Alveoli

Examples of Alveoli in the following topics:

• Alveoli

  • Alveoli are hollow cavities in the lung that perform gas exchange with the blood.
  • Its plural is alveoli, from the Latin alveolus, meaning little cavity.
  • The alveoli are highly elastic, so the alveoli can stretch as they are filled with air during inhalation.
  • In some alveolar walls there are pores between alveoli called the pores of Kohn, that connect alveoli in order to equalize air pressure between the different sacs of an alveolus.
  • Besides these epithelium cells, there are many macrophages found in the alveoli that provide immune system defense of the alveoli from pathogens and foreign material.

• Factors Affecting Pulmonary Ventilation: Surface Tension of Alveolar Fluid

  • The alveoli are highly elastic structures in the parenchyma of the lungs that are the functional site of gas exchange.
  • As the alveoli fill with air during inhalation they expand, and as air leaves the lung with exhalation, the alvoli return to their non-inflated size.
  • The reason for the elasticity of the alveoli is a protein found in the extracellular matrix of the alveoli, called elastin, as well as the surface tension of water molecules on the alveoli themselves.
  • Because the alveoli of the lungs are highly elastic, they do not resist surface tension on their own, which allows the force of that surface tension to deflate the alveoli as air is forced out during exhalation by the contraction of the pleural cavity.
  • Fortunately, the type II epithelial cells of the alveoli continually secrete a molecule called surfactant that solves this problem.

• Blood Flow in the Lungs

  • The pulmonary arteries divide into thin-walled capillaries closely associated with the alveoli, small air sacs in the lungs where gas exchange occurs.
  • Oxygen passively flows from the air inside the alveoli into the blood in the alveolar capillaries, while carbon dioxide passively flows in the opposite direction.
  • The alveoli are the site of oxygen and carbon dioxide exchange in the lungs.

• Development of the Respiratory System

  • By the end of this period, all of the major lung elements, except those required for gas exchange (e.g. alveoli), have appeared.
  • 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.
  • Lastly, the alveolar period spans from birth to eight years of age and during this stage the terminal saccules, alveolar ducts, and alveoli increase in number.
  • True alveoli appear as indentations in the saccular wall and septae form to produce divisions in the wall.

• Lungs

  • The exchange of gases is performed by the alveoli, the functional units of the lungs.
  • The interior of the lung contains the alveoli, where gas exchange occurs.
  • The alveoli branch off from the bronchioles and bronchi that connect to the trachea and allow air to pass into the lungs.
  • The major function of the lungs is gas exchange, which occurs in the alveoli of the lung.
  • Only a relatively small proportion of alveoli in the lungs are perfused with blood and actually take part in gas exchange.

• Systemic and Pulmonary Circulation

  • At the lungs, the blood travels through capillary beds on the alveoli where respiration occurs , removing carbon dioxide and adding oxygen to the blood.
  • The alveoli are air sacs in the lungs that provide the surface for gas exchange during respiration.
  • A diagram of the alveoli, illustrating the capillary beds where gas exchange with the blood occurs.

• Pneumonia

  • Pneumonia is an inflammatory condition of the lung caused by a bacteria, virus, fungi or parasite which affects the alveoli.
  • Pneumonia is an inflammatory condition of the lung especially affecting the microscopic air sacs (alveoli) that is associated with fever, chest symptoms, and a lack of air space (consolidation) on a chest X-ray.
  • Pneumonia fills the lung's alveoli with fluid and hinders oxygenation .

• Pressure Changes During Pulmonary Ventilation

  • Alveolar ventilation (VA):  The amount of gas per unit of time that reaches the alveoli and becomes involved in gas exchange.
  • In respiratory physiology, PAO2 and PACO2,refer to the partial pressures of oxygen and carbon dioxide in the alveoli.
  • Recall that gasses travel from areas of high pressure to areas of low pressure, so the greater pressure of oxygen in the alveoli compared to that of the deoxygenated blood explains why oxygen can passively diffuse into the bloodstream during gas exchange.
  • The partial pressure, and thus concentration of carbon dioxide, is greater in the in the capillaries of the alveoli compared to the alveolar air, so carbon dioxide will passively diffuse from the bloodstream into the alveoli during gas exchange.

• Functional Anatomy of the Respiratory System

  • At the molecular level, gas exchange occurs in the alveoli—tiny sacs which are the basic functional component of the lungs.
  • Alveolar Ventilation (VA):  The amount of gas per unit of time that reaches the alveoli (the functional part of the lungs where gas exchange occurs).
  • Dead Space Ventilation (VD): The amount of air per unit of time that doesn't reach the alveoli.
  • 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.

• Mammary Glands

  • The basic components of a mature mammary gland are the alveoli (hollow cavities, a few millimeters large) lined with milk-secreting cuboidal cells and surrounded by myoepithelial cells.
  • These alveoli join up to form groups known as lobules, and each lobule has a lactiferous duct that drains into openings in the nipple.
  • Secretory alveoli develop mainly in pregnancy, when rising levels of prolactin, estrogen, and progesterone cause further branching, together with an increase in adipose tissue and a richer blood flow.
  • When the lactiferous duct tree is almost ready, alveoli are differentiated from luminal epithelial cells and added at the end of each branch.
  • Their binding ensures correct placement of prolactin receptors on basal lateral side of alveoli cells and directional secretion of milk into lactiferous ducts.