Physiology Review
The endocrine system involves all the organs and their supporting tissues that are involved in secreting hormones into their respective capillaries that eventually travel through the blood and cause specific effects on target tissues of the body. Hormones are chemical agents that cause a specific effect on target tissues outside the initial place they are produced. Hormones work along with the nervous system to integrate and harmonize various physiological functions, such as growth and reproduction, related activity and homeostasis (a tendency to stability in the normal body states or internal environment).
Endocrine Tissues
Endocrine tissues or glands are distinguished from exocrine glands in that they have no ducts. Some endocrine secretory cells are located in non-endocrine organs (such as the enteroendocrine glands of the gastrointestinal tract), interstitial cells of the testes, secretory neurons in the brain (such as the hypothalamus), or may exist as microscopic islands (such as the beta cells of the Langerhans of the pancreas). The remaining endocrine tissues exist as an entity, namely the pituitary gland, pineal gland, thyroid glands, parathyroid glands, thymus, adrenal glands, ovaries, and testes.
Other Hormone Secreting Organs
Endocrine activity also involves certain organs that have crucial functions outside this role.
[D] Kidneys: For example, the kidney not only secretes renin involved in blood pressure, but also erythropoietin that stimulates red blood cell corpuscles.
GI Tract: The gastrointestinal tract is involved in production of hormones regulating digestion.
Placenta: The placenta secretes human chorionic gonadotropin (HCG), estrogen, progesterone, lactogen, and growth stimulating hormone.
Heart: The heart secretes atrial natriuretic peptide (ANP) involved in sodium excretion and inhibits smooth muscle contraction.
