The Respiratory System
Do you remember a time when you went shopping with your parents and you spotted a toy that you just had to have? Can you recall your reaction when your mom or dad said “no”? Did it involve holding your breath and stomping your feet? Did your parents seem uninterested in the fact that you were holding your breath? You most likely gave it a valiant effort, but after a few moments you had to give up and let out a big blast of air. Did your parents appear unconcerned? It is not that they did not care about you. Your parents knew about respiration and the breathing process.
Respiration Respiration is the process of exchanging oxygen and carbon dioxide with the external environment. In simple organisms, respiration occurs as gases pass through a moist membrane by diffusion. More advanced multicellular organisms require specialized structures like lungs or gills. The function of the respiratory system is to ensure that oxygen is available to all cells. Oxygen must be available for cellular respiration to take place. Cellular respiration provides cells with energy in the form of ATP. Carbon dioxide is a waste product formed during cellular respiration and it needs to be eliminated from cells.
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Respiratory System The main function of the respiratory system is to provide a large moist surface for gas exchange. Simple organisms that live in moist environments, like jelly fish and sponges, lack specialized respiratory systems. Both oxygen and carbon dioxide diffuse from the internal environment to the external environment. Organisms that live on land, but lack specialized structures must live in moist environments. Do you remember why earthworms only surface after a rainy day? More complex organisms use specialized internal structures like lungs or gills for gas exchange.
Specialised Respiratory System A specialized respiratory system is composed of four main parts: Ventilation/Breathing oxygen enters from the atmosphere. External Respiration- exchange of gases between respiratory system and circulatory system. Internal Respiration exchange of gases between the circulatory system and the individual cells. Cellular Respiration within cells, the breakdown of glucose in the presence of oxygen to form ATP and carbon dioxide.
Upper Respiratory System Nasal Cavity: It is preferred that air enters the nasal cavity rather than the oral cavity. Air that enters the nasal cavity is warmed by blood vessels located in the nose. It is cleaned by the tiny nose hairs that line the inside of the nostrils. Finally, air is moistened by mucus that is secreted within the nose. Pharynx (Throat): Air that has entered either from the mouth or nose collects in this area. Air then travels down the trachea.
Epiglottis: A protective flap that prevents food and liquids from entering the trachea. The epiglottis covers the opening of the trachea when swallowing to ensure all food and water travels down the esophagus to the stomach. Larynx (Voice Box): Sound is produced from air passing through the voice box causing the vocal chords to vibrate.
Lower Respiratory System Trachea (Windpipe): A thin narrow tube that runs parallel to the esophagus. The trachea connects the pharynx to the bronchiole tubes. Bronchial Tubes: The trachea branches off into two main bronchial tubes, one for each lung. The bronchial tubes continually divide into smaller and smaller branches called bronchioles.
Humans have a right lung and a left lung. The left lung is divided into two lobes and the right lung is divided into three lobes. The lungs are composed of sponge-like tissue which can inflate and deflate. The lungs resemble an upside down leafy tree. The trunk of the tree is the trachea and the branches represent the bronchial tubes. The lungs are surrounded by tissue that allows them to expand and contract. The pleura keep the surface of the lungs moist.
The ribs protect the lungs and support the chest cavity. Movement of the muscles in between the ribs causes the chest cavity to expand and retract. The ribs are not part of the respiratory system. The diaphragm is a muscle that lies just below the lungs. It is not part of the respiratory system but like the ribs, the contraction and relaxation of this muscle is necessary for external gas exchange.
Alveoli (sing. alveolus): Alveoli appear at the end of the smallest bronchioles. The alveoli are lined with capillaries. This is the area where gas exchange takes place. Alveoli resemble tiny bunches of grapes. The image on the right illustrates that the requirements needed for gas exchange are met by the alveoli. Recall, a large and moist surface area is needed. The circular shape of the alveolus and the presence of mucus glands are shown in the illustration.