These little glands are kind of pyramid shaped and situated on top of your kidneys, far back in your abdominal cavity, on each side of the spine. They share the space in between the retroperitoneum – the connective tissue that makes up the inner layer of the abdominal cavity, and the ribcage. Together they weigh about 10 g, but their actions are so much heavier!
They are very important actors in the endocrine (hormonal) system and have effects literally all over the body.
They consist of four layers; three outer ones, that together make up the cortex and one inner, making up the medulla, or the core. The cortex and medulla have different origins. The medulla is a part the Sympathetic Nervous system, which is one side of the coin that makes up the Autonomous Nervous System (ANS). It is actually a nerve bundle (ganglion) that secrets it’s signal substances (neurotransmitters) directly into the blood instead of connecting with another nerve cell as in the rest of the nervous system.
The cortex has the same origin as the cells making up the peritoneum and it surrounds the medulla completely The cortex secrets different types of steroid hormones.
The layers and their functions, from outside and in:
- Zona glomerulosa – The cells here produce aldosterone, a mineralocorticoid, that has a major role in regulating blood pressure and salt balance in the body. It has it’s main effects on the kidney and makes them save sodium and secrete potassium, hydrogen and magnesium. The re-uptake of sodium pulls water with it and through that blood pressure raises. Aldosterone also affects the large intestine and the sweat glands to hold on to sodium.
- Zona fasciulata – Glucocorticoids are secreted from these cells, the most known one being cortisol. This is a stress hormone, that has profound effects on the body. It releases glucose, sugar, into the blood and aids in the metabolism of fat, protein and carbohydrates in the cells. All to make more energy available for the fight or flight (stress) response. Cortisol suppresses the immune system, and various synthetic forms of this hormone is used for treating inflammatory diseases.
It also decreases the formation of bone.
- Zona reticularis – Androgens, Dehydroepiandrosterone (DHEA) (the precursor to the female sex hormone estrogen), DHEA sulfate and androstendion (the precursor to testosterone).
- Medulla – Since this is a direct extension of the ANS the neurotransmitters epinehprine and norepinehprine (catecholamines) are secreted from here. They are huge mediators of the immediate stress response of the body, the “fight-or-flight” system, and affects pretty much every tissue. Depending on the amount of epinehprine and the receptor type, the effects vary.
The over all result of catecholamine stimulation is
- increased heart rate and blood pressure
- direction of blood to the muscles and away from the gastrointestinal tract and the skin
- raising of blood glucose through inhibition of insulin and stimulation of glucacon
- secretion of ACTH, which raises cortisol,
- increased lipolysis (breakdown of fat)
- muscle contraction
- increased respiratory rate.
Over all the perfect combination for fighting or running away. The muscles are ready, the skin has little ciruclation to keep eventual bleeding to a minimum, a lot of nutrients are easily available and is quickly pumped through the body and the blood is better oxygenated by the faster breathing.
The actions listed above are all normal physiologic responses to your environment and are meant to make your body ready for challenges and to protect itself.
When it comes to the layers in the cortex they are mostly regulated through a intricate feed-back system called the HPA (Hypothalamus-Pituitary-Adrenal) axis. The hypothalamus is a part of your brain and it receives information from the whole nervous system and sends orchestrates a myriad of hormonal and non-hormonal pathways in the body. To signal to the Adrenals it will send out CRH – Corticotropin Releasing Hormone to the Pituitary, a little gland situated at the base of your skull. That stimulates the pituitary to release ACTH (AdrenoCorticoTropic Hormone) into the blood, which will stimulate the release of the cortical hormones of the Adrenal glands, listed above, mostly affecting the release of cortisol. As the picture shows, there is a negative feedback loop, that sends information back to both the pituitary and the hypothalamus that the desired action has taken place, hormone has been released and the secretion of stimulating ACTH and CRH slows down. This is a very smart, self regulating system that the body uses to keep the delicate balance needed.
Physical activity, stress, illness, the levels of cortisol in the blood and the circadian rhythm (sleep-wake-cycle) influences the this axis.
The hormones also have effects on other hormonal systems like the thyroid, sex hormones etc.
These small structures play major roles in our bodies, orchestrating our stress response. Our bodies evolved to take care of immediate stress, like running away when hunted or being able to make that kill to provide food for the community.
The brain/body can not make out the difference between a real, outer threat or an internal stress. So even if there is no angry tiger chasing you through life, the stress response to feeling chased by work or life circumstances will elicit the same response.
The reactions to an immediate outer threat and the experiences that come with those reactions are the same as those described by people having an anxiety attack. Because it’s the same systems running.
Are you running through your life, feeling constantly stressed and chased? Then you are constantly pushing the on-button for this system.
It is about time all of us figure out how to switch it off and get the rest that was usually coming in between the short stressful events that a hunt or a run-a-way would be. We need the opposite of this, the “rest-and-digest” badly.