1. What is Excretion?
Excretion is the process of removing cellular wastes.
The term excretion refers specifically to the elimination of wastes produced by cellular activity.
It is not removal of undigested food material!
 Goal: Maintain homeostasis!!

2. What is Excretion? (contd)
The most important waste products are CO2, nitrogen compounds, and salts.
CO2 – produced during cellular respiration (in addition to water)
Nitrogen compounds – (ammonia, urea, and uric acid) produced by the breakdown of amino acids (protein digestion)
Salts – produced by metabolism

3. Why do we need to excrete Ammonia?
All organisms produce ammonia as they metabolize nutrients (protein digestion)
Ammonia is a nitrogenous waste that is toxic and must be removed from the body
How an organism removes ammonia depends upon where it lives
Water = remove ammonia directly-,
Land = convert ammonia to a less toxic form (uric acid or urea) to be released later

4. Removing Nitrogenous Waste Products
(2) Urea:
- Many land animals and some bony fish (amphibians, mammals) dilute the toxic ammonia with water.
- This substance is called Urea & is filtered out by the kidneys.
- The problem is they do lose water in the process!
- Requires Energy

5. Removing Nitrogenous Waste Products
(3) Uric Acid
Not very toxic because insoluble
Evolved as an adaptation of land animals
Many organisms try to conserve water & excrete their Nitrogen waste as a solid! (little loss of water is involved)
Examples: insects, reptiles, birds

6. The Mystery behind Bird Poop
Unlike mammals, birds do not urinate.
Their kidneys extract nitrogenous wastes from the bloodstream, and excrete it in the form of uric acid.
Uric acid has a very low solubility in water, so it emerges as a white paste.

7. Human Excretion Where does excretion occur in humans?
Like other animals humans have a system
that excretes Nitrogen wastes as Urea, salt, and water
Urinary System: Kidneys, ureter, urethra, and bladder
Kidneys (located in back) play important role in homeostasis –
- remove waste products from blood
- maintain blood pH
- control water content of blood
SKin, kidneys,liver, lungs
Skin- sweat glands that excrete water and some urea - helps regulate heat loss

8. How The Kidneys Work Blood enters kidneys from renal artery
Blood is filtered by passing through millions of nephrons
Wastes pass through ureter to the bladder as urine
Clean blood returns to body through renal vein
Bladder stores urine and passes urine out of the body through the urethra

9. Nephrons: How the Body makes Urine
Your kidneys are composed of 1 million cells called Nephrons.
These long coiled tubes are where the blood is actually filtered and urine is produced

10. The Nephron Nephron has three functions:
1. Glomerular filtration: filter out water, N-wastes (urea), salt, glucose, amino acids
2. Tubular reabsorption: reabsorb materials that the body still needs (food molecules, water).
3. Tubular secretion: collect wastes as urine and pass them to the bladder (urea, salts, other substances)
Blood filters through the kidneys about 6 times a day.
99% of the water is reabsorbed and not excreted

11. Anatomy of 1 Nephron Three major players: Glomerus Bowman’s Capsule
Tubule
Blood enters kidney through renal artery and moves into the glomerulus – where filtration occurs – taking what we need out of the blood! - now just a liquid containing water, salts, n-waste – rest of blood remains
Glomerus is contained inside the BOWMAN’S CAPSULE – small moleucles can travel through but larger ones cannot – this is where blood cells stay – too big to enter
Tubule-
Tubular reabsorption – remove water and nutrients and pass them back into the blood but keep UREA in!!
Tubular secretion: wastes, toxins, drugs, are removed from blood if they were not filtered from Bowman’s capsule
Point out Loop of Henle
From the tubule – goes to collecting duct – fluid is now urine and will be excreted from body! Goes to ureter then bladder
So how does all of this reabsorption and secretion take place – through diffusion/active transport – what is needed to get what we want into the blood and remove the harmful stuff out? Oh yes – CAPILLARIES – wrap around the tubules – twist around nephron and join back to renal vein where blood travels to the posterior vena cava

12. Filtration: glomerus, bowmans capsule
Reabsorption: diffuse and actively transport needed materials back into blood via capillaires while wastes remain

13. Anatomy of 1 Nephron
Ask class to review structures

14. What kinds of animals have the most efficient kidneys?
Desert animals must be able to conserve moisture
Most terrestrial animals must drink fresh water often; however the kangaroo rat does not need to drink water very often – its kidneys absorb every little drop of water

15. Kidney Failure If renal failure occurs,
people must get their blood filtered through
Dialysis.
Blood is not being filtered properly – a machine called dialsis will filter blood for them – 5-10 hours, 2-3 times a day!

16. Gout Is a disease where the human body accumulates Uric acid in the joints. Heredity, alcohol & kidney failure lead to this problem.

17. Kidney Diseases Kidney Stones
A kidney stone is a hard mass developed from crystals that separate from the urine and build up on the inner surfaces of the kidney. Normally, urine contains chemicals that prevent or inhibit the crystals from forming. These inhibitors do not seem to work for everyone, however, so some people form stones. If the crystals remain tiny enough, they will travel through the urinary tract and pass out of the body in the urine without being noticed.
Kidney stones may contain various combinations of chemicals. The most common type of stone contains calcium in combination with either oxalate or phosphate. These chemicals are part of a person's normal diet and make up important parts of the body, such as bones and muscles.
A less common type of stone is caused by infection in the urinary tract. This type of stone is called a struvite or infection stone. A bit less common is the uric acid stone. Cystine stones are rare.