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Biology for Secondary Schools

base balance of the blood, preventing
3. Examine the role of the distal
convoluted tubule in urine formation acidosis which would result from high
and present your findings. level of carbonic acid in the blood.
4. How does the nephrone ensure the (d) Assisting in heat loss: Water vapor loss
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removal of metabolic wastes while through breathing contributes to body
maintaining homeostasis? temperature regulation.
5. Explain how the concentration of
urine varies based on body hydration These functions make the lungs vital
and hormonal regulation. in maintaining homeostasis through
excretion.

Other excretory organs in humans Liver
Lung The liver is one of the largest organs in the
The lungs are important excretory organs body of humans. It is located beneath the
in human responsible for the removal of diaphragm. It plays the role of excretion
gaseous waste. They eliminate carbon of bile pigments from the breakdown of
dioxide (CO ) and water vapor (H O), cholesterol and aged haemoglobin. The
2
2
which are byproducts of cellular respiration. liver also regulates the amount of nutrients
During exhalation, the lungs expel these substance which is released to the blood and
wastes, ensuring the body’s internal tissue fluid. It does this by absorbing and
environment remains balanced. storing excess fats in form of glycogen and

Role of lungs in excretion then releases it into the circulatory system
The lungs play a crucial role in excretion as per body needs.
by:-

(a) Removing carbon dioxide (CO ): The human liver has two lobes with many
2
During cellular respiration, cells blood capillaries. Gall bladder is located
produce CO as waste products. The between the lobes. The liver is made up
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body transports CO via blood in the of hepatic cells organized in small groups
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form of carbonic acid to the alveoli called lobules. Each lobule is composed
in the lungs. In the lungs the carbonic of a great number of liver cells. Between
acid in the blood is converted into CO lobules there are small blood vessels and
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and expelled during exhalation. small bile ducts. Major blood vessels in the
liver include hepatic artery which brings
(b) Eliminating water vapor (H O): Along oxygenated blood and hepatic portal vein
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with CO , water vapor is also excreted which brings blood rich in digested food
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through breathing, helping maintain from the alimentary canal. Hepatic vein
fluid balance. carries away deoxygenated blood from the
(c) Regulating blood pH: By expelling liver.
CO , the lungs help maintain acid-
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