Adrenal Physiology
Understanding structure and function.
Adrenal glands, also called suprarenal glands, are triangle-shaped glands on top of the kidneys.
Adrenal glands produce hormones that help regulate your metabolism, immune system, blood pressure, response to stress and other essential functions. The adrenal glands are controlled in part by the brain.
The adrenal gland is made up of the cortex and medulla. The cortex produces steroid including glucocorticoids, mineralocorticoids, and adrenal androgens, and the medulla produces the catecholamines, epinephrine, and norepinephrine.
Image 1: The kidney (including the surrounding fibrous tissue and fat layer, the renal pelvis, and the ureter) and the adrenal gland, as well as a close-up view of the renal pelvis.
Adrenal Cortex
The following hormones are produced by the adrenal cortex.
- Cortisol (glucocorticoid hormone) controls the use of carbohydrates, proteins, and fats by the body. It regulates blood pressure, blood glucose, and decreases bone formation. Cortisol also helps in the suppression of inflammation in the body.
- Aldosterone (mineralocorticoid hormone) regulates blood pressure and blood pH levels. The hormone regulates electrolytes, such as sodium and potassium, in the blood to maintain blood pH.
- Androgenic steroids and DHEA help in the production of sex hormones.
Image 2: Both adrenal glands sit atop the kidneys and are composed of an outer cortex and an inner medulla, all surrounded by a connective tissue capsule. The cortex can be subdivided into additional zones, all of which produce different types of hormones
Adrenal Medulla
Adrenaline (epinephrine) and noradrenaline (norepinephrine) are hormones produced by the adrenal medulla. These play a crucial role in stress response and regulate blood pressure and heart rate. They also function as neurotransmitters.
Image 3: A flow diagram showing the process of stimulation of adrenal medulla that makes it release adrenaline that further acts on adrenoreceptors leading to increased sympathetic activity.
Hormonal Regulation
The body controls the levels of corticosteroids according to need. The levels tend to be much higher early in the morning than later in the day. When the body is stressed from illness or otherwise, the levels of corticosteroids increase dramatically.
The job of the hypothalamus is to wake up the pituitary gland. Although the pituitary is only about the size of a small pea, it has a mighty job. The pituitary releases hormones, which are the messengers in the stress–response system. These hormones travel out of the brain to the adrenal glands. The adrenal glands release cortisol, the stress hormone, or messenger that is part of the hypothalamic pituitary adrenal axis (HPA).
Image 4: The hypothalamic-pituitary-adrenal axis integrates and mediates the stress response.
The Renin-angiotensin-aldosterone system (RAAS)
This is a hormone system within the body that is essential for the regulation of blood pressure and fluid balance. Comprised of the three hormones renin, angiotensin II and aldosterone. The RAAS is regulated mostly by the kidneys and rate of renal blood flow). The RAAS causes the adrenal glands to produce more or less aldosterone.
Image 5: The Renin-angiotensin-aldosterone system (RAAS)