Doctrine about endocrine organs endocrine glands

There are certain organs which are very similar to secreting glands, but differ from them in one essential particular, viz., they do not possess any ducts by which their secretion is discharged. These organs are known as endocrine glands. They are capable of internal secretion—that is to say, of forming, from materials brought to them in the blood, substances which have a certain influence upon the nutritive and other changes going on in the body. This secretion is carried into the blood stream, either directly by the veins or indirectly through the medium of the lymphatics.

  These glands include the thyroid, the parathyroids and the thymus; the pituitary body and the pineal body; the chromaphil and cortical systems to which belong the suprarenals, the paraganglia and aortic glands, the glomus caroticum and perhaps the glomus coccygeum. The spleen is usually included in this list and sometimes the lymph and hemolymph nodes described with the lymphatic system. Other glands as the liver, pancreas and sexual glands give off internal secretions, as do the gastric and intestinal mucous membranes.

ENDOCRINE GLANDS do not have the ducts, their secret gets immediately into blood. They have prettily abundant blood supplying, and their secret has special chemical and physiological activity. Endocrine system for origin subdivides into glands with endodermal, mesodermal or ektodermal origin.

Glands of endodermal origin subdivide into bronchiogenic group (thyroid, parathyroid and thymus glands) and glands developed from epithelium of intestinal tube (endocrine part of pancreas).

Glands of mesodermal origin (interrenal system) include interstitial cells of sexual glands and cortex of adrenal glands.

Glands of ectoderm group include hypophysis (neurogenic group) and medulla of suprarenal glands and paraganglia.

The Thyroid gland is situated in anterior neck area on level of the IV-VI cervical vertebrae and consists of right and left lobes communicated by isthmus, which continues upward by pyramidal portion. Thyroid gland is built by parenchyma, which subdivides into lobuli by septa. Follicles are situated in lobules, which contain hormones of thyroid gland: thyroxine, triiodthyronin, calcitonin. They influence on all types of metabolism.

The Parathyroid gland has pair superior parathyroid gland and inferior parathyroid gland that situated on back surface of thyroid gland. Accessory parathyroid glands can be present. Parathyroid gland excretes parathyroid hormone that regulates metabolism of phosphorus and calcium.

The Thymus is a central organ of immune system, which is situated in anterior mediastinum on level of the 4th ribs behind manubrium sterni. Behind thymus pericardium is situated. Thymus gland consists of lobes – right and left, which have the lobule that built by cortex and medulla of thymus gland. In medulla Т-lymphocyte matter acquire that peculiarities which contribute to protective function.

Endocrine part of sexual glands (testicle and ovary)

Interstitial (Leidig) cells are situated in parenchyma of testicle. They excrete testosteron, which influences on development of secondary sexual signs. Corpus luteum positioned in ovaric parenchyma produces a progesteron (it prepares a mucous membrane of the uterus membrane to embryo fixation, detains development of new follicles and stimulates development of mammary glands during pregnancy). Follicular epithelium excretes estrogen, which contributes to development of primary female sexual signs (ovary and uterus) also development of secondary female sexual signs, as growth of mammary gland, hair according female type cetera and assists the regulation of menses.

Endocrine part of pancreas is represented by islets of Langerhans. They produce insulin and glucagon, that regulate metabolism of carbohydrates, regulative a sugar contents in organism. Attached to insufficient production of these hormonal disease sugar diabetes arises.

The Adrenal gland is a pair endocrine gland, which lies on superior extremity of right and left kidneys on level of the Th 11 – Th 12 vertebrae. Each adrenal gland has triangle shape and has anterior surface, posterior surface and renal surface and superior margin and medial margin, and also has the hilus and consists of cortex and medulla matter. Cortex produces mineralocorticoids (aldosterone), glucocorticoids and androgens. Medulla of adrenal glands produces adrenalin and noradrenalin.

The Paraganglia are small agglomerations of chromaffin cells, placed closely near abdominal aorta (aortic paraganglia) or in thickness of sympathetic trunk (sympathetic paraganglion). Paraganglia has a function, analogic to function of medulla suprarenal gland.

a. The Thyroid Gland (Glandula Thyreiodea) is a highly vascular organ, situated at the front and sides of the neck; it consists of right and left lobes connected across the middle line by a narrow portion, the isthmus. Its weight is somewhat variable, but is usually about 30 grams. It is slightly heavier in the female, in whom it becomes enlarged during menstruation and pregnancy.

  The lobes (lobuli gl. Thyreoideæ) are conical in shape, the apex of each being directed upward and lateralward as far as the junction of the middle with the lower third of the thyroid cartilage; the base looks downward, and is on a level with the fifth or sixth tracheal ring. Each lobe is about 5 cm. long; its greatest width is about 3 cm., and its thickness about 2 cm. The lateral or superficial surface is convex, and covered by the skin, the superficial and deep fasciæ, the Sternocleidomastoideus, the superior belly of the Omohyoideus, the Sternohyoideus and Sternothyreoideus, and beneath the last muscle by the pretracheal layer of the deep fascia, which forms a capsule for the gland. The deep or medial surface is moulded over the underlying structures, viz., the thyroid and cricoid cartilages, the trachea, the Constrictor pharyngis inferior and posterior part of the Cricothyreoideus, the esophagus (particularly on the left side of the neck), the superior and inferior thyroid arteries, and the recurrent nerves. The anterior border is thin, and inclines obliquely from above downward toward the middle line of the neck, while the posterior border is thick and overlaps the common carotid artery, and, as a rule, the parathyroids.

  The isthmus (isthmus gl. thyreoidea) connects together the lower thirds of the lobes; it measures about 1.25 cm. in breadth, and the same in depth, and usually covers the second and third rings of the trachea. Its situation and size present, however, many variations. In the middle line of the neck it is covered by the skin and fascia, and close to the middle line, on either side, by the Sternothyreoideus. Across its upper border runs an anastomotic branch uniting the two superior thyroid arteries; at its lower border are the inferior thyroid veins. Sometimes the isthmus is altogether wanting.

  A third lobe, of conical shape, called the pyramidal lobe, frequently arises from the upper part of the isthmus, or from the adjacent portion of either lobe, but most commonly the left, and ascends as far as the hyoid bone. It is occasionally quite detached, or may be divided into two or more parts.

  A fibrous or muscular band is sometimes found attached, above, to the body of the hyoid bone, and below to the isthmus of the gland, or its pyramidal lobe. When muscular, it is termed the Levator glandulæ thyreoideæ.

  Small detached portions of thyroid tissue are sometimes found in the vicinity of the lateral lobes or above the isthmus; they are called accessory thyroid glands (glandulæ thyreoideæ accessoriæ).

Development.—The thyroid gland is developed from a median diverticulum, which appears about the fourth week on the summit of the tuberculum impar, but later is found in the furrow immediately behind the tuberculum. It grows downward and backward as a tubular duct, which bifurcates and subsequently subdivides into a series of cellular cords, from which the isthmus and lateral lobes of the thyroid gland are developed. The ultimo-branchial bodies from the fifth pharyngeal pouches are enveloped by the lateral lobes of the thyroid gland; they undergo atrophy and do not form true thyroid tissue. The connection of the diverticulum with the pharynx is termed the thyroglossal duct; its continuity is subsequently interrupted, and it undergoes degeneration, its upper end being represented by the foramen cecum of the tongue, and its lower by the pyramidal lobe of the thyroid gland.

Structure.—The thyroid gland is invested by a thin capsule of connective tissue, which projects into its substance and imperfectly divides it into masses of irregular form and size. When the organ is cut into, it is of a brownish-red color, and is seen to be made up of a number of closed vesicles, containing a yellow glairy fluid, and separated from each other by intermediate connective tissue.

  The vesicles of the thyroid of the adult animal are generally closed spherical sacs; but in some young animals, e. g., young dogs, the vesicles are more or less tubular and branched. This appearance is supposed to be due to the mode of growth of the gland, and merely indicates that an increase in the number of vesicles is taking place. Each vesicle is lined by a single layer of cubical epithelium. There does not appear to be a basement membrane, so that the epithelial cells are in direct contact with the connective-tissue reticulum which supports the acini. The vesicles are of various sizes and shapes, and contain as a normal product a viscid, homogeneous, semifluid, slightly yellowish, colloid material; red corpuscles are found in it in various stages of disintegration and decolorization, the yellow tinge being probably due to the hemoglobin, which is thus set free from the colored corpuscles. The colloid material contains an iodine compound, iodothyrin, and is readily stained by eosin. According to Bensley the thyroid gland prepares and secretes into the vascular channels a substance, formed under normal conditions in the outer pole of the cell and excreted from it directly without passing by the indirect route through the follicular cavity. In addition to this direct mode of secretion there is an indirect mode which consists in the condensation of the secretion into the form of droplets, having high content of solids, and the extension of these droplets into the follicular cavity. These droplets are formed in the same zone of the cell as that in which the primary or direct secretion is formed.

  This internal secretion of the thyroid is supposed to contain a specific hormone which acts as a chemical stimulus to other tissues, increasing their metabolism.

Vessels and Nerves.—The arteries supplying the thyroid gland are the superior and inferior thyroids and sometimes an additional branch (thyroidea ima) from the innominate artery or the arch of the aorta, which ascends upon the front of the trachea. The arteries are remarkable for their large size and frequent anastomoses. The veins form a plexus on the surface of the gland and on the front of the trachea; from this plexus the superior, middle, and inferior thyroid veins arise; the superior and middle end in the internal jugular, the inferior in the innominate vein. The capillary bloodvessels form a dense plexus in the connective tissue around the vesicles, between the epithelium of the vesicles and the endothelium of the lymphatics, which surround a greater or smaller part of the circumference of the vesicle. The lymphatic vessels run in the interlobular connective tissue, not uncommonly surrounding the arteries which they accompany, and communicate with a net-work in the capsule of the gland; they may contain colloid material. They end in the thoracic and right lymphatic trunks. The nerves are derived from the middle and inferior cervical ganglia of the sympathetic.

The parathyroid glands are small brownish-red bodies, situated as a rule between the posterior borders of the lateral lobes of the thyroid gland and its capsule. They differ from it in structure, being composed of masses of cells arranged in a more or less columnar fashion with numerous intervening capillaries. They measure on an average about 6 mm. in length, and from 3 to 4 mm. in breadth, and usually present the appearance of flattened oval disks. They are divided, according to their situation, into superior and inferior. The superior, usually two in number, are the more constant in position, and are situated, one on either side, at the level of the lower border of the cricoid cartilage, behind the junction of the pharynx and esophagus. The inferior, also usually two in number, may be applied to the lower edge of the lateral lobes, or placed at some little distance below the thyroid gland, or found in relation to one of the inferior thyroid veins.

Development.—The parathyroid bodies are developed as outgrowths from the third and fourth branchial pouches. A pair of diverticula arise from the fifth branchial pouch and form what are termed the ultimo-branchial bodies these fuse with the thyroid gland, but probably contribute no true thyroid tissue.

Structure.—Microscopically the parathyroids consist of intercommunicating columns of cells supported by connective tissue containing a rich supply of blood capillaries. Most of the cells are clear, but some, larger in size, contain oxyphil granules. Vesicles containing colloid have been described as occurring in the parathyroid, but the observation has not been confirmed.

  No doubt the parathyroid glands produce an internal secretion essential to the well-being of the human economy; but it is still a matter of dispute what symptoms of disease are produced by their removal and suppression of their secretion. Pepere believes that they show signs of exceptional activity during pregnancy, and that parathyroid insufficiency is a main factor in the production of tetany in infants and adults, of eclampsia, and of certain sorts of fits. It is probable that the tetany following parathyroidectomy is due to the accumulation of ammonium carbonate and Kendall has suggested that the function of the parathyroid is to convert ammonium carbonate into urea.

The Thymus is a temporary organ, attaining its largest size at the time of puberty (Hammar), when it ceases to grow, gradually dwindles, and almost disappears. If examined when its growth is most active, it will be found to consist of two lateral lobes placed in close contact along the middle line, situated partly in the thorax, partly in the neck, and extending from the fourth costal cartilage upward, as high as the lower border of the thyroid gland. It is covered by the sternum, and by the origins of the Sternohyoidei and Sternothyreoidei. Below, it rests upon the pericardium, being separated from the aortic arch and great vessels by a layer of fascia. In the neck it lies on the front and sides of the trachea, behind the Sternohyoidei and Sternothyreoidei. The two lobes generally differ in size; they are occasionally united, so as to form a single mass; and sometimes separated by an intermediate lobe. The thymus is of a pinkish-gray color, soft, and lobulated on its surfaces. It is about 5 cm. in length, 4 cm. in breadth below, and about 6 mm. in thickness. At birth it weighs about 15 grams, at puberty it weighs about 35 grams; after this it gradually decreases to 25 grams at twentyfive years, less than 15 grams at sixty, and about 6 grams at seventy years.

Development.—The thymus appears in the form of two flask-shaped entodermal diverticula, which arise, one on either side, from the third branchial pouch and extend lateralward and backward into the surrounding mesoderm in front of the ventral aortæ. Here they meet and become joined to one another by connective tissue, but there is never any fusion of the thymus tissue proper. The pharyngeal opening of each diverticulum is soon obliterated, but the neck of the flask persists for some time as a cellular cord. By further proliferation of the cells lining the flask, buds of cells are formed, which become surrounded and isolated by the invading mesoderm. In the latter, numerous lymphoid cells make their appearance, and are agregated to form lymphoid follicles. These lymphoid cells are probably derivatives of the entodermal cells which lined the original diverticula and their subdivisions. Additional portions of thymus tissue are sometimes developed from the fourth branchial pouches. Thymus continues to grow until the time of puberty and then begins to atrophy.

Structure.—Each lateral lobe is composed of numerous lobules held together by delicate areolar tissue; the entire gland being enclosed in an investing capsule of a similar but denser structure. The primary lobules vary in size from that of a pin’s head to that of a small pea, and are made up of a number of small nodules or follicles, which are irregular in shape and are more or less fused together, especially toward the interior of the gland. Each follicle is from 1 to 2 mm. in diameter and consists of a medullary and a cortical portion, and these differ in many essential particulars from each other. The cortical portion is mainly composed of lymphoid cells, supported by a network of finely branched cells, which is continuous with a similar network in the medullary portion. This network forms an adventitia to the bloodvessels. In the medullary portion the reticulum is coarser than in the cortex, the lymphoid cells are relatively fewer in number, and there are found peculiar nest-like bodies, the concentric corpuscles of Hassall. These concentric corpuscles are composed of a central mass, consisting of one or more granular cells, and of a capsule which is formed of epithelioid cells. They are the remains of the epithelial tubes which grow out from the third branchial pouches of the embryo to form the thymus.

  Each follicle is surrounded by a vascular plexus, from which vessels pass into the interior, and radiate from the periphery toward the center, forming a second zone just within the margin of the medullary portion. In the center of the medullary portion there are very few vessels, and they are of minute size.

  Watney has made the important observation that hemoglobin is found in the thymus, either in cysts or in cells situated near to, or forming part of, the concentric corpuscles. This hemo globin occurs as granules or as circular masses exactly resembling colored blood corpuscles. He has also discovered, in the lymph issuing from the thymus, similar cells to those found in the gland, and, like them, containing hemoglobin in the form of either granules or masses. From these facts he arrives at the conclusion that the gland is one source of the colored blood corpuscles. More recently Schaffer has observed actual nucleated red-blood corpuscles in the thymus. The function of the thymus is obscure. It seems to furnish during the period of growth an internal secretion concerned with some phases of body metabolism, especially that of the sexual glands.

Vessels and Nerves.—The arteries supplying the thymus are derived from the internal mammary, and from the superior and inferior thyroids. The veins end in the left innominate vein, and in the thyroid veins. The lymphatics are described on page 698. The nerves are exceedingly minute; they are derived from the vagi and sympathetic. Branches from the descendens hypoglossi and phrenic reach the investing capsule, but do not penetrate into the substance of the gland.

The hypophysis (pituitary body) is a small reddish-gray body, about 1 cm. in diameter, attached to the end of the infundibulum of the brain and resting in the hypophyseal fossa.

  The hypophysis consists of an anterior and a posterior lobe, which differ from one another in their mode of development and in their structure. The anterior lobe is the larger and is somewhat kidney-shaped, the concavity being directed backward and embracing the posterior lobe. It consists of a pars anterior and a pars intermedia, separated from each other by a narrow cleft, the remnant of the pouch or diverticulum. The pars anterior is extremely vascular and consists of epithelial cells of varying size and shape, arranged in cord-like trabeculæ or alveoli and separated by large, thin-walled bloodvessels. The pars intermedia is a thin lamina closely applied to the body and neck of the posterior lobe and extending onto the neighboring parts of the brain; it contains few bloodvessels and consists of finely granular cells between which are small masses of colloid material. The pars intermedia in spite of the fact that it arises in common with the pars anterior from the ectoderm of the primitive buccal cavity is often considered as a part of the posterior lobe which arises from the floor of the third ventricle of the brain. Although of nervous origin the posterior lobe contains no nerve cells or fibers. It consists of neuroglia cells and fibers and is invaded by columns which grow into it from the pars intermedia; imbedded in it are large quantities of a colloid substance histologically similar to that found in the thyroid gland. In certain of the lower vertebrates, e.g., fishes, nervous structures are present, and the lobe is of large size.

  From the pars intermedia a substance, no doubt an internal secretion, causes constriction of the bloodvessels with rise of arterial blood-pressure. This substance seems to have a stimulating effect on most of the smooth muscles, acting directly upon the muscle causing contraction. It also increases the secretion of the urine; of the mammary glands when in functional activity; and of the cerebrospinal fluid. Extracts of this lobe also influence the general metabolism of the carbohydrates by accelerating the process of glycogenolysis in the liver.

  The pars anterior exercises a stimulating effect on the growth of the skeleton and probably on connective tissues in general.

  Enlargement of the hypophysis and of the cavity of the sella turcica are found in the rare disease acromegaly, which is characterized by gradual enlargement of the face, hands, and feet, with headache and often a peculiar type of blindness. This blindness is due to the pressure of the enlarging hypophysis on the optic chiasma.

Development of the Hypophysis Cerebri.—This in the adult consists of a large anterior, consisting of the pars anterior and the pars intermedia, and a small posterior lobe: the former is derived from the ectoderm of the stomodeum, the latter from the floor of the fore-brain. About the fourth week there appears a pouchlike diverticulum of the ectodermal lining of the roof of the stomodeum. This diverticulum, pouch of Rathke, is the rudiment of the anterior lobe of the hypophysis; it extends upward in front of the cephalic end of the notochord and the remnant of the buccopharyngeal membrane, and comes into contact with the under surface of the fore-brain. It is then constricted off to form a closed vesicle, but remains for a time connected to the ectoderm of the stomodeum by a solid cord of cells. Masses of epithelial cells form on either side and in the front wall of the vesicle, and by the growth between these of a stroma from the mesoderm the development of the anterior lobe is completed. The upwardly directed hypophyseal involution becomes applied to the antero-lateral aspect of a downwardly directed diverticulum from the base of the fore-brain. This diverticulum constitutes the future infundibulum in the floor of the third ventricle while its inferior extremity becomes modified to form the posterior lobe of the hypophysis. In some of the lower animals the posterior lobe contains nerve cells and nerve fibers, but in man and the higher vertebrates these are replaced by connective tissue. A canal, craniopharyngeal canal, is sometimes found extending from the anterior part of the fossa hypophyseos of the sphenoid bone to the under surface of the skull, and marks the original position of Rathke’s pouch; while at the junction of the septum of the nose with the palate traces of the stomodeal end are occasionally present (Frazer).

The pineal body (epiphysis) is a small reddish-gray body, about 8 mm. in length which lies in the depression between the superior colliculi. It is attached to the roof of the third ventricle near its junction with the mid-brain. It develops as an outgrowth from the third ventricle of the brain.

  In early life it has a glandular structure which reaches its greatest development at about the seventh year. Later, especially after puberty, the glandular tissue gradually disappears and is replaced by connective tissue.

Structure.—The pineal body is destitute of nervous substance, and consists of follicles lined by epithelium and enveloped by connective tissue. These follicles contain a variable quantity of gritty material, composed of phosphate and carbonate of calcium, phosphate of magnesium and ammonia, and a little animal matter.

  It contains a substance which if injected intravenously causes fall of blood-pressure. It seems probable that the gland furnishes an internal secretion in children that inhibits the development of the reproductive glands since the invasion of the gland in children, by pathological growths which practically destroy the glandular tissue, results in accelerated development of the sexual organs, increased growth of the skeleton and precocious mentality.

Chromaphil or chromaffin cells, so-called because they stain yellow or brownish with chromium salts, are associated with the ganglia of the sympathetic nervous system.

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 medullary portions of the suprarenal glands and the glomus caroticum belong to the chromaphil system.

the Suprarenal Glands (Glandulæ Suprarenalis; Adrenal Capsule) 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.

Relations.—The relations of the suprarenal glands differ on the two sides of the body.

  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: 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 lymphatics end in the lumbar glands.

  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.

  Each is invested by a fibrous capsule and consists largely of spherical or irregular masses of cells, 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.

Glomus Coccygeum (Coccygeal Gland or Body; Luschka’s 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, 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.