Chapter 15
Endocrine System
By Boundless
![Thumbnail](../../../../../figures.boundless-cdn.com/34238/square/jgneprwsjgcoebwacewa.jpg)
The endocrine system is a system of ductless glands that secrete hormones—chemical messengers that are carried for long distances.
The nervous system and endocrine system both use chemical messengers to signal cells, but each has a different transmission speed.
![Thumbnail](../../../../../figures.boundless-cdn.com/14332/square/-201211071352324192161047.jpeg)
A hormone is a secreted chemical messenger that enables communication between cells and tissues throughout the body.
![Thumbnail](../../../../../figures.boundless-cdn.com/152/square/ii-nuclear-receptor-action.jpg)
Hormones activate a cellular response in the target cell by binding to a specific receptor in the target cell.
![Thumbnail](../../../../../figures.boundless-cdn.com/16463/square/pdb-2dez-ebi.jpeg)
There are three classes of hormones: peptide hormones, lipid hormones, and monoamine hormones.
![Thumbnail](../../../../../figures.boundless-cdn.com/3660/square/illu-endocrine-system.jpg)
Hormones synthesized by the endocrine glands are transported throughout the body by the bloodstream.
![Thumbnail](../../../../../figures.boundless-cdn.com/3667/square/nuclear-receptor-action.jpg)
Nuclear receptors function as transcription factors because they can bind to DNA and regulate gene expression.
Hormones target a limited number of cells (based on the presence of a specific receptor) as they circulate in the bloodstream.
![Thumbnail](../../../../../figures.boundless-cdn.com/16854/raw/-follicle-26-corpus-luteum.jpg)
A hormone's half-life and duration of activity are limited and vary from hormone to hormone.
![Thumbnail](../../../../../figures.boundless-cdn.com/6611/square/pituitary-gland.jpg)
The pituitary gland is connected to the hypothalamus and secretes nine hormones that regulate body homeostasis.
![Thumbnail](../../../../../figures.boundless-cdn.com/8643/square/grays-pituitary.jpg)
The pituitary gland consists of the anterior pituitary and the posterior pituitary.
![Thumbnail](../../../../../figures.boundless-cdn.com/6378/square/pituitary-gland-et-vessel.jpeg)
The anterior pituitary secretes seven hormones that regulate several physiological processes, including stress, growth, and reproduction.
![Thumbnail](../../../../../figures.boundless-cdn.com/1891/square/itary-gland-representation.jpg)
The posterior pituitary secretes two important endocrine hormones—oxytocin and antidiuretic hormone.
![Thumbnail](../../../../../figures.boundless-cdn.com/24486/square/thyroid-system.jpg)
The thyroid gland, in the anterior neck, controls body metabolism, protein synthesis, and a body's responsiveness to other hormones.
![Thumbnail](../../../../../figures.boundless-cdn.com/1892/square/thyroid-hormone-synthesis.jpg)
Thyroid hormones (T4 and T3) are produced by the follicular cells of the thyroid gland and regulated by thyroid-stimulating hormone (TSH).
![Thumbnail](../../../../../figures.boundless-cdn.com/1893/square/thyroid-system.jpg)
The primary function of the thyroid is to produce the hormones triiodothyronine (T3), thyroxine (T4), and calcitonin.
![Thumbnail](../../../../../figures.boundless-cdn.com/34295/square/cfar2oy5tasvg6cvsj6q.jpg)
The production of thyroxine and triiodothyronine is regulated by thyroid-stimulating hormone (TSH) that is released from the anterior pituitary.
![Thumbnail](../../../../../figures.boundless-cdn.com/1895/square/illu-adrenal-gland.jpeg)
In mammals, the adrenal glands (also known as the suprarenal glands) are endocrine glands that sit atop the kidneys.
![Thumbnail](../../../../../figures.boundless-cdn.com/15180/square/gray1185.jpg)
The adrenal cortex is devoted to the synthesis of corticosteroid and androgen hormones.
![Thumbnail](../../../../../figures.boundless-cdn.com/23997/square/gray1185.jpg)
The adrenal cortex is devoted to the synthesis of corticosteroid and androgen hormones.
![Thumbnail](../../../../../figures.boundless-cdn.com/30588/square/usen-0701-pancreatictissue.jpg)
Pancreatic islets, also called the islets of Langerhans, are regions of the pancreas that contain its hormone-producing endocrine cells.
![Thumbnail](../../../../../figures.boundless-cdn.com/8692/square/757px-islet.jpg)
The islets of Langerhans are the regions of the pancreas that contain many hormone-producing endocrine cells.
![Thumbnail](../../../../../figures.boundless-cdn.com/8693/square/800px-glucagon-rednblue.jpg)
Glucagon is a peptide hormone that works in conjunction with insulin to maintain a stable blood glucose level.
![Thumbnail](../../../../../figures.boundless-cdn.com/5252/raw/eicosanoid-synthesis.jpg)
The eicosanoids are signaling molecules that exert complex control over many bodily systems, mainly in inflammation or immunity.
![Thumbnail](../../../../../figures.boundless-cdn.com/6613/square/matopoietic-growth-factors.jpg)
A growth factor is a naturally occurring substance capable of stimulating cellular growth, proliferation, and cellular differentiation.
Many tissues within the body release hormones including the placenta, kidneys, digestive system, and adipose tissue.
![Thumbnail](../../../../../figures.boundless-cdn.com/8944/square/250px-gray589.jpg)
The gonads in males are the testes and the gonads in females are the ovaries.
![Thumbnail](../../../../../figures.boundless-cdn.com/8946/raw/placenta.jpg)
The placenta is an organ that connects the developing fetus to the mother's blood supply.
![Thumbnail](../../../../../figures.boundless-cdn.com/30923/square/basic-hpa-axis.jpeg)
The body's stress response is mediated by the sympathetic nervous system and the hypothalmic-pituitary-adrenal (HPA) axis.
The fight-or-flight response is regulated by the release of adrenaline or noradrenaline.
![Thumbnail](../../../../../figures.boundless-cdn.com/6614/square/b7-c6f9-4293-8d70-56c00ae072cb.jpeg)
Resistance is the second stage of the general adaptation syndrome, where the body has an increased capacity to respond to the stressor.
![Thumbnail](../../../../../figures.boundless-cdn.com/1899/square/eneral-adaptation-syndrome.jpeg)
Exhaustion is the depletion and inability to maintain normal function and often results in physical illness.
![Thumbnail](../../../../../figures.boundless-cdn.com/31404/square/ptsd-stress-brain.gif)
Over-activation of the stress response can result in pathology and disease.