Corpus: Adrenal gland

The adrenal glands are endocrine glands that typically sit like caps on top of each kidney, separated by a thin layer of fat.

The adrenal glands are located in the retroperitoneal space, positioned above the upper part of each kidney within a shared capsule. Anatomically, they appear almost pyramid-shaped, with the left adrenal gland having a more crescent-shaped profile and the right one appearing more triangular. Each gland measures approximately 5 cm in length and 3 cm in width, with an average weight of 5 to 10 grams.

The arterial supply to both adrenal glands comes from three main vessels:

• Superior adrenal artery: branch of the inferior phrenic artery
• Middle adrenal artery: direct outlet of the abdominal aorta
• Inferior adrenal artery: branch of the renal artery

The venous drainage of the adrenal glands occurs through the short, paired adrenal veins. The right adrenal vein drains directly into the inferior vena cava, while the left adarenal vein drains into the renal vein. Additionally, the left adrenal vein often has an anastomosis with the inferior phrenic vein.

3.1. Adrenal cortex

The adrenal cortex, located beneath the connective tissue capsule (capsula fibrosa) of the adrenal gland, can be divided into three distinct layers from the outermost to the innermost:

• Zona glomerulosa: Composed of acidophilic cells arranged in a ball-like structure, this layer produces mineralocorticoids, primarily aldosterone, in response to decreased sodium levels or increased potassium levels.
• Zona fasciculata: This broadest layer consists of large, lipid-containing cells arranged in columns, also known as spongiocytes. Blood capillaries, expanded into sinusoids, are found between these cell strands. The zona fasciculata primarily produces glucocorticoids, such as cortisone and cortisol.
• Zona reticularis: Composed of pigment-containing cell strands arranged in a network (reticular pattern), this layer produces androgens, particularly dehydroepiandrosterone (DHEA).

3.2. Adrenal medulla

The adrenal medulla contains specialized chromaffin cells, which are functionally modified sympathetic neurons. These cells are classified into two types:

• A-cells (80 %): These cells produce adrenaline
• N-cells (20 %): These cells produce noradrenaline

The adrenal gland is composed of two functionally and histologically distinct parts. The adrenal cortex originates from the mesoderm of the coelomic epithelium, with its development beginning around the 5th week of pregnancy. During further development, cells from the neuroectoderm migrate into the adrenal cortex, eventually becoming completely enclosed within it to form the adrenal medulla.

The adrenal gland comprises two distinct endocrine glands. The adrenal cortex synthesizes steroid hormones, primarily mineralocorticoids, glucocorticoids, and sex hormones. In contrast, the adrenal medulla functions as a modified peripheral sympathetic ganglion, releasing the neurohormones noradrenaline and adrenaline.

Adrenal cortical activity is regulated by the hypothalamic-pituitary-adrenal (HPA) axis. Adrenocorticotropic hormone (ACTH), produced in the pituitary gland, stimulates the adrenal cortical cells, which possess specific ACTH receptors (MC2R). The release of ACTH follows a circadian rhythm, with significantly higher concentrations in the morning than in the evening. Consequently, the levels of steroid hormones produced by the adrenal cortex also fluctuate throughout the day, reflecting this rhythm.

The adrenal gland can be affected by numerous diseases, including both endocrine hyperfunctions and hypofunctions in nearly all of its secreting systems. Tumors, particularly of the medulla such as pheochromocytomas, can also develop. These tumors can cause excessive release of adrenaline and noradrenaline, leading to dangerous blood pressure crises.

Endocrine diseases caused by adrenal gland malfunctions include:

• Cushing's disease
• Conn's disease
• Addison's disease

• "GFR": from outside to inside zona glomerulosa, fasciculata, reticularis.
• "Salt, Sugar, Sex - the deeper you go, the better it gets": for the various synthesis products of the adrenal cortex — mineralocorticoids, glucocorticoids, and androgen precursors.