viernes, 18 de febrero de 2011

The excretory process

We have to finish the nutrition function with the excretory system. As we saw in previous posts, in the nutrition process your body takes nutrients from food in the digestive system and oxygen in the respiratory sytem. Both pass to circulatory system and blood transports them to all the cells of the body. Cells obtain energy from nutrients and also produce waste products. Wastes go to the bloodstream and must be removed from the body. This process is called excretion. The excretory system is where it carries it out. But the excretory system not only releases wastes from the body, it maintains homeostasis by keeping the correct balance of water and salts in your body.
Homeostasis is the body’s attempt to maintain a constant internal environment. It involves keeping many internal factors at more or less constant levels. The factors include body temperature and properties of the blood as the right levels of acidity, salts, glucose,... in order for cells to function normally.For instance homeostasis of temperature. According to body temperature detected by receptors, the brain sends appropriate orders to return the body temperature to normal. If temperature is too higher, the body reacts to decrease that temperature (negative feedback control). Maybe you will learn better with this video of the sympathetic tim and Moby (with subtitle):

A little secret, you can see in spanish in this link
The kidneys are the main organs in excretion of wastes from the blood, but several other organs are also involved in this process as liver, skin, and lungs.
• The liver breaks down excess amino acids in the blood to form ammonia, and then converts the ammonia to urea, a less toxic substance. The liver also breaks down other toxic substances in the blood, including alcohol and drugs.
• The skin eliminates water and salts in sweat.
• The lungs exhale water vapor and carbon dioxide.
Those organs can be considered part of the excretory system but, in the study of excretion process we are going to refer only to the urinary system
Finally, a second video fron HEATINCca where is explained the Urinary system and the homeostasis

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