This website was developed by undergraduate biology researchers working with Dr. Karen Bernd at Davidson College.

Lungs Background

Breathing and Lung Physiology

Alveolar Histology

Defense and Pathology

 

Lung Physiology and Histology


Image from http://www.britannica.com/EBchecked/topic-art/351473/107200/The-alveoli-and-capillaries-in-the-lungs-exchange-oxygen-for

Breathing and Lung Physiology

  • The lung is the location of a fast exchange of carbon dioxide for oxygen. Carbon dioxide is a waste product of cellular respiration and is brought to the lungs by heoglobin and escapes the body. The empty hemoglobin can then bind oxygen carry it in the blood to all of the cells in the body.
  • Diaphragm contracts to pull on pleural membrane, allowing lungs to open
  • Air rushes through the buccal cavity, down the trachea, bronchi, and bronchioles until it reaches the alveoli
    • The alveoli are the site of gas exchange
    • There is only a 2µM distance between the lumen of the alveoli and the red blood cells in the capillaries
  • Partial pressure differences allow oxygen (in the alveoli) and carbon dioxide (in the red blood cells) to exchange places via passive diffusion (Sadava et al. 2008).

Alveolar Histology

  • Alveoli = comprised of 2 cells: type one pneumocytes and type 2 pneumocytes (Kathuria et al. 2007; Wang et al. 2006).
    • Type 1 cells
      • Comprise 95% of alveolar cells
      • Site of gas exchange
      • Provide the structural support of the alveoli
      • Help manage lung fluid homeostasis
      • Little mitotic activity
      • Easily injured
    • Type 2 cells
      • Approximately 5% of alveolar cells
      • Mitotically active
      • Secret and alter surfactant
      • Participate in both the immune and inflammatory responses
  • Type 2 cells proliferate and transform into Type 1 cells to repair alveolar walls; they are vital to lung function (Wang et al. 2006)


Image from http://legacy.owensboro.kctcs.edu/gcaplan/anat2/histology/histo%20F%
20respiratory%20system.htm

Lung Pathology

Lung Defense & Pathology
Because lung cells come in contact with the air they are vulnerable to air born pathogens (like bacteria) and antigens (like pollen). SInce they are the first line of defense, lung cells must protect not only themselves but also the rest of the body from airborn pathogens.
Mechanisms for protection rely on excluding the antigen or providing a barrier:

  • Muco-cilliary escalator
    1. Some lung cells secrete mucous to trap bacteria and potential pathogens
    2. Lung cells with specialized cilia sweep the mucous up towards the mouth
    3. Trapped pathogens then exit the body when the mucous is coughed up (Sadava et al. 2008).
  • Activation of the Innate Immune System
    1. The immune system “recognizes” an antigen through structural barriers or microbial pattern recognition sequences, then it will induce an inflammatory response (Hollingsworth et al. 2007).
    2. Inflammatory response is marked by the “respiratory burst” of activated leukocytes, causing surrounding cells to uptake oxygen and release reactive oxidative species (ROS) into the interstitial fluid (Chen et al. 2007; Balmes 1993).
    3. Uptake of oxygen allows neighboring cells to increase mitochondrial activity (vital for mitosis)
    4. Release of ROS is an attempt to harm antigens more than the organ itself (Felty et al. 2003).
    5. Results in decreased lung function due to pulmonary edema and epithelial cell injury (Chen et al. 2007; Balmes 1993).

Despite these defense mechanisms, certain antigens are still able to damage the lung tissue and cause the diseases such as asthma, acute respiratory distress syndrome (ARDS), chronic obstructive pulmonary disease (COPD) and cancer.



Image from http://www.jci.org/articles/view/6277/figure/1

 

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