Pulmonary surfactant

Examples of Pulmonary surfactant in the following topics:

• Factors Affecting Pulmonary Ventilation: Surface Tension of Alveolar Fluid

  • The surface tension of alveolar fluid is regulated by pulmonary surfactant, allowing efficient respiration.
  • They lack sufficient surfactant to initiate proper breathing, and therefore, go into respiratory distress.
  • Fortunately, the type II epithelial cells of the alveoli continually secrete a molecule called surfactant that solves this problem.
  • Surfactant is a lipoprotein molecule that reduces the force of surface tension from water molecules on the lung tissue.
  • It is treated through pulmonary surfactant replacement therapy and mechanical ventilator treatment until the infant's lungs are old enough to secrete enough surfactant to survive on their own.

• Development of the Respiratory System

  • Specialized cells of the respiratory epithelium appear including type II alveolar cells which secrete pulmonary surfactant.
  • This surfactant is important in reducing the surface tension at the air-alveolar surface, allowing expansion of the terminal saccules.
  • Pre-term birth can lead to infants with under-developed alveolar type II cells which produce surfactant.
  • The lungs of pre-term infants therefore may not function well because the lack of surfactant leads to increased surface tension within the alveoli leading to alveoli collapse and no gas exchange, a condition known as respiratory distress syndrome.

• The Work of Breathing

  • Breathing includes several components, including flow-resistive and elastic work; surfactant production; and lung resistance and compliance.
  • Surfactant works like a detergent to reduce the surface tension, allowing for easier inflation of the airways.
  • In pulmonary diseases, the rate of gas exchange into and out of the lungs is reduced.
  • Examples of restrictive diseases are respiratory distress syndrome and pulmonary fibrosis.
  • Obstructive diseases and conditions include emphysema, asthma, and pulmonary edema.

• Alveoli

  • Found in the lung parenchyma, the pulmonary alveoli are the terminal ends of the respiratory tree that outcrop from either alveolar sacs or alveolar ducts; both are sites of gas exchange with blood.
  • The surfactant produced by type II epithelial cells is very important for maintaining the elastic recoil of the lungs.
  • Surfactant is first produced by human lungs between 24 and 28 weeks in the womb, and many infants born prematurely do not have enough surfactant to breathe on their own after birth.
  • Surfactant replacement therapy is necessary to save the lives of these premature births.
  • This is a common occurrence in people with lung diseases like COPD (chronic pulmonary obstructive disorder, i.e., emphysema and bronchitis) or restrictive lung diseases like pulmonary fibrosis, in which scarring of the lung tissue hinders gas exchange in the alveoli, or lung infections like pnuemonia.

• Factors Affecting Pulmonary Ventilation: Compliance of the Lungs

  • Lung compliance refers to the magnitude of change in lung volume as a result of the change in pulmonary pressure.
  • Therefore, surfactant secreted by type II epithelial cells increases lung compliance by reducing the force of surface tension.
  • Low lung compliance is commonly seen in people with restrictive lung diseases, such as pulmonary fibrosis, in which scar tissue deposits in the lung making it much more difficult for the lungs to expand and deflate, and gas exchange is impaired.
  • Pulmonary fibrosis is caused by many different types of inhalation exposures, such as silica dust.
  • Pulmonary fibrosis stiffens the lungs through deposits of scar tissue, decreasing low compliance and making it more difficult for the lungs to inflate and deflate.

• Adjustments of the Infant at Birth

  • With the first breaths, there is a fall in pulmonary vascular resistance and an increase in the surface area available for gas exchange.
  • Over the next 30 seconds, the pulmonary blood flow increases and is oxygenated as it flows through the alveoli of the lungs.
  • These two changes result in a rapid redirection of blood flow into the pulmonary vascular bed, from approximately 4% to 100% of cardiac output.
  • Following birth, the expression and re-uptake of surfactant, which begins production at 20 weeks gestation, is accelerated.
  • Expression of surfactant into the alveoli is necessary to prevent alveolar closure.

• Blood Flow in the Lungs

  • The pulmonary circulatory system is the portion of the cardiovascular system in which oxygen-depleted blood is pumped away from the heart to the lungs, via the pulmonary artery.
  • Oxygenated blood is then returned to the heart via the pulmonary vein.
  • From the right ventricle of the heart, blood is pumped through the pulmonary semilunar valve into the left and right pulmonary arteries (one for each lung) and travels through the lungs.
  • The oxygenated blood then leaves the lungs through pulmonary veins, which return it to the left atrium of the heart, completing the pulmonary cycle.
  • Outline the path of pulmonary circulation: blood flow in the lungs

• Blood Supply to the Lungs

  • Pulmonary circulation refers to blood supply to the lungs for the purpose of gas exchange.
  • The right side of the heart deals with pulmonary circulation.
  • After blood fills in the right ventricle, it contracts and pumps the blood through the pulmonary valve, and into the pulmonary arteries.
  • The most serious issue in pulmonary circulation is a pulmonary embolism, which is where a blood clot travels to the lung and causes an infarction of the lung (tissue death from lack of oxygen).
  • Diagram of pulmonary circulation.

• Systemic and Pulmonary Circulation

  • From the right ventricle, blood is pumped through the pulmonary valve and into the pulmonary artery.
  • The pulmonary artery splits into the right and left pulmonary arteries and travel to each lung.
  • The oxygenated blood then leaves the lungs through pulmonary veins, which returns it to the left atrium, completing the pulmonary circuit.
  • Oxygen-rich blood from the lungs leaves the pulmonary circulation when it enters the left atrium through the pulmonary veins.
  • Diagram of pulmonary circulation.

• Functional Anatomy of the Respiratory System

  • A molecule called surfactant (secreted by the alveoli) prevents the surface tension from becoming too great and collapsing the lungs.
  • The pulmonary alveoli are the terminal ends of the respiratory tree, outcropping from either alveolar sacs or alveolar ducts, which are both sites of gas exchange with the blood.