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Pulmonary Anatomy and Physiology

Chapter 21 of Carol Porth’s Pathophysiology presents an introduction to respiratory anatomy and physiology. The following two chapters present pathologies that affect the system. I’ve outlined here the basics of lung A&P as notes from my reading of the chapter and I thought I would present that here as a guide for any of my students. I have yet to outline the second and third chapters, but there is a skeleton of conditions that we will cover. It is also worth noting that I expect my students to be able to recognize and identify the structural components of the respiratory system even though I did not include these elements in my outline …

Pulmonology Outline

  1. Structures and Functions (Chapter 21)
    1. Structures
      1. Upper Respiratory System
      2. Lower Respiratory System
  • Tissue and Cell types
    1. Ciliated columnar epithelial cells
    2. Goblet cells
  1. Alveoli – terminal air spaces in the lung & site of gas exchange
    1. Type I Alveolar Cells – this squamous cells making up ~95% of the alveolus
    2. Type II Alveolar Cells – secretory cells that produce surfactant, also serve as progenitors of Type I cells
    3. Alveolar Macrophages – responsible for removing organisms and debris that penetrated the lungs
  2. Pleura – a double layer of membrane lining the inner thoracic cavity and covering the lungs.
  1. Functions
    1. Conducting Airways
      1. Purpose: To deliver warm, moistened, cleaned air to Respiratory Tissue
    2. Respiratory Tissue: To perform gas exchange (O2 and CO2)
  • Gas Exchange
    1. Ventilation – Inspiration and Expiration
      1. Mechanically, ventilation depends upon the structure of chest cavity – i.e. it is entirely closed with the only opening to the exterior being the trachea
      2. Inspiration occurs as the diaphragm pulls down and opens the
    2. Perfusion – flow of blood through the alveolar capillary bed

Ventilation and Perfusion must be matched in order to optimally oxygenate blood in the lungs.

  1. Gas exchange (described by the Fick Law of Diffusion)
    1. V = [SA x KD (P1-P2)] / T
    2. Both O2 and CO2 are transported by blood
  2. Hb Dissociation Curve
  3. Partial Pressure – the pressure of some component of a gas. By definition, all partial pressures add up to the total pressure of a gas. (i.e. if a gas is comprised of O2 and CO2, then the partial pressures of O2 and CO2 must add up to the total pressure of the gas)
  4. The O2 / Hb dissociation Curve
    1. Measures the amount of O2 bound to Hb at any specific PO2
  5. Lung Volumes & Capacities (summarized in Table 21-1)
    1. Tidal Volume – volume of air going in and out of the lungs with each resting breath
    2. Total Lung Capacity (TLC) = tidal + inspiratory reserve + expiratory reserve + residual volumes
    3. Vital Capacity = tidal + inspiratory + expiratory reserve volumes
    4. Dead Air Space – Air in the lungs that does NOT participate in respiration

Questions

  1. Why is arterial (rather than venous) blood used to measure blood gases?
    1. What would venous blood gases measure?
  2. Using an O2 / Hb dissociation curve, show how Hb effectively carries O2 from the lung to the muscles, where it is released to myoglobin for use in respiration.

Pathologies

  1. General Issues
    1. Pleura effusions– are accumulations of fluid in the space between the pleural membranes around the lungs
    2. Infant Respiratory Distress Syndrome – alveolar collapse in young infants (esp prematures) due to lack of surfactant
    3. Dyspnea – general term for difficulty breathing. Can occur due to primary lung disease, heart disease, or neuromuscular disorders affecting the respiratory muscles
  2. Infections
    1. Pneumonia
    2. Influenza
    3. Fungal Infections
    4. Tuberculosis
  3. Congenital Problems
    1. CF
  4. Acquired Problems
    1. COPD
    2. Pulmonary Hypertension – causes and outcomes
  5. Respiratory Distress Syndrome
  6. Respiratory Failure
 
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Posted by on February 23, 2015 in Uncategorized

 

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Getting Oxygen Where It’s Needed

Oxygen is required by many organisms for survival, luckily it is plentiful in the air, but how does it get into all the tiny cells all over the body?

periodicFirst, Oxygen is a highly electronegative atom. This means that it attracts electrons very well and can pull them away from other molecules. Only one other atom is more electronegative and that’s the most reactive element in the periodic table, Fluorine. Electronegativity becomes useful biologically because electrons are capable to storing energy that can be passed along from one molecule to the next. But , to do this, each molecule must be more electronegative than the last. Therefore, it is not surprising that Oxygen is used as the final electron acceptor in the electron transport chain of cellular respiration. This reaction is required by many organisms, and can be highly beneficial even to some organisms that can live without Oxygen. An electron transport chain is a process by which molecules in a membrane pass en electron down the line using its energy in a controlled way to extract even more energy from sugar.

But how does Oxygen get to the cells that need it? Two molecules account for much of this action, myoglobin and hemoglobin, both illustrated below:

Image

Hb- hemoglobin, Mb-myoglobin.

What this image also elegantly portrays is the amazing similarity between the molecules that belies their evolutionary relationship.

Each of these molecules is capable of binding Oxygen, but each occurs in a different tissue. ImageHemoglobin is present in Red Blood Cells, making them capable of transporting oxygen from the lungs to other tissues. Myoglobin occurs in these ‘other’ tissues, particularly muscle cells.

Despite the fact that they both bind oxygen, they do not bind it equally well under all conditions. While hemoglobin is just as good at binding Oxygen in high concentration environments (like the lung after inhalation), it is not as good at retaining oxygen when found in less Oxygen-rich environments (such as tissues like muscle).  Under these conditions, myoglobin is much better at binding Oxygen and can pull the molecules away from hemoglobin.

Recently, several groups have published new data about how subtle differences amongst proteins involved in Oxygen transport through blood and muscle result in different binding properties. In turn, the variability in these properties underlie the amazing diversity of lifestyles found in nature, from humans to birds to giant whales capable of holding their breath for up to an hour.

Image That brings us back to the electron transport chain and Oxygen’s electronegativity, where Ois used as a ‘magnet’ for the electron traveling down the pathway from one molecule to the next. As it goes it loses some of its energy, which is converted into a new form that the cell can use. Once the electron, now at a lower energy state, gets to O2, the Oxygen splits  and takes up a Hydrogen ion to form water.

So, electronegativity and binding affinity are the forces that both transport Oxygen through the body and pulls electrons from one molecule to another. Together, the movement of electrons, like that of water through a mill, powers processes that lead to the synthesis of ATP, the energy currency of the cell (see below).

 

electron-transport-chain-cpg-notes

Note the electron traveling down the chain (in pink)

Given what we’ve discussed here, how do you think a baby ever gets to pull the Oxygen away from its mother’s blood / hemoglobin?

 
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Posted by on June 26, 2013 in Uncategorized

 

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