Question: Please Answer All Of The Following Questions In Complete Sentences. Be Sure To Use Details From The Case To Answer The Questions About Jenny. A) What Is The Name Of The White Blood Cell Responsible For Triggering An Asthma Attack? Name Two Chemicals That This Cell Secretes That Leads To Constriction Of Smooth Muscle. B) What Lung Volume(s) Is/are Commonly …

Case Presentation Jenny, a 16-year-old girl, is afflicted with asthma attacks. She has suffered from asthma for several years now. The attacks occur when she is exposed to dog hair, when she gets overly excited, or if she runs too fast. During her asthma attacks, she gets very short of breath and feels tight in the chest. This morning, Jenny was exercising with her friend Alisha when she had an asthmatic attack. Jenny got very short of breath and was rushed to the hospital emergency room by her mother. The ER (emergency room) nurse quickly measured Jenny’s VC (vital capacity) and FEV1.0 (1 second forced expiratory volume), which were 3510 ml and 52% respectively. The doctor listened to Jenny’s lungs with a stethoscope. Both inspiratory and expiratory wheezing were heard on auscultation. A sample of arterial blood was drawn from Jenny’s radial artery on her left hand. The blood sample was sent to the hospital pulmonary lab for STAT (immediate) analysis of arterial blood gases (ABGs). Jenny was treated by having her inhale a salbutamol solution with the aid of a nebulizer. Her breathing did not improve after a few minutes, so she was given a subcutaneous injection of epinephrine. Within a few minutes Jenny’s breathing seemed to get better. “I think I’m all right now, “remarked Jenny. Another measurement her VC and FEV1.0 lung volumes showed them to be 3605 ml and 75% respectively. The admission blood sample results came back with the following results: arterial pH= 7.42, PaO2= 81, PaCO2= 34, HCO3 =26. Because Jenny’s breathing was returning to normal, the health care team decided not to subject Jenny to another poke in the wrist for blood. Jenny was observed for an hour at the hospital and then was released and went home with her mother. Case Background Asthma is a type of immune reaction in which cells of the immune system overreact in response either to a foreign substance (antigen) in the body or to stress. During an asthma attack, a special category of leukocytes, called mast cells, release histamine and SRS-A (slow reactive substance of anaphylaxis). These two chemicals trigger smooth muscle cells surrounding lung airways to contract; leading to bronchoconstriction. The affected individual has difficulty breathing during an asthma attack because of the narrowed airways. Wheezing sounds can be heard, often without the use of a stethoscope. Because airflow into and out of the lungs is impeded, several aspects of lung physiology are affected during an asthma attack. As the affected individual experiences difficulty filling the lungs with air, she may hyperventilate; because CO2 diffuses about 20 times faster than 02, blood CO2, (PaCO2) will decrease as the CO2 is rapidly expired out of the lungs. If the asthma attack is severe with significant airway narrowing, CO2 retention can occur, raising the PaCO2 and lowering the blood pH. Blood oxygen (PaO2) will often decrease, because hyperventilation does not allow enough time for oxygen to diffuse from the lung alveoli into the blood. With lowering of PaCO2, the blood pH will rise, because CO2 is a potential source of acid (CO2 + H2O + H2CO3 + H+ and HCO3- ). The lung vital capacity (VC) will be unaffected because vital capacity measurement is not a timed measurement. Vital capacity is basically proportional to the number of lung alveoli possessed by an individual. Forced expiratory volumes (FEV1.0, FEV2.0) will be decreased, because airway narrowing with asthma impedes airflow. The FEV measurements represent the percent of the vital capacity that can be expired forcefully and rapidly in a given period of time, such as 1 second for the FEV1.0 (Figure 1). The calculation of the FEV1.0 can be performed as follows: FEV1.0 = [(Volume forcefully expired in 1 second, after maximal inhalation) / (VC)] x 100 Tidal volume (TV), the volume of air a person breathes in or out during normal breathing, will often be decreased if the asthmatic hyperventilates. Figure 1: Lung spirometry showing final tidal volume, vital capacity, and sample FEV1.0 measurement. 7000 Max Inhalation Max Inhalation 6000 5000 4000 LUNG VOLUME (cc) 3000 Forced Expiration Л n Vital Capacity M 2000 um M 1000 Max Exhalation 4 5 6 1 2 3 7 8 9 10 11 sec. Treatments Treatment of an asthma attack takes advantage of knowledge of cellular and molecular biochemistry. Formation of mast cell and smooth muscle cell cyclic AMP (CAMP) inhibits mast cell release of histamine and SRS-A and triggers smooth muscle cell relaxation. The goal then is to increase the CAMP concentrations in mast cells and smooth muscle cells to prevent the release of histamine and SRS-A, and to prevent smooth muscle cell constriction of airways. This can be accomplished by several means. The cell enzyme that degrades CAMP, CAMP phosphodiesterase, can be inhibited by a molecule known as theophylline. Theophylline is a common aerosol inhalant taken by asthmatics; it is also available in pill form. Theophylline, found in many teas, is an example of a class of molecules known as methylxanthines. Caffeine is another example of a commonly occurring methylxanthine. Stimulation of beta receptors on the surface of mast cells and smooth muscle cells leads to an increase in their cellular CAMP, thereby inhibiting release of histamine and SRS-A. Epinephrine (adrenalin) stimulates beta receptors and is thus helpful in treating an acute asthma attack. Unfortunately, beta receptors are also found on heart muscle and on other tissues as well. Selective stimulation of lung beta receptors would be optimal, and indeed desired, particularly in someone with heart disorders. Beta receptors differ (biochemically) between the lung and the heart-but only slightly. Lung beta receptors are termed beta-2 and heart beta receptors are termed beta-1. Because of the slight molecular differences between beta-1 and beta-2 receptors, chemists have designed drugs to bind to one stronger than the other. Selective beta-2 stimulants include metaproterenol, terbutaline, and salbutamol; such agents are useful in treating asthma and avoiding reflects on the heart. Because the mast cells are a leukocyte, they can be inhibited with corticosteroids, such as hydrocortisone and prednisone. Corticosteroids inhibit leukocyte function by multiple mechanisms, and also stimulate beta-2 receptor synthesis. Cromolyn sodium is a newer drug used to prevent asthma attacks. It works by preventing histamine and SRS-A release from mast cells.