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The adrenal glands are small, triangular-shaped glands located on top of each kidney. They play a crucial role in the body's endocrine system, producing a variety of hormones that are essential for life. Here is a detailed overview of their structure, function, and significance:

Structure
The adrenal glands have two main parts:

Adrenal Cortex: The outer region, which is further divided into three zones:

Zona Glomerulosa: Produces mineralocorticoids (e.g., aldosterone).
Zona Fasciculata: Produces glucocorticoids (e.g., cortisol).
Zona Reticularis: Produces androgens (e.g., dehydroepiandrosterone or DHEA).
Adrenal Medulla: The inner region, which produces catecholamines (e.g., adrenaline and noradrenaline).

Functions
Hormones of the Adrenal Cortex:

Mineralocorticoids (e.g., Aldosterone):
Regulate sodium and potassium balance.
Control blood pressure by influencing fluid balance.
Glucocorticoids (e.g., Cortisol):
Help regulate metabolism.
Influence blood sugar levels.
Aid in the body's response to stress.
Suppress inflammation and immune responses.
Androgens:
Contribute to the development of secondary sexual characteristics.
Play a role in the growth and development of muscles and bones.
Hormones of the Adrenal Medulla:

Catecholamines (e.g., Adrenaline and Noradrenaline):
Prepare the body for 'fight-or-flight' responses.
Increase heart rate and blood pressure.
Expand air passages in the lungs.
Redirect blood flow to essential organs (e.g., muscles, heart).
Significance
Stress Response:

The adrenal glands are crucial in the body's response to stress. Cortisol, often called the "stress hormone," helps maintain homeostasis during stressful conditions.
Adrenaline and noradrenaline rapidly prepare the body to handle acute stress.
Metabolism:

Cortisol influences carbohydrate, protein, and fat metabolism, helping to maintain stable blood glucose levels.
Electrolyte Balance:

Aldosterone regulates the balance of electrolytes by promoting sodium retention and potassium excretion in the kidneys.
Immune System Regulation:

Cortisol has potent anti-inflammatory and immunosuppressive properties, which can be crucial in controlling inflammation and autoimmune responses.
Disorders of the Adrenal Glands
Cushing's Syndrome:

Caused by excessive cortisol production.
Symptoms include weight gain, high blood pressure, diabetes, and osteoporosis.
Addison's Disease:

Caused by insufficient production of adrenal hormones.
Symptoms include fatigue, weight loss, low blood pressure, and hyperpigmentation of the skin.
Conn's Syndrome:

Caused by excessive production of aldosterone.
Symptoms include high blood pressure and low potassium levels.
Pheochromocytoma:

A tumor of the adrenal medulla causing excessive production of catecholamines.
Symptoms include high blood pressure, palpitations, and headaches.
Clinical Relevance
Diagnostic Tests:

Blood tests to measure hormone levels.
Imaging tests (e.g., CT or MRI) to detect tumors or abnormalities.

1. Adrenal Gland Communication II Zoology by Miller and Harley

2. In mammals, two adrenal glands rest on top of the kidneys. Each gland consists of two separate glandular tissues. The inner portion is the medulla, and the outer portion, which surrounds medulla, is the cortex.

3. Adrenal Cortex The adrenal cortex secretes three classes of steroid hormones: glucocorticoids (cortisol), mineralocorticoid (aldosterone), and sex hormones (androgens, estrogens). The glucocorticoids , such as cortisol, help regulate overall metabolism and the concentration of blood sugar. They also function in defense responses to infection or tissue injury. Aldosterone helps maintain concentrations of solutes (such as sodium) in the extracellular fluid when either food intake or metabolic activity changes the amount of solutes entering the bloodstream.

4. Aldosterone also promotes sodium reabsorption in the kidneys and, thus, water reabsorption; hence, it plays a major role in maintaining the homeostasis of extracellular fluid. Normally, the sex hormones that the adrenal cortex secretes have only a slight effect on male and female gonads. These sex hormones consist mainly of weak male hormones called androgens and lesser amounts of female hormones called estrogens.

5. The adrenal medulla is under neural control. It contains neurosecretory cells that secrete epinephrine (adrenaline) and norepinephrine (noradrenaline), both of which help control heart rate and carbohydrate metabolism. Brain centers and the hypothalamus govern the secretions via sympathetic nerves.
During times of excitement, emergency, or stress, the adrenal medulla contributes to the overall mobilization of the body through the sympathetic nervous system.

6. In response to epinephrine and norepinephrine, the heart rate increases, blood flow increases to many vital organs, the airways in the lungs dilate, and more oxygen is delivered to all cells of the body.
This group of events is sometimes called the “fight-or flight” response and permits the body to react strongly an quickly to emergencies