Adrenal Gland Health and Function in Dogs

Your Dog’s Adrenal Glands

The adrenal glands are a pair of small glands located in the abdominal space, near the left and right kidneys. They are so small that for centuries, they were ignored by anatomists!

The gland consists of two parts: an outer cortex and an inner medulla. These parts are composed of different cells and tissues, which originated from different embryonic structures, and have entirely different functions in relation to influencing metabolic pathways in the dog’s body.

The outer cortex is mostly yellow in appearance and has striations that are radially directed. The cortex is composed of three zones, namely the Zona Glomerulosa, Zona Fasciculata, and Zona Reticularis. Each zone is responsible for producing different hormones that play an important role in influencing functions and metabolic pathways in the body. The inner medulla, on the other hand, appears darker and more homogenous.

Adrenaline and Norepinephrine Production

The inner portion of the adrenal glands, called the medulla, is responsible for the production of two very important hormones when the dog is under severe and acute stress. The adrenal medulla is the main component responsible for the animal’s “fight or flight” response mechanism.

One of the hormones produced by the adrenal medulla is epinephrine, commonly known as adrenaline. This hormone is often considered the “fight or flight” hormone and plays an important role in influencing how the body responds to acute stress.

When a dog is subjected to a severely stressful condition, it stimulates the glands to produce adrenaline as a response. The hormone causes the animal’s heart rate to increase and force stronger cardiac contractions which help improve blood flow to the muscles and brain.

It also diverts energy consumption and blood flow from the gastrointestinal system to focus on the animal’s immediate need to either “fight or flee”. Stomach and intestinal activity slow down and stored glucose in the liver, in the form of glycogen, is converted back into glucose. This can provide an immediate source of energy for the dog should it be needed.

The second hormone produced by the adrenal gland’s inner medulla is norepinephrine, also known as noradrenaline. It’s also a hormone produced by the adrenal gland in response to stress. Norepinephrine stimulates the blood vessels to increase blood pressure and heart rate, much like adrenaline does. It also stimulates the dog’s central nervous system, making them more alert during the “fight or flight” mechanism.

Steroids and Other Hormones

As mentioned, the outer adrenal cortex has an entirely different function from the medulla. It produces a different set of hormones that have varying effects on the dog’s body. In general, the adrenal cortex is the main part responsible for the production of glucocorticoids and sex hormones. The cortex is divided into three layers or zones, each responsible for producing a specific metabolic hormone.

The outer zone, called the Zona Glomerulosa, produces and secretes mineralocorticoid hormone. Mineralocorticoids are a subgroup of corticosteroid hormones that are responsible for maintaining electrolyte balance in the dog’s body. The most potent mineralocorticoid, called aldosterone, influences the transport of important ions and electrolytes, such as sodium and potassium, inside the kidney tubules. It is responsible for accelerating the elimination of potassium and the retention of sodium which ultimately helps maintain the dog’s electrolyte and water balance.

The middle zone, called the Zona Fasciculata, is responsible for the production and secretion of cortisol and corticosterone. These glucocorticoid hormones have a very wide range of physiological effects that directly influence the health of the dog. Glucocorticoids greatly influence the animal’s immune system, inflammatory processes, and metabolism of different nutrients such as carbohydrates, fats, and proteins.

Cortisol and corticosterone both suppress immune and inflammatory responses of the dog’s system, helpful in cases of physical trauma or inflammatory conditions. These can be harmful as they also diminish the animal’s ability to fight off bacteria and viruses, making them vulnerable to infections.

Glucocorticoids also stimulate the production of glucose and increase the blood sugar level of the dog. Additionally, it slows down the body’s fat production and stimulates the breakdown of fat tissues in the body, releasing fatty acids and glycerol into the animal’s system. All of these result in readily available sources of energy for the animal.

The inner layer of the adrenal cortex, called the Zona Reticularis, is responsible for the secretion of adrenal sex hormones. Most sex hormones are produced by the reproductive organs, but a relatively small amount is produced by the adrenal cortex.

These include progesterone, androgens, and estrogen hormones. The effect of these hormones originating from the adrenal cortex is often insignificant, especially in intact dogs, because the majority of the sex hormones in the dog’s body are produced by the ovaries or testes. However, once a dog is spayed or neutered, these sex hormones produced by the adrenal glands may take on more significance in terms of physiological effects in the animal’s body.

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