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Biology 12 Respiratory System Respiratory System We have seen how the mitochondria in the cell use oxygen to carry out cellular respiration, and we have seen how the body gets oxygen to the cells via the circulatory system. We have also learned how the circulatory system transports the carbon dioxide created as waste by cellular respiration in what we have been calling deoxygenated blood. We will now look at how the body gets the oxygen in the surrounding air of the earth’s atmosphere to the circulatory system, and how it gets rid of the carbon dioxide. The earth’s atmosphere is made up of several gases; however, found in higher concentrations are the gases nitrogen (78%), oxygen (21%), argon (1%), and carbon dioxide (0.04%). Although nitrogen is important for building biological molecules, it is the oxygen in the air that we use directly for cellular respiration. There are four processes to get the oxygen in the atmosphere to help create ATP (energy for our cells) in the mitochondria of our cells. 1. Breathing – getting oxygen to the lungs by inhalation, and expelling carbon dioxide as waste by exhalation. 2. External Respiration – the exchange of oxygen and carbon dioxide between the blood and the air in the lungs. Oxygen enters the blood, while carbon dioxide exits the blood. 3. Internal Respiration – oxygen and carbon dioxide are exchanged between the circulatory system at the ________________________ and the ________________________. 4. Cellular Respiration (not covered in this unit) – once the oxygen is in the tissues the cells of the tissues can carry out cellular respiration with oxygen entering the process and carbon dioxide exiting as a waste. Respiratory Structures 1 Biology 12 Respiratory System The mechanism of breathing basically brings air in and out of our body past several structures on its route from nose to the lungs and back out again. As air makes this return trip it brings oxygen deep into the lungs, and brings carbon dioxide out. Air enters through the nose and the mouth; the former being the major entryway. o the nose has nostrils, which are lined with hairs and a mucosal cell layer; both act to trap and filter the air that is entering the lungs. o there is also a number of blood vessels in the nose which house white blood cells which offer further protection from foreign entities. We have seen the pharynx when we studied the ____________________ system. o common passageway for air and ______________. o the ________________ covers the top of the trachea when we are eating to prevent food from entering our airway; it remains open when we are breathing. the larynx is our voice box o found below the epiglottis o contains the vocal cords which control the pitch of sounds according to how taut they are. o below the larynx is the trachea o the trachea connects the pharynx to the smaller passageways that branch into the lungs o it is a hard, cylindrical structure that is made up of C-shaped rings of cartilage. The esophagus can be found in the open part of the “C”. o the shape and hardness prevent the structure from collapsing. the bronchi are smaller tubes that branch from the bottom of the trachea o these are also cartilaginous o the bronchi branch into even smaller passageways called bronchioles o the branching of the bronchioles forms the bronchiole tree bronchioles finally end at the alveoli 2 Biology 12 Respiratory System Alveoli these are blind, sac-like ending the passageway for air millions of alveoli are found in the adult lung, which provides a large amount of _____________________ for the diffusion of gases (____________________ respiration). alveoli are specialized four ways 1. Walls of the alveoli are one cell thick which helps with ___________________ of gases. 2. Lipoproteins on the inner surface which maintains surface tension, preventing them from collapsing during exhalation. 3. Stretch receptors are nerve endings sensitive to stretch. When the alveoli are fully stretched (i.e. during inhalation) these nerves send impulses to the medulla oblongata which triggers exhalation 4. Pulmonary capillaries highly vascularize (i.e. provide lots of blood vessels) the alveolar surfaces, ensuring maximum diffusion of gasses, and helps ensure that alveoli do not dry out. Moisture is required for the diffusion of the gases. Breathing: Inspiration and Expiration the respiratory centre is located in the medulla oblongata of the brain the medulla oblongata is sensitive to the carbon dioxide and hydrogen ions in the blood plasma; both are waste products from cellular metabolism when the concentrations of these waste products gets too high, the medulla oblongata sends nerve impulses to the muscular diaphragm and the intercostals muscles (inter = between + costal = ribs) the impulse stimulates the muscles to contract o contraction of the diaphragm moves it down, and the contraction of the intercostals moves them out and up o the combined effect of the contraction of these muscles increases the volume in the thoracic cavity; this creates a negative pressure (vacuum effect) in the cavity. o air is drawn from the higher pressure outside through the trachea to the lower pressure inside (due to the increased volume) o ATP is required for this process; therefore it is considered an “active” process. 3 Biology 12 Respiratory System FYI – Hiccups A hiccup is a contraction of the diaphragm that is usually rhythmic. This is an involuntary action (does not occur by conscious choice of individual) involving a reflex arc (i.e. signal does not pass directly to the brain, similar to the “knee-jerk” reflex). Holding your breath does increase the amount of carbon dioxide in your blood, which triggers the medulla oblongata to send a message to the diaphragm to contract. This might trick the diaphragm out of the rhythmic contractions of a hiccup. the surfaces of the lungs are covered with a pleural membrane, as well as the inside of the thoracic cavity; therefore, there are two membranes surrounding the lungs o their function is to help the lungs slide over the body wall easily, and seals off the thoracic cavity. o pneumothorax is caused when a lung collapses due to a puncture of the pleural membrane. it is not the lung that is punctured, but simply the pressure from the atmosphere entering through the puncture and pushing in on the lung. o pleurisy is an infection of the pleura causing inflammation and severe sharp pain. the stretch receptors of the alveoli detect when they are open (stretched) and signal the medulla oblongata to stop the contraction of the diaphragm and intercostals muscles when the diaphragm relaxes it bows upwards, and when the intercostals muscles relax gravity pulls them back down and in. o these actions decrease the volume of the thoracic cavity, and increase the pressure on the lungs o this causes exhalation. chemoreceptors in the carotid bodies (in the carotid arteries) and the aortic bodies (in the aorta) are sensitive to levels of oxygen in the blood. o if concentrations have decreased these bodies communicate with the medulla oblongata and the rate of breathing increases; and vice versa for increased levels of oxygen. o this is a second mechanism to control the amount of breathing needed by the respiratory system. The Conditioning of Inhaled Air air drawn into the air passageways needs to be conditioned for clean and proper gas exchange to occur. this happens in three ways 1. Air is cleaned – cleaning by the nose hairs and mucous, and then by cilia found along the walls of the trachea and bronchi cilia are microscopic protein filaments constantly in motion and move particles in the mucous back up the airway to the pharynx to be coughed out 2. Air is warmed – the air moving along the passageway is in close contact with tissues that are around the body’s temperature of 37C 3. Air is moistened – the air gets saturated with water as it passes over the mucous-lined passageways. helps keep the lungs from drying out 4 Biology 12 Respiratory System The Gas Exchange to exchange the gases between the atmosphere and the tissues it happens in two ways: external respiration and internal respiration External Respiration diffusion of oxygen into the pulmonary capillaries and the diffusion of carbon dioxide (with some water) into the alveoli to be exhaled the approximate conditions in the blood at the alveoli are 37C with a pH of 7.4 haemoglobin under these conditions is free to bind with oxygen haemoglobin has four binding spots for oxygen, and 99% of these sites will be occupied by oxygen when leaving the alveoli and entering the vascular system. oxygen (O2) + haemoglobin (Hb) = oxyhaemoglobin (HbO2) haemoglobin will carry oxygen to tissues throughout the body for internal respiration. Internal Respiration at the tissues the temperature is higher at 38C, and slightly more acidic at pH 7.35 hemoglobin in these conditions readily releases oxygen as blood enters the capillary beds when oxygen has been released into the plasma it __________________ across the capillary beds and into the _____________________. without oxygen at its binding site hemoglobin is free as a transport molecule (Hb). remember at the venule end of the capillary bed water along with wastes enter the bloodstream. carbonic anhydrase is an enzyme found in the red blood cell (and kidney cells) that works at an optimum temperature and pH found in the capillary beds of the tissues. o carbonic anhydrase catalyses the reaction between carbon dioxide and water in the plasma o this reaction is one of the fastest known enzymatic reactions o the reaction is summarized below carbonic anhydrase CO2 carbon dioxide + H2O water ↔ [H2CO3] carbonic acid ↔ HCO31bicarbonate ion + H1+ hydrogen ion bicarbonate ion: most widely known buffers in the human body (re: buffers _______________ coming from the stomach entering the ____________________) hydrogen ion: binds to hemoglobin and is transported as reduced haemoglobin (HHb) o hydrogen ions act to reduce the pH in plasma, so Hb operate as an effective buffer of blood carbon dioxide mostly enters the reaction above, but some will be taken up by Hb forming carbaminohaemoglobin (HbCO2) Once the blood has reached the venule side of the capillary bed it is ready to the pulmonary circuit. 5 Biology 12 Blood returning to the alveolar capillaries has the following characteristics Respiratory System o blood is carrying bicarbonate ions (______________) and a small amount of carbon dioxide o Haemoglobin is either carrying carbon dioxide (carbaminohaemoglobin) or hydroden ions (HHb) o remember the temperature is slightly __________ and the pH is slightly ___________ at the lungs, which creates an ideal environment for the release of CO2 and H+ from haemoglobin o the enzyme carbonic anhydrase catalyses the reverse reaction it did before CO2 carbon dioxide + H2O water ↔ [H2CO3] carbonic acid ↔ HCO31bicarbonate ion + H1+ hydrogen ion o the carbon dioxide released from this reaction, the HbCO2 and along with the small amount that is dissolved in the plasma diffuses into the alveoli and is exhaled into the atmosphere as CO2 haemoglobin as Hb is now free again to bond with _______________ and start the process over again. 6