Adrenal Medulla

Adrenal Gland Location

The adrenal glandPaired endocrine glands above the kidneys producing stress-related hormones. can be complex, as it functions like two glands in one. It is sometimes called the suprarenal gland. This is because it sits above the kidney. (“Supra” means above, and “renal” refers to the kidney). The adrenal gland shares a capsule with the kidney, which is strange.  Why would you want this very-important gland to be exposed to all the toxic waste in the kidney?  The adrenal gland has a pyramidal 3-D shape. In a 2-D view of a histological slide, it would look like a flattened triangle.

Adrenal Medulla

The gland consists of an outer cortex, which is fatty, and an inner medulla. The cortex has a striped appearance in diagrams, while the medulla contains blood vessels and neuronsThe functional cells of the nervous system that transmit signals.. The hypothalamusA small but vital brain region controlling hormones, temperature, and autonomic functions. connects directly to the adrenal medullaInner part of adrenal glands producing catecholamines (epinephrine, norepinephrine). through neurons.

The medulla, composed of specialized neurons called chromaffin cellsAdrenal medulla cells that secrete catecholamines., releases epinephrineadrenaline): Fight-or-flight hormone from the adrenal medulla. and norepinephrineA neurotransmitter involved in attention, arousal, and the fight-or-flight response.. These hormones are known collectively as catecholamines. They are distributed throughout the body via blood vessels in the medulla. This distribution provokes a general sympathetic (fight-or-flight) response.

Catecholamines Release

Stress perception begins in the hypothalamus, which has a direct neural connection to the adrenal medulla. This connection enables the medulla to release epinephrine and norepinephrine through action potentials. These hormones target specific organs to prepare the body for immediate action. The heart beats faster and with greater force. Blood vessels constrict to redirect blood to skeletal muscles. Bronchioles dilate to allow more oxygen intake.

Catecholamines Effects

CatecholaminesNeurotransmitters derived from tyrosine: dopamine, norepinephrine, and epinephrine. are all about preserving glucoseA simple sugar that is the main source of energy for cells. for two things. They help with responding to a threat. They also ensure enough energyThe capacity to do work or cause change. for the brain during this response.  The threat could be many things, real or hypothetical.  Sometimes, just the thought of stressful situations can evoke these effects, culminating in a very real panic attack. 

First, gluconeogenesis is the process of creating glucose from non-carbohydrate sources like fatty acids. This ensures there’s always a backup supply of glucose, even when dietary intake is low. Next is glycogenolysisBreakdown of glycogen into glucose., where stored glycogenA storage form of glucose found in animals. in the liverA large organ that produces bile, detoxifies blood, and stores nutrients. is broken down into glucose and released into the bloodstream. Together, these processes create a larger supply of ATPThe energy currency of cells used for muscle contraction. for running away and thinking.

Additionally, there’s the glucose-sparing effectGH and cortisol reducing glucose usage to save it for the brain., which directs other tissues, like muscles, to rely on fats for energy instead of glucose. This spares glucose specifically for the brain, ensuring it has enough fuel during critical moments.  Beyond reserving glucose, the body increases its readiness for action. It increases the respiratory rate. This ensures more oxygen is available for energy production. The heart rate increases. Circulation to skeletal muscles also increases. Nutrients and oxygen are provided to the muscles. This may be needed for running away from the threat.

Processes such as digestion and urineThe liquid waste excreted by the kidneys. creation are pretty much halted for short-term stress responses. This conserves available energy for organs that can contribute more in responding to the threat.