Science & Technology in Action

1st Edition

Kidneys – The Quality Controllers of the Blood


The function of the kidneys in maintaining homeostasis is the subject of this lesson. The role of the kidneys in excretion of waste material is explained. The health issues associated with the excessive consumption of table salt are examined.

Contains the full lesson along with a supporting toolkit, including teachers’ notes.

Lesson excerpt

Salt - the good and the bad
Salt is a very important component in our diets. However, it is one of those things that we only need a certain amount
of. An excess of salt can be extremely damaging to our health. That is why safefood, the Food Safety Promotion
Board has designed a safefood public information programme to raise our level of knowledge about salt and its effects.

This lesson presents important facts about the kidneys and their function in maintaining a state of homeostasis or ‘balance’ in the body’s internal environment. It also shows how you can avoid health problems caused by too much salt in your diet.

What is homeostasis?
Homeostasis is the ability of a living organism to maintain a constant internal environment despite changes in the
external environment. It is the ability to remain stable. The human body is a society of cooperative living cells, about
1014 in fact. These cells are surrounded by a very thin layer of tissue fluid. In order to ensure that this tissue fluid
environment can meet the needs of the cell, it is necessary to keep the blood in good condition.

Which major blood characteristics influence homeostasis?
Blood concentration, volume and pressure greatly affect the continuous refreshment and renewal of tissue fluid. The
supply of ‘fuel’ and other essential raw materials to the tissue cells is determined by the blood’s nutrient composition
and concentration. The pH of the blood must be kept tightly at 7.4, as even slight changes in cellular pH have a major
affect on enzyme action. By keeping the blood’s waste concentration low the various metabolic wastes can be
removed rapidly from the tissue cells and delivered to the excretory organs for expulsion. Finally, the temperature of
37°C, must be regulated to ensure a high constant rate of enzyme action to sustain normal metabolism.

Quiz questions

  1. The kidneys are important homeostatic organs. true
  2. The inner part of the kidney is called the cortex. false
  3. The efferent arteriole delivers blood to the glomerulus. false
  4. Kidneys form urine by plasma filtration and selective reabsorption. true
  5. The glomerular capillaries are impermeable. false
  6. Glomerular filtrate passes into Bowman's capsule. true
  7. The PCT has a minor role in selective reabsorption. false
  8. Glucose, amino acids and salts are reabsorbed by diffusion. false
  9. The Loop of Henle does not have a role in selective reabsorption. false
  10. The DCT selectively reabsorbs water and salts. true
  11. ADH influences the selective reabsorption of glucose. false
  12. The CD (collecting duct) delivers urine to the renal pelvis. true