chapter 9 respiratory and motor systems

• the importance of oxygen


  air consists of nitrogen, oxygen, carbon dioxide and trace amounts of other gases. Oxygen is vital for life. In cellular respiration, cells obtain energy through a chemical reaction where organic compounds are broken down using oxygen. Oxygen is the final electron acceptor in the electron transport chain. Humans cannot live for more than a few minutes without an adequate supply of oxygen. The average adult uses 250mL of O₂ every minute while resting. O₂ consumption may increase up to 20 times during intense exercise.
• respiration and breathing

  • breathing(ventilation) - the act of moving air into and out of the lungs.
  • inspiration - moving O₂ into the lungs.
  • expiration - moving O₂ out of the lungs.
  • respiration - all of the processes that supply O₂ to the cells of the body for the breakdown of glucose and the process by which CO₂ is transported to the lungs for exhalation.
• cellular respiration


  O₂ and glucose react producing CO₂ and water. The energy released is used for cell processes, such as growth, movement, and the formation of new molecules. The concentration of O₂ in the cells is much lower than in their environment because cells continuosly use O₂ for cellular respiration. Fresh O₂ must continuously be delivered to the cells for them to survive.
• • breathing is the process by which air enters and leaves the lungs.
  • external respiration takes place in the lungs and involves the exchange of O₂ and CO₂ molecules between the air and the blood.
  • internal respiration takes place within the body and involves the exchange of O₂ and CO₂ molecules between the blood and tissue fluids.
  • cellular respiration involves the production of ATP in body cells.
• human respiratory system


  air enters through 2 nasal cavities or the mouth. The nasal cavities warm and moisten incoming air. They contain mucus and tiny hairs which filter out foreign particles and keep the cells lining the cavities moist. The nasal cavities open into an air filled channel at the back of the mouth called the pharynx. Two openings branch off from the pharynx - the trachea(wind pipe) and the esophagus(carries food to the stomach).
• trachea


  lined with mucus-producing cells, some with cilia. The mucus traps debris that passed through the filtering system in the nasal passages. The debris is swept by the cilia from the trachea back into the pharynx. The wall of the trachea is supported by rings of cartilage, which keep the trachea open.
• epiglottis


  flaplike structure which closes off the trachea during swallowing so that food enters the esophagus and not the trachea. If food or liquids are swallowed too quickly and this reflex is bypassed, the person will start violently coughing to sweep the particles out of the respiratory tract.
• larynx(voice box)


  contains 2 thin sheets of elastic ligaments that make the vocal cords. They vibrate as air is passed over them. Protected by thick cartilage called the Adam's apple. During puberty, the cartilage and larynx in males increase in size and thickness. This creates a deeper voice.
• bronchi and bronchioles


  air passes from the trachea into 2 bronchi. These contain bands of cartilage as well. They carry air into the right and left lungs, where they branch into many more smaller airways called bronchioles. These do not contain cartilage. Air moves from the bronchioles into tiny air sacs called alveoli.
• alveoli


  each alveoli is surrounded by capillaries. In the alveoli, gases diffuse between the air and the blood down their concentration gradients. O₂ diffuses from the air in the alveoli into the capillaries, while CO₂ moves from the capillaries into the air in the alveoli. The alveoli are made up of one layer of cells which allows for rapid gas exchange. The alveoli are tiny which increases the surface area for gas exchange.
• pleural membrane


  a thin membrane that surrounds the outer surface of the lungs and lines the inner wall of the chest cavity. The space between these 2 membranes is filled with a small volume of fluid that reduces friction between the lings and chest cavity during inhalation.
• breathing


  pressure differences between the atmosphere and chest(thoracic) cavity cause air to move in and out of the lungs. Atmospheric pressure remains fairly constant, but the pressure inside the chest cavity will vary. Gases move from an area of high pressure to an area of low pressure. When we inhale(inspiration), atmospheric pressure is higher than the pressure inside the chest cavity so air moves into the lung. When we exhale(expiration), the pressure inside the chest cavity is higher than atmospheric pressure, so air moves out.
• diaphragm


  a dome shaped sheet of muscle that separates the chest cavity from the abdominal cavity.
• inspiration


  diaphragm contracts or shortens, and pulls down. This increases the chest volume and decreases the pressure.
• expiration


  the diaphragm relaxes and returns to its normal dome shape. This decreases the chest volume and therefore increases the pressure. Air moves out of the lungs.
• pressure and volume have and inverse relationship. An increase in volume, causes a decrease in pressure.
• intercostal muscle


  a muscle that raises and lowers the rib cage.
• inspiration


  intercostal muscles contract, moving the rib cage upward and out(chest rises). This increases the volume and decreases the pressure in the chest cavity. Air moves into the lungs.
• expiration 


  intercostal muscles relax and the rib cage falls. This decreases the chest volume and increases the pressure. Air moves out of the lungs.
• dalton's law


  states that each gas in a mixture exerts its own pressure or partial pressure.
• diffusion of gas


  moves from an area of high partial pressure to an area of low partial pressure.
• partial pressure of oxygen 


  the highest partial pressure of O₂ is found in atmospheric air. Therefore O₂ will move from the air(pressure 21.2kPa) into the lungs(pressure in alveoli 13.3kPa). The high partial pressure of O₂ found in the organs that carry large amounts of O₂ and must transport O₂(trachea, alveoli, artery)
• arteries


  carry O₂ rich blood away from the heart, while veins carry depleted blood back to the heart.
• capillaries


  arteries are connected to veins by capillaries, where gas exchange takes place. O₂ diffuses into the tissues here.
• partial pressure of oxygen


  O₂ is continuosly used in cellular respiration inside the cells of the tissues. O₂ will never build up inside cells. Therefore there is a large change in the partial pressure of O₂ between the arteries(12.6kPa) and the capillaries(5.3kPa). This forces O₂ to diffuse into the tissues at the capillaries.
• partial pressure of carbon dioxide


  CO₂, which is produced in cellular respiration, follows the opposite route. The partial pressure of CO₂ is highest in the tissues, where it is produced. It then enters the capillaries and travels through the veins to the heart and then lungs, diffusing from areas of higher partial pressure to lower partial pressure.
• oxygen transport


  O₂ moves from the air in the atmosphere to the alveoli. It diffuses from the alveoli into the blood and dissolves in the blood plasma(fluid portion of the blood). O₂ is not very soluble in blood and this method alone would not meet the O₂ demands of the body. Hemoglobin greatly increases the O₂ carrying capacity of the blood.
• hemoglobin


  the O₂ carrying molecule in red blood cells. The hemoglobin molecule is made up of 4 polypeptides(protein chains) that are composed of heme(an iron containing pigment) and globin(the protein component).Each heme group contains an iron atom, which binds with O₂. When O₂ dissolves in the plasma, hemoglobin forms at weak bond with the O₂ molecule to form oxyhemoglobin. The presence of hemoglobin increases the O₂ carrying capacity of the blood by almost 70 times.
• O₂ transport


  amount of O₂ that combines with hemoglobin depends on partial pressure. The partial pressure in the lungs is about 13.3kPa. Blood leaving the lungs is still nearly saturated with O₂. As blood enters the capillaries, the partial pressure drops to about 5.3kPa. This causes O₂ to split or dissociate from the hemoglobin. O₂ diffuses into tissues. Little O₂ is released from the hemoglobin until the partial pressure of O₂ reaches 5.3kPa of the tissue capillaries. Even venous blood carries O₂. About 70% of the hemoglobin is still saturated with O₂ when the blood returns to the heart.
• carbon dioxide transport in the blood


  there are 3 methods that CO₂ is transported.

  1. CO₂ is more soluble than O₂. About 9% of the CO₂ produced by the tissues is carried in the blood plasma.
  2. about 27% of the CO₂ combines with hemoglobin to form carbaminohemoglobin. Thus the hemoglobin bonds with CO₂ and transports it in the blood.
  3. the remaining 64% of the CO₂ in the body combines with water in the plasma to form carbonic acid(H₂CO₃(aq)). CO₂+H₂O=H₂CO₃(aq)
• carbon dioxide transport in the blood


  an enzyme(carbonic anhydrase) increases the rate of this reaction by 250 times. This rapid reaction decreases the concentration of CO₂ in the plasma. This maintains a low partial pressure of CO₂ ensuring that CO₂ continues to diffuse into the blood at the tissues. CO₂ is continually produced at the tissues due to cellular respiration. The formation of acids, such as carbonic acid, can create problems. Acids change the pH of the blood so they must be buffered. The carbonic acid is unstable and dissociates into bicarbonate ions and hydrogen ions.
• carbon dioxide transport in the blood 


  H₂CO₃(aq) = H⁺ + HCO₃⁻

  the H⁺ ions help dislodge O₂ from hemoglobin at the tissues. Then the H⁺ combines with the hemoglobin to form reduced hemoglobin. This removes the H⁺ from the plasma, preventing the pH from becoming too acidic. The hemoglobin is acting as a buffer. The bicarbonate ions (HCO₃⁻) are transported in the plasma. Once the venous blood reaches the lungs, O₂ dislodges the H⁺ from the hemoglobin.

  H⁺ + HCO₃⁻ = H₂O + CO₂

  the very concentrated CO₂ diffuses from the blood into the alveoli and is exhaled.
• regulation of breathing


  breathing is controlled by nerves from medulla oblongata in the brain stem. Information about the accumulation of CO₂ and acids, and the need for O₂ is detected by chemoreceptors. When CO₂ dissolves in blood to form H₂CO₃, if it begins to accumulate, chemoreceptors become activated. Once activated, medulla oblongata relays messages to the intercostal muscles and diaphragm to increase breathing movements. Breathing rate increases and levels of CO₂ in blood decrease. Once CO₂ levels fall, the chemoreceptors are inactivated and breathing rate returns to normal again.
• chemoreceptors

  1. O₂ receptors - sensitive to O₂.
  2. CO₂ or acid receptors - most sensitive and are the main regulators of breathing movements.
• O₂ receptors


  they are found in the carotid and aortic arteries. They are mainly responsible for detecting low levels of O₂. When O₂ levels fall, the O₂ receptors send a nerve impulse to the medulla oblongata. It then sends nerve impulses to the intercostal muscles and diaphragm to increase breathing. This will increase blood O₂.
• CO₂ receptors


  more sensitive to changes in blood chemistry. The O₂ receptors act as a back system. They are only used if O₂ levels fall, but CO₂ levels remain normal(that is at high altitudes or with CO poisoning).
• respiratory system disorders

  1. bronchitis
  2. bronchial asthma
  3. emphysema
  4. lung cancer
• bronchitis


  narrowing of air passages and inflammation of the mucous lining in the bronchial tubes. Caused by bacterial or viral infection, reaction to chemicals in the environment. Results in an increase in mucous secretion, inflammation of tissue, and decreasing air flow. Condition becomes more serious in the bronchioles as they are not supported by cartilage to keep them open as the trachea and bronchi are.
• bronchial asthma


  a respiratory disorder associated with inflammation of the bronchioles. They are not supported by cartilage to help keep them open. This narrowing of these air passages reduces air flow. greater effort is required to exhale as opposed to inhale. An inhaler is often used to open up the bronchioles and increase air flow. Causes include cigarette smoke, allergens, pets, air pollution, dust, mold, etc.
• emphysema


  the walls of the alveoli become inflamed. This causes these air sacs to lose their elasticity and eventually rupture. It becomes difficult for the patient to exhale and air gets trapped in the lungs. The number of alveoli is reduced so there is less surface area for gas exchange. This reduces O₂ levels so breathing rate increases to compensate. The circulatory system adjusts by increasing heart rate. The most common cause is smoking. Emphysema is associated with chronic bronchitis. Together they are called chronic obstructive pulmonary disease(COPD).