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ADRENAL
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ADRENAL GLANDS may be either median or paired, and, as they are placed between the kidneys, are often spoken of as interrenals. In the See also:Amphibia The adrenal glands or suprarenal capsules are two conical the glands are sunk into the See also:surface of the See also:kidney. In See also:reptiles and bodies, flattened from before backward, resting on the upper birds they are See also:long lobulated bodies lying See also:close to the testis or ovary poles of the kidneys close to the sides of the vertebral See also:column; and receiving an adrenal portal vein. In the See also:lower mammals they are not as closely connected with the kidneys as they are in See also:man, each has an anterior and posterior surface and a See also:concave See also:base and their shape is usually See also:oval or spherical which is in contact with the kidney. When viewed from in front the right gland is triangular and the See also:left crescentic. On THE See also:THYROID GLAND the anterior surface there is a transverse sulcus or hilum from which a large vein emerges. The See also:arteries are less See also:constant in The thyroid See also:body or gland is a deep red glandular See also:mass See also:con-their points of entry, and are derived from three See also:sources, the sisting of two lobes which See also:lie one on each See also:side of the upper See also:part phrenic, the abdominal aorta and the renal arteries. The glands of the trachea and lower part of the larynx; these are joined are entirely retro-peritoneal, though the right one, even on its across the See also:middle See also:line by the See also:isthmus which lies in front of the anterior surface,, is very little covered by peritoneum. In a second and third rings of the trachea. Occasionally, from the See also:vertical transverse See also:section each gland is seen to consist of two See also:top of the isthmus, a nearly but not quite median pyramidal See also:lobe parts, cortical and medullary. The cortical substance is See also:corn- runs up toward the hyoid See also:bone, while in other cases the isthmus posed of bundles of cells, separated by a stroma, which have a I may be absent. The gland is relatively larger in See also:women and A B See also:children than in the adult male. It is enclosed in a See also:capsule of cervical See also:fascia and is supplied by the See also:superior and inferior thyroid arteries on each side, though occasionally a median thyroidea ima artery is See also:present. On microscopical examination the gland shows a large number of closed tubular alveoli, lined by columnar See also:epithelial cells, unsupported by a See also:basement membrane, and filled with colloid or jelly-like material. These are supported by fibrous septa growing in from the true capsule, which is distinct from the capsule of cervical fascia. The lymphatic vessels are large and numerous, and have been shown by E. C. See also:Bober (Phil. Trans., 1881) to contain the same colloid material as the alveoli. See also:Accessory thyroids, close to the See also:main gland, are often found. See also:Embryology.—The median part of the gland is See also:developed from a See also:tube which grows down in the middle line from the junction of the buccal and pharyngeal parts of the See also:tongue (q.v.), between the first and second branchial See also:arches. This tube is called the thyro-glossal duct and is entodermal in origin. The development of the hyoid bone obliterates the middle part of the duct, leaving its upper part as the foramen caecum of the tongue, while its lower part bifurcates, and so the asymmetrical arrangement of the pyramidal lobe is accounted for. A. Kanthack (J. Anat. and Phys. vol. See also:xxv., 1891) has denied the existence of this duct, but on slender grounds. The lateral parts of the gland are developed from the entoderm of the See also:fourth visceral clefts, and, joining the median part, lose their pharyngeal connexion. Nearly, but not quite, the whole of the lateral lobes probably belong to this part. (For literature and further details see See also:Quain's See also:Anatomy, See also:London, 1892, and J. P. McMurrich's Development of the Human Body, London, 1906.) See also:Comparative Anatomy.—The endostyle or hypobranchial groove of See also:Tunicata (See also:sea squirts) and See also:Acrania (See also:Amphioxus) is regarded as the first See also:appearance of the median thyroid; this is a median entodermal groove in the See also:floor of the pharynx, secreting a glairy fluid in which See also:food particles become entangled and so pass into the See also:intestine. In the larval See also:lamprey (Ammocoetes) among the See also:Cyclostomata the connexion with the pharynx is present, but in the adult lamprey (Petromyzon), as in all adult vertebrates, this connexion is lost. In the Elasmobranchs the single median thyroid lies close to the mandibular symphysis, but in the bony See also:fish (Teleostei) it is paired. In the mud fish (Dipnoi) there is also an indication of a See also:division into two lobes. In the Amphibia the thyroid forms numerous vesicles close to the anterior end of the pericardium. In Reptilia it lies close to the trachea, and in the Chelonia and Crocodilia is paired. In birds it is also paired and lies near the origin of the See also:carotid arteries. In See also:Mammalia the lateral lobes make their first appearance. In the lower orders of this class the isthmus is often absent. (For further details and literature see R. Additional information and CommentsThere are no comments yet for this article.
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