Paper - The histological appearances of the mammalian pituitary body

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Herring PT. The histological appearances of the mammalian pituitary body. (1908) Quar. Jour. Ex. Physiol., 1: 121-159.

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This historic 1908 paper by Herring describes the pituitary. The histological structures identified in the posterior pituitary are named after this author, "Herring Bodies".



See also by his author - Herring PT. The development of the mammalian pituitary and its morphological significance. (1908) Quar. Jour. Ex. Physiol., 1: 161-185.

Links: 1908 Pituitary Histology | 1918 Rabbit Hypophysis | 1926 Human Hypophysis


Modern Notes: pituitary

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1903 Islets of Langerhans | 1904 interstitial Cells | 1908 Pancreas Different Species | 1908 Pituitary | 1908 Pituitary histology | 1911 Rathke's pouch | 1912 Suprarenal Bodies | 1914 Suprarenal Organs | 1915 Pharynx | 1916 Thyroid | 1918 Rabbit Hypophysis | 1920 Adrenal | 1935 Mammalian Hypophysis | 1926 Human Hypophysis | 1927 Hypophyseal fossa | 1932 Pineal Gland and Cysts | 1935 Hypophysis | 1937 Pineal | 1938 Parathyroid | 1940 Adrenal | 1941 Thyroid | 1950 Thyroid Parathyroid Thymus | 1957 Adrenal
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The Histological Appearances of the Mammalian Pituitary Body

By P. T. Herring.

From the Physiology Department, University of Edinburgh.

Received for publication 11th February 1908.

Introduction

The structure and significance of the pituitary body have long been objects of much speculation. Erroneous conceptions of its structure are responsible for some of the many theories which have been advanced with regard to its functions. The pituitary, indeed, derives its name from the old idea that it was a gland which discharges a secretion—pituita—into the nostrils.


Rathke (32) discovered the double origin of the pituitary, and on developmental grounds classed it among glands. Other observers looked upon it as part of the brain. Luschka (23) called it a “nerve-gland” in which the two parts are separated from one another by pia mater. Ecker (8), on the other hand, held the view that both portions of the pituitary combine to form a unit of the nature of a “ blood-vessel gland.”


Burdach (4.-), Luschka (23), and Virchow (46) regarded the posterior lobe as the anterior terminal end of the cerebro-spinal canal, a “filum terminale anterius,” resembling in structure the filum terminale of the spinal cord. Virchow also compared the anterior lobe to the thyroid gland, and described in it vesicles containing colloid material which show a striking resemblance to the follicles of the thyroid. Rogowitsch (34), H. Stieda (43), Schonemann (39), and others have attached great importance to this resemblance, and ascribe similar functions to the two glands. Removal of the thyroid is, according to their observations, followed by a compensatory hypertrophy of certain parts of the glandular lobe of the pituitary.


In 1886 Marie drew attention to a relationship between changes in the pituitary and the disease acromegaly or gigantism. Clinical and pathological experiences have led to the theory which assigns to the pituitary the role of regulating the normal development of the body, more especially of the extremities and bones. The nature of the change that the pituitary undergoes in acromegaly is uncertain, and before any light can be thrown upon its pathology it is necessary that the significance of the various histological elements that constitute the normal pituitary should be understood. Moreover, it appears that acromegaly may occur without any apparent change in the pituitary, and that tumours of the pituitary are not always attended by acromegaly. A feature as constant as acromegaly in affections of the pituitary is the occurrence of polyuria with or without sugar in the urine (Hansemann (16), Sternberg (41)).


Oliver and Schafer (28) in 1895 described the presence of a substance in saline extracts of the pituitary, which, when injected intravenously, produces a rise of blood-pressure. Howell (18) showed that this substance is only present in the posterior lobe. Magnus and Schafer (24) in 1901 noticed that intravenous injection of saline extract of the posterior lobe is followed by a marked increase of urine flow. Schafer and Herring (37) confirmed this observation, and showed the striking parallelism which exists between the suprarenal capsules and the pituitary in development, structure, and functions. In each there are two parts, one of which, a highly vascular epithelium, yields no active extract, while the other, of neuro—ectodermic origin, gives an extract which has a remarkable physiological effect upon the heart and arteries. The view was conjectured that in the epithelial part of each organ the material which is to furnish the active agent of the secretion passes through certain stages of formation, and that its production is merely completed in the neuro—ectodermic part, in which part alone the full activity of the secretion is acquired. That the posterior lobe of the pituitary should furnish an active secretion is difficult to reconcile with the usual views held on its structure. The older anatomists, W. Muller (27), Schwalbe (40), and Toldt (45), looked upon it as a mass of connective tissue cells and fibres which during development have destroyed all trace of the original nerve tissue. Berkley (2), on the other hand, describes in it a complex arrangement of nerve cells and nerve fibres, besides neuroglia and ependyma cells. Kolliker (19) takes up an intermediate position, and believes that there are no true nerve cells, but neuroglia and ependyma, a view similar to the one held by Virchow. Peremeschko (30) first recognised that the posterior lobe has an epithelial investment. Osborne and Swale Vincent (29) state that extracts of the central part of the posterior lobe are more active than extracts of the margin of the lobe, and believe that the epithelial investment would be found to be inactive if it could be properly isolated.


The pituitary body is found in all vertebrates, and, although differing widely in structure and in the arrangement of its component parts, possesses many features common to all. In fishes, the posterior lobe has a complex vascular structure of a glandular nature, which was called the “saccus vasculosus” by Gottsche (12). L. Stieda (44) proved that the saccns vasculosus communicates with the brain cavity, and Rabl-Riickhard (31) named it an infundibular gland. Their researches have been confirmed by Kupffer (21). The function of the saccus vasculosus is unknown, but its secretion, if it is a secretory gland, apparently mixes with the fluid contents of the ventricles of the brain. According to Kupffer, the posterior lobe of the mammalian pituitary in its early development retains for a time a glandular structure. In the adult mammal the epithelial investment of the posterior lobe is regarded by Ktilliker as the representative of an infundibular gland. B. Haller (14«) states that in mammals—as a type of which he takes the mouse——and in all other classes of vertebrates the anterior lobe of the pituitary and epithelial investment of the posterior lobe form a gland, the tubules of which open by a small median and ventral mouth into the space between the pia and dura mater. Haller believes that the pituitary in all vertebrates secretes directly into the subdural space. Edinger (9) denies that this is true of the human pituitary, Salzer (36) could find no opening in the pituitary of the rat and mouse, and Sterzi (42) found none in the pituitary of Petromyzon.

There are other views on the structure and functions of the pituitary body. Boeke (3) and Gemelli (11) describe appearances in the posterior lobe of fishes which they regard as indicative of sense organs. Cyon (6) looks upon it as an organ which regulates the amount of blood passing to the brain. Guerrini (13) and others believe that the pituitary produces a secretion which has a vague antitoxic action.

Our knowledge of the structure of the pituitary body is, therefore, far from exact, and is inadequate to account for the physiological effects which follow intravenous injection of extracts, especially of the posterior lobe. Even the important question as to whether the glandular portion secretes directly into the subdural space is still unsettled. The work, the results of which are given in this paper, was begun with the intention of investigating the physiological histology of the posterior lobe, but the two portions of the pituitary were found to be so closely associated that no part would be complete without careful consideration of the other. The development and comparative anatomy of the pituitary body have been examined, but are only touched upon in this paper where reference to them throws light upon the particular point considered.

Material and Methods Employed

The cat furnishes some of the best material for the study of the pituitary body, for in this animal the posterior lobe retains throughout life its original cavity in free communication with the third ventricle of the brain. The structure of the posterior lobe in the cat is thus rendered simpler because the arrangement of the cells which line the cavity persists in the adult in much the same manner as obtains in the developing organ. The parts which are derived from the buccal mucous membrane form an almost complete investment for the nervous portion, and the original lumen of the epithelial pouch also persists throughout life in the form of a well marked cleft. The so-called colloid cysts are also prominent features in the pituitary of the cat.


The pituitary of the monkey more closely resembles that of man, and is a type in which greater fusion of the original elements from which it is developed has taken place. The posterior lobe is solid throughout. Its investment by the epithelial portion is not so complete as it is in the cat, and only a small cleft remains as the representative of the original buccal pouch.


The pituitary of the dog offers in some respects a type which‘ is intermediate between that of the cat and that of the monkey. The posterior lobe is solid, but the cavity of the third ventricle of the brain is continued downwards and backwards towards the neck of the posterior lobe. The epithelial investment is very complete, and the cleft in it well developed as in the cat. The colloid cysts are more numerous than in the pituitary of the monkey, and their arrangement and structure present features which distinguish them from those of the cat’s pituitary. The morphology of the pituitary bodies of the cat, dog, and monkey will be described briefly, and the structure of the various parts more minutely detailed in the cat.


For the investigation of the finer structure of the pituitary body Flemming’s fixative gives the best results; a 10 per cent. solution of formol and saturated corrosive sublimate have also been employed. Sections have been cut serially in a vertical antero-posterior plane; these show the relations of the Various parts of the pituitary to one another better than do sections cut in other directions. Most of the material has been cut in paraflin, but the freezing microtome has also been used, and the Golgi preparations cut by hand.


The structure of the anterior lobe is shown to the best advantage by staining with eosin and methylene blue, or by the employment of some of the many methods devised for the staining of blood films. Many preparations were made by Ca_jal’s silver reduction method, which is especially valuable for showing the fibrils of the neuroglia, and the ependyma cells of the posterior lobe. Cox’s modification of Golgi’s method was also adopted for the investigation of the nervous elements. Fresh tissues have been teased out and examined in salt solution and in osmic acid, and chromic acid fixed preparations have been cut by the freezing microtome. The blood-vessels were also injected from the common carotids with carmine gelatine, and the vascular supply of the pituitary body studied in thick sections.


A word must be said about the removal of the pituitary body for purposes of examination. In order to investigate the question raised by B. Haller as to the presence of an opening on the median ventral aspect connecting the epithelial cleft with the subdural space by means of a lymph space, it is almost essential to remove the sella turcica and part of the brain from below, to decalcify the bone and cut sections of the pituitary in situ. This can be more readily done in the young animal. For most purposes it is suflicient in the adult animal to dissect the bone piecemeal from the dura mater, which forms an envelope to the pituitary, thickened at certain points, especially behind. Great care must be taken not to rupture the thin layer of epithelium which in the cat is continued backwards from the anterior lobe, to be reflected at the place where the blood-vessels enter the posterior lobe to form a closely fitting investment over the ventral aspect of the latter. Removal of the pituitary from the cranial cavity by raising the brain and dissecting from above is almost invariably followed by rupture of the neck of the posterior lobe. The dura mater should always be preserved intact without being pulled upon, and the best way to do this is to dissect off the bone from below, disturbing the base of the brain as little as possible. A portion of the brain can then be cut out with the pituitary attached, and the piece trimmed after hardening.



Fig. 1. Mesial sagittal section through pituitary body and sella turcica of new-born kitten. (Semi-diagrammatic.) a, optic chiasma; b, tongue-like process of pars intermedis; c, third ventricle; d, anterior lobe proper; e, epithelial cleft ; f, central cavity of posterior lobe ; g, nervous substance of posterior lobe ; h, posterior reflection of epithelium.

Morphology

The relations of the anterior and posterior lobes of the pituitary to one another, and to their immediate surroundings, can be most readily appreciated by reference to the comparatively simple pituitary of the new-born kitten. Fig. 1 is a diagram of a mesial sagittal section through the pituitary and sella turcica of a new-born kitten. The infundibulum cerebri is a continuation of the brain backwards and slightly downwards, and consists of a comparatively thin wall of brain substance enclosing a cavity which is a continuation of the third ventricle. The infundibulum has a funnel-shaped origin from the base of the brain, narrowing as it passes backwards to a tubular neck, then expanding to form a hollow club-shaped body which makes up the larger portion of the posterior lobe. The central cavity also enlarges behind the neck of the infundibulum.


The anterior lobe, composed of epithelial cells, lies below, and its thickest portion is in front of the infundibulum. It extends for some distance anteriorly, forming a tongue-shaped projection which reaches to the under surface of the tuber cinereum. The anterior lobe also spreads further laterally, and enfolds the sides of the infundibulum, the neck of which is encircled completely, so that, as in the figure, a portion of the anterior lobe appears above it. In some kittens the wrapping of the epithelium round the posterior lobe is more complete, and the only part of the lobe which is never covered by epithelium is a small part behind where the blood-vessels make their entrance. A narrow and somewhat S-shaped space lies inside the epithelium close to and following in its outline the under surface of the nervous portion of the posterior lobe, but separated from it by several layers of epithelium. The space or cleft is, as Kolliker (20) pointed out, the remnant of the cavity of the pouch of buccal epithelium from which the anterior lobe is derived. The layer of epithelium which lies between the cleft and the part of the posterior lobe developed from the brain is comparatively thin, and very closely applied to the nervous substance, thus forming an investment to it which is more or less complete according to the degree in which the anterior lobe has grown round the posterior. The cleft extends laterally, and in some cases almost surrounds the body of the posterior lobe. The posterior lobe as separated from the anterior by the cleft is therefore a composite body derived from the brain and from buccal epithelium, and it is to this structure of elements derived from two sources that the name of posterior lobe is usually applied, although strictly speaking the epithelial investment belongs developmentally to the anterior lobe. The cleft is sometimes more complicated, and branches of it may run into the substance of the anterior lobe. Serial sections show no opening below such as has been described by B. Haller (14), nor does there appear to be an opening at any point; the cleft is a closed cavity in the kitten, but very great care has to be taken in the removal and preparation of the pituitary to prevent rupture of the thin layer of epithelium which is continued backwards from the anterior lobe.


The greater portion of the anterior lobe is a solid structure made up of columns of cells and wide blood-channels. Granules are present in many of the cells of this part, but are not so marked a feature of the anterior lobe in the new-bom kitten as they are in the adult cat. Colloid cysts are not found in the pituitary of the new-bom kitten.

The relation of the pituitary body to the sella turcica is shown in fig. 1.


The gland lies on the body of the sphenoid bone, and is separated from it by the dura mater, which is thickened in front and behind, and contains blood—vessels, and what appears to be a lymph space. This space, which was described by B. Haller, is not a marked feature in the kitten, but is more pronounced in the foetus of the ox, where, at an earlier stage in development, it penetrates for some distance into the body of the sphenoid bone. Ossification of the bone at this point is delayed by the gradual disappearance of the epithelial stalk which connects the anterior lobe of the pituitary with the buccal epithelium. No trace of this connection is found in the new-born kitten, and there is no evidence of any opening of the glandular tubules or cleft of the pituitary into the lymph space either in the foetal ox or kitten.


Fig. 2. Mesial ssgittsl section through the pituitary body of an adult cat. (Semi-diagrammatic.) a, optic chiasma: b, tongue-like rocess oi pars intermedia; c, third ventricle ; d, anterior lobe proper; e, epithelial cleft ; f, cavity 0 sterior lobe ; f’, cavity of neck of posterior lobe; g, nervous substance of posterior lobe; i, epithelial nvestment of posterior lobe. The dark shading indicates the distribution of the characteristic cells of the anterior lobe; the lighter shading shows the position ot epithelium belonging to the pars intermedis.


The pituitary body of the adult cat is very similar in structure to that of the kitten, but presents several important modifications. In mesial sagittal section the posterior lobe appears larger than the anterior; the latter is, however, the larger, and extends further laterally, embracing the posterior lobe. The central cavity of the posterior lobe persists, and a tapering process of it runs upwards and backwards towards the place of entry of the blood-vessels into the infundibulum (fig. 2). This process is always present, and frequently runs up to the epithelial investment. The neck of the infundibulum is narrow and its lumen small.


The anterior lobe and epithelial investment of the nervous portion of the posterior lobe are separated by the cleft, which, as a rule, persists in its entirety. Occasionally the cleft is closed up to a large extent, especially in its posterior part, and the two layers of epithelium are more or less fused, but a space always remains between the main part of the anterior lobe and the epithelial investment of the neck of the infundibulum. The main mass of the anterior lobe in front of the cleft contains cells holding granules which stain deeply with eosin. These granular cells are not present in the epithelial investment of the posterior lobe, nor are they found in the tonguelike process of the anterior lobe which runs forwards towards the optic chiasma. The epithelial investment of the posterior lobe is well marked and thickened, especially round the neck of the infundibulum, where there are many layers of cells. The cells are frequently arranged in groups round a central lumen which contains a colloid material. These colloid vesicles are for the most part small and scattered at intervals; they are especially well developed round the neck of the infundibulum and in the tongue-like process, where they show a resemblance to the vesicles of the thyroid gland. They are rarely found among the eosinophil cells of the anterior lobe, and appear to be placed never far distant from the nervous portion of the pituitary.


Fig. 3. Mesial sagittal section through pituitary body of an adult cat. (Photograph.) Compare with fig 2.


Considerable variations occur in different cats in the relative size and arrangement of the parts described. This is especially the case With the eosinophil cells of the anterior lobe, which are sometimes continued far backwards over the posterior lobe, but separated always from it by the cleft. At other times they end abruptly, and there is nothing but a thin layer of connective tissue with occasional epithelial cells in it extending backwards from the posterior margin of the anterior lobe to the reflection on to the posterior aspect of the infundibulum. The thinning and partial disappearance of epithelium in this situation in the adult cat may possibly allow a communication between the cleft and the subdural space, but there is no direct opening to be seen, and where the epithelium persists, as it often does, serial sections show that the cleft is completely closed by it. The readiness with which rupture may take place here is easily appreciated from the appearance in fig. 3, which is a photograph of an actual specimen of the cat’s pituitary.



Fig. 4. Mesial sagittal section through the pituitary body of an adult dog. (Semi-diagrammatic.) a, optic chiasma: b, tongue-like process of pars intermedia; c, third ventricle; d, anterior lobe proper; d’, part of anterior lobe appearing above; e, epithelial cleft: g, nervous substance of posterior lobe; i, epithelial investment of posterior lobe. The dark shading indicates the anterior lobe proper; the lighter shading shows the position of the epithelium of the pars intermedia.


The pituitary body of the dog (fig. 4) presents further differences in the structure and arrangement of its parts. The body of the posterior lobe is solid, but a cavity occurs in its neck which opens by a comparatively wide mouth into the third ventricle of the brain.

The attachments of the pituitary body to the base of the brain are Very similar in the cat and dog. A thin lamina of brain substance runs forwards from the neck of the infundibulum for some distance to merge with the tuber cinereum. This lamina is closely invested below by the tongueshaped process of epithelium which runs forward from the anterior lobe.


The posterior lamina, after leaving the neck of the infundibulum, is sharply bent back upon itself, and appears in sagittal section as a long thin strip of brain substance tapering as it passes backwards until it joins the septum between the corpora mamillaria. The bend in the lamina encloses epithelium which is continuous with the epithelial investment of the posterior lobe, and which has in the cat a distinctly tubular character in this situation. In coronal section the opening of the neck into the third ventricle is not so wide, and the lateral laminae are shorter. The neck is really funnel-shaped, but compressed from side to side. It is completely invested by epithelium.


In the dog the anterior lobe almost completely embraces the posterior, but the main mass of the lobe containing eosinophil cells lies below it and at its sides. Prolongations of the anterior lobe pass over the dorsal aspect of the posterior lobe to unite with one another. The epithelium is reflected at the neck, and at the postero—superior extremity of the posterior lobe, to form an investment which covers the nervous portion of the lobe. The reflected portion of the epithelium is separated from the outer covering by the cleft, which is extremely well developed in the dog’s pituitary. Fingerlike processes of the epithelium which invests the posterior lobe frequently project into the cleft, and sometimes join with the outer layers of epithelium, forming strands across it. The cleft is a closed cavity in the dog, but the epithelium bounding it is very thin at the posterior reflection, and consequently liable to rupture there in course of preparation.


The investment of the posterior lobe is thick, and portions of it pass deeply into the nervous substance. It contains no eosinophil cells, but numerous colloid vesicles. The vesicles are larger in the dog than in the cat, and occur in groups which are for the most part situated in the deeper layers of the epithelium, and are not infrequently found in the adjacent nervous substance.


The pituitary body of the monkey (fig. 5) presents a very different type. The posterior lobe is solid and the cavity of the third ventricle is not even prolonged into its neck. The attachment of the pituitary to the brain is by a narrow solid stalk of nervous substance, which is surrounded by" a thin layer of epithelium continuous with the anterior lobe.


The anterior lobe lies in front of the posterior, and is partly separated from it by the cleft. The main mass of the anterior lobe lies in front of the cleft, and is made up of columns of cells, many of which stain deeply with eosin, and of blood-channels. The epithelial investment of the posterior lobe is moderately thick behind the cleft, and contains no eosinophil cells. It is continued round the posterior lobe and completely invests the neck, spreading on to the adjacent parts of the brain, but is usually deficient towards the middle line on the posterior aspect of the nervous lobe. The main blood-vessels enter and leave the posterior lobe in this situation, and in all animals examined the epithelial investment stops more or less short of this place. The epithelium frequently dips into the nervous substance, and strands of it may pass quite deeply into it, and even into the brain tissue in the neighbourhood of the floor of the third ventricle. The cleft is here again a closed cavity, and is not nearly so well developed as in the pituitaries of the cat and dog. In some cases very little of it remains, but the epithelium which lies between it and the nervous substance of the posterior lobe is always distinct from that of the main mass of the anterior lobe and contains no eosinophil cells. The same is true of the epithelium which invests the neck and sides of the posterior lobe. In this respect the epithelial investment of the nervous portion resembles that of the pituitaries of the cat and dog, and like them, too, may contain colloid—holding vesicles, but they are comparatively scarce in the monkey, and are not always present.


Fig. 5. Mesial sagittal section through the pituitary body of an adult monkey. (Semi-diagrammatic.)

a, optic chiasma; b, tongue-like process of pars intermedia; 4:, third ventricle; d, anterior lobe proper; e, epithelial cleft: g, nervous substance of posterior lobe; ti, epithelial investment of posterior lobe; Ic, epithelium of pars intermedia extending over and into adjacent brain substance. The dark shading indicates the anterior lobe proper; the lighter shading shows the position of the epithelium - of the pars intermedia.


In the pituitary body of the monkey there is, then, a very complete fusion of the tissues derived from the buccal mucous membrane and from into the nervous substance, and strands of it may pass quite deeply into it, and even into the brain tissue in the neighbourhood of the floor of the third ventricle. The cleft is here again a closed cavity, and is not nearly so well developed as in the pituitaries of the cat and dog. In some cases very little of it remains, but the epithelium which lies between it and the nervous substance of the posterior lobe is always distinct from that of the main mass of the anterior lobe and contains no eosinophil cells. The same is true of the epithelium which invests the neck and sides of the posterior lobe. In this respect the epithelial investment of the nervous portion resembles that of the pituitaries of the cat and dog, and like them, too, may contain colloid—holding vesicles, but they are comparatively scarce in the monkey, and are not always present.


Fig. 5. Mesial sagittal section through the pituitary body of an adult monkey. (Semi-diagrammatic.) a, optic chiasma; b, tongue-like process of pars intermedia; 4:, third ventricle; d, anterior lobe proper; e, epithelial cleft: g, nervous substance of posterior lobe; ti, epithelial investment of posterior lobe; Ic, epithelium of pars intermedia extending over and into adjacent brain substance. The dark shading indicates the anterior lobe proper; the lighter shading shows the position of the epithelium of the pars intermedia.


In the pituitary body of the monkey there is, then, a very complete fusion of the tissues derived from the buccal mucous membrane and from the brain. The cleft is rudimentary and may be almost completely closed, though great differences in this respect occur in different individuals. The pituitary of the monkey closely resembles that of man. The reactions to certain staining reagents, such as haematoxylin and eosin, differentiate it into three parts: an anterior glandular, which constitutes the bulk of the epithelial lobe and which contains eosinophil cells; a posterior lobe of nervous origin; and an intermediate portion (Edinger (9)), which is composed of epithelial cells closely investing the nervous portion. The intermediate portion, although derived from the same source as the main anterior lobe, differs from it in adult mammals in that it contains no eosinophil cells, and may exhibit the presence of vesicles resembling the colloid vesicles of the thyroid gland. The pituitary bodies of the ox, pig, and rabbit, also belong to the third type. Traces of a central cavity are sometimes found in the neck of the posterior lobe, but in general the pituitary bodies of these animals conform to the type illustrated in fig. 5.


Structure of the Anterior Lobe

The anterior or glandular lobe as seen from below when attached to the brain is the more prominent portion of the pituitary body, surrounding, as it does, a. large part of the posterior lobe; it also makes up the greater bulk of the organ. For the sake of description, however, it is convenient to consider as the anterior lobe only that portion of it which has already been distinguished from the “pars intermedia." The part thus designated as the anterior lobe is separated by the cleft and by the pars intermedia from the nervous portion of the pituitary. It is continuous with the epithelium of the pars intermedia above in the region of the neck of the infundibulum, and behind with the thin layer of epithelium which passes backwards to be reflected on to the body of the posterior lobe. It is a solid structure made up of columns of cells separated from one another by large and numerous blood-vessels and a small amount of connective tissue. The distinguishing histological feature of this lobe is the presence in it of two main kinds of cells, one of which has a marked aflinity for certain staining reagents.


The occurrence of two kinds of cells in the anterior lobe of the pituitary was recognised by Hannover (15) in 1844, but little attention was bestowed upon them until the researches of Flesch (10) and Dostoiewsky (7), appearing independently of one another in 1884, definitely established their existence. Both Flesch and Dostoiewsky described one kind of cell possessing a large, round, or polyhedral body full of big granules, which retain a deep red colour when treated with eosin and haematoxylin, and differentiated in alcohol. These cells are called “chromophil” cells by Flesch. Lothringer (22) states that they are probably identical with the “Mutterzellen” of Luschka. The other kind of cell is small, contains a large nucleus and little protoplasm, which is decolourised by the same method of procedure. This variety is the “chromophobe” cell. The two kinds of cells occur together in strings or clumps, sometimes the one preponderating, sometimes the other. The clumps are surrounded by a basement membrane, and vary in size according to the number and character of the enclosed cells. The distribution of the two kinds varies in difl'e,rent animals. Dostoiewsky says that in man and the ox the clear cells are chiefly grouped together in the central part of the gland, while in small animals, rat, cat, and rabbit, they are more scattered throughout the lobe. The gland is extremely vascular, and the blood-vessels are of the nature of wide channels. Rogowitsch (34) calls the “chromophobe” cell of Flesch the “Hauptzelle,” recognises the “chromophil” as a distinct cell, and states that a third variety exists in the form of nucleated masses of embryonic tissue. H. Stieda (43) comes to a similar conclusion and describes as “Kernhaufen” masses of embryonic tissue full of closely packed nuclei, having little protoplasm which behaves like that of the “Hauptzellen” to stains, and no cell borders Schonemann (39) goes still further, and believes that most of the socalled “Hauptzellen” have no real borders, and that they are to be regarded as “kernreiches Protoplasma.” According to Rogowitsch, Stieda, and Schonemann, the changes in the pituitary which follow removal of the thyroids are confined to the cells of the anterior lobe. Their results have a certain general agreement, but differ considerably in detail. Rogowitsch finds colloid in the “chromophil” cells, and states that it passes directly from them into the blood-vessels, both of which observations are strongly combated by Stieda. The latter believes that thyroidectomy is followed by increase in size of the “Hauptzellen,” and that no formation of colloid takes place. Rogowitsch describes hypertrophy of the “Kernhaufen” with vacuolisation and colloid formation. Schonemann is of the opinion that “chromophil ” cells are not a prominent feature of the healthy pituitary, that their development after thyroidectomy is a degenerative process, and, further, that they undergo colloid change, accompanied by proliferation of connective tissue and blood-vessels.


Saint-Remy (35) in 1892, after careful examination of the pituitary bodies of many vertebrates, came to the conclusion that there is only one kind of cell in the anterior lobe, and that the varieties previously described are merely the expressions of different functional stages of the same cell. The “chromophil” cell is really a “Hauptzelle,” or principal cell, in the protoplasm of which deeply staining granules have accumulated. The granules are probably transformed into some product of secretion and eliminated from the cell, which then becomes a smaller body recognisable as a principal cell. All stages between these extreme forms may be recognised in the normal gland.


Claus and Van der Stricht (5) came to similar conclusions. Benda (1) has more recently confirmed Saint-Remy’s views. He distinguishes three main forms showing transitional stages. The small, poorly granular cell is the young form, while the large, deeply-staining granular cell marks the acme of functional development. A third variety is the large cell devoid of granules, which he regards as a cell the function of which is temporarily or permanently interrupted. Benda pointed out that there is no evidence of any of the cells being the products of degenerative changes as supposed by Schonemann, and further that the granules bear no relation to the formation of colloid material. He believes that the granules break down into a. secretion which passes directly into the blood-vessels by diffusion through their thin walls.


Fig. 6. Mesial sagittal section through part of the pituitary body of an adult cat. a, anterior lobe showing different forms of epithelial cells: the blood channels are collapsed and their posltion indicated only by endothelial cells; b, epithelial cleft separating anterior from posterior lobe; c, epithelial investment of posterior lobe — “Epithelsaum” ut Lothtinger; d, nervous substance of posterior lobe.


My own observations are to a large extent confirmatory of the views expressed by Benda. In the anterior lobe of the cat’s pituitary there exist three main varieties of cells: a small polygonal cell with large nucleus and little protoplasm, containing few or no granules; a larger cell with similar nucleus and protoplasm, which may be clear, but frequently shows a difliuse arrangement of fine granules; and, lastly, cells which are full of deeply-staining material. The latter kind of cell is sometimes smaller than the diffusely granular form (cf. fig. 7), but this is not always the case, and the deeply-staining cell may be quite as large. In fig. 7 it looks as though there were two kinds of cells: a large, clear, and diffusely granular kind, and a smaller, deeply—staining cell. The picture presented by these cells varies according to the method and depth of staining, and difl'ers in different parts of the lobe in the same section. The fixative employed has also a great influence on the staining reactions, and with formalin or corrosive sublimate fixation there appear to be only two kinds of cells: the granular and clear. Occasionally a cell is seen which is diffusely granular in most of its body, but contains around its nucleus protoplasm of the deeply-staining variety. It is extremely difiicult to decide whether these appearances indicate distinct forms of cells, or whether they are merely expressions of different functional stages of one and the same kind of cell.


Fig. 7. Photograph of part of anterior lobe proper of an adult cat, x 500. Fixed in_ Flemming’s solution, stained with hot alcoholic eosin, differentiated in alkaline alcohol, and counterstained with picro-fuchsine. Shows clear cells and granular cells. The latter appear to be of two Viarletles—one kind consists of large cells whose protoplasm takes on a dlfluse stain; the other of smaller cells which are full of deeply-staining granules. The blood-channels are collapsed and their position is indicated by the dark lines.



The different cell forms are distributed fairly uniformly throughout the lobe; the clear cells sometimes predominate in certain localities, but are not constantly distributed in these positions. Where anterior lobe blends with the epithelium of the pars intermedia, a gradual transition is sometimes seen between the two kinds; at other times the dividing line is sharply marked (cf. fig. 8). The cells typical of the anterior lobe may spread right round the neck of the posterior lobe, or backwards over the body of the posterior lobe to _the posterior reflection of epithelium. The general appearances of the relation of the cells of the anterior lobe to the cleft and epithelium of the pars intermedia is shown in fig. 6, which is a drawing from a sagittal section through part of both lobes of the pituitary of the cat. In this specimen and in the one from which fig. 7 is taken, the bloodchannels are collapsed and their position is indicated by endothelial cells. The cells are arranged in solid columns, between which run thin-walled blood-channels. The columns show no central lumen, nor is there any colloid met with either in the cells or between them. Where colloid is present it lies among the clearer cells of the pars intermedia, and never in relation to the characteristic granular cells of the anterior lobe.


The cells of the anterior lobe and of the pars intermedia are derived from the same origin and become differentiated during foetal life. In the kitten the cells of the anterior lobe do not show such marked differences in size and the possession of granules as they do in the adult. The clear cell and the granular cell are recognisable, and there are transitional forms. While it is almost impossible as yet to settle the exact nature of these cells, I am inclined to believe that all the varieties represent varying stages of functional activity of one and the same kind of cell, and that the deeplystaining material is the product of the cell destined to be poured as an internal secretion into the blood-vessels.


The blood-vessels of the anterior lobe are extremely numerous and wide. When injected with carmine gelatine from the carotids they are seen to form wide channels resembling to some extent the sinusoids of the liver. The endothelial cells are closely applied to the epithelial cells Without intervening connective tissue cells. In this respect also they resemble the sinusoids of Minot. There ‘is, however, no evidence of any intracellular canalisation of the epithelial cells, such as is found in the liver (17). A fine reticulum of connective tissue is present in most places, resembling the “Gitterfasern” of the liver lobules. Whether lymphatics exist or not is doubtful; the sinusoidal character of the blood-vessels and the closely fitting endothelial cells render their presence unlikely in many parts of the anterior lobe. In certain situations near the cleft and pars intermedia true capillaries and connective tissue are found, and lymphatic vessels appear to exist in these situations.


The anterior lobe in the cat is usually separated from the cleft by a single layer of flattened cells, which are larger than endothelial cells, and are continuous at the anterior and posterior ends of the cleft with the cells of the epithelial reflection (fig. 6).


In the dog the anterior lobe is permeated by extraordinarily large, thinwalled blood sinuses. Lothringer (22) compared the structure of the anterior lobe in this animal to cavernous tissue. In the monkey, too, the blood-vessels are in the form of wide, thin-walled sinuses running more or less parallel to one another in an antero-posterior direction.


The changes in structure of the anterior lobe which have been alleged to follow thyroidectomy in the rabbit require further investigation. The normal variation in structure and arrangement of the cells varies within epithelium of the pars intermedia is shown in fig. 6, which is a drawing from a sagittal section through part of both lobes of the pituitary of the cat. In this specimen and in the one from which fig. 7 is taken, the bloodchannels are collapsed and their position is indicated by endothelial cells. The cells are arranged in solid columns, between which run thin-walled blood-channels. The columns show no central lumen, nor is there any colloid met with either in the cells or between them. Where colloid is present it lies among the clearer cells of the pars intermedia, and never in relation to the characteristic granular cells of the anterior lobe.


The cells of the anterior lobe and of the pars intermedia are derived from the same origin and become differentiated during foetal life. In the kitten the cells of the anterior lobe do not show such marked differences in size and the possession of granules as they do in the adult. The clear cell and the granular cell are recognisable, and there are transitional forms. While it is almost impossible as yet to settle the exact nature of these cells, I am inclined to believe that all the varieties represent varying stages of functional activity of one and the same kind of cell, and that the deeplystaining material is the product of the cell destined to be poured as an internal secretion into the blood-vessels.


The blood-vessels of the anterior lobe are extremely numerous and wide. When injected with carmine gelatine from the carotids they are seen to form wide channels resembling to some extent the sinusoids of the liver. The endothelial cells are closely applied to the epithelial cells Without intervening connective tissue cells. In this respect also they resemble the sinusoids of Minot. There ‘is, however, no evidence of any intracellular canalisation of the epithelial cells, such as is found in the liver (17). A fine reticulum of connective tissue is present in most places, resembling the “Gitterfasern” of the liver lobules. Whether lymphatics exist or not is doubtful; the sinusoidal character of the blood-vessels and the closely fitting endothelial cells render their presence unlikely in many parts of the anterior lobe. In certain situations near the cleft and pars intermedia true capillaries and connective tissue are found, and lymphatic vessels appear to exist in these situations.


The anterior lobe in the cat is usually separated from the cleft by a single layer of flattened cells, which are larger than endothelial cells, and are continuous at the anterior and posterior ends of the cleft with the cells of the epithelial reflection (fig. 6).


In the dog the anterior lobe is permeated by extraordinarily large, thinwalled blood sinuses. Lothringer (22) compared the structure of the anterior lobe in this animal to cavernous tissue. In the monkey, too, the blood-vessels are in the form of wide, thin-walled sinuses running more or less parallel to one another in an antero-posterior direction.


The changes in structure of the anterior lobe which have been alleged to follow thyroidectomy in the rabbit require further investigation. The normal variation in structure and arrangement of the cells varies within wide limits. Different methods of fixation and staining give very diverse pictures. The most useful method for showing the finer structure of the pituitary body as a whole is Flemming’s fixative followed by Muir’s eosin and methylene blue stain. Some of the clear cells of the anterior lobe occasionally seem wanting in outline, but careful staining shows that they are not “Kernhaufen.” Cajal’s silver reduction method leaves no doubt that they are cells, and their outlines are readily seen when this method is employed.


The anterior lobe of the pituitary‘ is evidently an important glandular body, and probably furnishes a secretion which passes directly into the blood-vessels; in this sense it is a blood-vessel gland, as was surmised by Ecker. Its function is unknown; extracts of it, when injected into the blood-vessels, have no immediate physiological action beyond that common to most glandular extracts. It is possible that this part of the pituitary has something to do with the regulation of the growth of the body, but in the meantime there is not evidence enough to form a basis for any definite statement.

Structure of the Intermediate Part of the Pituitary

The intermediate part of the pituitary body has its origin in common with the anterior lobe. It arises from the epithelial pouch which grows inwards from the buccal mucous membrane, being a development of that portion of its wall which is closely applied to the nervous portion of the pituitary. It is separated from the anterior lobe by the cleft throughout a large part of its extent in the eat, but is continuous with it, in front round the neck of the infundibulum, and behind at the posterior reflection. The connection between it and the nervous portion is very intimate. The portion which surrounds the neck of the infundibulum shows a structure differing somewhat from the part which covers the body of the posterior lobe. In the cat the epithelium surrounding the neck of the infundibulum is distinctly tubular, but the lumen is not a continuous one. The cells are arranged round a central lumen, which frequently contains a colloid material. The tubules are continued forwards in the tongue-like process already mentioned. Between them" are numerous large blood-vessels; this portion of the gland is very vascular. Fig. 8 shows the structure of the tongue-like process of the pituitary of an adult cat, and its line of separation from the granular cells of the anterior lobe.


The tubules do not appear to open into the subdural space, and are probably columns of cells in which lumina only appear at intervals where the colloid material accumulates between the cells. In the region of the anterior part of the cleft the tubules sometimes appear to open into the latter, but their lumina are frequently interrupted. Colloid materialihas been noted by many observers in the cleft, and may enter it in this

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Histological Appearances of the Mammalian Pituitary Body 151


like the so—called colloid material, and may be of that nature ; but is unlike in many respects the colloid of the thyroid gland. In the posterior lobe of the dog’s pituitary somewhat similar appearances present themselves, but in this case the epithelial islets frequently consist of a number of cells which group themselves round a central cavity containing colloid material. Isolated cysts, the walls of which are composed of a single layer of cells, are not uncommon, and were noted by Lothringer. In the dog, too, the larger cysts of the epithelial investment are not always complete, and the contained material may abut against the neuroglial tissue. The colloid substance, when completely or partly enclosed by epithelial cells, varies considerably in its staining properties in different parts of the same pituitary. As a rule it takes on little depth of colour with stains, and is unlike the colloid of the thyroid in this respect; it has a hyaline rather than a colloid appearance. Occasionally, however, the substance is denser and takes on a deeper stain, and in the dog sometimes looks as though it were a swollen cell with disintegrating nucleus. The hyaline material of the nervous portion of the posterior lobe also varies in appearance, and in its staining properties; most of it might be of the same nature as the so-called colloid of the epithelial investment and of the intermediate part generally, but in a diluted form. Some of this material must be the product of the epithelial cells, for it occurs in places where no other kind‘ of cell is present. The universal occurrence of this material in the nervous substance, often at considerable distances from epithelial cells, is dificult to explain, unless we can suppose it to be carried from them by lymphatic vessels. The substance often does lie in distinct spaces lined by what appears to be endothelial cells. The general tendency of the direction of the material seems to be towards the neck of the infundibulum in the cat, and it increases in amount towards this situation. Large masses are sometimes seen lying among the ependyma cells, and similar material may be present in large amount in the central cavity, communications between the two being evident in places.


In fig. 15 a typical portion of the neck of the infundibulum of a cat's pituitary is seen. The central cavity is lined by ependyma cells, outside which are cells with large nuclei and little protoplasm. Occupying the central cavity is a mass of hyaline material, aud masses of a similar substance lie beneath the ependyma cells and between the ependyma fibres. In other places in the posterior lobe the material is distinctly present in lymph channels accompanying the blood-vessels. Evidence strongly points to the probability that the material is on its Way to the central cavity, and so into the ventricles of the brain. In this sense the posterior lobe of "the pituitary is a gland which pours its secretion into the third ventricle of the brain. It is possible that the ependyma and neuroglia cells have also a secretory function, but improbable that they secrete the material described. They may, however, have some influence upon it. The most likely supposition is that the ependyma and neuroglia cells form a scaffolding for the posterior lobe of the pituitary, upon which is built up a covering of epithelial cells.1The relations of the two structures become very intimate; their blood supply is derived from arteries which enter the nervous substance posteriorly; the veins begin immediately below the epithelium, and return through the nervous substance. Interchange of material between blood-vessels and cells must be through the medium of lymph, seeing that most of the epithelial investment is extra-vascular. Cells from the investing layer grow into the nervous framework, giving rise to epithelial columns and cell islets. Secretion goes on either by an emptying of material from the cells into the lymph, or possibly by a breaking down and destruction of the whole cell. The latter indeed is the more probable fate of isolated epithelial cells, and seems to occur at times in the epithelial investment itself. The material known as colloid substance, which has been supposed by many to be identical with the colloid of the thyroid gland, occurs in comparatively large amounts in the pituitary of the eat, an animal which cannot long survive thyroid extirpation. Further chemical and experimental research is necessary to prove whether the colloid substance of the pituitary is identical in composition, or in its physiological action, with the colloid of the thyroid gland. The physiological action is apparently quite different, but this may be due to the presence in the lobe of other substances. Any secretion formed in the pars intermedia of the pituitary must pass into the adjacent substance of nervous origin either by blood—vessels or lymphatics. There is a possible exception to this rule in the tongue-like process of the cat’s pituitary, but even here blood—vessels from it pass into the adjacent anterior lamina connecting the neck of the infundibulum with the tuber cinereum, and the tubules are surrounded by connective tissue containing lymphatics, the course of which is unknown. They may possibly accompany the blood-vessels. The epithelial cells do not resemble in staining properties the cells of the medulla of the suprarenal capsule; they have no affinity for chromic acid. Nor do they resemble them in their relations to blood-vessels, the absence of which is so characteristic of most of the pars intermedia.


Fig. 15. Section of part of neck of posterior lobe of the pituitary body of an adult cat. From specimen fixed in Flemming’s solution and stained with eosin and methylene blue. Shows colloid material lying among ependyma fibres and in the central cavity of the neck. a, ependyma cells lining central cavity; b, colloid material in central cavity; c, ependyma fibres; d, colloid material: 4:, granular body lying among ependyma fibres.


  • 1 In the posterior lobe of a Belgian hare, a ganglion with large ganglion cells and medullated fibres was found. The ganglion occupie a large portion of one side of the posterior part of the lobe, and the fibres appeared as though entering it obliquely from the side and not through the neck of the lobe. Red bone marrow was also present, and the ganglion may have be part of one of the Gasserian ganglia, which, in the rabbit, are very close to the pituitary by a large part of the nervous portion of the lobe was destroyed by it. The intermediate portion was large in amount, and its cells thickly massed around the neck. The animal was a healthy adult.


A question of importance arose in the early investigations of the structure of the pituitary. Peremeschko (30) described the cleft of the epithelial part as being continuous with the central cavity of the neck of the infundibulum, and so with the third ventricle of the brain. If this were the case it would furnish a proof of Kupffer’s view (21) that the epithelial portion represents a “ palaeostoma ” or old mouth of an ancestral form of vertebrate, and there would be in the mammalian embryo a communication between the neural canal and buccal cavity. Subsequent observers have denied the accuracy of Peremeschko’s observations. In the pituitaries of the pig and man, in which Peremeschko described the continuation, there is obviously no such thing, for the body of the infundibulum is solid in both cases. Nor is there any indication of it in the embryo of either pig or man, so far as I have been able to see. It is far more likely to occur in the pituitary of the cat, in which the central cavity of the infundibulum is well developed and prolonged far backwards. In the adult cat the epithelium, as already stated, frequently invades the posterior end of the cavity, so that epithelial cells may even form part of its lining. This peculiarity affords some support for Kupfi'er’s view. In the adult cat I have never been able to find a direct communication between the cleft and the cavity of the infundibulum, although many specimens have been examined with this object. In one embryo kitten, however, I have found such a communication. Cleft and cavity in this specimen are undoubtedly in direct continuity at the postero-superior angle of the posterior lobe. In other kittens, at a comparatively late stage of embryonic life, a direct continuity is occasionally seen between tubular epithelium at the end of the cleft, and the ependyma cells lining the -central cavity of the infundibulum. In the kitten this coming together of the two portions occurs some time after the epithelial duct between buccal mucous membrane and epithelial portion of the pituitary has disappeared, so that there is never a direct continuity between the neural canal and the exterior. The observations, nevertheless, give support to Kupffer’s views on the morphological significance of the pituitary.

Vascular Supply of the Pituitary Body

The arrangement of the blood-vessels in the pituitary body has already been described along with the structure of its several parts, but a general survey of the vascular distribution in the cat's pituitary may be given. The most noticeable feature of the injected organ is the difference in vascu- larity of the two lobes. The anterior lobe is filled with wide channels, making it one of the most vascular structures of the body; the posterior lobe, on the other hand, resembles in the number and arrangement of its vessels the adjacent white matter of the brain. A large blood sinus is found on either side of the pituitary body below. The anterior lobe is supplied by arteries, apparently from the internal carotid, which enter it at the sides of the infundibulum above, and break up immediately into large, thin-walled vessels. The posterior lobe is supplied by a median artery which enters it at its postero—superior extremity; branches run forwards near the central cavity, and break up into capillaries. The veins of the posterior lobe are situated immediately beneath the epithelial investment, and converge towards the place of entrance of the artery; leaving the lobe in this situation, they turn outwards to join the large lateral sinus on either side. Some of the veins from the anterior lobe appear to take a similar course, passing through the epithelial investment of the neck of the infundibulum to run in the nervous portion; others leave the anterior lobe at its neck and pass outwards into the lateral sinus. The presence of so many large arteries and veins in the immediate vicinity of the pituitary body would render the operation of removing it an extremely diflicult one, even were the organ so situated as to be convenient of access. Minot (26) states that the blood-vessels of the anterior lobe of the pituitary will probably be found to have a sinusoidal development. This appears to be partly true at any rate of the anterior lobe of the pig’s pituitary.


Fig. 16. Mesial sagittal section of pituitary body of adult cat ; blood-vessels injected with carmine gelatine. (Photograph.) a, optic chiaama; b, tongue-like process of pars intermedia; c. third ventricle; d, anterior lobe; e, pars intermedia lying above neck of posterior lobe; f, posterior lobe; 9, central artery entering posterior lobe at its poatero-superior angle; h, large vein, lying between nervous substance and epithelial investment of posterior lobe.

Conclusions

We may conclude from the histological appearances of the mammalian pituitary body that it is an organ of physiological importance It may be divided into two parts, which show structural differences probably indicative of distinct functions.


The anterior lobe, consisting of large granular cells and numerous blood vessels, is a gland producing an internal secretion which is poured directly into the blood. It is a blood-vascular gland, the function of which is undetermined, but which may exercise an influence on growth. The careful examination of the pituitary body in cases of acromegaly may throw some light upon this question; at present any statement as to its probable functions must be purely speculative.


The posterior lobe is made up of two structures. Of these, the part developed from the brain and consisting of neuroglia and ependyma cells and fibres acts as a framework. It is more or less surrounded and invaded by epithelium, which probably furnishes its active part. There is histological evidence of a secretion produced by the epithelial cells, which apparently passes into lymph-vessels, and is destined to enter the ventricles of the brain. The posterior lobe of the mammalian pituitary is a brain gland, not by virtue of tissue of brain origin, but by the growth into it of epithelial cells of ectodermic origin. Extracts have the property of producing marked effects on cardiac and plain muscle fibres comparable in some respects to the action of the medulla of the suprarenal capsule. They have also a selective action upon the kidney, causing dilatation of the renal blood-vessels and diuresis. Disturbances of the posterior lobe of the pituitary are - probably responsible for the occurrence of the diabetic conditions which have been so frequently recorded at some time or other in the history of cases of acromegaly and of affections and lesions associated with the base of the skull.

Summary

Three types of mammalian pituitary body are recognised. In one, e.g., the cat, the posterior lobe is hollow and its cavity is in free communication with the third ventricle of the brain, while the epithelium of the anterior lobe affords an almost complete investment for the posterior lobe; in the second type, e.g., the dog, the body of the posterior lobe is solid, but the neck is hollow, and communicates with the third ventricle: the posterior lobe is here again almost completely surrounded with epithelium; in the third type, e.g., man, monkey, ox, pig, and rabbit, the body and neck of the posterior lobe are solid, although traces of a cavity are occasionally found in the neck; in this type the epithelium does not invest the posterior lobe so completely, but is aggregated around the neck and spreads over and into the adjacent surface of the brain.


The epithelial portion of the pituitary body is differentiated into two distinct parts: an anterior lobe proper, consisting of solid columns of cells, between which run wide and thin-walled blood-channels ; and an intermediate portion, which lies between the anterior lobe and the nervous tissue of the pituitary, forming a closely-fitting investment of the latter.


The anterior lobe contains cells which are clear or hold in their protoplasm varying amounts of deeply-staining granules. They are probably different functional stages of one and the same kind of cell, and the granules give rise to a secretion which is absorbed by the blood-vessels.


The intermediate portion consists of finely granular cells arranged in layers of varying thickness closely applied to the body and neck of the posterior lobe and to the under surface of adjacent parts of the brain. The part of it which is separated from the anterior lobe by the cleft is almost devoid of blood—vessels. In the cat the portion lying in front of the anterior lobe has a tubular appearance and is very vascular. Colloid material occurs between the cells of the pars intermedia, and in most situations appears to pass into the adjacent nervous substance, to be absorbed by blood-vessels or lymphatics.


The nervous portion of the pituitary body is made up of neuroglia cells and fibres. Ependyma cells line the central cavity in the cat and send long fibres forwards and upwards towards the brain, most of which terminate in the outer part of the neck. There are no true nerve cells and the nerves supplying the pituitary probably reach it through sympathetic fibres accompanying the blood—vessels (Berkley). The nervous portion is invaded to a large extent by the epithelial cells of the pars intermedia. Columns of epithelial cells grow into it, especially in the region of the neck, and islets of these cells are frequently found throughout the posterior lobe; in the pituitary of the cat epithelial cells may even grow into its central cavity.


A substance histologically resembling the colloid of the thyroid gland, but probably of a different nature, occurs in large quantities in the nervous portion of the posterior lobe. It appears to be a product of the epithelial cells, and, in the cat at any rate, to be carried by lymphatics into the central cavity, and so into the third ventricle of the brain. In this respect the posterior lobe of the pituitary is an infundibular gland. Whether this substance is modified by its passage through the nervous substance or not is unsettled. Its distribution corresponds with the site of the tissue, the extracts of which have active physiological results when injected into the blood.


The anterior lobe of the pituitary is extremely vascular and its circulation sinusoidal. The posterior lobe is supplied for the most part by a central artery which enters it at its postero-superior angle and runs forward giving of? branches; the veins begin immediately below the epithelial investment and run backwards in this situation, to emerge near the entry of the artery. The veins of both lobes enter large blood sinuses lying close to the sides of the pituitary body.


Histological evidence is against the statement of Bela Haller that the anterior lobe is a tubular gland which pours its secretion directly into the subdural space.


I am indebted to Mr Richard Muir for the care with which he has executed the drawings and photographs accompanying this paper.


The expenses of the research have been defrayed by a grant from the Moray Fund for the prosecution of research in the University of Edinburgh.

Literature Referred to in the Text

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Cite this page: Hill, M.A. (2018, November 16) Embryology Paper - The histological appearances of the mammalian pituitary body. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_The_histological_appearances_of_the_mammalian_pituitary_body

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