Secretion vs Excretion
Both excretion and secretion involve the movement of materials in the animal body, but they are different in many ways. Both processes are very important to maintain homeostasis of the animal body. Homeostasis is maintaining of relatively constant internal body conditions, different from their external environment. These two important processes exist in single celled organisms to most advanced animals. In complex organisms, certain organs have developed for the excretion and secretion. Some organs are capable of doing both excretion and secretion processes (E.g. Kidneys).
What is Secretion?
Secretion is the process of releasing and transporting a specific chemical substance from one place to another. The substances are normally released from a cell or gland in animals. In prokaryotes, since they do not have specific glands, secretion means the translocation of specific molecules (E.g. proteins, enzymes, toxins etc.) from a bacterial cell to its exterior via the plasma membrane.
In many advanced animals, glands and certain cells are evolved to do the process of secretion. These glandular cells have well-developed endoplasmic reticulum and Golgi apparatus. In humans, the liver is the largest gland in the body and, it secretes the bile, which plays a role in digestion. Sebaceous glands can secrete sebum to lubricate the skin and hair. The glandular cells in the gastrointestinal tract secrete digestive enzymes, mucous, and gastric acid while the glandular cells in the respiratory system are capable of secreting the mucous. Apart from this, digestive glands, pancreas, gallbladder, endocrine glands like thyroid, pituitary, ovary and testes also play a crucial role in the secretion in humans.
What is Excretion?
Excretion is a vital process in all forms of life. It involves the removal of metabolic waste from the animal body, and it balances the water and salt. Excretion also maintains proper concentrations of dissolved substances and water in the cells and fluids of organisms. In prokaryotes, waste products are simply discharged through their cell membrane, but multicellular animals have evolved more complex excretory methods with complexity of their body structure.
Lungs and kidneys are the major organs of excretion in the human body. The skin, large intestine and liver also play a minor role in excretion. The primary metabolic waste products of the human are carbon dioxide, water, salt and nitrogenous molecules. Most nitrogenous wastes are released as urea. The lungs excrete carbon dioxide and water vapor while the kidneys excrete urine as excretory products.
What is the difference between Secretion and Excretion?
• In secretion, the secreting product may have a certain function, but usually, the excretory product is a waste, and it may not include a certain function.
• Lungs and kidneys are the main excretory organs while liver, glands, and glandular cells are involved in the process of secretion.
• Secretion process involves the movement of material from one place to another while both places being important. Unlike secretion, the process of excretion involves discharging of a material from a living thing.
• Unlike secretion, excretion is more important to balance water and salt concentrations in the body.