1. Slideshow B4: The skin and liver

2. The kidneys and the lungs Discussion questions: What is excretion? What do the kidneys do? What is the main waste in urine called? What waste do the lungs get rid of?

3. The skin Functions of the skin The skin has many functions, most of which are involved in protecting you and regulating your body’s internal functions: protects the body's internal living tissues and organs protects against invasion by infectious organisms protects the body from dehydration protects the body against changes in temperature helps dispose of waste materials acts as a receptor for touch, pressure, pain, heat and cold stores water and fat. How does the skin get rid of waste materials? There are two types of sweat glands: sweat glands that open into hairs e.g. those found in the armpits sweat glands that form sweat pores at the skin surface. These are found all over the skin. Sweat is a salty liquid that contains waste products, e.g. urea.

4. The structure of the skin

5. The liver Functions of the liver The main jobs are: it cleans your blood it produces an important liquid called bile. Bile is a digestive juice that helps the body pass fat into the bloodstream it stores energy in the form of a sugar called glycogen. Carbohydrates in our food are broken down into a type of sugar called glucose. Glucose is the main source of fuel for our cells. Glucose stored in the liver is called glycogen. Glycogen is like your backup fuel. When the body needs a quick energy boost the liver releases glucose into the bloodstream.

7. The liver as an excretory organ The liver takes waste substances out of the blood, e.g. from breaking down protein. The liver also cleans blood that has just been enriched with vitamins and minerals during digestion. Waste or extra substances, that the body does not need, can be carried by bile back into the intestine or go in the blood to the kidneys. If something harmful is eaten the liver tries to break it down and get rid of it.