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THE DUCTLESS GLANDS.
ORIGINALLY BY THE LATE D. J. CUNNINGHAM, F.R.S.,
REVISED AND REWRITTEN BY A. C. GEDDES, M.D., F.R.S.E.,
THE title, the ductless glands, denotes a group of organs whose function is to elaborate a special product and to discharge it into the blood or lymph. These activities constitute the act of internal secretion.
The group includes the hypophysis and the pineal body, which are described with the brain; the suprarenal glands, which are compound organs and are the principal representatives of two important systems of glandular tissue called respectively the chromaphil and cortical systems; the glandulæ caroticæ, which are outlying parts of the chromaphil system; the thyreoid and parathyreoid glands, and the thymus, which are developed from the entodermal lining of the embryonic pharynx; the spleen and the glomus coccygeum, which are associated with the circulatory system.
Physiologically, the liver, pancreas, gastric and intestinal mucous membranes; the kidneys, prostate, and testes; the uterus, ovaries, corpus luteum, and possibly some other organs form internal secretions, and act therefore as "ductless glands" in addition to fulfilling their more obvious functions. Anatomically, the lymph and hæmo-lymph glands are "ductless glands," but it is not customary to speak of them as such.
1. THE CHROMAPHIL AND CORTICAL SYSTEMS AND THE SUPRARENAL GLANDS.
A. THE CHROMAPHIL SYSTEM.
(SYNONYMS: Chromophil, Chromaffin, Pheochrome, Phaöchrome System.)
The chromaphil system is composed of a number of discrete masses of tissue which produce and discharge adrenin (lævo-adrenalin, C,H,,NO, (Aldrich)). The name chromaphil is given to the tissue because the cells forming it contain granules which, in the presence of chromium salts, stain to any tint between bright yellow and dark brown. The distribution of the masses of tissue forming the system is shown in Fig. 1053. There are (i.) a series of isolated masses, the paraganglia, associated singly or in groups with the ganglia of the sympathetic nervous system, (ii.) a number of masses, chromaphil bodies of the sympathetic plexuses (aortic bodies) in close relation to the abdominal sympathetic plexuses, (iii) the glandulæ caroticæ, and (iv.) the medullary portions of the suprarenal glands.
(i.) The paraganglia are rounded masses of chromaphil tissue, 1-3 mm. in diameter, placed inside, half inside, or immediately outside the capsules of the ganglia of the sympathetic system. Typically one paraganglion, exceptionally a pair of paraganglia, is associated with each ganglion of the gangliated trunks and with each ganglion of the cœliac, renal, suprarenal, aortic, and hypogastric plexuses. Inconstantly, paraganglia
are associated with the ganglia of the cardiac and inferior mesenteric plexuses. They
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Superior Cervical Ganglion
Paraganglia of Gangliated Trunk
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Medulla of Suprarenal Gland
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Chromaphil Bodies of the
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Accessory Cortical Body
Accessory Suprarenal Gland
FIG. 1053.-DIAGRAM OF THE CHROMAPHIL AND CORTICAL SYSTEMS. Modified from Swale Vincent.
(ii.) The Chromaphil Bodies of the Sympathetic Plexuses.-From seven to seventy masses of chromaphil tissue are developed in relation to the abdominal sympathetic plexuses, independently of the ganglia and in addition to the paraganglia. Of these, the most important are the two aortic bodies, which lie one on either side of the aorta in the region of the origin of the inferior mesenteric artery. In the new-born child they are smooth brownish structures, 8-11 mm. in length, not infrequently united by an isthmus superiorly (Zuckerkandl). They degenerate as life advances, ceasing to be visible soon after puberty, but remaining discoverable, microscopically, until about the age of forty.
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(iii.) The glandula carotica (B.N.A. glomus caroticum; O.T. intercarotid body) a bilateral paired organ situated in close but slightly variable relation to the bifurcation the common carotid artery. Frequently it lies deep to the bifurcation; sometimes it wedged in between the internal and external carotids at their commencement; somenes it is placed between them at a slightly higher level. Its shape varies with its sition. When free from pressure it is oval; when compressed by the internal and ternal carotids it is wedge-shaped. On the average, its height is 7 mm., its breadth Not infrequently it is split into two or more nodules. Its colour is grayish, llowish, or brownish red.
Structure. The glandula carotica is built up of nodules of chromaphil tissue surrounded d supported by fibrous tissue. The nodules are penetrated by a mass of sinus-like blood pillaries and surrounded by large lymph vessels. Scattered nerve-cells are present, and the hole organ is permeated by non-medullated nerve-fibres, which establish intimate connexion ith the chromaphil cells.
(iv.) The medullary portions of the suprarenal glands, although belonging to he chromaphil system, are described below (p. 1346).
Development of the Chromaphil System.-All chromaphil tissue develops in intimate elation with the sympathetic nervous system. It is not derived from the sympathetic tissue or is the sympathetic tissue derived from it. Both are the descendants of a primitive, different, sympatho-chromaphil blastema, which in a 16-mm. embryo occupies the regions orresponding to those occupied by the sympathetic system of the adult. It is composed of ghtly packed deeply staining cells about 5 μ in diameter. The ancestry of these cells can be raced back with strong probability to the cells of the neural crest (see Development of the Sympathetic Nervous System).
The differentiation of chromaphiloblasts from sympathoblasts begins when the embryo is bout 18 mm. in length, but is not completed until late in gestation, if then. The process is narked by an increase in size of the chromaphil formative cells and by a diminution in the ntensity of their reaction to ordinary stains. Later, the specific chrome reaction develops, but the exact stage at which this occurs is unknown. It is important to note that if any cells in an area differentiate, all do. The result is that, in spite of their intimate relations and common origin, an intermixture of chromaphil and sympathetic cells is extremely rare.
The first of the chromaphil masses to differentiate are the aortic bodies. They are prominent structures in a 20-mm. embryo. Later, the paraganglia of the sympathetic plexuses develop, and last the paraganglia of the gangliated trunk.
The development of the glandula carotica requires special description. It takes origin from a strand of sympatho-chromaphil blastema, which extends ventrally from the region of the superior cervical sympathetic ganglion, deep to the internal carotid artery or between the internal and external carotids. Differentiation begins when the embryo is about 20 mm. in length, and is completed by the time it is 30 mm. long. In connexion with the development of the glandula, there is a peculiar thickening of the wall of the internal carotid artery near the developing gland. In the dog a similar thickening of the wall of the internal carotid artery takes place, although in that animal the glandula lies beside the external carotid. Further, in a 45-mm. fœtus in which the glandula is fully differentiated the thickening is still present. These facts show that in the higher animals the thickening has no connexion with the development of the glandula, though the association of chromaphil bodies with blood-vessels in cyclostomata and elasmobranchs (see Comparative Anatomy of the Chromaphil and Cortical Systems) compels caution in excluding the possibility of there being at least some phylogenetic relation between the two. It has frequently been stated, and is widely held, that the glandula carotica is developed from or receives some contribution from the entoderm of the third pharyngeal pouch. This is not the case (see Parathyreoid Glands, Development).
B. THE CORTICAL SYSTEM.
The cortical system is composed of several masses of glandular tissue peculiarly rich in lipoids. Its function is undetermined. The distribution of the masses is shown in Fig. 1053. There are (i.) the cortical portions of the suprarenal glands, (ii) accessory cortical bodies. These are described below (see Accessory Suprarenal Glands and Cortical System, Development).
C. GLANDULE SUPRARENALES.
The suprarenal glands (O.T. suprarenal bodies or capsules, adrenal glands) are compound organs consisting of a capsule of cortical substance enclosing a medulla of chromaphil tissue. Typically, there are two suprarenal glands, a right and left, placed in the epigastric region, one on each side of the vertebral
column. They lie in the same plane as, and in intimate relation to, the superomedial aspects of the kidneys. Their colour is yellowish brown; their size varies within wide limits. To some extent it depends upon the cause of death-being large in subjects dead of acute septic intoxication, small after sudden death from violence. Average dimensions are: height, 5 cm.; breadth, 3 cm.; thickness. slightly under 1 cm. ; weight about 7 gm.
Surface in relation
A. Anterior surface of right suprarenal gland. B. Anterior surface of left suprarenal gland. The superior and medial parts of each kidney are indicated in outline. On the right gland the dotted line indicates the superior limit of the peritoneal covering.
Rarely only one gland is present; occasionally one is quite small, the other unusually large; as a rule they are unequal in size, the left being more frequently the larger. Sometimes the two glands are fused (cf. horse-shoe kidney). Frequently there are accessory glands. These develop in the neighbourhood of the main gland, and usually remain there. but may become attached, early in embryonic life, to organs which subsequently change their position. As a result, they may be found not only beside the main gland but also in
Surface in relation
A to kidney
Surface in relation
Surface in relation to left crus of diaphragm
A. Posterior surface of right suprarenal gland. B. Posterior surface of left suprarenal gland.
the ligamentum latum, on the spermatic funiculus, or even attached to the epididymis Like the main glands, accessory suprarenals are compounded of cortex and medulla, and require to be distinguished from chromaphil bodies and accessory cortical bodies, which may be found in any of the positions in which accessory suprarenal glands occur.
Forms and Relations. The suprarenal glands possess fairly constant forms and relations. The right gland is flat and triangular in outline. It is moulded, antero-laterally
7 the liver; antero-medially by the vena cava inferior; postero-medially by the diaphragm Dove, and by the kidney below. In a formalin-hardened specimen these areas are parated by prominent ridges. Near the apex of the gland, within the area of contact ith the vena cava inferior, there is a short fissure, the hilum. From this emerges a vein hich immediately joins the vena cava. The left gland is also flat, but is semilunar in tline. It is moulded antero-laterally, by the stomach above, and by the pancreas
Medulla of suprarenal gland
Cortex of suprarenal gland
Left crus of diaphragm
below; postero-medially by the diaphragm above, and by the kidney below. Upon the anterior surface, near its lower end, is a well-marked fissure, the hilum. From this emerges a vein which almost immediately joins the left renal vein.
The relations of the right and left glands to the kidneys are different. The right lies like a cap upon the superior pole of the right kidney; the left is in contact with the antero-medial border of the left kidney from the hilus to the superior pole. The relation
FIG. 1057.-RECONSTRUCTION OF SUPRARENAL GLAND OF A DOG. (From Marshall Flint.) The upper part shows the arrangement of blood-vessels upon the surface of the gland, the lower part their arrangement within its substance.
of the glands to the peritoneum is not only different but variable. On the right side the peritoneum may cover the lower part of the antero-lateral surface of the gland; or this part may be in contact with the duodenum, in which case a small area about the middle of the surface may be covered by peritoneum; or the peritoneum may not come into relation with the gland at all. On the left side the upper part of the anterior surface is commonly covered by the peritoneum of the omental bursa, the lower part being