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Overview

Cellular Respiration is the final process that occurs to bring oxygen to body cells. It occurs in four steps: 

  1. Breathing: inspiration and expiration of air 

  2. External Respiration: gas exchange that occur at the alveoli to bring oxygen in and carbon dioxide out.

  3. Internal Respiration: gas exchange that occurs at the tissue to get oxygen into the tissues and carbon dioxide out. 

  4. Cellular Respiration: the use of oxygen by the mitochondria of cells to create ATP to function (used for metabolism).

Respiratory Structures

Nose:

  • The nostrils are richly lined with capillary beds (vessels) and mucous secreting glands

  • Air needs to be cleaned, warmed and moistened before it reaches the delicate and sensitive lung membrane

  • Nose Hairs aid mucous and trap dust particles in the air to to clean and filter it 

  • Mucous traps debris from the air and discharges it out of the nose 

  • Blood Vessels found in the nose carry a rich supply of blood which warms the air that is moist and heat exchange occurs from the blood vessels to the air which allows the air to be warmed. 

Mechanics of Breathing

  • The Medulla Oblongata is sensitive to the concentration of carbon dioxide and hydrogen ions in the blood plasma which is created during cell metabolism, both CO2 and H+ are wastes that need to be excreted. 

Cellular Respiration: C6H12O6 + 6O2 ---> 6CO2 + 6H2O + ATP​

  • When CO2 and H+ concentration get too high the medulla oblongata signals the diaphragm and intercostal muscles to contract 

    • Intercostal muscles run between the ribs and help the chest cavity expand and contract as we breath​

  • When contraction occurs the diaphragm moves down and the rib cage moves UP and OUT ​

    • Became the diaphragm moves down and the rib cage ​moves out the volume of the thoracic cavity increase creating a VACUUM EFFECT so air is drawn into the lungs. Inhalation is an active process requiring ATP.

  • The surface of the lungs are covered with a PLEURAL MEMBRANE as is the inside of the thoracic cavity â€‹

    • The pleural membrane is a double layered membrane which allows the lungs to slide without abrasions and fill/seal the thoracic cavity  ​

  • A puncture to the pleural membrane will result in a PNEUMOTHORAX (collapsed lung) as the negative pressure in the lungs will cause the air to be taken through the puncture wound. Air will fill up in the pleural membrane instead of in the lung and this will cause pressure to be put on the lung and will result in the lung collapsing or deflating. 

  • When stretch receptors on the surface of the alveoli detect that the alveoli has been stretched enough they will send a signal to the medulla to stop the contraction of the diaphragm and intercostal muscles. 

    • When the diaphragm relaxes it will bow upwards and the intercostal muscles cause the rib cage to move down ​

    • This puts pressure on the thoracic cavity and causes the outward movement of air (exhalation)

      • Aortic Arch and Carotid Arteries contain chemoreceptors that are sensitive ​to oxygen content in the blood. When oxygen levels are low they initiate inhalation by signaling the medulla oblongata. This is SECONDARY MECHANISM FOR INHALATION

      • The medulla oblongata senses high CO2 and H+ levels in the blood plasma which triggers inhalation. This is PRIMARY MECHANISM FOR INHALATION.

Steps of Breathing 

  1. Medulla oblongata detects either high CO2 and H+ levels (low pH) in the blood or low oxygen levels in the aortic arch and carotid artery and sends a signal to the diagram and intercostal muscles to contract

  2. Diaphragm flattens and moves down and the intercostal muscles contract and move the rib cage up and out. This increases the volume in the thoracic cavity. 

  3. Negative pressure is created in the thoracic cavity (lower pressure than atm) which creates a vacuum effect and allows air to be drawn into the lungs.

  4. Air is drawn into the lungs and the lungs stretch until the stretch receptors send a signal to the medulla oblongata telling ot they have stretched enough

  5. Medulla sends a signal to the diaphragm and intercostal muscles to relax.

  6. Diaphragm moves back up to its bowed shape and intercostal muscles move down (rib cage contracts) and this increases the pressure in the thoracic cavity and causes air to be forced back out. 

**INHALATION IS ALWAYS AN ACTIVE PROCESS SINCE MUSCLES HAVE TO CONTRACT TO FORCE AIR INTO THE LUNGS

Conditioning of Inhaled Air 

  1. Air is cleaned of debris (ie. dust and bacteria) in one of two ways:

  • Initial cleaning occurs in our nose where nose hairs and mucous filter the air in the nasal cavity​

  • Then as air moves down the trachea and bronchi which contain protein filaments called cilia which are attached to epithelial cells and a mucous lining

  • The mucous lining catches and filters the air of any remaining debris 

    • The cilia are in a constant beating motion and push this mucous lining that traps debris upwards to the pharynx where the mucous can be removed ​

​

2. Air is adjusted to body temperature 

  • As air moves through the nasal cavity it is warmed by the many vessels (heat exchange occurs) from 21 to 22 degrees Celsius to 37 degrees Celsius which is the optimum temperature in the alveoli. 

​

3. Air is moistened 

  • As air passes through the nasal cavity it becomes saturated with water as H2O moves out of the arterioles at the many capillary beds in the nose 

    • Air must be moistened by the time it reaches the alveoli otherwise, gas diffuse will not occur properly.​

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