The Endocrine System

This lesson introduces the endocrine system and the role it plays in the maintenance of homeostasis.

Functions of the Endocrine System

The endocrine system works with the nervous system to regulate the activities critical to the maintenance of homeostasis. The following are the main functions of the endocrine system:

  • Water balance
  • Uterine contractions and milk release
  • Growth, metabolism, and tissue maturation
  • Ion regulation
  • Heart rate and blood pressure regulation
  • Blood glucose control
  • Immune system regulation
  • Reproductive functions control

Chemical Signals

Chemical signals, or ligands, are molecules released from one location that move to another location to produce a response. Intracellular chemical signals are produced in one part of a cell, such as the cell membrane, and travel to another part of the same cell and bind to receptors, either in the cytoplasm or in the nucleus. Intercellular chemical signals are released from one cell, are carried in the intercellular fluid, and bind to receptors that are found in other cells, but usually not in all cells of the body.

Intercellular chemical signals can be placed into functional categories on the basis of the tissues from which they are secreted and the tissues they regulate.

  • Autocrine chemical signals: These chemical signals are released by cells and have a local effect on the same cell type. Example: prostaglandin-like chemicals that are secreted in response to inflammation.
  • Paracrine chemical signals: These chemical signals are released by cells and have effects on other cell types. Example: somatostatin, secreted by the pancreas, inhibits the release of insulin by other cells in the pancreas.
  • Neuromodulators and neurotransmitters: These chemical signals are secreted by nerve cells and aid the nervous system. Example: acetylcholine produced during stressful encounters.
  • Pheromones: These chemical signals are secreted into the environment and modify the behavior and physiology of other individuals. Example: those produced by women can influence the length of the menstrual cycle of other women.
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