 This video will cover the following objective from respiratory physiology, list the major functions of the respiratory system. The major organs of the respiratory system are the lungs as well as the airways that connect in and out of the lungs and the muscles of respiration that are responsible for ventilation, for pulmonary ventilation, drawing air in and out of the lungs. So the airways are connected to the nasal cavity and oral cavity and the pharynx is the throat which the pharynx connects to both the nasal and oral cavities. As air is being drawn in through the nasal cavities, it will be humidified, warmed and filtered and then it passes down through the pharynx into the larynx. The larynx is also commonly referred to as the voice box and it contains the vocal cords responsible for sound production. And then air continues from the larynx down into the lower respiratory tract starting with the trachea which is the large airway which then branches into the right main bronchus and left main bronchus. Each bronchus branches further into secondary tertiary bronchi in the lungs which branch further into bronchioles which are small airways that eventually terminate in air sacs known as the alveoli where the external respiration, gas exchange occurs where gas like oxygen moves from the atmospheric air inside of the alveoli into the blood to be transported inside of the red blood cells. The role of the muscles in the respiratory system like the diaphragm, the diaphragm contracts in order to increase the volume of the thoracic cavity where the lungs are located and as that volume increases there's a decrease in pressure inside of the lungs that causes air to flow in increasing the volume of the lungs. Ulfaction is one of the functions that the respiratory system contributes to in order to draw air in the respiratory system can draw air in through the nasal cavity and then molecules that are in the air can dissolve in the mucus of the olfactory epithelium and bind to the olfactory receptors which relay information in through the cranial nerve one into the olfactory bulbs and olfactory tracks that carry the information into the olfactory cortex in the temporal lobe where the sense of smell is being processed. Sound production for speech is another major function of the respiratory system in the larynx there are vocal cords that are elastic ligaments that vibrate as air is forced in between these bands of elastic connective tissue that vibration creates the sound that we use for speech. This should be a familiar diagram of the path of blood flow through the pulmonary and systemic circulation and so the pulmonary circuit is the blood supply to and from the lungs the pulmonary arteries are carrying de-oxygenated blood to the lungs and pulmonary veins drain oxygenated blood back from the lungs to the left atrium of the heart. External respiration is the aspect of gas exchange which occurs in the lungs and so is a major function of the respiratory system is gas exchange and in particular external respiration where we have gas exchange between the blood of the pulmonary capillaries and air inside of the lungs the air inside of the alveoli which are the small sac-shaped terminal ends of the airways inside of the lungs the air inside of the lungs is exchanging with gas that's dissolved in the blood across the wall of the alveoli and across the wall of the capillary. In external respiration oxygen moves from the alveoli or alveolus as we can see on this diagram is the singular of alveoli so oxygen is moving from an alveolus into the blood plasma and then that oxygen in the blood plasma can move into the red blood cell and um oxygen will then bind to hemoglobin inside of the red blood cell where hemoglobin will function to help transport oxygen in the blood. Carbon dioxide which is found inside of the red blood cell and also dissolves in the plasma moves the other direction across the capillary wall from the blood toward the alveolus and so carbon dioxide is moving out of the blood into the lungs during external respiration and oxygen is moving from the lungs into the blood during external respiration. The fact that the respiratory system allows us to remove carbon dioxide from the blood enables another major function of the respiratory system which is acid base homeostasis the respiratory system contributes to the balance of the ph of the body by removing carbon dioxide from the blood because carbon dioxide reacts with water in the blood forming carbonic acid and carbonic acid can release a hydrogen ion into the surrounding solution lowering the ph the enzyme carbonic anhydrase is responsible for interconversion of the carbonic acid with water and carbon dioxide and so the chemical reaction that converts carbonic acid to carbon dioxide and water is very quick and is catalyzed by this enzyme carbonic anhydrase which is one of the fastest enzymes that humans have ever studied this is a reversible reaction so if we have excess carbon dioxide that carbon dioxide can be converted into carbonic acid by this enzyme carbonic anhydrase and if we have excess carbonic acid carbonic acid can be converted into carbon dioxide by this enzyme so it can move either direction and when the ph of the body is becoming very acidic as the ph is becoming too low it will stimulate an increase in the respiratory drive leading to increased pulmonary ventilation that is increased rate of airflow in and out of the lungs which speeds up gas exchange helping to remove carbon dioxide from the body and this will have the effect of helping to raise the ph of the blood restoring homeostasis so here's a diagram just summarizing the mechanism through which the respiratory system can contribute to the rapid regulation of acid-base balance in the body if the ph of the body becomes too low which is also known as acidosis there are chemoreceptors that are detecting that change in ph the central chemoreceptor in the brain is very sensitive to a change in the ph of the cerebrospinal fluid and if that falls too low it will lead to a stimulation of the respiratory drive leading to increased respiratory rate removing carbon dioxide from the body helping to lower the carbon or the carbonic acid concentration of the blood and this brings the ph of the body back to the homeostatic set point around a ph of 7.4 and the opposite will happen if the ph of the body becomes too high if the ph is above 7.4 this is alkalosis so there's a little bit of room so above 7.45 would be alkalosis a normal range would be around 7.35 to 7.45 but if it gets above that 7.45 the ph of the body is too high known as alkalosis which is also going to be detected by receptors the central chemoreceptors in the brain are going to respond to that alkalosis leading to a decrease in the respiratory rate which causes the carbon dioxide to accumulate in the blood it slows the rate at which carbon dioxide is being removed from the blood so the blood carbon dioxide concentration rises and the blood carbonic acid level rises and as that carbonic acid level rises that causes a decrease in the ph of the blood helping to restore the homeostatic set point around a ph of 7.4