The Endocrine System

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• Publisher: Academic Press
• Year: 1969
• Print ISBN: 9780123504029
• eBook ISBN: 9780080585222
• Topic: Physical Sciences
• Subtopic: Geophysics

The Endocrine System

1

The Pituitary Gland: Anatomy and Histophysiology

J.N. Ball and Bridget I. Baker

I Introduction

A The Pituitary Gland in General

B Adenohypophysial Histophysiology and Cytophysiology

II The Pituitary Gland in Teleosts

A General Organization

B Histophysiology of the Adenohypophysis

G The Neurohypophysis in Teleosts

D Blood Supply to the Teleostean Pituitary

E Hypothalamic Control of the Adenohypophysis

III The Pituitary Gland in Primitive Bony Fishes

A Superorder Chondrostei

B Superorder Holostei

IV The Pituitary Gland in Lungfishes

V The Pituitary Gland in Elasmobranchs

VI The Pituitary Gland in Cyclostomes

Acknowledgments

References

I. Introduction

A. The Pituitary Gland in General

In all vertebrates, the pituitary gland or hypophysis consists of two parts, separable on the bases of embryology, structure, and function. These are the neurohypophysis, a downgrowth from the floor of the diencephalon, and the adenohypophysis originating as an ectodermal upgrowth (Rathke’s pouch) from the roof of the embryonic buccal cavity (Wingstrand, 1966a). The two parts meet and enclose between them a mesodermal rudiment which gives rise to their intrinsic blood vessels (Green and Maxwell, 1959; Green, 1966). Thus the gland is a composite organ, and it has many different endocrine functions.

The adenohypophysis is the site of synthesis, storage, and release into the blood of several different peptide hormones; and the greater part of pituitary histophysiology is concerned with the allocation of each of these hormones to the type of pituitary cell that secretes it. The adenohypophysis is divided into the pars distalis, site of secretion of most adenohypophysial hormones, and the pars intermedia. The neurohypophysis in fishes is rather simpler than in land vertebrates (Wingstrand, 1966a) and consists essentially of a hypophysial stalk, suspending the gland from the ventral region of the diencephalon (hypothalamus) and containing an extension of the third ventricle (infundibular recess), and at the distal end of the stalk an enlargement, the neurohypophysial lobe or core, which forms the middle of the gland (Figs. 1 and 2). The stalk contains the axonal fibers of neurosecretory cells, the cell bodies being located in the hypothalamus. The neurohypophysial core consists largely of the endings of these fibers interspersed with cells termed “pituicytes.” The neurohypophysis seems to be in general a storage-release center for materials which are actually synthesized in the hypothalamus and then transported to the neurohypophysial core along the neurosecretory axons (Section II, C). In many fishes, the neurohypophysial stalk is virtually absent, the pituitary then being pressed close to the ventral surface of the hypothalamus, while in a few teleosts (e.g., Lophius) the neurohypophysial stalk is extremely long (Wingstrand, 1966a).

Fig. 1 Anguilla anguilla. Diagram of midsagittal section through the eel pituitary, anterior to the right. Follicles of prolactin cells (p), mixed with TSH cells (t), and bordered posteriorly by ACTH cells (c) form the rostral pars distalis. The proximal pars distalis comprises cords of cells below the neurohypophysis (n), mainly composed of growth hormone cells or somatotrops (s) in the sexually immature fish, with scattered immature gonadotrops (g). Posteriorly is the pars intermedia (i), deeply invaded by processes of the neurohypophysis, which in this region displays masses of AF + ve neurosecretory material (horizontal shading). The saccus vasculosus (sv) projects behind the pituitary (Section II,

); IIIv indicates third ventricle, the floor and sides being the hypothalamus, the floor being also termed the “infundibular floor.”. From Olivereau (1967a)

Fig. 2 Poecilia latipinna. Sagittal section through pituitary of a female fish, anterior to the right. The mass of prolactin cells (bright red) together with the bands of colorless ACTH cells projecting into the neurohypophysis posteriorly form the rostral pars distalis. In the proximal pars distalis, note the ventral mass of blue gonadotrops and the dorsally projecting fingers of orange growth hormone cells, mixed with a few blue TSH cells. The pars intermedia is small in cyprinodonts and forms a thin ventral rim to the posterior neurohypophysis, which contains large Herring bodies (neurosecretory material). Azan.

B. Adenohypophysial Histophysiology and Cytophysiology

Purves (1966) has usefully divided the cytological criteria used in the study of the adenohypophysis into two groups. The first category consists of features that are indicators of the specific nature of the functions of individual cell types such as granule size, staining reactions and chemical nature, cell morphology, and reactions to specific physiological alterations; these features are the data of special cytology, which is particularly concerned with allocation of function to each cell type. The second category includes those features which are indicators of the functional state of the cell, indicating high or low rates of metabolic or secretory activity such as nuclear size, nucleolar size, amount of cytoplasmic RNA, state of the Golgi apparatus, and accumulation or loss of secretory granules. These features constitute the field of general cytology. In the study of fishes, as in other vertebrate groups, workers on the pituitary have been concerned with both kinds of criteria. However, more than in the highly worked field of mammalian pituitary histophysiology, most investigations on fishes are still primarily concerned with special cytology. This implies that there is, as yet, no complete general agreement about the functions of the various types of cell distinguishable in the fish pituitary; although perhaps with the greater technical standardizations that have come about in recent years, especially the use of methods developed in mammalian studies by Herlant (1956, 1960), and first applied to the fish pituitary by Olivereau and Herlant (1954, 1960), the actual morphological and tinctorial characteristics of the teleostean adenohypophysial cell types would now be agreed upon by most workers. However, there is still disagreement about the functions of these cell types since the experimental allocation of function to the cells has been attempted systematically in only a few species. It follows that not all workers in this field would agree on a generally applicable functional nomenclature of cell types. In this review, the nomenclature used is the one established partly on functional and partly on tinctorial grounds following experimental studies in the eel, Anguilla, and the molly, Poecilia (Olivereau, 1963b; Olivereau and Ball, 1964). It is a mixed nomenclature, in Purves’ terms (1966), based partly on similarities in staining properties of the secretory granules to those in mammalian cells of demonstrated function but mainly (primarily) on the characteristic responses of the cells in fishes to experimental situations designed to alter the secretion rates of the different adenohypophysial hormones. Logically, one is on equivocal grou...

Table of contents

• Cover image
• Title page
• Table of Contents
• Contributors
• Copyright page
• List of Contributors
• Preface
• Contents of Other Volumes
• Chapter 1: The Pituitary Gland: Anatomy and Histophysiology
• Chapter 2: The Neurohypophysis
• Chapter 3: Prolactin (Fish Prolactin or Paralactin) and Growth Hormone
• Chapter 4: Thyroid Function and Its Control in Fishes
• Chapter 5: The Endocrine Pancreas
• Chapter 6: The Adrenocortical Steroids, Adrenocorticotropin and the Corpuscles of Stannius
• Chapter 7: The Ultimobranchial Glands and Calcium Regulation
• Chapter 8: Urophysis and Caudal Neurosecretory Systemxs
• Author Index
• Systematic Index
• Subject Index