The Human Excretory System

The function of the excretory system is the excrete (get rid of) wastes that are not helpful to the body.

EXCRETION

Excretion is:

• removal of metabolic wastes

• removal of excess heat

Main Excretory organs involved are:• kidneys• liver• lungs• skin

A Note About Metabolism• Metabolism • This is the series of activities that cells do in

order to keep the organism alive. • Cellular activities usually involve chemical

reactions that produce products necessary for life and bi-products (wastes) that are often toxic to cells.

• Example: Cellular Respiration produces ATP energy for the cells but it also produces Carbon Dioxide, which is very harmful to the cells.

Cellular Waste

• Wastes that are removed include carbon dioxide, water, salt, urea and uric acid.

• All excreted wastes travel at some time in the blood.

Major Metabolic wastes:

• carbon dioxide, water– CO2 and H2O are from cellular respiration

• certain nitrogen compounds – Breakdown of amino acids from proteins produces

nitrogen compounds• Urea• Ammonia• Uric acid

• Mineral salts from metabolism– Sodium chloride (NaCl)– Potassium sulfate K2SO4

Structures of the Excretory System

1. Skin 2. Lungs3. Liver4. Urinary System5. Large Intestine

Can you guess how these structures are a part of the excretory system? What makes the Large Intestine different from the rest?

Large Intestine• The large intestine

removes solid, undigested food from the body after it passes through the digestive system.

• Waste is stored in rectum until it is excreted from the body as solid waste. NOTE: This is NOT waste produced by the cells (cellular waste) as a part of your metabolism!!!!!

Skin

Wastes such as excess water, salt, urea and uric acid are removed from the body in sweat.

Skin2. Excretion-

– Small amounts of urea and salts in sweat– Removal of excess heat (Major Function)

• 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

Excess carbon dioxide waste is removed from the body when we exhale.

CO2

Liver

The liver is a part of what other system?The digestive

system

Liver

The liver has many functions, including (but not limited to):

1. to produce substances that break down fats2. produce urea (the main substance of urine)3. make certain amino acids (the building blocks

of proteins)4. filter harmful substances from the blood

(such as alcohol)5. The liver is also responsible for producing

cholesterol. It produces about 80% of the cholesterol in your body.

The Liver and Waste

• The liver produces urea and uric acid as a by-product of the breakdown of proteins

• Urea and uric acid are sent to the kidneys to be processed

Liver

Formation of Urea in Liver:

• Amino acids are broken down.

1) amino group, NH2→ changed to

ammonia, NH3 → changed to urea (less poisonous)

• Finally: Urea diffuses back into bloodstream and is filtered out by the kidneys.

Human Excretion• Liver’s role

–Detoxification- • changes harmful substances into

inactive or less poisonous substances• These inactive substances are returned to

blood and are filtered by kidneys.

The urinary system

• The kidneys filter the blood to form urine, which is excess water, salt, urea and uric acid

Urinary SystemKidneys-> ureter-> urinary bladder-> urethra

Kidneys2 main functions1. Remove wastes from cellular metabolism2. Regulate the concentrations of substances found

in the body fluids

*****If kidneys cannot perform these functions a person will die.*****

Kidney structure3 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

NephronNephron- waste filtering unit of the kidney found

in the cortex and the medulla• 1.25 million nephrons in each kidney

Filtration in Nephron 1. Blood enters kidney through renal artery,2. Small substances (water, salts and minerals)

and wastes (urea) diffuse from the capillaries into the nephron of the kidneys.

3. Urea, excess water and excess substances travel to the renal pelvis to form urine.

4. Water and some dissolved substances are reabsorbed into the blood through the capillaries.

5. Clean blood leaves the kidney through the renal vein.

Urine- final waste fluid excreted• Made up of water, urea and various salts.• 1-1.5 liters of urine are produced every 24

hours

Structures Involved in Getting Rid of Urine!

Ureter- tube connects kidney to urinary bladder•Function –conducts urine 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