Hematopoietic tissue. Erythropoiesis
Hematopoietic tissue is composed of reticular fibers and cells, blood vessels, and sinusoids (thin-walled blood channels). Myeloid, or blood cell-forming tissue, is found in the bone marrow and provides the stem cells that develop into erythrocytes, granulocytes, agranulocytes, and platelets. Red marrow is characterized by active hemato-poiesis; yellow bone marrow is inactive and contains mostly fat cells. In the human adult, hematopoiesis takes place in the mar row of the flat bones of the skull, ribs and sternum, the vertebral column, the pelvis, and the proximal ends of some long bones. Erythropoiesis is the process of RBC formation. Bone marrow stem cells (colony-forming units, CFUs) differentiate into proerythroblasts under the influence of the glycoprotein erythropoietin, which is produced by the kidney.
Proerythroblast is a large basophilic cell containing a large spherical euchromatic nucleus with prominent nucleoli.
Basophilic erythroblast is a strongly basophilic cell with nucleus that comprises approximately 75% of its mass. Numerous cytoplasmic polyribosomes, condensed chro-matin, no visible nucleoli, and continued hemoglobin synthesis characteristics of this cell.
Polychromatophilic erythroblast is the last cell in this line undergoes mitotic divisions. Its nucleus comprises approximately 50% of its mass and contains condensed chroma-tin which appears in a «checkerboard» pattern. The po-lychnsia of the cytoplasm is due to the increased quantity of acidophilic hemoglobin combined with the basophilia of cytoplasmic polyribosomes.
Normoblast (orthochromatophilic erythroblast) is a cell with a small heterochromatic nucleus that comprises approximately 25% of its mass. It contains acidophilic cytoplasm because the large amount of hemoglobin and degenerating organelles. The pyknotic nucleus, which is no longer capable of division, is extruded from the cell.
Reticulocyte (polychromatophilic erythrocyte) is an immature acidophilic denucleated RBC, which still contains some ribosomes and mitochondria involved in the synthesis of a small quantity of hemoglobin. Approximately 1% of the circulating RBCs are reticulocytes.
Erythrocyte is the mature acidophilic and denucleated RBC. Erythrocytes remain in the circulation approximately 120 days and are then recycled by the spleen, liver, and bone marrow.
New words
reticular – сетчатый
sinusoids – синусоиды
granulocytes – гранулоциты
agranulocytes – агранулоциты
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active – активный
yellow – желтый
glycoprotein – гликопротеин
erythropoietin – эритропоэтин
amount – количество
hemoglobin – гемоглобин
degenerating – дегенерирующие
condensed – сжатый
Hematopoietic tissue. Granulopoiesis, thrombopoiesis
Granulopoiesis is the process of granulocyte formation. Bone marrow stem cells differentiate into all three types of granulocytes.
Myeloblast is a cell that has a large spherical nucleus containing delicate euchromatin and several nucleoli. It has a basophilic cytoplasm and no granules. Myeloblasts divide differentiate to form smaller promyelocytes.
Promyelocyte is a cell that contains a large spherical indented nucleus with coarse condensed chromatin. The cytoplasm is basophilic and contains peripheral azurophi-lic granules.
Myelocyte is the last cell in this series capable of division. The nucleus becomes increasingly heterochromatic with subsequent divisions. Specific granules arise from the Golgi apparatus, resulting in neutrophilic, eosinophilic, and basophilic myelocytes.
Metamyelocyte is a cell whose indented nucleus exhibits lobe formation that is characteristic of the neutrophil, eos-inophil, or basophil. The cytoplasm contains azurophilic granules and increasing numbers of specific granules. This cell does not divide. Granulocytes are the definitive cells that enter the blood. Neutrophilic granulocytes exhibit an intermediate stage called the band neutrophil. This is the first cell of this series to appear in the peripheral blood.
It has a nucleus shaped like a curved rod or band.
Bands normally constitute 0,5-2% of peripheral WBCs; they subsequently mature into definitive neutrophils.
Agranulopoiesis is the process of lymphocyte and mono-cyte for mation. Lymphocytes develop from bone marrow stem cells (lymphoblasts). Cells develop in bone marrow and seed the secondary lymphoid organs (e. g., tonsils, lymph nodes, spleen). Stem cells for T cells come from bone marrow, develop in the thymus and, subsequently, seed the secondary lym phoid organs.
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Promonocytes differentiate from bone marrow stem cells (monoblasts) and multiply to give rise to monocytes.
Monocytes spend only a short period of time in the marrow before being released into the bloodstream.
Monocytes are transported in the blood but are also found in connective tissues, body cavities and organs.
Outside the blood vessel wall, they are transformed into macrophages of the mononuclear phagocyte system.
Thrombopoiesis, or the formation of platelets, occurs in the red bone marrow.
Megakaryoblast is a large basophilic cell that contains a U-shaped or ovoid nucleus with prominent nucleoli. It is the last cell that undergoes mitosis.
Megakaryocytes are the largest of bone marrow cells, with diameters of 50 mm or greater. They undergo 4-5 nuclear divi sions without concomitant cytopla-smic division. As a result, the megakaryocyte is a cell with polylobulated, polyploid nucleus and abundant granules in its cytoplasm. As megakaryocyte maturation proceeds, «curtains» of platelet demarcation vesicles form in the cytoplasm. These vesicles coalesce, become tubular, and eventually form platelet demarcation membranes. These membranes fuse to give rise to the membranes of the platelets.
A single megakaryocyte can shed (i. e., produce) up to 3 500 platelets.
New words
capable – способный
spherical – сферический
indented – зазубренный
chromatin – хроматин
Arteries
Arteries are classified according to their size, the appearance of their tunica media, or their major function.
Large elastic conducting arteries include the aorta and its large branches. Unstained, they appear yellow due to their high con tent of elastin.
The tunica intima is composed of endothelium and a thin sub jacent connective tissue layer. An internal elastic membrane marks the boundary between the intima and media.
The tunica media is extremely thick in large arteries and con sists of circularly organized, fenestrated sheets of elastic tissue with interspersed smooth muscle cells. These cells are responsi ble for producing elastin and other extracellular matrix com ponents. The outermost elastin sheet is considered as the external elastic membrane, which marks the boundary between the media and the tunica adventitia.
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The tunica adventitia is a longitudinally oriented collection of collagenous bundles and delicate elastic fibers with associated fibroblasts. Large blood vessels have their own blood supply (vasa vasorum), which consists of small vessels that branch profusely in the walls of larger arteries and veins. Muscular distributing arteries are medium-sized vessels that are characterized by their predominance of circularly arranged smooth muscle cells in the media interspersed with a few elastin compo nents. Up to 40 layers of smooth muscle may occur. Both internal and external elastic limiting membranes are clearly demonstrated. The intima is thinner than that of the large arteries.
Arterioles are the smallest components of the arterial tree. Generally, any artery less than 0,5 mm in diameter is considered to be a small artery or arteriole. A suben-dothelial layer and the inter nal elastic membrane may be present in the largest of these vessels but are absent in the smaller ones. The media is composed of several smooth muscle cell layers, and the adventitia is poorly devel oped. An external elastic membrane is absent.
New words
endothelium – эндотелий
media – средняя
arteries – артерии
to be classified – классифицированный
according – соответственно
their – их
size – размер
appearance – вид
tunica – оболочка
major – главный
elastic – эластичный
conducting – проведение
arteries – артерии
to include – включать
aorta – аорта
branches – ветви
up to – до
layers – слои
smooth – гладкий
may – может
infima – внутренняя полость артерии
Capillaries
Capillaries are thin-walled, narrow-diameter, low-pressure vessels that generally permit easy diffusion across their walls. Most capillar ies have a cross-sectional diameter of 7-12 mm. They are composed of a simple layer of endothelium, which is the lining of the entire vas cular system, and an underlying basal lamina. They are attached to the surrounding tissues by a delicate reticulum of collagen. Associated with these vessels at various points along their length are specialized cells called pericytes. These cells, enclosed within their own basal lamina, which is continuous with that of the endothelium, contain contractile proteins and thus may be involved in the control of capillary dynamics. They may also serve as stem cells at times of vascular repair. Capillaries are generally divided into three types, according to the structure of their endothelial cell walls
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Continuous (muscular, somatic) capillaries are formed by a single uninterrupted layer of endothelial cells rolled up into the shape of a tube and can be found in locations such as connective tissue, muscle, and nerve
Fenestrated (visceral) capillaries are characterized by the presence of pores in the endothelial cell wall. The pores are covered by a thin diaphragm (except in the glomeruli of the kidney) and are usually encountered in tissues where rapid substance interchange occurs (e. g., kidney, intestine, endocrine glands)
Sinusoidal capillaries can be found in the liver, hematopoietic and lymphopoietic organs, and in certain endocrine glands. These tubes with discontinuous endothelial walls have a larger diame ter than other capillaries (up to 40 mm), exhibit irregular cross-sec tional profiles, have more tortuous paths, and often lack a con tinuous basal lamina. Cells with phagocytic activity (macrophages) are present within, or just subjacent to, the en-dothelium.
New words
capillaries – капилляры
to thin-walled – окруженный тонкой стеной
narrow-diameter – узкий диаметр
low-pressure – низкое давление
that – тот
generally – главным образом
permit – разрешение
easy – легкий
diffusion – распространение
cross-sectional – поперечный
to be composed – быть сложным
simple – простой
endothelium – эндотелий
lining – выравнивание
entire – весь
vas cular – сосудистый
underlying – лежащий в основе
basal – основной
lamina – тонкая пластинка
Veins
Veins are low-pressure vessels that have larger lumina and thinner walls than arteries. In general, veins have more collagenous connec tive tissue and less muscle and elastic tissue than their arterial coun terparts. Although the walls of veins usually exhibit the three layers, they are much less distinct than those of the arter ies. Unlike arteries, veins contain one-way valves composed of exten sions of the intima that prevent reflux of blood away from the heart. Veins can be divided into small veins or venules, medium veins, and large veins.
Venules are the smallest veins, ranging in diameter from approxi mately 15-20 mm (post-capillary venules) up to 1-2 mm (small veins). The walls of the smaller of these are structurally and func tionally like those of the capillaries; they consist of an endothelium surrounded by delicate collagen fibers and some pericytes. In those vessels of increased diameter, circularly arranged smooth muscle cells occur surrounding the intima layer, but unlike in the small arteries, these cells are loosely woven and widely spaced. Venules are important in inflammation because their endothelial cells are sensitive to hista-mine released by local mast cells. This causes endotheli-al cells to contract and separate from each other, exposing a naked basement membrane. Neutrophils stick to the exposed collagen and extravasate (i. e., move out into the connective tissue). Histamine also causes local arterioles to relax, affect ing a rise in venous pressure and increased leaking of fluid. This produces the classic signs of inflammation: redness, heat, and swelling.
Medium veins in the range of 1-9 mm in diameter have a well - developed intima, a media consisting of connective tissue and loosely organized smooth muscle, and an adventitia (usually the thickest layer) composed of collagen bundles, elastic fibers, and smooth muscle cells oriented along the longitudinal axis of the vessel. Venous valves are sheet-like outfoldings of endothelium and underlying connective tissue that form flaps to permit uni-di rectional flow of blood.
Large veins, such as the external iliac, hepatic portal, and vena cavae, are the major conduits of return toward the heart. The intima is similar to that of medium veins. Although a network of elastic fibers may occur at the boundary between the intima andmedia, a typical internal elastic membrane as seen in arteries is not present. A tunica media may or may not be present. If pre sent, smooth muscle cells are most often circularly arranged. The ad-ventitia is the thickest layer of the wall and consists of elastic fibers and longitudinal bundles of collagen. In the vena cava, this layer also contains well-developed bundles of longitudinally oriented smooth muscle.
New words
vein – вена
low-pressure – низкое давление
collagenous – коллагеновый
intima – интима
reflux – рефлюкс
inflammation – воспаление
longitudinal – продольный
flaps – створки
iliac – подвздошный
hepatic – печеночный
Heart
Intrapulmonary bronchi: the primary bronchi give rise to three main branches in the right lung and two branches in the left lung, each of which supply a pulmonary lobe. These lobar bronchi divide repeatedly to give rise to bronchioles.
Mucosa consists of the typical respiratory epithelium.
Submucosa consists of elastic tissue with fewer mixed glands than seen in the trachea.
Anastomosing cartilage plates replace the C-shaped rings found in the trachea and extra pulmonary portions of the pri mary bronchi.
Bronchioles do not possess cartilage, glands, or lymphatic nodules; however, they contain the highest proportion of smooth r muscle in the bronchial tree. Bronchioles branch up to 12 times to supply lobules in the lung.
Bronchioles are lined by ciliated, simple, columnar epithelium with nonciliated bronchiolar cells. The musculature of the bronchi and bronchioles con tracts following stimulation by parasympathetic fibers (vagus nerve) and relaxes in response to sympathetic fibers. Terminal bronchioles consist of low-ciliated epithelium with bronchiolar cells.
The costal surface is a large convex area related to the inner surface of the ribs.
The mediastinal surface is a concave medial surface, contains the root, or hilus, of the lung.
The diaphragmatic surface (base) is related to the convex sur face of the diaphragm. The apex (cupola) protrudes into the root of the neck.
The hilus is the point of attachment for the root of the lung. It contains the bronchi, pulmonary and bronchial vessels, lym phatics, and nerves. Lobes and fissures ventricular con traction (systole). Semilunar valves (aortic and pulmonic) prevent reflux of blood back into the ventricles during ventricular relaxation (diastole). Impulse conducting system of the heart consists of specialized cardiac myocytes that are characterized by auto-maticity and rhythmicity (i. e., they are independent of nervous stimulation and possess the ability to initiate heart beats). These specialized cells are located in the sino-atrial (SA) node (pacemaker), intern-odal tracts, atrioven-tricular (AV) node, AV bundle (of His), left and right bundle branches, and numerous smaller branches to the left and right ventricular walls. Impulse conduct ing myocytes are in electrical contact with each other and with normal contractile myocytes via communicating (gap) junctions. Specialized wide-diameter impulse conducting cells (Purkinje myocytes), with greatly reduced myofilament components, are well-adapted to increase conduction velocity. They rapidly deliver the wave of depolarization to ventricular myocytes.
New words
heart – сердце
muscular – мышечный
cardiac – сердечный
to pump – качать
endocardium – эндокардиум
innermost – самый внутренний
conducting system – проведение системы
subendocardial – внутрисердечный
impulse – импульс
fibrosi – фиброзные кольца
Lungs
Intrapulmonary bronchi: the primary bronchi give rise to three main branches in the right lung and two branches in the left lung, each of which supply a pulmonary lobe. These lobar bronchi divide repeatedly to give rise to bronchioles.
Mucosa consists of the typical respiratory epithelium.
Submucosa consists of elastic tissue with fewer mixed glands than seen in the trachea.
Anastomosing cartilage plates replace the C-shaped rings found in the trachea and extra pulmonary portions of the pri тагу bronchi.
Bronchioles do not possess cartilage, glands, or lymphatic nodules; however, they contain the highest proportion of smooth r muscle in the bronchial tree. Bronchioles branch up to 12 times to supply lobules in the lung.
Bronchioles are lined by ciliated, simple, columnar epithelium with nonciliated bronchiolar cells. The musculature of the bronchi and bronchioles con tracts following stimulation by parasympathetic fibers (vagus nerve) and relaxes in response to sympathetic fibers. Terminal bronchioles consist of low-ciliated epithelium with bronchiolar cells.
The costal surface is a large convex area related to the inner surface of the ribs.
The mediastinal surface is a concave medial surface, contains the root, or hilus, of the lung.
The diaphragmatic surface (base) is related to the convex sur face of the diaphragm. The apex (cupola) protrudes into the root of the neck.
The hilus is the point of attachment for the root of the lung. It contains the bronchi, pulmonary and bronchial vessels, lym phatics, and nerves. Lobes and fissures.
The right lung has three lobes: superior, middle and inferior.
The left lung has upper and lower lobes.
Bronchopulmonary segments of the lung are supplied by the segmental (tertiary) bronchus, artery, and vein. There are 10 on the right and 8 on the left.
Arterial supply: Right and left pulmonary arteries arise from the pulmonary trunk. The pulmonary arteries deliver deoxygenated blood to the lungs from the right side of the heart.
Bronchial arteries supply the bronchi and nonrespiratory por tions of the lung. They are usually branches of the thoracic aorta.
Venous drainage. There are four pulmonary veins: superior right and left and inferior right and left. Pulmonary veins carry oxygenated blood to the left atrium of the heart.
The bronchial veins drain to the azygos system.
Bronchomediastinal lymph trunks drain to the right lymphatic duct and the thoracic duct.
Innervation of Lungs: Anterior and posterior pulmonary plexuses are formed by vagal (parasympathetic) and sympathetic fibers. Parasympathetic stimulation has a bronchoconstrictive effect. Sympathetic stimulation has a bronchodilator effect.
New words
lungs – легкие
intrapulmonary bronchi – внутрилегочные бронхи
the primary bronchi – первичные бронхи
lobar bronchi – долевые бронхи
submucosa – подслизистая оболочка
Respiratory system
The respiratory system is structurally and functionally adapt ed for the efficient transfer of gases between the ambient air and the bloodstream as well as between the bloodstream and the tissues. The major functional components of the res piratory system are: the airways, alveoli, and bloodvessels of the lungs; the tissues of the chest wall and diaphragm; the systemic blood vessels; red blood cells and plasma; and respi ratory control neurons in the brainstem and their sensory and motor connections. LUNG FUNCTION: provision of 02 for tissue metabolism occurs via four mechanisms. Ventilation - the transport of air from the environment to the gas exchange surface in the alveoli. 02 diffusion from the alveolar air space across the alveolar-capillary membranes to the blood.
Transport of 02 by the blood to the tissues: 02 diffusion from the blood to the tissues.
Removal of C02 produced by tissue metabolism occurs via four mechanisms. C02 diffusion from the tissues to the blood.
Transport by the blood to the pulmonary capillary-alveolar membrane.
C02 diffusion across the capillary-alveolar membrane to the air spaces of the alveoli. Ventilation - the transport of alveolar gas to the air. Functional components: Conducting airways (conducting zone; anatomical dead space).
These airways are concerned only with the transport of gas, not with gas exchange with the blood.
They are thick-walled, branching, cylindrical structures with ciliated epithelial cells, goblet cells, smooth muscle cells. Clara cells, mucous glands, and (sometimes) cartilage.
Alveoli and alveolar septa (respiratory zone; lung parenchyma).
These are the sites of gas exchange.
Cell types include: Type I and II epithelial cells, alveolar macrophages.
The blood-gas barrier (pulmonary capillary-alveolar membrane) is ideal for gas exchange because it is very thin (‹ 0,5 mm) and has a very large surface area (50-100 m2). It consists of alveolar epithelium, basement membrane interstitium, and capillary endothelium.
New words
respiratory – дыхательный
air – воздух
bloodstream – кровоток
airways – воздушные пути
alveoli – альвеолы
blood vessels – кровеносные сосуды
lungs – легкие
chest – грудь
diaphragm – диафрагма
the systemic blood vessels – системные кровеносные сосуды
red blood cells – красные кровяные клетки
plasma – плазма
respi ratory control neurons – дыхательные нейроны контроля
brainstem – ствол мозга
sensory – сенсорный
motor connections – моторные связи
ventilation – вентиляция
transport – транспортировка
environment exchange – окружающая среда
surface – поверхность
Lung volumes and capacities
Lung volumes - there are four lung volumes, which when added together, equal the maximal volume of the lungs. Tidal volume is the volume of one inspired or expected normal breath (average human = 0,5 L per breath). Inspiratory reserve volume is the volume of air that can be inspired in excess of the tidal volume. Expiratory reserve volume is the extra an that can be expired after a normal tidal expiration.
Residual volume is the volume of gas that re lungs after maximal expiration (average human = 1,2 L).
Total lung capacity is the volume of gas that can be con tained within the maximally inflated lungs (average human = 6 L).
Vital capacity is the maximal volume that can be expelled after maximal inspiration (average human = 4,8 L).
Functional residual capacity is the volume remaining in the lungs at the end of a normal tidal expiration (average luman = 2,2 L).
Inspiratory capacity is the volume that can be taken into the lungs after maximal inspiration following expiration of a normal breath. Helium dilution techniques are used to determine residual volume, FRC and TLC. A forced vital capacity is obtained when a subject inspires maximally and then exhales as forcefully and as completely as possible. The forced expiratory volume (FEV1) is the volume of air exhaled in the first second. Typically, the FEV1 is approximate 80% of the FVC.
GAS LAWS AS APPLIED TO RESPIRATORY PHYSIOLOGY: Dalton's Law: In a gas mixture, the pressure exerted by each gas is independent of the pressure exerted by the other gases.
A consequence of this is as follows: partial pressure = total pressure x fractional concentration. This equation can be used to determine the partial pressure of oxygen in the atmosphere. Assuming that the total pressure (or barometric pressure, PB) is atmospheric pressure at sea level (760 mmHg) and the fractional concentration of O2is 21%, or 0,21: P02 = 760 mmHg Ч 0,21 = 160 mmHg. As air moves into the airways, the partial pressures of the va-ri ous gases in atmospheric air are reduced because of the addi tion of water vapor (47 mmHg). Henry's Law states that the concentration of a gas dissolved in liquid is proportional to its partial pressure and its solubility coef fi-cient (Ks). Thus, for gas X, [X] = Ks Ч Px
Fick's Law states that the volume of gas that diffuses across a barrier per unit time is given by:
Vgas = Y x D x (P1 - P2)
where A and T are the area and thickness of the barrier, P1 and P2 are the partial pressures of the gas on either side of the barrier and D is the diffusion constant of the gas. D is directly proportional to the solubility of the gas and inversely proportional to the square root of its molecular weight.
New words
lung – легкое
tidal – вдыхаемый и выдыхаемый
inspired – вдохновленный
breath – дыхание
human – человек
residual – oстаточный
helium – гелий
dilution – растворение
techniques – методы
the conducting – проведение
Ventilation
Total ventilation (VT, minute ventilation) is the total gas flow into the lungs per minute. It is equal to the tidal volume (VT) x the respiratory rate (n). Total ventilation is the sum of dead space ventilation and alveolar ventilation.
Anatomic dead space is equivalent to the volume of the conducting airways (150 mL in normal individuals), i. e., the trachea and bronchi up to and including the terminal bronchioles. Gas exchange does not occur here. Physiologic dead space is the volume of the respiratory tract that does not participate in gas exchange. It includes the anatomic dead space and partially functional or nonfunctional alveoli (e. g., because of a pulmonan embolus preventing blood supply to a region of alveoli). In normal individuals, anatomic and physiologic dead space are approximately equal. Physiologic dead space can greatly exceed anatomic dead space in individuals with lung disease.
Dead space ventilation is the gas flow into dead space per minute. Alveolar ventilation is the gas flow entering functional alveoli per minute.
Alveolar ventilation: It is the single most important parameter of lung function. It cannot be measured directly. It must be adequate for removal of the CO2produced by tissue metabolism whereas the partial pressure of inspired O2is 150 mmHg, the partial pressure of O2in the alveoli is typically 100 mmHg because of the displacement of O2with CO2. PAo2 cannot be measured directly.
New words
total – общее количество
ventilation – вентиляция
flow – поток
per minute – в минуту
equal – равный
airways – воздушные пути
exchange – обмен
tract – трактат
to be measured – быть измеренным
directly – непосредственно
displacement – смещение
Air flow
Air moves from areas of higher pressure to areas of lower pres sure just as fluids do. A pressure gradient needs to be established to move air.
Alveolar pressure becomes less than atmospheric pressure when the muscles of inspiration enlarge the chest cavity, thus lowering the intrathoracic pressure. Intrapleural pressure decreases, causing expansion of the alveoli and reduction of intra-alveolar pressure. The pressure gradient between the atmosphere and the alveoli drives air into the airways. The opposite occurs with expiration.
Air travels in the conducting airways via bulk flow (mL/min). Bulk flow may be turbulent or laminar, depending on its velocity. Velocity represents the speed of movement of a single particle in the bulk flow. At high velocities, the flow may be turbulent. At lower velocities transitional flow is likely to occur. At still lower velocities, flow may be laminar (streamlined). Reynold's number predicts the air flow. The higher the number, the more likely the air will be turbulent. The velocity of particle movement slows as air moves deeper into the lungs because of the enormous increase in cross-sectional area due to branching. Diffusion is the primary mechanism by which gas moves between terminal bronchioles and alveoli (the respiratory zone).
Airway resistance: The pressure difference necessary to produce gas flow is directly related to the resistance caused by friction at the airway walls. Medium-sized airways (› 2 mm diameter) are the major site of airway resistance. Small airways have a high individual resistance. However, their total resistance is much less because resistances in parallel add as reciprocals.
Factors affecting airway resistance: Bronchocon-striction (increased resistance) can be caused by parasympathetic stimulation, histamine (immediate hyper-sensitivity reaction), slow-reacting substance of anaphylaxis (SRS-A = leukotrienes C4, D4, E4; mediator of asthma), and irritants. Bronchodilation (decreased resistance) can be caused by sympathetic stimulation (via beta-2 receptors). Lung volume also affects airway resistance. High lung volumes lower airway resistance because the surrounding lung parenchyma pulls airways open by radial traction. Low lung volumes lead to increased airway resistance because there is less traction on the airways. At very low lung volumes, bronchioles may collapse. The viscosity or density of inspired gases can affect airway resistance. The density of gas increases with deep sea diving, leading to increased resistance and work of breathing. Low-density gases like helium can lower airway resistance During a forced expiration, the airways are compressed by increased intrathoracic pressure. Regardless of how forceful the expiratory effort is, the flow rate plateaus and cannot be exceeded. Therefore, the air flow is effort-independent; the collapse of the airways is called dynamic compression. Whereas this phenomenon is seen only upon forced expiration in normal subjects, this limited flow can be seen during normal expiration in patients with lung diseases where there is increased resistance (e. g., asthma) or increased compliance (e. g., emphysema).
New words
intrapleural – внутриплевральный
intra-alveolar – внутриальвеолярный
collapse – коллапс
viscosity – вязкость
density – плотность
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 intercostals 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 breathing, 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 certain disease states. Abdominal muscles (rectus abdominis, internal and external obliques, and transversus abdominis) increase intra-abdominal pressure, which pushes the diaphragm up, forcing 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 interstitium 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 compliance. 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:
QO2= CO х 1,34 (ml/g) х [Hg] Ч SaO2 + 0,003 (ml/ml per mm Hg) х РаО2,
where QO2is oxygen delivery (ml/min), CO is cardiac output (L/min). Hg is hemoglobin concentration (g/L), SaO2is the fraction of hemoglobin saturated with oxygen, and PaO2is 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
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 a phospholipid (comprised primarily of dipalmitoyl phosphatidylcholine) 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 syndrome 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 CO2retention.
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 – сферическийsoap bubble – мыльный пузырь
inner – внутренний
to exert – проявить
interconnected – связанный
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 neurons (olfactory cells), supporting cells, brush cells, and basalcells. The receptor portions of the bipolar neurons are modified 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
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
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 epithelium, 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 epithelium.
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 epithelium – 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
Respiratory bronchioles
Respiratory bronchioles are areas of transition (hybrids) between the conducting and respiratory portions of the airways. In addition to the typical bronchiolar epithelium of the terminal bronchioles, 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 epithelium. 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 (apical and basal membranes) and its basal lamina, the basal lamina 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 membrane-bound granules of phospholipid and protein (lamellar 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 particles 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
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 (pneumothorax), 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 introduction of air into the pleural cavity may cause the lung to collapse (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. Costomediastinal recess is a space where the left costal and mediastinal parietal pleura meet, leaving a space due to the cardiac notch of the left lung. This space is occupied by the lingula of the left lung during inspiration.
In nervation of the parietal pleura: The costal and peripheral portions of the diaphragmatic pleura 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
Nasal cavities
The anatomical structures that play a central role in the respiratory 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 sinuses 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 ethmoidal 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
Pharynx and related areas
The pharynx is a passageway shared by the digestive and respira tory systems. It has lateral, posterior, and medial walls through out, but is open interiorly in its upper regions, communicating with the nasal cavity and the oral cavity. The anterior wall of the laryngopharynx is formed by the larynx. The pharyngeal wall con sists of a mucosa, a fibrous layer, and a muscularis, which is com posed of an inner longitudinal layer and an outer circular layer.
Nasopharynx is the region of the pharynx located directly poste rior to the nasal cavity. It communicates with the nasal cavity through the choanae.
The torus tubarius is the cartilaginous rim of the auditory The pharyngeal recess is the space located directly above and behind the torus tubarius; it contains the nasopharyn-geal tonsil. The salpingopharyngeal fold is a ridge consisting of mucosa and the underlying salpingopharyngeus muscle.
Oropharynx is the region of the pharynx located directly posterior to the oral cavity. It communicates with the oral cavity through a space called the fauces. The fauces are bounded by two folds, consisting of mucosa and muscle, known as the anterior and posterior pillars.
The tonsillar bed is the space between the pillars that houses the palatine tonsil.
Laryngopharynx is the region of the pharynx that surrounds the larynx. It extends from the tip of the epiglottis to the cricoid car tilage. Its lateral extensions are known as the piriform recess.
Oral cavity: the portion of the oral cavity that is posterior to the lips and anterior to the teeth is called the vestibule. The oral cavi ty proper has a floor formed by the mylohyo-id and geniohyoid muscles, which support the tongue. It has lateral walls, consisting of the buccinator muscles and buccal mucosa, and a roof formed by the hard palate anteriorly and the soft palate posteriorly. Its posterior wall is absent and is replaced by an opening to the oropharynx, which is flanked by the pillars of the fauces.
The palate separates the nasal and oral cavities.
Hard palate is formed by the palatine process of the maxilla and the horizontal palate of the palatine bone. Its mucosa is supplied with sensory fibers from CN V2.
Soft palate consists of a fibrous membrane, the palatine aponeurosis, covered with mucosa. The portion that hangs down in the midline is the uvula.
The tongue is a mobile, muscular organ necessary for speech. It is divisible into an anterior two-thirds and a posterior one-third by the sulcus terminalis.
Muscles of the tongue. These include the intrinsic and extrinsic muscles (i. e., palatoglossus, stylogiossus, hyoglos - sus, genioglossus). All of the muscles are innervated by CN XII except the palatoglossus, which is supplied by CN X. Arterial supply: The tongue is supplied by the lingual branch of the external carotid aitery.
Venous drainage. The lingual veins, which lie on the un-der-surface of the tongue, drain to the internal jugular veins.
Lymphatic drainage. The tip of the tongue drains to the submental nodes, and the remainder of the anterior two-thirds drains first to submandibular, then to deep cervical nodes. The posterior one-third drains directly to deep cervi cal nodes.
New words
digestive – пищеварительный
pharyngeal – глоточный
mucosa – слизистая оболочка
fibrous layer – волокнистый слой
posterior nasal apertures – задние носовые апертуры
nasopharyngeal tonsil – миндалина
Oral cavity
The oral cavity forms in the embryo from an in-pocketing of the skin, stomodeum; it is, thus, lined by ectoderm. Functionally, the mouth forms the first portion of both the digestive and respiratory systems. In humans the margins of the lips mark the junction between the outer skin and the inner mucous lining of the oral cavity The roof of the mouth consists of the hard palate and, behind this, the soft palate which merges into the oropharynx. The lateral walls consist of the distensible cheeks. The floor of the mouth is formed principally by the tongue and the soft tissues that lie between the two sides of the lower jaw, or mandible. The tongue, a muscular organ in the mouth, provides the sense of taste and assists in chewing, swallowing, and speaking. It is firmly anchored by connective tissues to the front and side walls of the pharynx, or throat, and to the hyoid bone in the neck. The posterior limit of the oral cavity is marked by the fauces, an apperture which leads to the pharynx. On either side of the fauces are two muscular arches covered by mucosa, the glossopalatine and pharyngopalatine arches; between them lie masses of lymphoid tissue, the tonsils. Hiese are spongy lymphoid tissues composed mainly of lymphocytic cells held together by fibrous connective tissue. Suspended from the posterior portion of the soft palate is the soft retractable uvula. The palate develops from lateral folds of the primitive upper jaw. The hard palate, more anterior in position, underlies the nasal cavity The soft palate hangs like a curtain between the mouth and nasal pharynx. The hard palate has an intermediate layer of bone, supplied anteriorly by paired palatine processes of the maxillary bones, and posteriorly by the horizontal part of each palate bone. The oral surface of the hard palate is a mucous membrane covered with a stratified squamous epithelium. A submucosal layer contains mucous glands and binds the membrane firmly to the periosteum of the bony component. Above the bone is the mucous membrane that forms the floor of the nasal cavity.
The soft palate is a backward continuation from the hard palate. Its free margin connects on each side with two folds of mucous membrane, the palatine arches, enclosing a palatine tonsil. In the midline the margin extends into a fingerlike projection called uvula. The oral side of the soft palate continues as the covering of the hard palate, and the submucosa contains mucous glands. The intermediate layer is a sheet of voluntary muscle.
Besides separating the nasal passages from the mouth, the hard palate is a firm plate, against which the tongue manipulates food. In swallowing and vomiting the soft palate is raised to separate the oral from the nasal portion of the pharynx. This closure prevents food from passing upward into the nasopharynx and nose.
New words
mouth – рот
lips – губы
junction – соединение
distensible – растяжимый
cheeks – щеки
tongue – язык
taste – вкус
chewing – жевание
swallowing – глотание
Oral glands
All mammals are well supplied with oral glands. There are labial glands of the lips, buccal glands of the cheeks, lingual glands of the tongue, and palatine glands of the palate. Besides these, there are larger paired salivary glands. The parotid gland, near each ear, discharges into the vestibule. The submaxillary or submandibular gland lies along the posterior part of the lower jaw; its duct opens well forward under the tongue. The sublingual gland lies in the floor of the mouth. Saliva is a viscid fluid containing a mixture of all the oral secretions. It contains mucus, proteins, salts, and the enzymes ptyalin and maltase. Most of the ptyalin in human saliva is furnished by the parotid gland. The digestive action of saliva is limited to starchy food. Other uses of saliva include the moistening of food for easier manipulation by the tongue, the consequent facilitation of swallowing, and a lubrication by mucus that ensures a smoother passage of food down the esophagus to the stomach. Tonsils are spongy lymphoid tissues at the back of the throat, composed mainly of lymphocytic cells held together by fibrous connective tissue. There are three types of tonsils. The palatine tonsils, usually referred to as «the tonsils», are visible between the arches that extend from the uvula to the floor of the mouth. The pharyngeal tonsils, usually referred to as the adenoids, lie at the back of the throat. The lingual tonsils are on the upper surface of each side of the back of the tongue. The tonsils function to protect the pharynx and the remainder of the body from infectious organisms that become trapped in the mucous membrane lining the mouth, nose and throat. Chronic or acute inflammation of the tonsilses, called the tonsillitis.
The tongue, a muscular organ in the mouth, provides the sense of taste and assists in chewing, swallowing, and speaking. It is firmly anchored by connective tissues to the front and side walls of the pharynx, or throat, and to the hyoid bone in the neck.
The mammalian tongue is divided into two parts by a V-shaped groove, the terminal sulcus. At the apex of this V is a small blind pit, the foramen cecum. The larger part, or body, of the tongue belongs to the floor of the mouth, whereas the root forms the front wall of the oral pharynx. The body of the tongue is separated from the teeth and gums by a deep groove. A midline fold, the frenu-lum, is near he tip on the undersurface. The upper surface of the body, called the dorsum, has a velvety appearance because of filiform papillae. Distributed among these are occasional larger, rounded fungiform papillae and some large conical papillae. Immediately in front of the groove separating the body of the tongue from the root is a series of still larger vallate papillae arranged in a V-shaped row. The apex of the V points down the throat. Posteriorly along each side of the body of the tongue and near the root, is a series of parallel folds constituting the foliate papillae. The surface of the root of the tongue, which belongs to the pharynx, has no papillae but bears nodules containing lymphoid tissue.
New words
buccal – относящийся ко рту или щеке
palatine – небный
salivary glands – слюнные железы
parotid gland – околоушная железа
sublingual – подязыковой
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