrine system with the adrenal gland position on the top of each kidney.
The adrenals release adrenaline into your body.

NASTY DISEASES
While there are many diseases of the excretory system, even more problems can be created by a malfunctioning set of kidneys.
Blood pressure is closely tied to the amount of fluid in your body.
If a kidney does not work and filter properly, blood pressure can increase to dangerous levels. If that weren't bad enough, urea would accumulate in your tissues and would slowly poison the cells of your body.
People with malfunctioning kidneys often have to go through a process called dialysis where they are hooked up to a machine that filters their
blood. The machine acts as an artificial kidney and tries to re-establish normal levels of ions and water in their bodies. Many people on dialysis are waiting for kidney transplants.

Kidney Stones
Excretory video

Although the Kidneys are Tiny Organs They Receive 25% of the Cardiac Output in the body.
�
The two kidneys are only 0.4% of the body weight but receive about 25% of the blood.
�
Their most important function in the body is to regulate the composition and volume of body fluids.
�
Blood flows in and out of kidney leaving behind the 1% which becomes urine.
�
The urine produced flows through ureters to the bladder and through urethra to outside world.
�
The typical kidneys filter approximately 180 liters of plasma/day and each of the 3 liters of plasma gets filtered about 60 times.
�
To replace this much water you would have to drink a 12 ounce soft drink every 3 minutes of the day;
� fortunately 99% of the filtrate gets reabsorbed, leaving 1.5-2 liters of urine per day.
�
This is an incredible amount of filtration that is performed every day.

1. Dialysis most closely mimics the function of which organ?
A. the lungs
B. the gall bladder
C. the kidney
D. the liver
E. the bladder
2. Which of the following is not filtered out of the glomerular capillaries?
A. glucose
B. urea
C. large molecules
D. water
E. sodium chloride
3. How does the kidney concentrate urea in the renal tubules?
A. by actively transporting it into the renal tubules
B. the kidney does not concentrate urea in the renal tubules
C. by reabsorbing water from the renal tubules
D. by selectively filtering urea out of the blood
E. by binding it to uriglobin

4. One of the many functions of the liver is:
A. to convert ammonia into urea
B. to convert urea into ammonia
C. to store urea until it can be eliminated from the body
D. to regulate blood pressure
E. to filter urea out of the blood