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Biology 2nd Baccalaureate

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6.1. Excretion


As we have seen in the last few topics, cells carry out metabolism in order to carry out their vital activities. From the nutrients obtained in the digestive system, from the oxygen provided by the respiratory system, and with the intervention of the circulatory system, cells can manufacture their own organic matter and the energy they need. But these chemical reactions also produce waste substances that have to be expelled from the body.

Aparatos que intervienen en la nutrición

The excretion is the process by which the organism is removed from the waste products resulting from cell activity (metabolism).

The main products of metabolism are:

  • Carbon dioxide (CO2), from combustion reactions, where energy is obtained.
  • Urea and uric acid, from the degradation of amino acids and nucleic acids, respectively.
  • Other toxic substances that have been ingested.

So that these toxic waste products do not harm the body, they are highly diluted in the blood, and when they are excreted in the kidney, they also come out with a lot of water.

These substances resulting from the chemical reactions of metabolism are collected by the blood and transported to the excretory organs, which are responsible for their elimination.

The organs involved in excretion are:

  • The kidney is the main organ of the urinary system, with a complex structure that allows it to recover much of the water and useful substances that accompany waste substances .
  • The sweat glands remove waste substances that the body does not need in the form of sweat. It has two functions:
    • Excrete excess sodium chloride and toxic substances that have been ingested, such as alcohol and some medications.
    • Regulates body temperature.
  • The lungs are responsible for the excretion of CO2 (when leaving the blood towards the alveoli) and its elimination (when exhaling).
  • The liver, which removes toxic products formed in metabolism:
    • The urea and acid uric excreted by the kidney.
    • The bile salts, obtained from the degradation of hemoglobin, excreted by the alimentary tract.

The apparatus excretory, see, is not composed only of the urinary system, but there are other devices involved. Besides eliminating toxic substances, the excretory system also contributes to maintain the vital signs of the body, regulating, for example, the amount of water present in the tissue, the body temperature, concentration of salts in blood, etc.

Activity: Don't confuse processes.

Activity: Any question about excretion.

Video: Formation of sweat on the fingertips.

Answer in your notebook

6.1.- Give the name of all the organs or devices involved in excretion and what each of them eliminates.

Answer in your notebook

6.2.- Why is excretion necessary?

Answer in your notebook

6.3.- Why is defecation not included as a type of excretion?


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Biology and Geology teaching materials for Compulsory Secondary Education (ESO) and Baccalaureate students.