1.4 Adrenal Glands: Zona Glomerulosa

Anatomy of the Adrenal Glands

  • Location:

    • Adrenal glands situated posterior to the peritoneum, similar to the kidneys.

    • Described as retroperitoneal due to their position behind the peritoneum.

  • Structure:

    • Glands are tranquil-shaped and appear fatty in structure.

    • Referred to as suprarenal because they sit superior to the renal (kidney) structures.

Internal Structure of Adrenal Glands

  • Regions:

    • Capsule: The outermost protective layer.

    • Cortex: Outer region comprising three layers:

      • Zona Glomerulosa:

        • Most superficial layer.

        • Target cells respond to Angiotensin II and produce mineralocorticoids, predominantly Aldosterone.

      • Zona Fasciculata:

        • Middle layer.

        • Target cells respond to ACTH and secrete Glucocorticoids, mainly Cortisol.

      • Zona Reticularis:

        • Deepest layer of the cortex.

        • Also responds to ACTH and secretes Androgens.

    • Adrenal Medulla: Deep region containing chromaffin cells.

Chromaffin Cells

  • Function:

    • Neuroendocrine cells respond to nervous system stimuli.

    • Secrete Norepinephrine (NE) and Epinephrine (E) into circulation.

    • NE acts as a hormone here, unlike its typical role as a neurotransmitter.

Zona Glomerulosa

  • Structure: Cells arranged in a spherical (glomerular) shape.

  • Hormonal Production:

    • Mineralocorticoids, with Aldosterone as the primary hormone.

    • Functions of Aldosterone:

      • Increases sodium chloride absorption in the GI tract and kidneys.

      • Promotes potassium and hydrogen ion excretion.

      • Maintains blood volume and helps regulate blood pressure.

Aldosteronism

  • Definition: Hypersecretion of mineralocorticoids, primarily Aldosterone.

  • Effects:

    • Excess sodium and chloride increase blood volume, leading to high blood pressure.

Regulation of Aldosterone Release

  • Stimuli for Release:

    • Detected by juxtaglomerular cells in the kidneys in response to decreased blood pressure.

    • Secrete Renin, triggering conversion of Angiotensinogen to Angiotensin I, then II through ACE in lungs.

  • Aldosterone Mechanism:

    • Angiotensin II acts on Zona Glomerulosa for Aldosterone production.

    • Aldosterone functions to retain sodium, chloride, and water, increasing blood volume.

  • Potassium Regulation:

    • Aldosterone also secretes to regulate potassium levels directly.

    • Avoids lethal conditions caused by high extracellular potassium affecting excitable tissues like muscle and nerves.

Summary Points

  • The adrenal glands consist of the adrenal cortex and medulla, each with specific functions.

  • Each zone of the adrenal cortex produces different hormones critical for physiological balance.

  • Proper function of these glands is essential for maintaining blood pressure, electrolyte balance, and overall homeostasis.