deflation of the lungs. Collagen within the pulmonary interstit—ium resists further expansion at high lung volumes. Compliance is defined as the change in volume per unit change in pressure (AV/AP). In vivo, compliance is measured by esophageal balloon pres sure vs. lung volume at many points during inspiration and expiration. Each measurement is made after the pressure and volume have equilibrated and so this is called static compli ance. The compliance is the slope of the pressure—volume curve. Several observations can be made from the pressure—volumecurve.
Note that the pressure—volume relationship is different with deflation than with inflation of air (hysteresis). The compliance of the lungs is greater (the lungs are more distensible) in the middle volume and pressure ranges.
The equation for oxygen is:
QO 2 = CO ? 1,34 (ml/g) ? [Hg] ? SaO 2 + + 0,003 (ml/ml per mm Hg) ? РаО 2,
where QO 2 is oxygen delivery (ml/min), CO is cardiac output (L/min). Hg is hemoglobin concentration (g/L), SaO 2 is the fraction of hemoglobin saturated with oxygen, and PaO 2 is the partial pressure of the oxygen dissolved in plasma and is trivial compare to the amount of oxygen carried by hemoglobin. Examination of this equation reveals that increasing hemoglobin concentration and increasing cardiac output can enhance oxygen delivery. Saturation is normally greater than 92 % and usually is easily maintained through supplemental oxygen and mechanical ventilation. Cardiac output is supported be insuring adequate fluid resuscitation (cardiac preload) and manipulating contractility and after load pharmacologically (usually cat— echolamines).
New words
Equation – уравнение
Delivery – доставка
Cardiac output – сердечный выброс
Fraction – фракция
Contractility – сократимость
33. Surface tension forces
In a liquid, the proximity of adjacent molecules results large, intermolecular, attractive (Van der Waals) forces that serve to stabilize the liquid. The liquid—air surface produces inequality of forces that are strong on the liquid side and weak on the gas side because of the greater distance between molecules in the gas phase. Surface tension causes the surface to maintain as small an area as possible. In alveoli, the result a spherically— curved, liquid lining layer that tends to be pulled inward toward the center of curvature of the alveolus. The spherical surface of the alveolar liquid lining behaves in manner similar to a soap bubble. The inner and outer surface of a bubble exert an inward force that creates a greater pressure inside than outside the bubble. Interconnected alveoli of different sizes could lead to collapse of smaller alveoli (atelectasis) into larger alveoli, because of surface tension, the pressure inside the small alveolus (smaller radius of curvature) is greater than that of the larger alveolus. Without surfactant, gas would therefore move from smaller to larger alveoli, eventually producing or giant alveolus.
Pulmonary surfactant: Pulmonary surfactant is aphospho—lipid (comprised primari ly of dipalmitoyl phosphatidylcholi—ne) synthesized by type II alveolar epithelial cells. Surfactant reduces surface tension, thereby preventing the collapse of small alveoli. Surfactant increases the compliance of the lung and reduces the work of breathing.
Surfactant keeps the alveoli dry because alveolar collapse tends to draw fluid into the alveolar space. Surfactant can be produced in the fetus as early as gestational week 24, but is synthesized most abundantly by the 35 th week of gestation. Neonatal respiratory distress syn drome can occur with premature infants, and results in areas of atelectasis, filling of alveoli with transudate, reduced lung compliance, and V/Q mismatch leading to hypoxia and CO 2 retention.
New words
surface tension forces – поверхностные силы напряжения
liquid – жидкость
proximity – близость
adjacent – смежный
intermolecular – межмолекулярный
to stabilize – стабилизироваться
surface – поверхность
distance – расстояние
phase – фаза
tension – напряжение
spherically—curved – сферически—кривой
lining – выравнивание
inward – внутрь
toward – к
curvature – искривление
spherical – сферический
soap bubble – мыльный пузырь
inner – внутренний
to exert – проявить
interconnected – связанный
34. The nose
The respiratory system permits the exchange of oxygen and carbon dioxide between air and blood by providing a thin cellular membrane deep in the lung that separates capillary blood from alveolar air. The system is divided into a conduct ing portion (nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles) that carries the gases during inspiration and expiration, and a respiratory portion (alveoli) that provides for gas exchange between air and blood.
The nose contains the paired nasal cavities separated by the nasal septum. Anteriorly, each cavity opens to the outside at a nostril (naris), and posteriorly, each cavity opens into the nasopharynx. Each cavity contains a vestibule, a respiratory area, and an olfactory area, and each cavity communicates with the paranasal sinuses.
Vestibule is located behind the nares and is continuous with the skin.
Epithelium is composed of stratified squamous cells that are similar to the contiguous skin.
Hairs and glands that extend into the underlying connective tissue constitute the first barrier to foreign particles entering the respiratory tract.
Posteriorly, the vestibular epithelium becomes pseudo—stratified, ciliated, and columnar with goblet cells (respiratory epithelium).
Respiratory area is the major portion of the nasal cavity.
Mucosa is composed of a pseudostratified, ciliated, columnar epithelium with numerous goblet cells and a subjacent fibrous lamina propria that contains mixed mucous and serous glands.
Mucus produced by the goblet cells and the glands is carried toward the pharynx by ciliary motion.
The lateral wall of each nasal cavity contains three bony pro jections, the conchae, which increase the surface area and pro mote warming of the inspired air. This region is richly vascularized and innervated.
Olfactory area is located superiorly and posteriorly in each of the nasal cavities.
The pseudostratified epithelium is composed of bipolar neu rons (olfactory cells), supporting cells, brush cells, and basalcells. The receptor portions of the bipolar neurons are modi fied dendrites with long, nonmotile cilia.
Under the epithelium, Bowman's glands produce serous fluid, which dissolves odorous substances.
Paranasal sinuses are cavities in the frontal, maxillary, ethmoid and sphenoid bones' that communicate with the nasal cavities.
The respiratory epithelium is similar to that of the nasal cavi ties except that it is thinner.
Numerous goblet cells produce mucus, which drains to the nasal passages. Few glands are found in the thin lamina propria.
