Adrenal gland: structure, location and hormones

 The adrenal glands are small glandular structures located top each kidney. Within the human body, there are two adrenal glands that secrete hormones directly into the bloodstream. These hormones are then transported through the bloodstream to various target tissues and organs, where they exert their effects.

Adrenal gland: structure, location and hormones

The adrenal glands secrete both steroid hormones and catecholamine hormones directly into the bloodstream.

In this article, we will explore the anatomy of the adrenal glands, including their location, structure, and vascular supply.

Where are my adrenal glands?

In the human body, there are two adrenal glands, with each gland positioned top one kidney. In adults, the weight of each adrenal gland is approximately 4-5 grams.

The size of each adrenal gland is approximately 4-6 cm in length and 2-3 cm in width.

The adrenal glands are positioned in the posterior abdomen, between the superomedial aspect of the kidneys and the diaphragm. They are retroperitoneal organs, meaning that they are located behind the peritoneum, and only their anterior surfaces are covered by the parietal peritoneum.

The right adrenal gland has a pyramidal shape, while the left adrenal gland has a semi-lunar shape.

Both adrenal glands are enclosed by the perinephric (or renal) fascia, which also surrounds the kidneys. This fascia connects the adrenal glands to the diaphragmatic crura. The adrenal glands are separated from the kidneys by the perirenal fat.

Structure of Adrenal gland

Divided into outer cortex and inner medulla

1. Adrenal cortex:

  • It accounts for about 90% of weight of adrenal gland which weight for 5-7 gram.
  • the cortex has three distinct zone
 i. Zona glomerulosa:

  • It lies directly beneath the capsule.
  • It supplies cells for all other three zone. it is actually germinal layer.
  • It produce mineralocorticoid.

ii. Zona faciculata:

  • It lies beneath zona glomerulosa.
  • It make up bulk of adrenal cortex.
  • It secretes glucocorticoids and small amount of gonadocorticoids.

iii. Zona reticularis:

  • It is the deepest layer.
  • The adrenal gland contains cells similar to those found in the zona fasciculata, but these cells are arranged irregularly.
  • It produce Dehydroepiandrosterone ( an intermediate hormone needed for production of sex hormone Androstenedione).

Hormones secreted by Adrenal cortex

1. Glucocorticoid

  • Regulate blood glucose level
  • Stimulate gluconeogenesis
  • Enhance synthesis of aminoacids which are substrate for gluconeogenesis
  • Promote protein and nucleic acid metabolism
  • Regulated by ACTH
  • Acts as anti-inflammatory agents

2. Mineralocorticoid

  • It is group of Steroid hormone (eg. Aldosterone), regulate concentration of mineral
  • Help in maintaining blood pressure
  • The adrenal glands play a role in promoting sodium (Na+) reabsorption while facilitating the excretion of potassium (K+), hydrogen ions (H+), and ammonium ions (NH4+).

3. Gonadocorticoid

  • Sex hormone, stimulate gonads
  • Regulated by ACTH

2. Adrenal medulla:

  • The inner portion of the adrenal gland is known as the adrenal medulla.
  • Medulla acts as a separate endocrine gland. It secretes separate hormones than cortex.
  • While the hormones produced by the adrenal medulla are not considered as essential as the cortical hormones, they still play important physiological roles. The medulla produces hormones such as adrenaline (epinephrine) and noradrenaline (norepinephrine), which are involved in the body's stress response and help regulate various bodily functions, including heart rate, blood pressure, and metabolism. While the cortical hormones are involved in a broader range of functions and have more diverse effects, the hormones from the adrenal medulla still contribute to the overall hormonal balance and response in the body.
  • The secretory cells of the adrenal medulla are called chromaffin cells due to their tendency to stain dark colors when exposed to certain dyes. This staining property is attributed to the presence of chromaffin granules within these cells, which contain the hormones adrenaline and noradrenaline.
  • chromaffin cell synthesize, store and secrete epinephrine and nor-epinephrine which prepare body for fright, flight and fight.

Hormones secreted by Adrenal Medulla

1. Epinephrine (adrenaline)

  • commonly known as Adrenaline
  • Increase rate of metabolism, heart rate and blood pressure
  • Increase glycogenolysis, respiration rate, O2 consumption

2. Nor-epinephrine (Nor-Adrenaline)

  • Increase heart rate, cardiac output, blood pressure
  • Enhance lipid metabolism
  • Relaxes smooth muscles of GI tract.
  • Release free fatty acid from adipose tissue.

Disorder/disease of adrenal gland:

1. addition’s disease:

  • bronze color pigmentation of skin
  • low Na+ and high K+ level in blood plasma
  • decrease resistance to infection

2. Cushing syndrome:

  • abnormal obesity
  • high Na+ and Low K+ level in blood

3. Aldosteronism:

  • In blood Low K+ level and High Na+ level 
  • high blood pressure and increase blood volume
4. Adrenal virilism:

  • Adrenal virilism is a syndrome characterized by the excessive production of adrenal androgens, resulting in virilization. This condition is diagnosed based on elevated levels of androgens in clinical tests. Symptoms of adrenal virilism include the development of excess facial and body hair (hirsutism), deepening of the voice, male pattern baldness, acne, and increased muscularity. These manifestations are attributed to the masculinizing effects of the excessive androgen hormones.
  • male type external character such as beard, moustaches and voice develops in female

    What could go wrong with my adrenal glands?

Excessive production of aldosterone can occur, often due to a benign tumor in the adrenal gland, leading to a condition known as primary hyperaldosteronism or Conn's Syndrome. Aldosterone, in excess, causes the kidneys to retain sodium and water while promoting potassium loss through urine. This imbalance results in high blood pressure (hypertension), which may be resistant to conventional blood pressure medications, and can be accompanied by low potassium levels (hypokalemia) in the blood. Studies suggest that hyperaldosteronism may account for approximately 5% of individuals with hypertension and an even higher proportion (up to 20%) of those with difficult-to-control hypertension.

In rare instances, the adrenal glands may become either overactive or underactive, leading to specific disorders related to glucocorticoid function. Overactivity of the adrenal glands results in Cushing's syndrome, characterized by excessive production of cortisol. Conversely, underactivity of the adrenal glands leads to Addison's disease, which is marked by insufficient production of cortisol and sometimes aldosterone.

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