100Illu endocrine system

Major endocrine glands. (Male on the left, female on the right.) 1. Pineal gland 2. Pituitary gland 3. Thyroid gland 4. Thymus 5. Adrenal gland 6. Pancreas 7. Ovary 8. Testes

The endocrine system is a system of glands that involve the release of extracellular signaling molecules known as hormones. The endocrine system is instrumental in regulating metabolism, growth, development and puberty, and tissue function and also plays a part in determining mood. The field of study that deals with disorders of endocrine glands is endocrinology, a branch of the wider field of internal medicine.


The endocrine system is an information signal system much like the nervous system. However, the nervous system uses nerves to conduct information, whereas the endocrine system mainly uses blood vessels as information channels. Glands located in many regions of the body, for example the testis, release into the bloodstream specific chemical messengers called hormones. Hormones regulate many functions of an organism, including mood, growth and development, tissue function, and metabolism.

Types of signaling[]

The typical mode of cell signaling in the endocrine system is endocrine signaling. However, there are also other modes, i.e., paracrine, autocrine, and neuroendocrine signaling. Purely neurocrine signaling between neurons, on the other hand, belongs completely to the nervous system.


Main article: Endocrine signalling

The endocrine system is made up of a series of ductless glands that produce chemical messages called hormones

A number of glands that signal each other in sequence is usually referred to as an axis, for example, the hypothalamic-pituitary-adrenal axis. Typical endocrine glands are the pituitary, thyroid, and adrenal glands. Features of endocrine glands are, in general, their ductless nature, their vascularity, and usually the presence of intracellular vacuoles or granules storing their hormones. In contrast, exocrine glands, such as salivary glands, sweat glands, and glands within the gastrointestinal tract, tend to be much less vascular and have ducts or a hollow lumen. Also controls metabolism in our body system.


Main article: Autocrine signalling

Other signaling can target the same cell.


Main article: Paracrine signalling

Paracrine signaling is where the target cell is nearby.


Main article: Juxtacrine signalling

Juxtacrine signals are transmitted along cell membranes via protein or lipid components integral to the membrane and are capable of affecting either the emitting cell or cells immediately adjacent.

Role in disease[]

Main article: Endocrine diseases

Diseases of the endocrine system are common, including conditions such as diabetes mellitus, thyroid disease, and obesity. Endocrine disease is characterized by dysregulated hormone release (a productive pituitary adenoma), inappropriate response to signaling (hypothyroidism), lack of a gland (diabetes mellitus type 1, diminished erythropoiesis in chronic renal failure), or structural enlargement in a critical site such as the testis (toxic multinodular goitre). Hypofunction of endocrine glands can occur as a result of loss of reserve, hyposecretion, agenesis, atrophy, or active destruction. Hyperfunction can occur as a result of hypersecretion, loss of suppression, hyperplastic or neoplastic change, or hyperstimulation.

Endocrinopathies are classified as primary, secondary, or tertiary. Primary endocrine disease inhibits the action of downstream glands. Tertiary endocrine disease is associated with dysfunction of the hypothalamus and its releasing hormones.

Cancer can occur in endocrine glands, such as the thyroid, and hormones have been implicated in signaling distant tissues to proliferate, for example, the estrogen receptor has been shown to be involved in certain breast cancers. Endocrine, paracrine, and autocrine signaling have all been implicated in proliferation, one of the required steps of oncogenesis.

List of endocrine glands[]

  • Hypothalamus
  • Pineal body (epiphysis)
  • Pituitary Gland (hypophysis)
    • Anterior pituitary lobe (adenohypophysis)
    • Posterior pituitary lobe (neurohypophysis)
    • Intermediate pituitary lobe (pars intermedia)
  • Thyroid
  • Parathyroid
  • Heart
  • Striated muscle
  • Skin
  • Adipose tissue
  • Stomach
  • Duodenum
  • Liver
  • Pancreas
  • Kidney
  • Adrenal glands
    • Adrenal cortex
    • Adrenal medulla
    • Testes
  • Ovary
  • Placenta (when pregnant)
  • Uterus (when pregnant)