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BIOL 273
Catherine Studholme

Chapter 17: Mechanics of Breathing  Aerobic metabolism in cells depends on a steady supply of oxygen and nutrients from the environment, coupled with the removal of carbon dioxide  Most multi-celled animals require specialized respiratory organs associated with a circulatory system  Exchange surface must be thin and moist to allow gas exchange from air into solution but also must be protected from drying out  Four primary functions of the respiratory system: 1. Exchange of gases between atmosphere and blood 2. Homeostatic regulation of body pH 3. Protection from inhaled pathogens and irritating substances 4. Vocalization  Bulk air flow- the exchange of air between environment and interior space of lungs  External respiration can be divided into 4 processes 1. The exchange of air between the atmosphere and the lungs, aka ventilation. Inspiration/inhalation = movement of air into lungs. Expiration/exhalation = movement of air out of lungs 2. The exchange of O and CO between lungs and blood 2 2 3. Transport of O a2d CO by2the blood 4. Exchange of gases between blood and cells  Upper respiratory tract = mouth, nasal cavity, pharynx and larynx  Lower respiratory tract = trachea, two primary bronchi and their branches, and lungs  Pericardial sac contains the heart, pleural sacs contain the lungs  Pleural fluid a) creates moist, slippery surface so opposing membranes can slide across each other as lungs move within the thorax, b) holds lungs tight against thoracic wall  Air > mouth/nose > pharynx (throat; food, liquid, air) > larynx > trachea (windpipe/vocal cords) > primary bronchi > bronchioles  Breathing through the mouth is not as effective at warming and moistening air as breathing through your nose  Mucus contains immunoglobulin that can disable many pathogens. Once mucus reaches pharynx it can be spit out/swallowed (stomach acid destroys any remaining microorganisms)  Cystic fibrosis – inadequate ion secretion decreases fluid movement in the airways. Without the saline layer, cilia become trapped in thick, sticky mucus. Mucus cannot be cleared, and bacteria colonize in airways, resulting in recurrent lung infections  Alveoli are composed of a single layer of epithelium - type II alveolar cells synthesize and secrete surfactant (mixes with thin fluid lining of alveoli to aid lungs as they expand during breathing) - type I alveolar cells occupy about 95% of alveolar surface area and are very thin so gases can diffuse rapidly through them  the rate of blood flow through the lungs is much higher than the rate in other tissues because the lungs receive the entire cardiac output of the right ventricle: 5 L/min.  Partial pressure – the pressure of a single gas in a mixture  Surface of the lungs is covered by the visceral pleura and the portion of the sac that lines the thoracic cavity is called the parietal pleura  When the thoracic cavity moves during breathing, the lungs move with it as they are unable to expand and contract on their own  Pneumothorax = air in the pleural cavity breaking the fluid bond holding the lung to the chest wall  Intrapleural pressure never equilibrates with atmospheric pressure because the pleural cavity is a closed compartment  Compliance – the ability of the lung to stretch  Emphysema – elastin fibers found in lung tissue are destroyed. Destruction of elastin results in lungs that exhibit high compliance and stretch easily during inspiration. However, these lungs also have decreased elastance, so they do not recoil to their resting position during expiration  Some forms of fibrotic lung disease result from chronic inhalation of fine particulate matter such as asbestos and silicon, that escape the mucus lining the airways and reaches the alveoli. Wandering alveolar macrophages then ingest the particulate matter. If organic, the macrophages can digest them with lysosomal enzymes. However, if the particles cannot be digested or if they accumulate in large numbers, inflammation occurs. Macrophages then secrete growth factors that stimulate fibroblasts in lung’s connective tissue to produce inelastic collagen. Pulmonary fibrosis cannot be reversed  3 factors contributing to resistance: 1. the system’s length 2. the viscosity of the substance flowing through the system 3. the radius of the tubes in the system (this one tends to be the most important, the other two are relatively constant)  Bronchoconstriction – increases resistance to air flow and decreases the amount of fresh air that reaches the alveoli  Carbon dioxide in the airways is the primary paracrine that affects bronchiolar diameter. Increased CO in2expired air relaxes bronchiolar smooth muscle and causes bronchodilation  Total pulmonary ventilation – volume of air moved into and out of the lungs each minute (= ventilation rate x tidal volume) Chapter 18: Gas Exchange and Transport  Hypoxia – a state of too little oxygen occurs when the diffusion of gases between alveoli and blood is significantly impaired, or if oxygen transport in the blood is inadequate  Hypercapnia – state of elevated concentrations of carbon dioxide  To avoid hypoxia and hypercapnia, the body uses sensors to respond to 3 variables: 1. Oxygen 2. Carbon dioxide 3. pH  2 possible causes of low alveolar P O2 1. the inspired air has low oxygen content  main factor is altitude  partial pressure of oxygen decreases as you move to higher altitudes 2. alveolar ventilation  hypoventilation – characterized by lower-then-normal volumes of fresh air entering alveoli  pathological changes that can result in alveolar hypoventilation include decreased lung compliance, increased airway resistance, or CNS depression that slows ventilation rate and decreases depth  gas exchange in the lungs is rapid, blood flow through pulmonary capillaries is slow, and diffusion reaches equilibrium in less than 1 second  Pathological changes that adversely affect gas exchange include: 1. Surface area 2. Diffusion barrier permeability 3. Diffusion distance  Pulmonary edema – accumulation of interstitial fluid increases the diffusion distance and slows gas exchange  The movement of gas molecules from air into a liquid is directly proportional to 3 factors 1. Pressure gradient of the gas 2. Solubility of the gas in the liquid 3. Temperature (usually constant in mammals)  Fetal hemoglobin (HbF) has two gamma protein chains in place of the two beta chains found in adult hemoglobin. The presence of gamma chains enhances the ability of fetal hemoglobin to bind oxygen in the low-oxygen environment of the placenta  Carbon dioxide is transported in 3 ways: 1. CO 2nd Bicarbonate Ions  About 70% of CO t2at enters blood is transported to the lungs as bicarbonate ions dissolved in plasma  Conversion of CO to HCO serves two purposes: i) it provides 2 3 an additional means of CO t2ansport from cells to lungs, and ii) HCO i3 available to act as a buffer for metabolic acids, thereby helping stabilize body’s pH  Carbon dioxide is converted into the bicarbonate ion by carbonic anhydrase, an enzyme found concentrated in RBCs 2. Hemoglobin and H + +  Removes free H from the RBC cytoplasm  Hemoglobin within the RBC acts as a buffer and binds hydrog
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