How excretion differs from egestion
Egestion and excretion are both terms used to describe the removal of waste from the body.
Egestion is the final stage of the digestive process, which includes getting rid of the
undigested material from food.
Excretion is a more general term describing removal of the waste products of cell
Organs of excretion
Lungs remove carbon dioxide, a product of respiration.
The liver
converts excess protein into urea.
The kidneys
remove unwanted substances such as urea, excess water and salt.
Several organs are important in removing waste from the body.
The skin provides a surface for small amounts of water and salt to move out of the body.
Why does urea need to be excreted?
Excess amino acids in the body are broken down by the liver, producing a waste substance called urea.
Once formed, urea is transported by the circulatory system to the kidneys.
The kidneys filter the blood, removing urea and excess water and salt, which
forms urine. Urine is stored in the bladder before being excreted from the body.
Why is water important?
Water is produced by the body during
respiration, and absorbed from food and drink.
Water is lost from the body in exhaled air, sweat, urine and faeces.
How is water gained and lost?
The human body is 60–70% water.
Water molecules and ions are essential for all life processes. Their concentrations in the body cells must be carefully regulated in order for cells to work properly.
Dehydration and its causes
If the body loses too much water, it may become dehydrated. A decrease of just one percent of body weight due to water loss is enough to cause mild dehydration.
Mild dehydration can lead to dizziness, a dry mouth and
concentrated urine. More severe dehydration damages cells in the body and can even result in death. Dehydration is
caused by:
heavy sweating
low water intake
eating salty food
breathing dry air
ADH is controlled by negative feedback
normal salt concentration
of blood
decrease in salt concentration increase in salt
concentration
change detected by receptors in the change detected by
receptors in the hypothalamus
pituitary gland pituitary gland releases more ADH
kidneys become more permeable to water concentrated urine kidneys become less permeable to water dilute urine must expel excess water must conserve water
