1. The excretory system
Section 30.4

2. What waste products do our bodies produce?
Our body generates a lot of waste as part of it’s every day function
Excess salt
Carbon dioxide
Ammonia is one of the most toxic waste compounds produced – how?
It is produced when amino acids from proteins are used for energy
It is converted to Urea, which is less toxic but still needs to be eliminated
The body uses skin, the lungs, the liver and kidneys to eliminate excess waste

3. How does a kidney work? Kidneys are essentially natural filters
Blood enters through renal artery
Kidney removes Urea, excess water and minerals, and other waste products
Clean filtered blood leaves through renal vein
Blood purification takes place at nephrons – kidneys have nearly a million
Involves two steps – Filtration and Reabsoprtion

4. What is the difference between Filtration and Reabsorption?
Filtration is when a liquid or gas is passed through a filter to remove waster
This takes place in the Glomerulus
A small dense network of capillaries encased in the upper end of each nephron in a hollow structure called a Bowman’s capsule
Bowman’s capsules and wall of capillaries are permeable
Fluid flows into bowman’s capsules
Filtrate (material that is filtered) contains water, urea, salt, glucose, amino acids and some vitamins
Large substances such as blood cells and proteins are too large to pass through capillary wall
Most of the material that passes through the Bowman’s capsule re-enters the blood - Reabsorption
180 liters of filtrate pass through nephron tubules each day
Much of the filtrate (salts, vitamins, amino acids, fats and glucose) are removed from the filtrate by active transport
Water follows by osmosis
Essentially, nearly everything is thrown away, but then the body reabsorbs what it needs
Loop of Henle conserves water and minimizes filtrate, before passing material on to the collecting ducts, ureter, and ultimately bladder.

5. What role do the kidney’s play in homeostasis?
Kidneys Remove waste, maintain blood pH and regulate water content – they respond directly to the composition of the blood (with some help from the endocrine system)
Your pituitary gland will release Antidiuretic hormone into your blood if you have not drunk enough fluids
Tells the kidneys to reabsorb more water and excrete less into urine

6. What can you learn from urine?
Not only does the color tell you how dehydrated you are, but your urine can store a lot of other information
Presence of protein or glucose can be an indicator of a serious disease/disorder such as diabetes or high blood sugar
Urine samples are often used for drugs tests, as drugs remain in the filtrate

7. What happens if a kidney doesn’t work properly?
Kidney stones – when a ureter gets blocked due to calcium, magnesium or uric acid crystalizing in urine. Can be treated with ultrasound waves
Kidney damage – often related to high blood pressure and type I diabetes
High blood pressure damages filtering mechanism
High blood sugar levels results in increased filtration and more strain
Can lead to kidney failure
Kidney Failure – two options: Dialysis or transplant
Dialysis is when a machine essentially performs the job of a kidney
Needs to be done 3 times a week, 4 hr sessions, and patients have restricted diet
Transplant – complete replacement
A person can survive with only one kidney!

8. Key concepts What organs are involved with excretion?
Why is excretion important for homeostasis?
What substances do kidneys remove from the blood?
What happens during filtration, reabsorption and urine excretion?
How do kidneys help maintain water balance?
Why are protein or glucose in urine a sign of kidney damage?