Endocrine
9.4 Corticosteriods
Adrenal: A&P Basics Review
The adrenal gland consists of the adrenal cortex that is composed of glandular tissue and the adrenal medulla that is composed of nervous tissue. Each region secretes its own set of hormones.
The adrenal cortex is a component of the hypothalamic-pituitary-adrenal (HPA) axis. The hypothalamus stimulates the release of ACTH from the pituitary, which then stimulates the adrenal cortex to produce steroid hormones that are important for the regulation of the stress response, blood pressure and blood volume, nutrient uptake and storage, fluid and electrolyte balance, and inflammation.
The adrenal medulla is neuroendocrine tissue composed of postganglionic sympathetic nervous system (SNS) neurons, that secretes the hormones epinephrine and norepinephrine. It is an extension of the autonomic nervous system, which regulates homeostasis in the body. See Figure 9.4a for an illustration of the adrenal gland and associated hormones.[1]
One of the major functions of the adrenal gland is to respond to stress. The body responds in different ways to short-term stress and long-term stress, following a pattern known as the general adaptation syndrome (GAS). Stage one of GAS is called the alarm reaction. This is short-term stress, also called the fight-or-flight response, and is mediated by the hormones epinephrine and norepinephrine from the adrenal medulla. Their function is to prepare the body for extreme physical exertion. If the stress is not soon relieved, the body adapts to the stress in the second stage called the stage of resistance. If a person is starving for example, the body may send signals to the gastrointestinal tract to maximize the absorption of nutrients from food. If the stress continues for a longer term however, the body responds with symptoms such as depression, suppressed immune response, or severe fatigue. These symptoms are mediated by the hormones of the adrenal cortex, especially cortisol.Adrenal hormones also have several non–stress-related functions, including the increase of blood sodium and glucose levels, which will be described in further detail below.
Mineralocorticoids: Aldosterone
The most superficial region of the adrenal cortex is the zona glomerulosa, which produces a group of hormones collectively referred to as mineralocorticoids because of their effect on body minerals, especially sodium and potassium. These hormones are essential for fluid and electrolyte balance.
Aldosterone is the major mineralocorticoid that is important in the regulation of the concentration of sodium and potassium ions in the body. The secretion of aldosterone by the adrenal cortex is prompted by the HPA axis when the hypothalamus triggers ACTH release from the anterior pituitary. It is released in response to elevated blood levels of potassium (K+), low blood levels of sodium (Na+), low blood pressure, or low blood volume. Aldosterone targets the kidneys and increases the excretion of K+ and th