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