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Endocrine system

Not medically reviewed · Content last updated · 1 min read ·

This is the date the draft was written, not a medical review date.

The endocrine system comprises ductless glands and tissues that secrete hormones into the blood to regulate distant target organs. It controls metabolism, growth, reproduction, stress responses and fluid and electrolyte balance in close partnership with the nervous system.

Terminologia Anatomica (Latin): Organa endocrina

Components

The principal glands are the hypothalamus, pituitary, pineal, thyroid, parathyroids, adrenals and pancreatic islets, together with the gonads. Other organs such as the kidney, heart, adipose tissue and gut also secrete hormones.

Function

Hormones act through receptors on target cells and are controlled mainly by negative feedback, often organised as hypothalamic-pituitary-end-organ axes. Their actions include regulation of glucose, calcium, metabolic rate, blood pressure and sexual development.

Clinical correlations

Diabetes mellitus, thyroid disease, adrenal disorders, pituitary tumours and disorders of calcium metabolism are the commonly encountered conditions. Diagnosis combines clinical features, hormone assays and imaging; reference ranges depend on the assay and laboratory.

Common exam points

  • Hormone classes: peptide, steroid and amine, with their receptor locations.
  • Posterior pituitary releases oxytocin and ADH made in the hypothalamus; anterior pituitary secretes its own hormones under hypophysial portal control.
  • Adrenal cortex zones (glomerulosa, fasciculata, reticularis) and the medulla.
  • Thyroid and parathyroid hormones in calcium and metabolic regulation.
  • Negative feedback loops, and how primary versus secondary gland failure differ in the hormone pattern.

References

  1. Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. Elsevier — Tier 3 (textbook)
  2. Hall JE, Hall ME. Guyton and Hall Textbook of Medical Physiology. Elsevier, 14th edition (2020) — Tier 3 (textbook)
  3. Williams Textbook of Endocrinology. Elsevier, 14th edition (2019) — Tier 3 (textbook)

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