CHAPTER 3 EXCRETION

HUMAN EXCRETION

• Excretion: process of removing substances that are of no use or in excess from the body.

• Urea, carbon dioxide, excess mineral salts and excess water are examples of excretory products.

• eliminated through specific excretory organs, like the skin, lungs and kidneys.

• If these excretory products are allowed to accumulate in the body, it will become poisonous (toxic) and endanger health.

SKIN

• skin excretes waste products in the form of sweat.

• The sweat gland absorbs excretory products like water, mineral salts and urea from blood capillaries around it.

• Sweat is eliminated from the sweat gland through sweat pores to the surface of the skin.

LUNG

• eliminate carbon dioxide and water.

• Carbon dioxide in the blood capillaries diffuses into the alveolus and is eliminated from the lungs when exhaling.

• Water is eliminated from the lungs in the form of water vapour.

KIDNEY

• many substances are eliminated in large quantities through kidney

• Filter blood and produce urine

• Urine: yellowish liquid that contains water, mineral salts and urea

URINARY SYSTEM IN HUMAN BEINGS

• consists of

(a) a pair of kidneys (c) a urinary bladder

(b) a pair of ureters (d) urethra

• Blood is carried to each kidney by renal artery and away from it by renal vein

• Blood is filtered within kidney

• Waste products (e.g. urea) and excess substances (e.g. mineral salts and water) are converted into urine

• Ureters carry the urine from kidneys to the urinary bladder

• Urinary bladder stores urine and gradually expands like balloon

• When muscle in the wall of bladder contract, urine is expelled to exterior via urethra. This process is called urination

KIDNEY

• dark red in color and are bean-shaped.

• internal structure of the kidney is kidney divided into

(a) the outer part which is dark red in colour named cortex

(b) the inner part which is light red in colour named medulla.

• Functions of the kidney

• eliminating excess water and mineral salts from the body

• Keep the amount of water and mineral salts in the body in balance

• regulating the blood concentration

• helping to remove nitrogenous substances like urea and uric acid from the body

KIDNEY FAILURE

• Maybe due to:

• Bacterial infection

• Injury

• High blood pressure

• 2 ways to treat kidney failure:

• Dialysis machine

• Kidney transplant

KIDNEY HEALTH

• Ways to maintain healthy kidneys include:

• Limiting salt and protein intake

• Maintaining blood sugar control for diabetics

• Drinking at least 8 glasses of water a day

EXCRETION IN PLANTS

Excretory product Source UseLatex Rubber tree To make vehicle tyresRennin Certain tree stems like the

casuarina treeTo make varnish and gum

Gum Certain tree stems like the acacia tree

To make cough medicine

Acid (tannic acids or tannin)

Bark of plants like the tea, coffee and mangrove tree

To make ink

Quinine Bark of cinchona To make medicine to treat malaria

Oil Flowers or leaves of certain trees

To make perfume andointment for insect bites

Excretory product Source Reason for danger

Opium Flowers of the poppy plant Are drugs that ruin health

Morphine Made from opium

Heroin Made from morphine

Cocaine Leaves of coca plant

Ganja Leaves and dried flowers of the cannabis sativa plant

Caffeine Coffee beans Causes addiction

Nicotine Tobacco leaves Smoking damages the lungs and the breathing channel