Book - A textbook of histology, including microscopic technic (1910) Special Histology 4
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Böhm AA. and M. Von Davidoff. (translated Huber GC.) A textbook of histology, including microscopic technic. (1910) Second Edn. W. B. Saunders Company, Philadelphia and London.
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IV. Organs of Respiration
A. The Larynx
THE greater portion of the laryngeal mucous membrane is covered by a stratified columnar ciliated epithelium containing goblet cells, and resting on a thick basement membrane. The epithelium covering the free margin of the epiglottis, the true vocal cords, and part of the arytenoid cartilage as far as the cavity between these cartilages, is of the stratified squamous variety, and is provided with connective-tissue ridges and papillae. The mucosa consists of fibrous connective tissue, contains many elastic fibers, which become larger and more prominent as the deeper layers of the mucosa are approached, and is rather firmly connected with the structures underneath it, but is somewhat more loosely connected in the regions supplied with squamous epithelium. The mucosa contains numerous lymphocytes and leucocytes, which now and then, especially in the region of the Ventricles, form simple follicles. In it are found branched tubulo-alveolar glands, which may be single or arranged in groups. These are found at the free posterior portion of the epiglottis, in the region of the latter' s point of attachment i. e., in the so-called cushion of the epiglottis. Larger collections of glands are found in the false vocal cords, and on the cartilages of Wrisberg (cuneiform cartilages), which appear almost imbedded in the glandular tissue and in the ventricles. In the remaining parts of the larynx glands are found only at isolated points. The true vocal cords have no glands. The glands of the larynx are of the mucous variety, containing crescents of Gianuzzi.
Fig- 245. Vertical section through the mucous membrane of the human larynx ; X 5
The cartilages of the larynx are of the hyaline variety, with the exception of the epiglottis, the cartilages of Santorini (the latter are derivatives of the epiglottis, Goppert), the cuneiform cartilages, the processus vocalis, and a small portion of the thyroid at the points of attachment of the vocal cords, which consist of elastic cartilage.
The vascular supply of the larynx is arranged in three superimposed networks of blood-vessels. The capillaries are very fine, and lie directly beneath the epithelium. The lymphatic network is arranged in two layers, the superficial being very fine and directly beneath the network of blood capillaries.
The nerves of the laryngeal mucous membrane will be described in connection with those found in the trachea.
B. The Trachea
The Template:Trachea is lined by a stratified ciliated columnar epithelium containing goblet cells and resting on a well-developed basement membrane. The mucosa is rich in elastic tissue. In the superficial portion of the mucosa the elastic fibers form dense strands, which usually take a longitudinal direction. The deeper layer of the mucosa is more loosely constructed, and passes over into the perichondrium of the semilunar cartilages of the trachea without any sharp line of demarcation. Numerous leucocytes are scattered throughout the mucosa, and are also frequently found in the epithelium. Connecting the free ends of the semilunar cartilages, which are of the hyaline variety, are found bundles of nonstriated muscle tissue, the direction of which is nearly transverse.
The trachea contains numerous branched tubulo-alveolar glands of the mucous variety containing here and there crescents of Gianuzzi. The glands are especially numerous where the tracheal wall is devoid of cartilage.
The larynx and trachea receive their nerve supply from sensory nerve-fibers and sympathetic neurones. These have been described by Ploschko (97) working in Arnstein's laboratory. According to this observer, the sensory fibers divide in the mucosa, forming subepithelial plexuses from which fibrils are given off which enter the epithelium of the larynx and trachea and, after further division, end on the epithelial cells in small nodules, or small clusters of nodules. In the trachea of the dog, such fibrils were traced to the ciliary border of the columnar ciliated cells before terminating. Numerous sympathetic ganglia are found in the larynx and trachea. In the latter they are especially numerous in the posterior wall. The neuraxes of the sympathetic neurones forming these ganglia were traced to the nonstriated muscular tissue of the trachea. The cellbodies of these sympathetic neurones are surrounded by end-baskets of small medullated fibers terminating in the ganglia. Medullated nerve-fibers, ending in the musculature of the trachea in peculiar end-brushes, were also described by Ploschko.
Fig. 246. From longitudinal section of human trachea, stained in orcein: a, Layer of elastic fibers ; i>, cartilage.
C. The Bronchi, their Branches, and the Bronchioles
The primary bronchi and their, branches show the same general structure as the trachea, showing, however, irregular plates and platelets of cartilage instead of half-rings, which surround the bronchi. The cartilage is absent in bronchial twigs of less than 0.85 mm. in diameter. The epithelium of the bronchi of medium size (up to 0.5 mm. in diameter) consists of a ciliated epithelium having three strata of nuclei. Kolliker (81) distinguishes a deep layer of basilar cells, a middle layer of replacing cells, and a superficial zone consisting of ciliated and goblet cells. The number of the last varies greatly. Glands are found only in bronchial twigs that are not less than I mm. in diameter ; as in the trachea, they are branched tubulo-alveolar glands of the mucous variety. In these structures the mucosa contains a large number of elastic fibers, the greater part of which have a longitudinal direction. Furthermore, numerous lymph-cells are found, and here and there a lymph-nodule. The muscularis presents, as a rule, circular fibers, which do not, however, form a continuous layer.
The smaller bronchi subdivide into still finer tubules of less than 0.5 mm. in diameter (bronchioles), which contain neither cartilage nor glands. The stratum proprium, as well as the external connective-tissue sheath, becomes very thin ; and the epithelium now consists of but one layer,, but is still ciliated.
Fig. 247. Transverse section through human bronchus ; X 27
D. Terminal Divisions of Bronchi and Ultimate Air-Spaces
The bronchioles are continued as the respiratory bronchioles (See below.) The walls of the respiratory bronchioles are relatively thin, consisting of fibro-elastic connective tissue and nonstriated muscle. Our knowledge of the further divisions of the bronchioles and of their relation to the terminal air-spaces has been increased greatly by Miller, who has made use of Born's method of wax-plate reconstruction in the study of these structures. His account is here followed. According to Miller, the respiratory bronchioles divide into or become the terminal bronchioles or alveolar ducts. These are somewhat dilated at their distal ends and communicate, by means of three to six round openings, with a corresponding number of spherical cavities, known as atria. Each atrjum communicates with a variable number of somewhat irregular spaces or cavities, the air-sacs, the walls of which are beset with numerous somewhat irregular hemispheric bulgings, the air-cells or lung alveoli. The air-cells or alveoli are also numerous in the walls of the atria and the terminal bronchioles or alveolar ducts, and may even be found in the walls of the respiratory bronchioles. The terminal bronchioles or alveolar ducts have an epithelium which is of the cubic variety in their proximal portions, and which changes to a squamous epithelium in their distal portions.
Figs. 248 and 249. Two sections of cat's lung : Fig. 248, X 5 2 > Fig. 249, X 35 The epithelium of the latter is ciliated in patches, but soon becomes nonciliated and assumes the character of respiratory epithelium.
Fig. 250. Internal surface of a human respiratory bronchiole, treated with silver nitrate ; X 2 34 (after Kolliker).
The epithelium of the distal portions of the terminal bronchioles or alveolar ducts, atria, and air-sacs (i I fj. to 15 fj. in diameter) and of the alveoli (the so-called respiratory epithelium) consists of two varieties of cells (F. E. Schulze) smaller nucleated elements and larger nonnucleated platelets (the latter derived very probably from the former). The arrangement of the epithelial cells is generally such that the nonnucleated platelets rest directly upon the blood capillaries, while nucleated cells lie between them. In amphibia the epithelium of the alveoli consists of cells, of which the portion containing the nucleus forms a broad cylindric base; from the free end of each cell a lateral process extends over the adjoining capillary to meet a similar process from the neighboring cell. When viewed from above, the basal portion of the cell appears dark and granular, while the processes are clear and transparent. These cells, together with their prolongations, are about 50 [J. in diameter. The surface view greatly resembles that of the human respiratory epithelium (Duval, Oppel, 89).
Fig. 251. Inner surface of human alveolus treated with silver nitrate, showing respiratory epithelium ; X 2 4 (after Kolliker).
The terminal bronchioles or alveolar ducts have a distinct layer of nonstriated muscle having annular thickenings about the openings which lead to the atria. Muscular tissue is not found in the walls of the atria, air-sacs, and air-cells or alveoli (Miller).
Beneath the respiratory epithelium in the atria, air-sacs, and aircells, there is found a thin basement membrane, which is apparently homogeneous. Here and there are found some fibrils of fibrous tissue and fixed connective-tissue cells. Elastic fibers are, however, numerous, forming networks beneath the basement membrane.
The work of Miller has given a clearer conception of what may be regarded as the units of lung structure, namely, the lobules. Such a unit or lobule is composed of a terminal bronchiole or alveolar duct, with the air-spaces atria, air-sacs, and air-cells connected with it, and their blood- and lymph-vessels and nerves. The general arrangement of these structures may be observed in Fig. 253, which gives a diagram of a lung lobule. The shape of the atria, air-sacs, and air-cells may be seen in Fig. 254, which is from a wax reconstruction of these structures.
The blood-vessels of the lung, including their relation to the structures of the lung lobules, have been investigated by Miller ; his account is closely followed in the following description: The pulmonary artery follows closely the bronchi through their entire length. An arterial branch enters each lobule of the lung at its apex in close proximity to the terminal bronchiole. After entering the lobule the artery divides quite abruptly, a branch going to each atrium ; from these branches the small arterioles arise which supply the alveoli of the lung. " On reaching the air-sac the artery breaks up into small radicals which pass to the central side of the sac in the sulci between the air-cells, and are finally lost in the rich system of capillaries to which they give rise. This network surrounds the whole airsac and communicates freely with that of the surrounding sacs." This capillary network is exceedingly fine and is sunken into the epithelium of the air-sacs so that between the epithelium and the capillary there is only the extremely delicate basement membrane. Only one capillary network is found between any two contiguous air-cells or airsacs. The atria, the alveolar ducts and their alveoli, and the alveoli of the respirator}- bronchioles are supplied with similar capillary networks. The veins collecting the blood from the lobules lie at the periphery of the lobules in the interlobular connective tissue, and are as far distant from the intralobular arteries as possible. These veins unite to form the larger pulmonary veins. The bronchi, both large and small, as well as the bronchioles, derive their blood supply from the bronchial arteries, which also partly supply the lung itself. Capillaries derived from these arteries surround the bronchial system, their caliber varying according to the structure they supply finer and more closely arranged in the mucous membrane, and coarser in the connective-tissue walls. In the neighborhood of the terminal bronchial tubes the capillary nets anastomose freely with those of the respiratory capillary system. From the capillaries of the bronchial arteries, veins are formed which empty either into the bronchial veins or into the branches of the pulmonary veins.
Fig. 252. Scheme of the respiratory epithelium in amphibia : The upper figure gives a surface view : f>, Basilar portion ; a, the thin process. The lower figure is a section : <?, Respiratory epithelial cell ; b, bloodvessel ; c, connective tissue around the alveoli.
Fig. 253. Scheme of lung lobule after Miller : b. r. , Respiratory bronchiole ; d. al., alveolar duct (terminal bronchus); a, a, a, atria; s. al., air-sacs; a. /., aircells or alveoli.
Fig. 254. Reconstruction in wax of a single atrium and air-sac with the alveoli : V, Surface where atrium was cut from alveolar duct ; P, cut surface, where another air-sac was removed ; A, atrium ; S, air-sac with air-cells (alveoli) (after Miller).
The lymphatics of the lung are classified by Miller as follows : (#) lymphatics of the bronchi ; (<) lymphatics of the arteries ; (c) lymphatics of the veins; (d} lymphatics of the pleura. The bronchial lymphatics are arranged in two plexuses as far as cartilage is present in the walls of the bronchi, one internal and one external to the cartilage. Beyond the cartilage only a single plexus is found. In the terminal bronchioles there are found three lymphatic vessels, two of which pass to the vein and one to the artery of the lobules. No lymphatics are found beyond the terminal bronchioles. The larger arteries are accompanied by two lymphatic vessels; the smallfer ones, only one. The same is true in general of the lymphatics accompanying the vein. The bronchial lymphatics and those accompanying the arteries and veins anastomose in the regions of the divisions of the bronchi. The pleura possesses a rich network of lymphatics with numerous valves.
Accompanying the bronchi and bronchial arteries are found numerous nerve -fibers, of the nonmedullated and medullated varieties, arranged in bundles of varying size, in the course of which are found sympathetic ganglia. Berkley (94), who has studied the distribution of the nerves of the lung with the chrome-silver method, finds that in the external fibrous layer of the bronchi is found a plexus of very fine and of coarser fibers, from which branches are given off which end in the muscle tissue of the bronchi, and others which pass through this layer to form, after further division, a subepithelial plexus from which fibrils may be traced into the connective-tissue folds in the larger bronchi and between the bases of the epithelial cells in the smaller bronchi and bronchioles. Some few fibrils were traced between alveoli situated near bronchi, " terminating, apparently, immediately beneath the pavement epithelium in an elongated or rounded minute bulb ; " these may, however, represent endings on nonstriated muscle tissue. The bronchial arteries have an exceedingly rich nerve supply.
Fig. 255. From section of human lung stained in orcein, showing the elastic fibers surrounding the alveoli.
Fig. 256. Section through injected lung of rabbit.
The visceral and parietal layers of the pleura consist of a layer of fibrous tissue containing numerous elastic fibers. Both layers are covered by a layer of mesothelial cells. The presence of stomata in the pleural mesothelium is denied by Miller. The blood-vessels of the visceral layer of the pleura arise, according to Miller, from the pulmonary artery, these forming a wide-meshed network, which empty into veins which pass into the substance of the lung. Sensory nerve-endings, similar to those found in connective tissue, have been observed in the parietal layer of the pleura.
E. The Thyroid Gland
The thyroid gland is developed from three sources : Its middle portion, the isthmus of the gland, and a portion of the lateral lobes originate as a diverticulum of the pharyngeal epithelium, from what is later the foramen caecum of the tongue; a part of both lateral portions, the right and left lobes, are formed from a complicated metamorphosis of the epithelium of the fourth visceral pouch. These various parts unite in man into one, so that in the adult the structure of the organ is.continuous. The thyroid gland consists of numerous noncommunicating acini or follicles of various sizes lined by a nearly cubic epithelium ; the lobules are separated from each other by a highly vascularized connective tissue, continuous with the firm connective-tissue sheath surrounding the whole gland. The connective -tissue framework of the thyroid has been studied by Flint by means of the destructive digestion method. Relatively greater amounts of connective tissue are found in connection with the bloodvessels, while the follicular membranes are delicate. The follicles are either round, polyhedral, or tubular, and are occasionally branched (Streiff). At an early stage the acini are found to contain a substance known as "colloid" material.
Fig. 257. Portion of a cross-section of thyroid gland of a man ; X 3- &dgj Interstitial connective tissue ; bg, blood-vessel ; c, colloid substance ; fs, gland alveoli.
Langendorff has shown that two varieties of cells exist in the acini of the thyroid body the chief cells and colloid cells. Those of the first variety apparently change into colloid cells, while the latter secrete the colloid substance. During the formation of this material the colloid cells become lower, and their entire contents, including the nuclei, change into the colloid mass. Hiirthle distinguished two processes of colloid secretion ; in the one the cells remain intact, in the other they are destroyed. He claims that the colloid cells of Langendorff participate in the former process, while in the latter they are first modified (flattened) and then changed into the colloid substance. The secretion is formed in the cells in the form of secretory granules. The colloid material may enter the lymph-channels, either directly by a rupture of the acini, or indirectly by a percolation of the substance into the intercellular clefts, whence it is carried into the larger lymphatics.
The thyroid gland has a very rich blood supply. The vessels, which enter through the capsule, break up into smaller branches which form a very rich capillary network surrounding the follicles. The veins, which are thin-walled, arise from this capillary network. The gland is provided with a rich network of lymphatic vessels.
Anderson (91) and Berkley (94) have studied the distribution of the nerve-fibers of the thyroid gland with the chrome-silver method ; 'the account given by the latter is the more complete and will be followed here. The nonmedullated nerves entering the gland form plexuses about the larger arteries, which are less dense around the smaller arterial branches. Some of these nerve-fibers are vascular nerves and end on the vessels ; others form perifollicular meshes surrounding the follicles of the gland. From the network of nervefibers about the follicles, Berkley was able to trace fine nerve filaments which seemed to terminate in end-knobs on or between the epithelial cells lining the follicles. Even in the best stained preparations, however, not nearly all the follicular cells possess such a nerve termination. In methylene-blue preparations of the thyroid gland (Dr. De Witt) some few medullated fibers were found in the nerve plexus surrounding the vessels. In a number of preparations these were traced to telodendria situated in the adventitia of the vessels, showing that at least a portion of these medullated nerves are sensory nerves ending in the walls of the vessels.
Small glandular structures found on the posterior surfaces of the lateral lobes of the thyroid were discovered by Sandstrom in 1880. They are surrounded by a thin connective-tissue capsule and divided into small imperfectly developed lobules by a few thin fibrous-tissue septa or trabeculae, which support the larger vessels. The epithelial portions of these structures consist of relatively large cells and capillary spaces. According to Schaper (95), who has recently subjected these structures to a careful investigation, the epithelial cells have a diameter which varies from 10 /i to 12 //, possessing nuclei 4 // in diameter. These cells are of polygonal shape and have a thin cell-membrane, a slightly granular protoplasm, and a nucleus presenting a delicate chromatic network. The cells are arranged either in larger or smaller clusters or, in some instances, in anastomosing trabeculae or columns, consisting either of a single row or of several rows of cells. Between the clusters or columns of cells are found relatively large capillaries, the endothelial lining of which rests directly on the epithelial cells. Connective-tissue fibrils do not, as a rule, follow the capillaries between the cell-masses. These vessels may therefore be regarded as sinusoids (Minot). The structure of the parathyroid resembles in many respects that of certain embryonic stages of the thyroid, and it has been suggested that these bodies represent small masses of thyroid gland tissue, retaining their embryonic structure. Schaper has observed parathyroid tissue, the cells of which were here and there arranged in the form of small follicles, some of which contained colloid substance. Such observations lend credence to the view regarding the parathyroid as an embryonic structure. Whether in this stage they form a special secretion has not been fully determined. (See Schaper, 95.)
Fig. 258. From parathyroid of man.
For the demonstration of the larynx and trachea, young and healthy subjects should be selected. Pieces of the mucous membrane or the whole organ should be immersed in a fresh condition. Sections through the entire organ present only a general structural view ; but if a close examination of accurately fixed mucous membrane be desired, the latter should be removed with a razor before sectioning and treated separately.
Chromic-osmic acid mixtures are recommended as fixing agents, and safranin as a stain. Besides the nuclear differentiation, the goblet cells stain brown, and the elastic network of the stratum proprium and the submucosa a reddish -brown.
For examining the epithelium, isolation methods are employed, such as the y$ alcohol of Ranvier.
The examination of the respiratory epithelium is attended with peculiar difficulty ; it is, perhaps, best accomplished by injecting a 0.5% solution of silver nitrate into the bronchus until the lumen is completely filled, and then placing the whole in a 0.5% solution of the same salt. After a few hours, wash with distilled water and transfer to 70% alcohol. Thick sections are now cut and portions of the respiratory passages examined ; the silver lines represent the margins of the epithelial cells. Such sections should not be fastened to the slide with albumen, as the latter soon darkens and blurs the picture. These specimens may also be stained.
For the elastic fibers, especially those of the alveoli, fixation In Miiller's fluid or in alcohol and staining with orcein is a good method, as also Weigert's differential elastic tissue stain. Fresh pieces of lung tissue treated with potassium hydrate show numerous isolated elastic fibers.
Pulmonary tissue may be treated by Golgi's method, which brings out a reticular connective-tissue structure in the vessels and alveoli.
The pulmonary vessels may be injected with comparative ease.
The thyroid gland is best fixed in Flemming's solution ; it is then stained with M. Heidenhain's hematoxylin solution or, better still, with the Ehrlich-Biondi mixture which differentiates the chief from the colloid cells ; the former do not stain at all, while the latter appear red with a green nucleus (Langendorff). The colloid substance of the thyroid gland does not cloud in alcohol or chromic acid, nor does it coagulate in acetic acid, but swells in the latter; 33% potassium hydrate hardly causes the colloid material to swell at all, though in weaker solutions it dissolves after a long time.
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Reference: Böhm AA. and M. Von Davidoff. (translated Huber GC.) A textbook of histology, including microscopic technic. (1910) Second Edn. W. B. Saunders Company, Philadelphia and London.
Cite this page: Hill, M.A. (2020, October 22) Embryology Book - A textbook of histology, including microscopic technic (1910) Special Histology 4. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_A_textbook_of_histology,_including_microscopic_technic_(1910)_Special_Histology_4
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