The adrenal gland consists of 2 main parts:1. an outer cortex which secretes several classes of steroid hormones;
2. an inner medulla which is the source of the catecholamines epinephrine and norepinephrine.The adrenal also has a thin outer fibrous capsule which can vary in thickness from gland to gland, and in some cases, even within the same gland.
The outer cortex has separate embryological origin and is distinct in its function and structure. The hormones produced by the cortex have a steroid infrastructure. The inner medulla which only accounts for 10% by weight produces catecholamines.Courtesy of: Ashley Davidoff, M.D.
When the adrenal gland is reviewed under the microscope, three different layers are identified in the cortex and one layer in the medulla. In the following images the yellow and orange layers represent the cortical layers and the red represents the medulla.
This image shows the relative volume of cortex (in yellow and orange) to the lesser volume of medulla (red).Courtesy of: Ashley Davidoff, M.D.
The cortex is divided into the 3 zones based on the arrangement of cells.
zona glomerulosa is the outer most rounded groups of cell.
zona fasciculata, is the middle column of cells and arranged radially.
zona reticularis is the innermost irregularly arranged cylindrical masses of cells.
“GFR” is a good pneumonic to remember. It stands for glomerular filtration rate but also stands for the three layers, from outer to inner, – glomerulosa, fasciculata, and reticularis.
The outermost of the three layers of cortex is the zona glomerulosa which consists of rounded groups of cells. The middle and largest layer is the zona fasciculata, in which the cells are radially arranged. The zona reticularis, is the innermost layer and is made of irregularly arranged cylindrical masses of cells. Remember the pneumonic “GFR” = from outer to inner glomerulosa, fasciculata, and reticularis.Courtesy of: Ashley Davidoff, M.D.
Parts – Functional
The outermost layer, the zona glomerulosa produces aldosterone. The middle layer of the cortex produces cortisol, and the inner layer produces androgens. The medulla produces adrenaline, a type of catecholamine.Courtesy of: Ashley Davidoff, M.D.Aldosterone is responsible for water and salt balance which in turn is intimately related to blood pressure control. Cortisol, is responsible for responding to physically stressful situations. Androgens are responsible for developing male characteristics. The medulla produces adrenaline which is responsible for urgent “fight or flight” situations.Courtesy of: Ashley Davidoff, M.D.
Anatomy and Physiology of the Adrenal Glands: Parts – Imaging
In imaging it is usually not possible to differentiate between the cortex and the medulla, and we divide the adrenal into the medial and lateral limbs which are joined together at the apex of the gland.
In this image we have been able to identify each of the four limbs that make up the two adrenal glands. Each has a medial and a lateral limb joined together at the apex. The left adrenal vein is noted as the blue overlay.Courtesy of: Ashley Davidoff, M.D.In this early arterial phase, there appear to be a number of layers in the left adrenal. We have interpreted them as the cortex and medulla as seen in the yellow and red overlay. With the advancing multidetector technology, the distinction between cortex and medulla may be uncovered. This is an exciting prospect!Courtesy of: Ashley Davidoff, M.D.
