1.5 Excretion and the excretory system

Natural sciences

Grade 9

Excretion and the human excretory system

Grade 6

Life processes: healthy life

All waste material that is formed in the cells during metabolism has to be discarded.

The EXCRETORY SYSTEM does this. The main excretory system in humans is the URINARY SYSTEM , which consists of:

• two kidneys
• two ureters
• the bladder
• a single urethra

Urinary system

• EXCRETION is the process by which waste is removed.
• SECRETION is the process by which beneficial substances like hormones are secreted.
• EXCRETORY PRODUCTS are the various substances that have to be cleared away.

Kidneys work like filters and have to filter about 15 000 litres of blood per day. The only filtrate that leaves the body from the kidneys is urine – approximately 1,5 litres per day.

Urine is made up of 96 % water, 2 % urea, 1 % salts and 1 % other metabolic substances.

The kidneys function most efficiently if 6 to 8 glasses of water are consumed during the day. It is also advisable to avoid excessive amounts of coffee, coloured cool drinks and salt. These things make the kidneys work harder.

A person is able to function efficiently on one kidney. People who suffer from acute diseases of the kidneys have to undergo dialysis, which means being linked to a machine (kidney machine) that cleans the blood. Such patients usually are candidates for kidney transplants and are on a waiting list for a donor.

ILLUSTRATION SHOWING THE KIDNEY:

• Draw a simple sketch to illustrate the structure of the kidney. First examine and dissect a pig kidney.

• QUESTIONS DEALING WITH THE KIDNEY:

1. How are the kidneys protected within the body?

2. Explain what kidney stones are and how they are treated nowadays.

3. What is the function of the bladder?

4. Explain the function of the sphincter at the outlet of the bladder.

5. What is incontinence? Have a class discussion about people’s sensitivity about this matter.

6. Explain the implications of the following substances in the urine:

a) Glucose

b) Proteins

Assessment: Sketch of the KIDNEY

Were you able to do the sketch and answer the questions?

LO 2.1

Assessment

Learning Outcomes 2 : Constructing Science knowledge

The learner will know and be able to interpret and apply scientific, technological and environmental knowledge.

We know this when the learner:

• recalls meaningful information;interprets information.

Memorandum

The human excretory and secretory systems

QUESTIONS ON THE KIDNEYS:

1. layer of fat

2. Uric acid forms crystals – solvent and laser

3. stores urine

4. holds liquid and controls release

5. inability to control the sphincter

6. a) diabetes b) infection the kidneys or pregnancy