1. Excretory System

2. Goal:
  To regulate the volume and molecular and ionic constitution of internal body fluids and eliminates metabolic waste products from the internal environment.
Metabolism: the sum total of the
chemical reactions that keep an
organism alive

3. Kidneys perform a number of homeostatic functions:
Maintain volume of extracellular fluid
Maintain ionic balance in extracellular fluid
Maintain pH and osmotic concentration of the extracellular fluid.
Excrete toxic metabolic by-products such as urea, ammonia, and uric acid.

4. Kidney
(fig )
Main role – to filter blood and eliminate waste

5. Kidney Parts
CORTEX. Filtering layer of the kidney, jammed packed with nephrons.
MEDULLA. The middle layer known as the collecting layer. Tubes carrying filtered wastes travel from the cortex, through the medulla towards the pelvis.
RENAL PELVIS.
This is the area where all of the collecting tubules come together & connect with the ureter.
The ureter transports the wastes (urine) to the urinary bladder.

6. THE NEPHRON How do we filter?
Blood is carried to the kidneys by the renal arteries, which branch into smaller arteries inside the cortex and then lead to clusters of capillaries called  glomeruli.
Each glomerulus is surrounded by a "C"-shaped structure called the Bowman's Capsule.  It is here that materials such as urea, salts, water, glucose, & others pass from the blood into the nephron.

7. These materials pass the loop of Henle
These materials pass the loop of Henle.  As the filtrate travels through the tubule, useful substances are reabsorbed into the surrounding capillaries.
About 180 liters of filtrate is produced each day, but only 1.5 liters of urine. 
These metabolic wastes form urine, which is transported to the urinary bladder by the collecting tubule.

8. (Fig 37.14)

9. Problems for different organisms
Freshwater fish - plenty of water, problems with diffusion, constantly urinating and not drinking
Marine fish - problems with osmosis (water loss), constantly drinking water
Terrestrial organisms - face water loss