CHAPTER 3

EXCRETIONEXCRETION

HUMAN EXCRETIONHUMAN EXCRETION

1. All the chemical processes that take place in the body are called metabolism.

2. Metabolism produces waste products which are often toxic.

3. The elimination of the metabolic waste products from the body is called excretion. This is done by excretory organs.

EXCRETION EXCRETION SYSTEMSYSTEM

SKINSKIN LUNGSLUNGS KIDNEYSKIDNEYS LIVERLIVER

5. The importance of excretion a. Disposal of toxic or poisonous

wastes. For example, urea and carbon dioxide.

b. Disposal of excess substances. For example, mineral salts and water.

4. The excretory organs consist of skin, lungs and kidneys.

SKINSKIN The skin has many sweat glands which produce sweat. The sweat gland leads to a sweat duct which opens on the skin

surface as sweat pore. Sweat is extracted from the blood

capillaries surrounding the sweat glands.

Sweat contains water, mineral salts and urea.

Sweat gland

Sweat duct

Sweat poreSweat

LUNGSLUNGS During respiration, the

cells produce carbon dioxide and water.

Carbon dioxide diffuses out of the blood capillaries into the alveoli.

Carbon dioxide and water vapour are expelled from the lungs by exhalation.

KIDNEYSKIDNEYS Kidneys are the main organs

in the excretory system. Kidneys filter the blood and

produce urine. Urine is yellowish liquid that

contains water, mineral salts and urea.

Kidneys also regulate the water and chemical balance in the body.

Excretory organ Waste products

SKINSKIN Water, mineral salts, ureaWater, mineral salts, urea

LUNGSLUNGS Water vapour, carbon dioxideWater vapour, carbon dioxide

KIDNEYSKIDNEYS Water, mineral salts, ureaWater, mineral salts, urea

THE URINARY SYSTEM IN THE URINARY SYSTEM IN HUMAN BEINGSHUMAN BEINGS1. The urinary system consists of a pair

of kidneys, a pair of ureters, the urinary bladder and the urethra.

2. Blood is carried to each kidney by the renal artery and away from it by the renal vein.

3. The blood is filtered by within the kidney.

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

5. Urination is the process of expelling the urine from the body.

6. The system of tubes leading from the kidney to the exterior is called the urinary tract.

Parts of the urinary system

kidney

ureter

urinary bladder

urethra

Organ Functions Ureters Ureters Carry the urine from the kidneys to

the urinary bladderUrinary Urinary bladderbladder

Stores urine and gradually expands like a balloon

Urethra Urethra Expels urine from the body

Parts of the urinary system and its functions

The kidneysThe kidneys1. The kidneys are a pair of red-brown,

bean shaped organs.2. The kidneys are covered and

protected by thick layer of fats.

3. Parts of the kidney consists of cortex, medulla, pyramids and pelvis.

Cortex – the dark red outer region

Medulla – the pale red inner region

Pyramids – cone-shaped tissues that filled medulla

Pelvis – the funnel shaped cavity at the apices of the pyramid open

Pelvis drains urine into the ureter

The longitudinal section of the human kidney

(to the kidney)

(from the kidney)

(urine to the urinary bladder)

Functions of the kidneysFunctions of the kidneys1. The kidneys filter the blood which contains

both useful substances and waste products, dissolved in excess water.

2. The excess water with the dissolved substances pass through the kidneys and forms urine.

3. Useful substances such as glucose will remain in the blood and transported back to other part of the body.

4. If you drink more water than is required by your body, your kidneys will reabsorb only a small proportion of the water. As a result, larger volume of dilute urine will be produced and excreted.

5. If excess mineral salts are taken into your body, the kidneys will remove the excess mineral salts. As a result, urine with a higher salt concentration is produced.

6. The other functions of the kidneys are: Remove nitrogenous waste products such

as urea. Keep the water and mineral contents in

our body in balance. Control the amount of mineral salts in the

body fluid. Maintain the pH of blood and tissue fluid.

Living with kidney failureLiving with kidney failure1. Kidney failure may be due to a. bacterial infection b. injury c. high blood pressure2. Two ways to treat kidney failure: a. dialysis machine or kidney machine b. kidney transplant

DIALYSIS MACHINEA machine that filters a patient's blood to remove excess water and waste products when the kidneys are damaged, dysfunctional, or missing.

Dialysis machineDialysis machinei. Blood is withdrawn from

an artery in the arm or leg is circulated through the machine before being returned to the same vein.

ii. In the machine, the blood flows through the dialysis tube.

iii. The dialysis tube is surrounded by dialysate solution.

The dialysis machine works in similar ways to the real kidneys

Contains dissolved sugar and salts just like plasma but do not contains urea

iv. Urea and excess salt pass from the blood flowing within the tube into the dialysate by diffusion.

v. The dialysate is discarded.

Kidney transplantKidney transplanti. A kidney from a suitable donor can be

transplanted into the patient.ii. Kidney may be obtained from victims of road

accidents or people who have died from brain tumour.

iii. The tissue of the donated kidneys has to match with the patient.

iv. However, there are not enough suitable donor kidneys for all the patients.

Kidney healthKidney health1. We should keep our kidney healthy to avoid

kidney diseases and kidney failure.2. Ways to maintain healthy kidney’s include: a. taking urine and blood tests b. limiting salt and protein intake c. maintaining blood sugar control for diabetics d. drinking at least 8 glasses of water a day e. learning about symptoms of kidney diseases

EXCRETION IN PLANTSEXCRETION IN PLANTS1. Plants are less active than animals so they

accumulate waste more slowly.2. Plants do not have specialised excretory organs

to eliminate their excretory products.3. The waste products of plants are water, carbon

dioxide, oxygen, mineral salts and nitrogenous wastes.

4. Certain excretory products are converted into insoluble crystals and stored in leaves, flowers and fruits which are later lost from the plant.

latex

Crystal salt

tannins

The main waste products in plantsExcretory product

Source Method of excretion

Carbon Carbon dioxidedioxide

Respiration Removed from tissues by diffusion through intercellular spaces in the leaves, stems and roots during the night.In leaves, the gas escapes through the stomata.In roots, the gas diffuses out into the air space of the soil.

Oxygen Oxygen Photosynthesis

The gas lost from the leaves by diffusion through stomata during the day.

Excretory product

Source Method of excretion

Water Water Transpiration Water is lost through transpiration.

Calcium Calcium oxalateoxalate

Metabolism Deposited in the form of crystals in leaves and stems.They are removed from the plants when the leaves fall.

TanninsTannins Metabolism Stored in leaves and fruits.They are removed when these are shed from the plants.

4. Some other complex waste products of plants include latex, resins and gum. These substances are stored in plants and are released when the plants die and decay.

5. Some of them are useful to human beings. a. latex – tyres, gloves and shoes b. resins - paints