Excretory
System
Removes cellular
wastes from the
body
Excretion is:
 the removal of
metabolic wastes
Main Excretory organs involved are:
 kidneys
 liver
 lungs
 skin
Major metabolic wastes:
 carbon dioxide and water
 CO2 and H2O are from cellular respiration
 certain

nitrogen compounds
Breakdown of amino acids from proteins
produces nitrogen compounds
 Urea
 Ammonia
 Uric
 mineral


acid
salts from metabolism
Sodium chloride (NaCl)
Potassium sulfate (K2SO4)
Liver
Detoxification
 changes
harmful substances into
inactive or less poisonous substances
 These inactive substances are
returned to blood and are filtered by
kidneys.
liver
Formation of Urea in Liver:

Amino acids are broken down.
amino group, NH2→ changed to ammonia, NH3 → changed to urea (less poisonous)

Urea diffuses back into bloodstream and is filtered
out by the kidneys.
Urinary System
Kidneys
ureter
urinary bladder
urethra
Kidneys
Two main functions:
1. Filters the blood (removes wastes from cellular
metabolism)
2. Reabsorbs water
***If kidneys cannot perform these functions a person will die due to toxins
building up.
Kidney Structure
3 layers of the kidney
 Cortex- outer layer blood is filtered to remove waste
and excess substances
 Medulla- middle layer made up of tubes called
collecting ducts that carry the filtered substances
(filtrate) to the innermost layer of the kidney
 Pelvis- cavity that collects the filtrate and connects
the kidney to the ureter which exits the kidney
Nephrons
 waste filtering unit of
the kidney found in the
cortex and the medulla
1.25 million nephrons in each kidney
 Contains glomerulus, Bowman’s capsule and a renal tubule

Filtration in Nephrons
1.
2.
3.
4.
Blood enters kidney through renal artery,
Small substances and wastes diffuse from the glomerulus
capillaries into the Bowman’s capsule collecting cup and
into the renal tubule of the pelvis,
Water and some dissolved substances are reabsorbed into
the blood through the capillary
Clean blood leaves the kidney through the renal vein
So where does the waste go???
Urine- final waste fluid excreted
 made up of water, urea and various salts
 1-1.5 liters of urine are produced every 24 hours
Ureter- tube connects kidney to urinary bladder;
urine travels from kidney to bladder
Urinary Bladder- collects and stores urine for
excretion
Urethra- during urination urine travels from the
bladder to the outside of the body
Skin
Excretion Small amounts of urea and salts in sweat
 Removal of excess heat




Blood vessels dilate bringing more warm blood to skin surface
Sweat is produced by sweat glands
Sweat absorbs body heat and evaporates to water vapor and body
heat leaves the body in the water vapor
Body cools as a result of the evaporation
Lungs
Excretion Removes CO2 and water from cellular
respiration
Excretion Disorders

Renal Failure- kidneys stop filtering the blood and
wastes and fluid build up in the body and death can
result

Treatment- dialysis- artificial machine filters and cleans
the blood (works because of diffusion)
*Presence of protein, sugar, or other needed substances indicates other
conditions such as diabetes or cardiovascular disease