<unk> s, anterior (left) and posterior (right) surface. The<unk> s are located on both sides of the body in the retroperitoneum, above and slightly medial to the kidneys. In humans, the right<unk>  is pyramidal in shape, whereas the left is semilunar or crescent shaped and somewhat larger. The<unk> s measure approximately 5 cm in length, 3 cm in width, and up to 1 cm in thickness. Their combined weight in an adult human ranges from 7 to 10 grams. The glands are yellowish in colour. The<unk> s are surrounded by a fatty capsule and lie within the renal fascia, which also surrounds the kidneys. A weak septum (wall) of connective tissue separates the glands from the kidneys. The<unk> s are directly below the diaphragm, and are attached to the crura of the diaphragm by the renal fascia. Each<unk>  has two distinct parts, each with a unique function, the outer adrenal cortex and the inner medulla, both of which produce hormones. Adrenal cortex under the microscope, showing its different layers. From the surface to the center: zona glomerulosa, zona fasciculata, zona reticularis, medulla. In the medulla, the central adrenomedullary vein is visible. The adrenal cortex is the outer region and also the largest part of an<unk> . It is divided into three separate zones: zona glomerulosa, zona fasciculata and zona reticularis. Each zone is responsible for producing specific hormones. The adrenal cortex is the outermost layer of the<unk> . Within the cortex are three layers, called "zones". When viewed under a microscope each layer has a distinct appearance, and each has a different function. The adrenal cortex is devoted to production of hormones, namely aldosterone, cortisol, and androgens. Zona glomerulosa The outermost zone of the adrenal cortex is the zona glomerulosa. It lies immediately under the fibrous capsule of the gland. Cells in this layer form oval groups, separated by thin strands of connective tissue from the fibrous capsule of the gland and carry wide capillaries. This layer is the main site for production of aldosterone, a mineralocorticoid, by the action of the enzyme aldosterone synthase. Aldosterone plays an important role in the long-term regulation of blood pressure. Zona fasciculata The zona fasciculata is situated between the zona glomerulosa and zona reticularis. Cells in this layer are responsible for producing glucocorticoids such as cortisol. It is the largest of the three layers, accounting for nearly 80% of the volume of the cortex. In the zona fasciculata, cells are arranged in columns radially oriented towards the medulla. Cells contain numerous lipid droplets, abundant mitochondria and a complex smooth endoplasmic reticulum. Zona reticularis The innermost cortical layer, the zona reticularis, lies directly adjacent to the medulla. It produces androgens, mainly dehydroepiandrosterone (DHEA), DHEA sulfate (DHEA-S), and androstenedione (the precursor to testosterone) in humans. Its small cells form irregular cords and clusters, separated by capillaries and connective tissue. The cells contain relatively small quantities of cytoplasm and lipid droplets, and sometimes display brown lipofuscin pigment. Medulla The adrenal medulla is at the centre of each<unk> , and is surrounded by the adrenal cortex. The chromaffin cells of the medulla are the body's main source of the catecholamines, such as adrenaline and noradrenaline, released by the medulla. Approximately 20% noradrenaline (norepinephrine) and 80% adrenaline (epinephrine) are secreted here. The adrenal medulla is driven by the sympathetic nervous system via preganglionic fibers originating in the thoracic spinal cord, from vertebrae T5–T11. Because it is innervated by preganglionic nerve fibers, the adrenal medulla can be considered as a specialized sympathetic ganglion. Unlike other sympathetic ganglia, however, the adrenal medulla lacks distinct synapses and releases its secretions directly into the blood. Blood supply The<unk> s have one of the greatest blood supply rates per gram of tissue of any organ: up to 60 small arteries may enter each gland. Three arteries usually supply each<unk> : * The superior suprarenal artery, a branch of the inferior phrenic artery * The middle suprarenal artery, a direct branch of the abdominal aorta * The inferior suprarenal artery, a branch of the renal artery These blood vessels supply a network of small arteries within the capsule of the<unk> s. Thin strands of the capsule enter the glands, carrying blood to them. Venous blood is drained from the glands by the suprarenal veins, usually one for each gland: * The right suprarenal vein drains into the inferior vena cava * The left suprarenal vein drains into the left renal vein or the left inferior phrenic vein. The central adrenomedullary vein, in the adrenal medulla, is an unusual type of blood vessel. Its structure is different from the other veins in that the smooth muscle in its tunica media (the middle layer of the vessel) is arranged in conspicuous, longitudinally oriented bundles. Variability The<unk> s may not develop at all, or may be fused in the midline behind the aorta. These are associated with other congenital abnormalities, such as failure of the kidneys to develop, or fused kidneys. The gland may develop with a partial or complete absence of the cortex, or may develop in an unusual location.
Adrenal gland
Adrenal cortex
Pituitary gland
Kidney
Liver
Ovary
Breast
Callus