Excretion and the Excretory Organs

Challenges to clear

• Pair every organ with what it removes.
• Connect the rectum to the reason it does not really belong on this list.

The task

Match each organ to the waste it actually removes from the body.

What this lesson covers

• Kidneys — Urea, excess salts and excess water, passed out as urine (The kidneys are the primary excretory organs. Urea is highly poisonous, and if it builds up in the blood beyond a certain level it causes death.)
• Lungs — Carbon dioxide, given off as a gas in the expired air (Every living cell makes carbon dioxide while oxidising glucose. Note that passing out carbon dioxide is counted as part of respiration rather than true excretion.)
• Skin — Sweat: mostly water and sodium chloride, with traces of urea and lactic acid (Sweat glands release sweat only when the body needs cooling, so strictly speaking they are not excretory in function.)
• Liver — Bile pigments such as bilirubin, left over from broken-down haemoglobin (The liver also detoxifies ammonia by turning it into urea, and breaks down alcohol, nicotine, drugs and bad cholesterol.)
• Rectum — Undigested food as faeces, which is defaecation and not excretion at all (Excretion means removing wastes made inside the body by metabolism. Undigested food never entered the body tissues, so passing it out is a different process.)
• Ureter — Nothing: it only carries urine from the kidney to the urinary bladder (The ureter arises from the notch or hilum of the kidney and connects behind with the bladder. It transports urine but forms none of it.)

Hint

Tears, saliva, milk and insulin are secretions because the body still has a use for them. Only urine on that list is a genuine excretion.