CHAPTER 3 : EXCRETION 3.1 : Human Excretion�3.2 : The Urinary System�3.3 : Excretion in Plants �

Prepared  by  Ms  Sue  Soh  Ya  Lee  

3.1 : Human Excretion What is Excretion ?

•  Unwanted substances must be removed from the body, else, they will be harmful to the body

•  EXCRETION : Removal of excretory products by excretory organs e.g. the skin, kidneys and lungs

LUNGS   SKIN  

LIVER  KIDNEY  

Prepared  by  Ms  Sue  Soh  Ya  Lee  

3.1 : Human Excretion The SKIN as an Excretory Organ

•  Skin has sweat glands all over the body

•  Mostly found in palms, soles of feet and under armpits

•  Each sweat gland consists of a coiled tube with a sweat duct which opens on the surface of the skin as a sweat pore

Prepared  by  Ms  Sue  Soh  Ya  Lee  

3.1 : Human Excretion The SKIN as an Excretory Organ

•  Sweat glands absorb excess water from blood capillaries in the skin and give it out through sweat ducts & sweat pores as sweat

•  Main excretory products in sweat: –  Mineral salts (mostly sodium chloride) –  Urea (excess amino acids from protein digestion

formed in the liver)

Prepared  by  Ms  Sue  Soh  Ya  Lee  

3.1 : Human Excretion The LUNG as an Excretory Organ

•  Lungs excrete carbon dioxide & water vapour

•  Carbon dioxide comes mainly from cell respiration and expelled during exhalation

•  Exhaled air contains 4% CO2 and inhaled air 0.03% CO2

Prepared  by  Ms  Sue  Soh  Ya  Lee  

3.1 : Human Excretion The KIDNEY as an Excretory Organ

•  Kidneys removes excess water, mineral salts and nitrogenous waste products (urea)

•  Each kidney is connected to a : –  renal artery –  renal vein –  a ureter

Prepared  by  Ms  Sue  Soh  Ya  Lee  

3.1 : Human Excretion The KIDNEY as an Excretory Organ

•  Renal artery carries blood with excretory products

•  The blood is filtered by the kidneys

•  Waste products are removed as urine

•  Urine flows to urinary bladder via ureter (to be stored)

•  Urine is released via urethra when bladder is full

•  Filtered blood is carried out from kidney by renal veins

Prepared  by  Ms  Sue  Soh  Ya  Lee  

3.1 : Human Excretion The Importance of Excretion

•  Removes harmful waste products : urea, ammonia

•  Removes excess substances : water, mineral salts

•  Removes carbon dioxide from deoxygenated blood

•  Maintains the body in a normal healthy condition

Prepared  by  Ms  Sue  Soh  Ya  Lee