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Classification of Endocrine System Organs and Cells

For medical students2 min readUpdated 2026-10-10

Hormone secretion in the body is carried out by two major groups of structures: specialized endocrine glands and isolated clusters of endocrine cells scattered across various tissues. An imbalance in this system leads to a standard form of pathology known as an endocrinopathy.

Basis of pathologyEndocrinopathy (deviation of hormone effects from optimum)
Two types of structuresSpecialized glands and cells of other organs
RegulationHigher control by the cerebral cortex and hypothalamus

Main Endocrine Glands

The first group of hormone-synthesizing structures consists of true endocrine glands. These are independent anatomical formations whose primary and sole function is the production of regulatory substances.

Classical endocrine glands include:

Endocrine Cells of Organs and Tissues

In addition to specialized glands, hormones can be synthesized by isolated cellular pools located inside organs that perform entirely different primary functions. This diffuse organization allows the body to perform fine local and systemic regulation.

Clusters of endocrine cells are present in the following structures:

Endocrinopathy: Nature and Consequences

Endocrinopathy is considered a standard form of endocrine system pathology.

Its main characteristic is the deviation of the effects of a single hormone or a group of hormones from the optimal level. This deviation can manifest as either an increase or a decrease in hormonal impact on target organs. A direct consequence of this imbalance is the development of corresponding functional and structural disorders throughout the body.

Initial Links of Pathogenesis

The development of endocrinopathies begins with a breakdown at a specific level of regulation or execution. There are three main variants of the initial links of pathogenesis:

  1. Centrogenic — associated with higher control centers.
  2. Primary glandular — the problem lies within the secretory tissue itself.
  3. Post-glandular — the disruption occurs at the stage of hormone transport or its interaction with target cell receptors.

Special attention should be paid to the centrogenic link. It is characterized by impaired regulation of endocrine glands by higher centers. These centers include the cerebral cortex and the hypothalamic-pituitary system. A failure at this level inevitably leads to distortion of signals arriving at peripheral glands.

Frequently asked questions

Which exact hormones are synthesized by cardiac endocrine cells?

Cardiac endocrine cells synthesize natriuretic hormones that affect renal function and vascular tone. These include:

  • Atrial natriuretic peptide (ANP / atriopeptin) — produced predominantly by cardiomyocytes of the right atrium, stimulates renal excretion of sodium and water, and lowers blood pressure.
  • Other natriuretic hormones — produced by endocrine cells of the heart ventricles.
What hormones are produced by the endocrine cells of the kidneys?

Renal endocrine cells produce a number of hormones and biologically active substances that regulate hemodynamics and metabolism:

  • Erythropoietin — secreted by interstitial cells, stimulates hematopoiesis (erythropoiesis).
  • Renin — an enzyme of the juxtaglomerular apparatus acting as the initial link of the renin-angiotensin-aldosterone system.
  • Calcitriol — the active form of vitamin D, regulating calcium metabolism and its absorption.
  • Prostaglandins ($E_2$) and Bradykinin — affect vascular tone.
What specific mechanisms underlie the post-glandular link of endocrinopathy pathogenesis?

The post-glandular link is based on disruptions at the stages of hormone circulation, transport, and peripheral action. Specific mechanisms include:

  • Impaired transport — excessive increase or decrease in hormone binding to blood transport proteins, altering the active fraction level.
  • Hormone inactivation — destruction of the hormone in blood and tissues (e.g., by antibodies or proteases).
  • Receptor dysfunction — resistance of target tissues (receptor hyposensitization).
  • Metabolic disorders — disruption of hormone-dependent intracellular processes or formation of inactive metabolites (e.g., reverse T3).
What pathological processes cause the primary glandular link of endocrinopathies?

The primary glandular link is caused by impaired hormone production directly within the endocrine glands. Processes and mechanisms include:

  • Direct gland damage — due to intoxications, infectious processes, or autoantibodies.
  • Changes in gland mass — excessive enlargement or reduction, including congenital malformations and genetic defects.
  • Impaired hormone synthesis — deficiency of synthesis substrates, impaired energy supply, altered activity or levels of synthesis enzymes.
  • Impaired storage and/or release of hormones from endocrine cells.
  • Exhaustion of hormone production processes resulting from prolonged gland hyperfunction.
  • Gland damage by physical, chemical, or biological factors.
  • Immune autoaggression.
  • Trophic disturbances — blood circulation and/or innervation disorders of the glands.
  • Iatrogenic factors — surgical removal or damage to glands during operations.
What is the difference between endocrine glands and endocrine cells?

Endocrine glands (such as the thyroid gland) are independent organs specialized solely in hormone production. Endocrine cells are embedded in the tissues of other organs (heart, kidneys, GI tract) for which hormone secretion is an additional function.

What is an endocrinopathy?

It is a standard form of pathology where the effects of a hormone or group of hormone effects pathologically increase or decrease compared to the optimal level, leading to systemic disorders.

What does the centrogenic link of pathogenesis include?

The centrogenic link implies impaired control over the endocrine glands by higher regulatory apparatuses — the cerebral cortex and/or the hypothalamic-pituitary system.

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