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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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.
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.