Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
P215 Discussion 13 Problem 1: Asthma Jan has had a mild form of asthma for most of her life. When asthma strikes, she has a problem with air flow in the respiratory system as airways become inflamed, obstructed and narrowed. This is a problem because air flow is a lot like blood flow: i) it flow is from higher pressure to lower pressure ii) flowing air encounters resistance from the walls of the air ways along which it passes iii) resistance to air flow depends on airway diameter; constriction and dilation affect air flow iv) air flowing through airways can be partly or completely blocked by substances in the airway An important part of asthma is the immune system. Some of the changes in airways are caused or worsened by exposure to allergens such as pollen, dander, dust and bug feces. It’s a dirty world. The immune system response in airways involves chronic (long-term) inflammation, including swelling and fluid secretion. small airway cross-section (normal) open airway; smooth muscle in walls small airway cross-section (asthma) fluid and mucus in open airway; contracted smooth muscle in walls; some swelling of airway tissue ? The difficulty posed by fluid and mucus in the airways is obvious. But, how does a decrease in bronchiole diameter during an asthmatic episode affect resistance to air flow? decrease in diameter increases resistance to air flow And how might such a change in resistance to airflow during an asthmatic episode affect actual air flow? decrease in air entering and leaving lungs ? Is asthma considered to be a restrictive or obstructive repsiratory disorder obstructive One common way to treat asthma is to administer corticosteroid drugs. ? Why would such drugs be prescribed to treat asthma? (Think back a few weeks for the answer.) limit activity of the immune system Like many asthma sufferers, Jan treats the chief symptom (difficult ventilation) with an inhaled medication called Albuterol she can spray into her mouth when needed. The drug soon reaches her airways. Albuterol is a short-acting beta 2 adrenergic agonist. Albuterol works because it binds to receptors for substances naturally present in the body and brings about a strong response in airways. ? How does an adrenergic agonist make it easier to breathe in just a few moments? (If the answer isn’t clear, you should be able to figure this in the seven steps found below.) the drugs mimic a sympathetic autonomic response - relax smooth muscle in airways - widen airways - reduce resistance to air flow - improved air flow ? Step #1 Does the word “agonist” mean the drug does the same as the natural substance when it binds to its agonist = same receptorsor does it means the drug does the opposite of the natural substance ? The identity of the natural substances are indicated by the word “adrenergic.” ? Step #2 Does “adrenergic” refer to the parasympathetic or sympathetic division of the autonomic motor system? sympathetic AMS ? Step #3 What are the two similar natural substances (a neurotransmitter, an endocrine hormone) that bind to norepinephrine and epinephrine receptors at adrenergic synapses? There are several types of adrenergic receptors, including the beta 2 receptors. The beta 2 receptors are present on smooth muscle cells in the walls of our bronchioles. ? Step #4 Does the use of a drug that mimics these natural substances that bind to beta 2 adrenergic receptors increase or reduce contraction of smooth muscle in bronchioles? reduce contraction ? Step #5 Does this response of bronchiole smooth muscle constrict or dilate airway diameter? dilate ? Step #6 Does this change in airway diameter increase or decrease resistance to air flow? decrease resistance ? Step #7 How does this change in resistance help someone through an asthmatic episode? - reduced resistance to air flow - improved air flow Problem 2: Three Learned Gentleman Discuss Ventilation ? First, some background. Define the following four terms. i) tidal volume = amount of air moved in and out of the lungs and airways during one normal breath ii) anatomical dead space = amount of space within the conducting zone of the airways, equal to 150 ml. iii) minute ventilation = (breaths per minute) x (tidal volume) iv) alveolar ventilation = (breaths per minute) x (tidal volume - dead space) Three learned physicians (Dr. Howard, Dr. Fine and Dr. Howard) are debating the best way to deliver the most fresh air to the alveoli. Moe (Dr. Howard) says just breathe pretty much normally. Larry (Dr. Fine) says breathe many times a minute, but quite shallowly. Curly (the other Dr. Howard) says breathe only a few times a minute but very deeply. (Shemp says nothing because he isn’t in this episode.) Moe’s Suggestion 14 breaths per minute 500 ml tidal volume Larry’s Suggestion 20 breaths per minute 350 tidal volume Curly’s Suggestion 8 breaths per minute 875 ml tidal volume ? What is the minute ventilation for each of the suggestions? (breaths per minute) x (tidal volume) Moe’s Suggestion Larry’s Suggestion 7000 ml/minute 7000 ml/minute Curly’s Suggestion 7000 ml/minute ? What is the alveolar ventilation for each of the suggestions? (breaths per minute) x (tidal volume - dead space) (Assume dead space is 150 ml.) Moe’s Suggestion 4900 ml/minute Larry’s Suggestion 4000 ml/minute Curly’s Suggestion 5800 ml/minute where a tidal volume of 500 ml ends up ? Why is alveolar ventilation less than minute ventilation? (The drawing at the right may help.) minute ventilation depends on the entire tidal volume; alveolar ventilation depends on part of the tidal volume, the part that fills the respiratory zone conducting zone of air ways respiratory zone of airways no gas exchange 150 ml 350 ml gas exchange ? What’s the best tactic to deliver the most fresh air to the alveoli- Moe’s, Larry’s or Curly’s? Curly’s. Coytenly! ? In this debate, which factor - faster breathing rate or greater depth of breathing - is the most effective at delivering more fresh air to the alveoli? greater depth of breathing Ventilation (breathing) and gas exchange are two prime functions of the respirator system. ? Why is alveolar ventilation more important than minute ventilation for gas exchange? gas exchange occurs in the respiratory bronchioles and alveoli; only air in the respiratory zone is involved in gas exchange; alveolar ventilation (not minute ventilation) measures fresh air in the conducting zone In the real world, the situation isn’t a simple choice between the good doctors’ tactics. For example, breathing rate and tidal volume both increase to raise alveolar ventilation during exercise. Initially, increasing the depth of breathing contributes most to raising alveolar ventilation. However, after depth of breathing has increased several times its resting volume, the lungs are expanding about as much as they can, and increasing the breathing rate starts to makes a bigger contribution to raising alveolar ventilation. Problem 3: Breathing and Surfactant Breathing is work. Moving air out of the airways and lungs - normal expiration - isn’t so hard. It only requires muscle to relax. To move air into the lungs - inspiration - that’s a job that requires skeletal muscles to contract. One of the factors the muscle must work against is the attraction of water molecules for each other within the respiratory system. A watery film coats walls of small airways. During inspiration, the air spaces increase in volume as the lung expands. The attraction of water molecules for each other must be counteracted. expansion of respiratory zone respiratory zone alveolar duct alveolar duct film film air space air space between breaths during inspiration close up view of watery film lining parts of airways close up view of watery film lining parts of airways expansion of airways is resisted by interactions of water molecules water molecules interact with each other ? What characteristic of water molecules enables them to interact more positive H H with one another? O more negative they’re polar molecules positvely charged regions in water molecules are attracted to negatively charged regions in other water molecules The interaction among water molecules resists expansion of the respiratory zone. Surfactant helps makes the job of inspiration easier. It can mix with water molecules in the fluid film along the walls of the respiratory zone. ? What is surfactant? a complex of lipid and proteins ? What cells produce surfactant? type II alveolar cells non-polar part polar part surfactant molecule ? What part (polar or non-polar) of surfactant interacts with water molecules? polar part Surfactant reduces the interactions of water molecules in the film lining the respiratory zone. Surface tension of the film declines. Water doesn’t “pull together” as strongly to resist expansion of air spaces. On the next page are two instances in which surfactant plays a vital role. Baby T.H. is a premature newborn with respiratory distress syndrome. ? Why is it such a struggle for immature infants like T.H. to breathe? her immature lungs cannot produce adeuate amount of surfactant must work against attraction of water molecules ? Before the struggle for breath exhausts them, infants with respiratory distress can be helped by supplemental oxygen and breathing assistance. They can also inhale a surfactant preparation. How would giving surfactant help them? reduce interaction of water molecules in respiratory zone have benefits of surfactant until lungs mature and produce it ? Adults can also suffer from insufficient production of surfactant. For example, pain following the abdominal or thoracic surgery often makes people take shallow breaths. These patients are regularly visited by respiratory therapists who help them make a series of deep breaths despite the discomfort. The question is why? (Think about what kind of alveolar cells produce surfactant and when they tend to do it.) deeper breathing leads to more surfactant release by type II alveolar cells Problem 4: A Pleural Sac Perforation Jimmy G. got in the way of the sharp end of a knife. The blade passed through his chest wall and entered the pleural sac surrounding his right lung and the lung itself. Shortly thereafter, most of his right lung collapsed. As a result, Jimmy experienced difficulty in breathing. Medical care was not long in coming and Jimmy survived. Given the proper treatment, his right lung eventually expanded. trachea chest wall chest wall lung lung pleural sac Questions ? What’s the name for the surface of the pleural sac that lines the inner surface of the chest wall? parietal pleura ? What’s the name for the surface of the pleural sac that lines the outer surface of the lung? visceral pleura ? Let’s assume the atmospheric pressure is 760 mm Hg. If the airways are open and no air is moving into or out of the lungs, what is the air pressure in the alveoli? same 760 mm Hg ? How does intrapleural pressure compare to intrapulmonary pressure? lower than intrapulmonary pressure ? How does this difference in pressure (the transpulmonary pressure) affect the shape of the lungs? helps keep them inflated --- lower pressure outside lungs than inside ? How does intrapleural pressure compare to atmospheric pressure? it’s lower than atmospheric pressure ? How does this difference in pressure affect the shape of the chest wall? helps keep chest wall in normal position --- higher pressure outside chest than inside When the pleural sac and right lung were punctured by the knife wound, atmospheric pressure, intrapulmonary pressure and intrapleural pressure can become equal. ? How did the position of Jimmy’s chest wall change when the pleural sac was opened to the atmospheric pressure?moved outward from normal position ? Why did the right lung collapse? elastic recoil of lung when no difference in air pressure between inside and outside What would happen to someone who had a lung disease (such as severe infection or tumor) that perforated ? the surface of the pleural sac on the outer surface of the lung? same thing ? What is the medical term for Jimmy’s condition? pneumothorax