Текст книги "Английский язык для медиков"

Автор книги: Елена Беликова

сообщить о нарушении

Текущая страница: 5 (всего у книги 8 страниц)

32. Mechanics of breathing

Muscles of respiration: inspiration is always an active process. The following muscles are involved: The diaphragm is the most important muscle of inspiration. It is convex at rest, and flattens during contraction, thus elongating the thoracic cavity. Contraction of the external in—tercostals lifts the rib cage upward and outward, expanding the thoracic cavity. These muscles are more important for deep inhalations. Accessory muscles of inspiration, including the scalene (elevate the first two ribs) and sternocleidomastoid (elevate the sternum) muscles, are not active during quiet breath ing, but become more important in exercise. Expiration is normally a passive process. The lung and chest wall are elastic and naturally return to their resting positions after being actively expanded during inspiration. Expiratory muscles are used during exercise, forced expiration and cer tain disease states. Abdominal muscles (rectus abdominis, internal and exter nal obliques, and transversus abdominis) increase intra—abdominal pressure, which pushes the diaphragm up, forc ing air out of the lungs. The internal intercostal muscles pull the ribs downward and inward, decreasing the thoracic volume. Elastic properties of the lungs: the lungs collapse if force is not applied to expand them. Elastin in the alveolar walls aids the passive 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 χ 1,34 (ml/g) χ [Hg] χ SaO 2 + + 0,003 (ml/ml per mm Hg) χ 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.

New words

respiratory system – дыхательный аппарат

oxygen – кислород

carbon – углерод

dioxide – диоксид

nasal cavity – носовая впадина

pharynx – зев

larynx – гортань

trachea – трахея

bronchi – бронхи

bronchioles – бронхиолы

nasal septum – носовая перегородка

nostril – ноздря

vestibule – вестибулярный

respiratory area – дыхательная область

olfactory area – обонятельная область

paranasal sinuses – параназальные пазухи

35. Nasopharynx and larynx

Nasopharynx is the first part of the pharynx.

It is lined by a pseudostratified, ciliated, columnar.

Epithelium with goblet cells: under the epithelium, a gland—containing connective tissue layer rests directly on the periosteum of the bone.

The cilia beat towards the oropharynx, which is composed of a stratified, squamous, nonkeratinized epithelium.

The pharyngeal tonsil, an aggregate of nodular and diffuse lymphatic tissue, is located on the posterior wall of the nasopharynx subjacent to the epithelium. Hypertrophy of this tissue as a result of chronic inflammation results in a condition known as adenoiditis. Larynx is a passageway that connects the pharynx to the trachea and contains the voicebox. Its walls are composed of cartilage held together by fibroelastic connective tissue.

The mucous layer of the larynx forms two pairs of elastic tissue folds that extend into the lumen. The upper pair are called the vestibular folds (or false vocal cords), and the lower pair con stitute the true vocal cords. The epithelium of the ventral side of the epiglottis and of the vocal cords is composed of stratified, squamous, nonkeratinized cells. The remainder of the larynx is lined with ciliated, pseudostratified, columnar epithelium. All cilia, from the larynx to the lungs, beat upward toward the nasopharynx.

New words

nasopharynx – носоглотка

first – сначала

pseudostratified – псевдомногослойный

ciliated – снабженный ресничками

columnar – колоночный

epithelium – эпителий

goblet cells – кубические клетки

gland—containing – содержащий железу

connective tissue – соединительная ткань

layer – слой

directly – непосредственно

periosteum – надкостница

bone – кость

cilia – ресница

oropharynx – верхняя часть глотки

stratified – стратифицированный

squamous – чешуйчатый

nonkeratinized – некеритизированный

somewhere – где—нибудь, куда—нибудь, где—то, куда—то

36. Trachea

The trachea, a hollow cylinder supported by 16–20 cartilaginous rings, is continuous with the larynx above and the branching primary bronchi below.

Mucosa of the trachea consists of the typical respiratory epitheli um, an unusually thick basement membrane, and an underlying lamina propria that is rich in elastin. The lamina propria contains loose elastic tissue with blood vessels, lymphatics, and defensive cells. The outer edge of the lamina propria is defined by a dense network of elastic fibers.

Submucosa consists of dense elastic connective tissue with seroriltfcous glands whose ducts open onto the surface of the epithe lium.

Cartilage rings are C—shaped hyaline cartilage pieces whose free extremities point dorsally (posteriorly). They are covered by a perichondrium of fibrous connective tissue that surrounds each of the cartilages. Smooth muscle bundles (trachealis muscle) and ligaments span the dorsal part of each cartilage.

Adventita a consists of peripheral dense connective tissue that binds the trachea to surrounding tissues.

Primary bronchi

The trachea branches at its distal end into the two primary bronchi. Short extrapulmonary segments of the primary bronchi exist before they enter the lungs at the hilus and then branch further. The histologic structure of the walls of the extrapulmonary segment of the primary bronchi is similar to that of the tracheal wall.

New words

hollow – пустота

cylinder – цилиндр

supported – поддержанный

cartilaginous

rings – хрящевые кольца

larynx – гортань

above – выше

branching – переход

primary bronchi – первичные бронхи

below – ниже

mucosa – слизистая оболочка

typical – типичный

respiratory epitheli um – дыхательный эпителий

an unusually – нетипитчно

thick – толстый

basement – основание

underlying – основной

lamina – тонкая пластинка

rich – богатый

elastin – эластин

loose – свободный

vessel – сосуд

lymphatics – лимфатический

defensive cells – защитные клетки

outer – внешний

edge – край

37. Respiratory bronchioles

Respiratory bronchioles are areas of transition (hybrids) between the conducting and respiratory portions of the airways. In addi tion to the typical bronchiolar epithelium of the terminal bron chioles, these passageways contain outpouchings of alveoli, which comprise the respiratory portion of this system.

Terminal bronchioles give rise to respiratory bronchioles.

Respiratory bronchioles branch to form two to three alveolar ducts, which are long sinuous tubes.

Alveolar sacs are spaces formed by two or more conjoined alveoli. They are lined by the simple squamous alveolar epithe lium. Alveoli are the terminal, thin—walled sacs of the respiratory tree that are responsible for gas exchange. There are approximately 300 million alveoli per lung, each one 200–300 mm in diameter. Blood—air interface. Oxygen in the alveoli is separated from hemoglobin in the red blood cells of alveolar capillaries by five layers of membrane and cells: the alveolar epithelial cell (api cal and basal membranes) and its basal lamina, the basal lami na of the capillary and its endothelial cell (basal and apical membranes), and the erythrocyte membrane. The total thick ness of all these layers can be as thin as 0,5 mm.

Alveolar epithelium contains two cell types. Type I cells completely cover the alveolar luminal surface and provide a thin surface for gas exchange. This simple squamous epithelium is so thin (-25 nm) that its details are beyond the resolution of the light microscope.

Type II cells are rounded, plump, cuboidal—like cells that sit on the basal lamina of the epithelium and contain mem brane—bound granules of phospholipid and protein (lamel lar bodies). The contents of these lamellar bodies are secreted onto the alveolar surface to provide a coating of surfactant that reduces alveolar surface tension.

Alveolar macrophages (dust cells) are found on the surface of the alveoli.

Derived from monocytes that extravasate from alveolar capillaries, alveotar macrophages are part of the mononu – clear phagocyte system. Dust cells, as their name implies, continuously remove parti cles and other irritants in the alveoli by phagocytosis.

New words

respiratory bronchioles – дыхательные бронхиолы

hybrids – гибриды

respiratory portions – дыхательные части

airways – воздушные трассы

bronchiolar – бронхиолярный

terminal bron chioles – предельные бронхиолы

passageway – проходы

tocomprise – включить

ducts – трубочки

sinuous tubes – извилистые трубы

thin—walled – окруженный тонкой стеной

sacs – мешочки

respiratory tree – дыхательное дерево

hemoglobin – гемоглобин

apical – апикальный

38. Pleura

Visceral pleura is a thin serous membrane that covers the outer surface of the lungs. A delicate connective tissue layer of collagen and elastin, containing lymphatic channels, vessels, and nerves, supports the membrane. Its surface is covered by simple squamous mesothelium with microvilli.

Parietal pleura is that portion of the pleura that continues onto the inner aspect of the thoracic wall. It is continuous with the visceral pleura and is lined by the same me—sothelium.

Pleural cavity is a very narrow fluid—filled space that contains monocytes located between the two pleural membranes. It contains no gases and becomes a true cavity only in disease (e. g., in pleural infection, fluid and pus may accumulate in the pleural space). If the chest wall is punctured, air may enter the pleural space (pneumotho—rax), breaking the vacuum, and allowing the lung to recoil. Parietal pleura lines the inner surface of the thoracic cavity; visceral pleura follows the contours of the lung itself.

Pleural cavity: The pleural cavity is the space between the parietal and viscer al layers of the pleura. It is a sealed, blind space. The introduc tion of air into the pleural cavity may cause the lung to col lapse (pneumothorax).

It normally contains a small amount of serous fluid elaborated by mesothelial cells of the pleural membrane.

Pleural reflections are areas where the pleura changes direction from one wall to the other. The sternal line of reflection is where the costal pleura is con tinuous with the mediastinal pleura behind the sternum (from costal cartilages 2–4). The pleural margin then passes inferiorly to the level of the sixth costal cartilage. The costal line of reflection is where the costal pleura becomes continuous with the diaphragmatic pleura from rib 8 in the mid—clavicular line, to rib 10 in the midaxillary line, and to rib 12 lateral to the vertebral column. Pleural recesses are potential spaces not occupied by lung tissue except during deep inspiration. Costodiaphragmatic recesses are spaces below the inferior borders of the lungs where costal and diaphragmatic pleura are in contact. Costomedia—stinal recess is a space where the left costal and mediasti—nal parietal pleura meet, leaving a space due to the cardiac notch of the left lung. This space is occupied by the lingu—la of the left lung during inspiration.

In nervation of the parietal pleura: The costal and peripheral portions of the diaphragmatic pleu ra are supplied by intercostal nerves.

The central portion of the diaphragmatic pleura and the medi astinal pleura are supplied by the phrenic nerve.

New words

visceral – висцеральный

pleura – плевра

dcollagen – коллаген

elastin – эластин

lymphatic channels – лимфатические сосуды

nerves – нервы

squamous – чешуйчатый

microvilli – микроворсинки

parietal pleura – париетальная плевра

visceral pleura – висцеральная плевра

costal – реберный

39. Nasal cavities

The anatomical structures that play a central role in the res piratory system are located in the head and neck as well as the thorax.

Nasal cavities are separated by the nasal septum, which consists of the vomer, the perpendicular plate of the ethmoid bone, and the septal cartilage. The lateral wall of each nasal cavity features three scroll—shaped bony structures called the nasal conchae. The nasal cavities communicate posteriorly with the nasopharynx through the choanae. The spaces inferior to each concha are called meatus. The paranasal sinu—ses and the nasolacrimal duct open to the meati. The inferior concha is a separate bone, and the superior and middle conchae are parts of the ethmoid bone.

Inferior meatus. The only structure that opens to the inferior meatus is the nasolacrimal duct. This duct drains lacrimal fluid (i. e., tears) from theTneaTaraspect of the orbit to the nasal cavity.

Middle meatus: the hiatus semilumaris contains openings of frontal and maxillary sinuses and americy ethmo—idal air cells. The bulla ethmoidalis contains the opening for'the middle ethmoidal air cells.

Superior meatus contains an opening for thff'posterior ethmoidal air cells.

Sphenoethmoidal recess is located above the superior concha and contains an opening for the sphenoid sinus.

Innervation: Somatic innervation. General sensory information from the lateral wall and septum of the nasal cavity is conveyed to the CNS by branches of V, and V2.

Autonomic innervation. Preganglionic parasympathetic fibers destined to supply the glands of the nasal mucosa and the lacrimal gland travel in the nervus intermedius and the greater superficial petrosal branches of the facial nerve (CN VII). These fibers synapse in the pte—rygopalatine ganglion, which is located in the pterygopa—latine fossa. Postganglionic fibers traveling to the mucous glands of the nasal cavity, paranasal air sinuses, hard and soft palate, and the lacrimal gland follow branches of V2 and in some cases V1, to reach their destinations.

New words

anatomical – анатомический

respiratory system – дыхательная система

head – голова

neck – шея

nasal cavities – носовые впадины

the perpendicular plate – перпендикулярная пластина

ethmoid – решетчатый

septal – относящийся к перегородке

nasal conchae – носовой раковина

paranasal – параносовой

sinuses – пазухи

nasolacrimal – назолакримальный

duct – трубочка

drain – проток

tears – слезы

orbit – орбита

maxillary – верхнечелюстной

bulla – булла