section_path: Function/Other
section_name: Other
paragraph_text: Other
  
  In addition to their function in respiration, the lungs have a number of other functions. They are involved in maintaining homeostasis, helping in the regulation of blood pressure as part of the renin–angiotensin system. The inner lining of the blood vessels secretes angiotensin-converting enzyme (ACE) an enzyme that catalyses the conversion of angiotensin I to angiotensin II. The lungs are involved in the blood's acid–base homeostasis by expelling carbon dioxide when breathing.
  
  The lungs also serve a protective role. Several blood-borne substances, such as a few types of prostaglandins, leukotrienes, serotonin and bradykinin, are excreted through the lungs. Drugs and other substances can be absorbed, modified or excreted in the lungs. The lungs filter out small blood clots from veins and prevent them from entering arteries and causing strokes.
  
  The lungs also play a pivotal role in speech by providing air and airflow for the creation of vocal sounds, and other paralanguage communications such as sighs and gasps.
  
  Research suggests a role of the lungs in the production of blood platelets.