Brad is 45 years old and has been working as a coal cutter in a ...

[itsmyluck]

Brad is 45 years old and has been working as a coal cutter in a mine for the last 25 years. He likes the job because it pays well and the same mine had employed his father.
 
  Like many of his colleagues, Brad has had problems with a chronic cough. He has avoided his annual checkups for fear that he will be told he has black lung or coal worker's pneumoconiosis. The disease causes fibrosis, decreased diffusing capacity, and permanent small airway dilation. In later stages, pulmonary capillaries, alveoli, and airways are destroyed.
 
  How can the disease described above create a mismatch between ventilation and perfusion? Use your understanding of alveolar dead space and physiologic shunt to explain your answer.
 
  Individuals with chronic obstructive pulmonary disease have more difficulty exhaling than inhaling. Why is this so?
 
  In general terms, what mechanisms in lung disease can affect diffusing capacity across alveolar membranes? Use the Fick law to explain your answer.

Question 2

Patricia was called at work by a woman at the local daycare center. She told Patricia to come and pick up her son because he was not feeling well. Her son, 3 -year-old Marshall, had been feeling tired and achy when he woke up.
 
  While at daycare, his cheeks had become red and he was warm to touch. He did not want to play with his friends, and by the time Patricia arrived, he was crying. Later that afternoon, Marshall's condition worsened. He had fever, chills, a sore throat, runny nose, and a dry hacking cough. Suspecting Marshall had influenza, Patricia wrapped him up and took him to the community health care clinic.
 
  Why did Marshall's presentation lead Patricia to think he had influenza and not a cold? Why is it important to medically evaluate and diagnose a potential influenza infection?
 
  Describe the pathophysiology of the influenza virus. Outline the properties of influenza A antigens that allow them to exert their effects in the host.
 
  Marshall may be at risk at contracting secondary bacterial pneumonia. Why is this so? Explain why cyanosis may be a feature associated with pneumonia.

[quynhmickitran]

Answer to Question 1

Chronic lung disease can cause impairments in both pulmonary ventilation and perfusion if circulatory and alveolar tissues are destroyed. Alveolar dead space is a term that can be used to describe inflated alveoli without a local blood flow, as seen when capillaries are nonfunctional. Physiological shunt describes a blood supply to an area of the lung that is inadequately ventilated, as seen when lung tissue is damaged. In both situations, the oxygenation of blood is compromised.

Airway resistance is lower during inhalation because of the elastic properties of the lung. When inhalation occurs, elastic fibers have the effect of pulling airways open as the thoracic cage expands. During exhalation, the natural recoiling of the lung tissue results in a narrowing of the passages. Obstructive lung diseases increase airway resistance and therefore add to the resistance already present during exhalation.

The Fick law states that a volume of a gas moving across the alveolar membrane in a given amount of time is proportional to the partial pressure difference of the gas in question, the surface area of the membrane, and the diffusion coefficient. It also stipulates that diffusion is inversely proportional to membrane thickness. In lung disease, such as pneumoconiosis, the destruction of tissues and fibrotic lay down decrease the surface area and increase membrane thickness, respectively. Both events result in the decline of diffusing capacity across alveolar membranes.

Answer to Question 2

Influenza is characterized by a rapid onset of symptoms, particularly malaise. The common cold has a less aggressive onset with the initial appearance of nasal sinus irritation and excessive nasal secretions.
A proper investigation prevents the unwarranted use of antibiotics in a symptomatic patient. The reporting of influenza to public health authorities also contributes to the accurate monitoring of contagious illness within a population.

The influenza A virus damages the epithelial cells of the respiratory tract. They undergo necrosis and shed away to leave gaps between underlying basal cells. Extracellular fluid escapes through the basal membrane and contributes to fluid accumulation in the respiratory passages. Damaged ciliated cells are unable to move mucous within the airways, so mucous accumulation and congestion become an additional component to the infection.
Surface antigen HA facilitates the movement of the influenza A virus into the epithelial cells of the respiratory tract. The NA glycoprotein promotes viral replication and release from the host cell.

Viruses damage the protective mucous membranes in the nasopharynx. Because they also encourage mucous secretions, macrophage activity on pneumococci is inhibited while bacterial adhesion to the epithelium is enhanced. Pneumonia is a condition that causes inflammation of the alveoli. Cyanosis occurs as a result of the decrease in gas exchange through the inflamed alveolar membrane and subsequent decline in hemoglobin saturation.

[itsmyluck]

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