The outer zona glomerulosa, which is made up of whorls of cells, merges into the zona fasciculata formed of columns of cells with prominent venous sinuses. The cortex consists of three distinct zones. Ninety per cent of the cells are of the epi-nephrine-secreting type. Two cell types are found: larger cells with fewer granules that secrete epinephrine, and smaller cells with numerous dense vesicles that secrete norepinephrine. There are numerous venous sinuses separating the cells. It consists of interlacing cords of densely innervated cells which contain granules. Preganglionic sympathetic nerve fibres that release acetylcholine richly innervate the adrenal medulla. Blood is drained through a single adrenal vein that leaves at the hilum of the gland to join the inferior vena cava. These arteries form a plexus on the capsule of the gland and blood flows through sinusoids to the medulla. The adrenal gland derives its blood supply from three blood vessels: a direct branch from the aorta, one from a branch of the phrenic artery and one from the renal artery. In keeping with all the other endocrine glands, the adrenals are richly vascularized. The cortex and medulla have different embryological origins, the cortex from mesoderm and the medulla from the neural crest. Medullary tissue may also be found at extra-adrenal sites along the course of the abdominal aorta. The adrenal glands are situated at the superior poles of each kidney and may be thought of as two separate glands: an outer cortex and the inner medulla.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |