The Excretory System

Excretion To eliminate unwanted substances from the body e.g. CO2 from lungs Urea from kidneys Urea from liver Heat from the skin

These unwanted substances are the by-products of metabolism (cells produce energy from nutrients) and are toxic to keep in the body.

Excretion is needed in order to achieve homeostasis- the balance of everything in the body

The Organs of the Excretory System Lungs Kidney Liver Skin

The Lungs

Lung Excretion 1. ↑ body activity 2. ↑ cellular metabolism 3. ↑ production CO2 4. ↑ CO2 in blood 5. CO2 detected by nerves in brain (medulla oblongata) 6. ↑ respiration rate 7. ↓ CO2 in blood

The Liver

Liver Excretion responsible for detoxifying and breaking down toxins (chemicals and poisons that enter our bodies) converts Ammonia (from the breakdown of amino acids found in proteins) to urea, which is excreted in urine.

Liver: Links to Digestion and Circulation Produces bile: stored in the gallbladder, small intestine uses bile to break down acidic waste (ammonia, fats, ethanol) by converting into less harmless waste (emulsification) Maintains glucose levels in the blood: using the blood’s insulin levels, the liver regulates how much glucose should be in the blood

Effects of Alcohol Alcohol interferes with the functions of the liver and can cause an inflammation of the liver’s cells – this leads to a buildup of fat in the liver Oxidative Stress: this is when the liver is working too hard to break down the alcohol and results in cellular damage and scar tissue Toxins from gut bacteria: if alcohol damages the intestines, the resulting toxins will enter the liver and can cause damage and scar tissue

The Kidney

Kidney Excretion Each kidney contains one million nephrons. Nephrons filter the blood.

Kidney Excretion Wastes (urea, uric acid) and excess substances (e.g. sugar, salts) are removed from blood and excreted into the ureters (tubes from kidney to bladder) Return purified blood to the renal vein (vein from kidney to heart) This regulates the water and mineral content of the blood

The Bladder Urine is collected in the bladder, resembles an expandable bag Urine is excreted from bladder via the urethra (from bladder out of body)

Components of Urine 95% of urine is water 5% is solutes (chemicals dissolved in water e.g. urea, uric acid, salts, etc.)

Urine should be: Clear to dark amber in colour depending on hydration of the body. Unusual colours can indicate different problems. Usually odourless (except after certain foods e.g. asparagus)

Clear. Turbid (cloudy) urine can be due to infections or crystals Neutral. A pH of around 7. 1-2 L a day Have a density or specific gravity of 1.003 to 1.035 g/ml

YIKES! Proteinuria- the protein albumin, in urine can occur if the kidneys or blood vessels are damaged. This can be caused by infection, diabetes, or cardiovascular disease. Diabetes- glucose in urine can be caused when the body does not produce enough insulin and the excess blood sugar is excreted

Hyperuricosuria- too much uric acid in urine would produce a pH less than 7. This could be a sign of gout, or kidney stones.

The Skin

Skin Excretion Heat regulation: Dilated (increase in diameter) blood vessels increase blood flow to surface and excrete heat (e.g. flushed face when hot) constricted (decrease in diameter) vessels reduce blood flow and conserve heat. (e.g. bluish lips when cold)

Skin Excretion Excreted sweat contains a small amount of urea sweating is a secondary function to temperature regulation.