The correct option is Lungs.
Explanation
Excretion involves the removal of metabolic waste products from the body. While the kidneys are the primary excretory organs, other organs such as the lungs, liver, and skin function as accessory excretory organs to eliminate specific waste substances.
Detailed Analysis:
- Lungs: The lungs are the primary organs for respiration, but they also play a significant role in excretion. They remove large amounts of carbon dioxide (approximately 200 mL/minute), which is a byproduct of cellular respiration. Additionally, significant quantities of water are eliminated daily in the form of water vapour during expiration.
- Pancreas: This is a mixed gland with both exocrine and endocrine functions. It secretes digestive enzymes and hormones (insulin and glucagon) to regulate blood sugar levels, but it is not involved in the elimination of respiratory gases or water vapour.
- Spleen: The spleen functions primarily as a blood filter, removing old or damaged red blood cells and participating in the immune response. It does not perform excretory functions related to carbon dioxide.
- Thyroid: The thyroid is an endocrine gland located in the neck. It secretes hormones that regulate metabolism, growth, and development, having no direct role in the excretion of metabolic wastes like CO2.
Key Takeaway: The lungs act as accessory excretory organs by eliminating carbon dioxide and water vapour produced during metabolic activities.