Excretory products and organs
Excretory Products
Definition
Excretory products are waste substances produced by metabolism, or substances present in excess of the body’s requirements, that are removed from the body by excretion.
1. Carbon dioxide (CO₂)
Formation
• Produced during aerobic respiration in body cells.
Excretion
• Transported in the blood to the lungs.• Removed from the body during exhalation.
Importance
• Prevents the blood from becoming too acidic.• Helps maintain a stable internal environment (homeostasis).
2. Urea
Formation
• Formed in the liver when excess amino acids are broken down (deamination).• The toxic ammonia produced is converted into urea.
Excretion
• Carried in the blood to the kidneys.• Removed from the body in urine.
Importance
• Prevents the build-up of toxic nitrogen-containing waste.• Makes ammonia safer to transport and remove.
3. Water
Formation
• Produced during aerobic respiration.• Also enters the body through food and drinks.
Excretion
• Removed by the kidneys in urine.• Removed by the lungs as water vapour.• Removed by the skin in sweat.
Importance
• Prevents excess water from accumulating.• Helps maintain the body’s water balance.
4. Excess mineral ions (salts)
Source
• Obtained from food and drinks.
Excretion
• Removed mainly by the kidneys in urine.• Small amounts are removed in sweat.
Importance
• Prevents excess ions from disrupting normal cell function.• Helps maintain the correct concentration of mineral ions in the body.
Organs present in excretion:
1. Kidneys:
The kidneys are the main excretory organs. They filter the blood to remove urea, excess water, and excess mineral ions, producing urine.
Process:
• Blood enters the kidneys through the renal artery.
• Inside the kidneys are millions of tiny filtering units called nephrons.
• The nephrons filter the blood, removing urea, excess water, excess mineral ions, and other waste substances.
• Useful substances, such as glucose, most water, and the required amount of mineral ions, are reabsorbed back into the blood.
• The remaining waste forms urine.
• Urine passes through the ureters to the bladder, where it is stored before leaving the body through the urethra.
Importance:
• Removes toxic urea before it can accumulate and damage cells.
• Regulates the amount of water in the body by removing excess water or conserving it when needed.
• Keeps mineral ion concentrations within the normal range needed for cells to function properly.
• Helps maintain homeostasis by keeping the composition of the blood stable.
2. Lungs:
The lungs are excretory organs that remove carbon dioxide and water vapour produced during aerobic respiration.
Process:
• Body cells produce carbon dioxide and water during aerobic respiration.
• Carbon dioxide diffuses into the blood and is transported to the lungs.
• In the alveoli, carbon dioxide diffuses from the blood into the air spaces.
• Water leaves as water vapour.
• Both are expelled from the body during exhalation.
Importance:
• Prevents carbon dioxide from accumulating in the body.
• Helps maintain a normal blood pH by preventing the blood from becoming too acidic.
• Removes water produced during respiration.
3. Skin:
The skin is an excretory organ that removes small amounts of water, mineral ions, and urea through sweat.
Process:
• Sweat glands take water, mineral ions, and small amounts of urea from the blood.
• These substances form sweat.
• Sweat travels through ducts to the skin’s surface and leaves through pores.
• As sweat evaporates, it cools the body.
Importance:
• Removes small amounts of metabolic waste and excess substances.
• Helps regulate the body’s water and mineral ion balance.
• Cooling by sweat evaporation helps regulate body temperature.
4. Liver:
The liver is involved in excretion by converting toxic ammonia into urea, which can be safely removed from the body.
Process:
• Excess amino acids are broken down in the liver by deamination.
• This produces ammonia, which is highly toxic.
• The liver converts ammonia into urea, which is much less toxic.
• Urea enters the bloodstream and is transported to the kidneys.
• The kidneys filter the urea from the blood and remove it in urine.
Importance:
• Prevents toxic ammonia from accumulating in the body.
• Produces urea, which is safer to transport in the blood.
• Enables nitrogen-containing waste to be removed from the body by the kidneys.