Excretory SystemAlso called the Urinary System!!

Excretory System

• The excretory system, also called the urinary system, is closely tied to the digestive system.

• Where the digestive system is responsible for the ingestion, digestion, absorption, and egestion of nutrients, the excretory system is responsiblefor the removal of nitrogenous wastes as a by-product of digestion.

Amino Acids

• Protein in the human diet is broken down into amino acids that are then used for protein synthesis within the cells.

• Not all the amino acids are needed and they are then used as a nutrient source and broken down to produce ATP in a process called deamination.

• The amino group (-NH2) of the amino acid is not used and must be removed from the body because the amino group is easily converted into ammonia (NH3).

• This is a major concern because ammonia is extremely toxic.

Amino Acids

• Humans deal with the production of ammonia during the deamination process using the excretory system.

• The liver converts the highly toxic ammonia into urea that is only slightly toxic.

• Urea along with other wastes is carried in the blood stream from the liver to the kidneys where they are filtered out and stored in the bladder for later excretion.

Anatomy of the Excretory System• The excretory system is composed of the kidneys, ureter, urinary bladder, and urethra.

• The kidneys are the main filtering organs where the other structures of the excretory system are used for the transport and storage of the waste products that are to be excreted.

Anatomy of the Excretory System• The kidney is a fist-sized organ found on the abdominal wall on either side of the spinal column.

• There are two kidneys and they have a distinctive kidney bean shape with each weighing about 500 grams.

• At any given moment about 25% of the body's blood supply can be found in the kidneys.

Anatomy of the Excretory System• Blood to be filtered is supplied to the kidneys from the renal artery that branches from the aorta.

• The aorta is the main artery that leaves the heart.

• The filtered blood is returned to the body by the renal vein into the vena cava that returns the blood to the heart.

Anatomy of the Excretory System• As the kidney filters the blood, urine is produced.

• This urine is carried from the kidney to the urinary bladder through the ureter. The ureter drains the kidneys into the urinary bladder.

• The urinary bladder is responsible for the storage of urine. It is capable of holding about 400 mL of urine before the sensory neurons trigger an urge to urinate.

• **Additional volume can be stored but once the bladder exceeds.

The Nephron –Urine Formation• The functional unit of the kidney is the nephron.

• Each kidney contains about one million of them.

• They are thin tubules that are responsible for filtering out nitrogenous wastes.

• In simple terms the nephron separates the blood from the fluid plasma, then puts the fluid back into the blood but keeps all the waste products.

The Nephron –Urine Formation• In the kidney there is a network of capillaries that are fed from the renal artery.

• These capillaries are found throughout the kidney but depending on their location, they perform different functions.

• The cluster of capillaries responsible for filtering out the blood is called the glomerulus.

The Nephron –Urine Formation• The glomerulus is found inside the Bowman's capsule that collects the fluid that is filtered out of the blood.

• The fluid that is filtered out is the filtrate; it will eventually be called urine as water is removed and urea is concentrated.

• The filtrate is produced by blood pressure that forces about 25% of the plasma through the walls of the capillary into the Bowman's capsule.

• Blood cells and other large molecules do not pass through but dissolved compounds such as urea can.

The Nephron –Urine Formation• As the filtrate travels from the Bowman's capsule it moves into the proximal tubule.

• Reabsorption of the filtrate occurs in the proximal tubule.

• Glucose, sodium, and amino acids are transported back into the blood (by passive and active transport) while urea stays in the tubule.

The Nephron –Urine Formation• From the proximal tubule the filtrate travels into the loop of Henle.

• When the glucose, sodium, and amino acids are pumped back into the blood in the proximal tubule, a concentration gradient is formed.

• This causes water to flow out of the loop (by osmosis) back into the blood. The amount of water in the urine is reduced and urea is kept inside the tubule.

The Nephron –Urine Formation• From the loop of Henle the urine travels into the distal tubule. In the distal tubule additional water is reabsorbed if the body is dehydrated.

• If the body is not dehydrated, the water is left in the urine to dilute it and to further reduce its toxicity.

The Nephron –Urine Formation• As urine is produced by the nephron it finally ends its journey when it enters into the collecting duct.

• From the collecting duct it enters the ureter and is collected in the bladder.

• After a sufficient amount has been collected it passes through the urethra and is excreted.

The Nephron –Urine Formation• The process removes about 25 g of urea per day.

• Not only does it rid the body of urea but it also maintains homeostasis by adjusting the amount of water allowed to leave the body.

• If a person is dehydrated a greater amount of water is reabsorbed. If a person is over hydrated it can also increase the urine output.

Dealing with Kidney Failure

• The kidneys have the job of maintaining the proper balance of water and ions in your blood.

• When someone suffers from kidney failure, the body cannot maintain the proper balance of water and ions in the blood, and more importantly cannot get rid of the nitrogenous wastes.

• When this happens we turn to technology and our understanding of diffusion and osmosis to help.

Dealing with Kidney Failure

• Hemodialysis is a procedure that simulates kidney function and is performed in a hospital or dialysis clinic.

• During this procedure the patient has a large tube running from the large artery in the arm into the hemodialysis machine and the purified blood is then returned to the body by another tube.

• The procedure takes about 3 to 5 hours to complete and must be done at least 3 to 4 times a week.

Dealing with Kidney Failure

• Hemodialysis works by using osmosis.

• The blood from the patient is pumped through the blood compartment of the dialysis machine that has a semi-permeable membrane with dialysate on the other side.

• As the blood travels through the blood chamber, the low concentration of waste products on the dialysate side allows them to move through the membrane and out of the blood.

Dealing with Kidney Failure

• The dialysate also has the correct concentration of ions for a healthy person so if the person receiving treatment has high or low ion concentrations, the ions will move to create equilibrium and give the patient a normal ion concentration.