Development.They arise in common with the sympathetic cells from the neural crest, and are therefore ectodermal in origin. The chromaphil and sympathetic cells are indistinguishable from one another at the time of their migration from the spinal ganglia to the regions occupied in the adult. Differentiation of chromaphil cells begins in embryos about 18 mm. in length but is not complete until about birth. The chromaphiloblasts increase in size more than the sympathoblasts and stain less intensely with ordinary dyes. Later the chrome reaction develops. The aortic bodies differentiate first and are prominent in 20 mm. embryos. The paraganglia of the sympathetic plexuses differentiate next and last of all the paraganglia of the sympathetic trunk. The carotid body is completely differentiated in 30 mm. embryos. After birth the chromaphil organs degenerate but the paraganglia can be recognized with the microscope in sites originally occupied by them.
The paraganglia are small groups of chromaphil cells connected with the ganglia of the sympathetic trunk and the ganglia of the celiac, renal, suprarenal, aortic and hypogastric plexuses. They are sometimes found in connection with the ganglia of other sympathetic plexuses. None have been found with the sympathetic ganglia associated with the branches of the trigeminal nerve.
The aortic glands or bodies are the largest of these groups of chromaphil cells and measure in the newborn about 1 cm. in length. They lie one on either side of the aorta in the region of the inferior mesenteric artery. They decrease in size with age and after puberty are only visible with the microscope. About forty they disappear entirely. Other groups of chromaphil cells have been found associated with the sympathetic plexuses of the abdomen independently of the ganglia.
the Suprarenal Glands (Glandulæ Suprarenalis; Adrenal Capsule) (Figs. 1183,1184)The suprarenal glands are two small flattened bodies of a yellowish color, situated at the back part of the abdomen, behind the peritoneum, and immediately above and in front of the upper end of each kidney; hence their name. The right one is somewhat triangular in shape, bearing a resemblance to a cocked hat; the left is more semilunar, usually larger, and placed at a higher level than the right. They vary in size in different individuals, being sometimes so small as to be scarcely detected: their usual size is from 3 to 5 cm. in length, rather less in width, and from 4 to 6 mm. in thickness. Their average weight is from 1.5 to 2.5 gm. each.
Development.Each suprarenal gland consists of a cortical portion derived from the celomic epithelium and a medullary portion originally composed of sympatho-chromaffin tissue. The cortical portion is first recognizable about the beginning of the fourth week as a series of buds from the celomic cells at the root of the mesentery. Later it becomes completely separated from the celomic epithelium and forms a suprarenal ridge projecting into the celom between the mesonephros and the root of the mesentery. Into this cortical portion cells from the neighboring masses of sympatho-chromaffin tissue migrate along the line of its central vein to reach and form the medullary portion of the gland.
The right suprarenal is situated behind the inferior vena cava and right lobe of the liver, and in front of the diaphragm and upper end of the right kidney. It is roughly triangular in shape; its base, directed downward, is in contact with the medial and anterior aspects of the upper end of the right kidney. It presents two surfaces for examination, an anterior and a posterior. The anterior surface looks forward and lateralward, and has two areas: a medial, narrow, and non-peritoneal, which lies behind the inferior vena cava; and a lateral, somewhat triangular, in contact with the liver. The upper part of the latter surface is devoid of peritoneum, and is in relation with the bare area of the liver near its lower and medial angle, while its inferior portion is covered by peritoneum, reflected onto it from the inferior layer of the coronary ligament; occasionally the duodenum overlaps the inferior portion. A little below the apex, and near the anterior border of the gland, is a short furrow termed the hilum, from which the suprarenal vein emerges to join the inferior vena cava. The posterior surface is divided into upper and lower parts by a curved ridge: the upper, slightly convex, rests upon the diaphragm; the lower, concave, is in contact with the upper end and the adjacent part of the anterior surface of the kidney.
The left suprarenal, slightly larger than the right, is crescentic in shape, its concavity being adapted to the medial border of the upper part of the left kidney. It presents a medial border, which is convex, and a lateral, which is concave; its upper end is narrow, and its lower rounded. Its anterior surface has two areas: an upper one, covered by the peritoneum of the omental bursa, which separates it from the cardiac end of the stomach, and sometimes from the superior extremity of the spleen; and a lower one, which is in contact with the pancreas and lienal artery, and is therefore not covered by the peritoneum. On the anterior surface, near its lower end, is a furrow or hilum, directed downward and forward, from which the suprarenal vein emerges. Its posterior surface presents a vertical ridge, which divides it into two areas; the lateral area rests on the kidney, the medial and smaller on the left crus of the diaphragm.
The surface of the suprarenal gland is surrounded by areolar tissue containing much fat, and closely invested by a thin fibrous capsule, which is difficult to remove on account of the numerous fibrous processes and vessels entering the organ through the furrows on its anterior surface and base.
Small accessory suprarenals (glandulæ suprarenales accessoriæ) are often to be found in the connective tissue around the suprarenals. The smaller of these, on section, show a uniform surface, but in some of the larger a distinct medulla can be made out.
Structure.On section, the suprarenal gland is seen to consist of two portions (Fig. 1185): an external or cortical and an internal or medullary. The former constitutes the chief part of the organ, and is of a deep yellow color; the medullary substance is soft, pulpy, and of a dark red or brown color.
The cortical portion (substantia corticalis) consists of a fine connective-tissue net-work, in which is imbedded the glandular epithelium. The epithelial cells are polyhedral in shape and possess rounded nuclei; many of the cells contain coarse granules, others lipoid globules. Owing to differences in the arrangement of the cells, three distinct zones can be made out: (1) the zona glomerulosa, situated beneath the capsule, consists of cells arranged in rounded groups, with here and there indications of an alveolar structure; the cells of this zone are very granular, and stain deeply. (2) The zona fasciculata, continuous with the zona glomerulosa, is composed of columns of cells arranged in a radial manner; these cells contain finer granules and in many instances globules of lipoid material. (3) The zona reticularis, in contact with the medulla, consists of cylindrical masses of cells irregularly arranged; these cells often contain pigment granules which give this zone a darker appearance than the rest of the cortex.
The medullary portion (substantia medullaris) is extremely vascular, and consists of large chromaphil cells arranged in a network. The irregular polyhedral cells have a finely granular cystoplasm that are probably concerned with the secretion of adrenalin. In the meshes of the cellular network are large anastomosing venous sinuses (sinusoids) which are in close relationship with the chromaphil or medullary cells. In many places the endothelial lining of the blood sinuses is in direct contact with the medullary cells. Some authors consider the endothelium absent in places and here the medullary cells are directly bathed by the blood. This intimate relationship between the chromaphil cells and the blood stream undoubtedly facilitates the discharge of the internal secretion into the blood. There is a loose meshwork of supporting connective tissue containing non-striped muscle fibers. This portion of the gland is richly supplied with non-medullated nerve fibers, and here and there sympathetic ganglia are found.
Vessels and Nerves.The arteries supplying the suprarenal glands are numerous and of comparatively large size; they are derived from the aorta, the inferior phrenic, and the renal. They subdivide into minute branches previous to entering the cortical part of the gland, where they break up into capillaries which end in the venous plexus of the medullary portion.
The suprarenal vein returns the blood from the medullary venous plexus and receives several branches from the cortical substance; it emerges from the hilum of the gland and on the right side opens into the inferior vena cava, on the left into the renal vein.
The nerves are exceedingly numerous, and are derived from the celiac and renal plexuses, and, according to Bergmann, from the phrenic and vagus nerves. They enter the lower and medial part of the capsule, traverse the cortex, and end around the cells of the medulla. They have numerous small ganglia developed upon them in the medullary portion of the gland.
In connection with the development of the medulla from the sympathochromaffin tissue, it is to be noted that this portion of the gland secretes a substance, adrenalin, which has a powerful influence on those muscular tissues which are supplied by sympathetic fibers.
Glomus Caroticum (Carotid Glands; Carotid Bodies)The carotid bodies, two in number, are situated one on either side of the neck, behind the common carotid artery at its point of bifurcation into the external and internal carotid trunks. They are reddish brown in color and oval in shape, the long diameter measuring about 5 mm.
FIG. 1186 Section of part of human glomus caroticum. (Schaper.) Highly magnified. Numerous bloodvessels are seen in section among the gland cells. (See enlarged image)
Each is invested by a fibrous capsule and consists largely of spherical or irregular masses of cells (Fig. 1186), the masses being more or less isolated from one another by septa which extend inward from the deep surface of the capsule. The cells are polyhedral in shape, and each contains a large nucleus imbedded in finely granular protoplasm, which is stained yellow by chromic salts. Numerous nerve fibers, derived from the sympathetic plexus on the carotid artery, are distributed throughout the organ, and a net-work of large sinusoidal capillaries ramifies among the cells.
FIG. 1187 Section of an irregular nodule of the glomus coccygeum. (Sertoli.) X 85. The section shows the fibrous covering of the nodule, the bloodvessels within it, and the epithelial cells of which it is constituted. (See enlarged image)
Glomus Coccygeum (Coccygeal Gland or Body; Luschkas Gland)The glomus coccygeum is placed in front of, or immediately below, the tip of the coccyx. It is about 2.5 mm. in diameter and is irregularly oval in shape; several smaller nodules are found around or near the main mass.
It consists of irregular masses of round or polyhedral cells (Fig. 1187), the cells of each mass being grouped around a dilated sinusoidal capillary vessel. Each cell contains a large round or oval nucleus, the protoplasm surrounding which is clear, and is not stained by chromic salts.183