A closer look at the Endocrine system

What composes the Endocrine system?
The Endocrine system is composed of several glands including pineal, pituitary, hypothalamus, parathyroid, thyroid, thymus, adrenal, pancreas, testes and ovaries.  These endocrine glands can synthesize and release hormones directly into the blood in response to specific signals (McCance & Huether, 2017). 

How is the Endocrine system regulated?
Endocrine glands secretion can be regulated by a hormone manufactured by another gland or nervous system input (Mallya & Ogilvy-Stuart, 2018).  In fact, the endocrine system works together with the nervous system to accomplish and maintain homeostasis.  The mechanism usually used by the endocrine system to regulate biologic control is the negative feedback loop (Patton & Thibodeau, 2013).

What are some types of stimuli?
There are three types of stimuli that usually initiate the synthesis and release of hormones; the hormonal, humoral and neural mechanisms.  The hormonal stimuli function by controlling the release of a hormone that’s been stimulated by another hormone. The humoral is activated by changes in blood levels of ion and nutrients, such as glucose or calcium (McCance & Huether, 2017).  Lastly, the neural control functions by the release of electrical signals from one neuron to the next, such as the sympathetic nervous system releasing catecholamines from the adrenal medulla during stress (Patton & Thibodeau, 2013). 

What is the pituitary gland made up of?
The pituitary gland is located within the sella turcica and is connected to the hypothalamus by a stalklike infundibulum (Patton & Thibodeau, 2013).  The pituitary gland is made up of two separate glands, the anterior pituitary gland (adenohypophysis) and posterior pituitary gland (neurohypophysis).

What is the location and function of the hypothalamus?
The hypothalamus is located at the base of the brain, near the pituitary gland (McCance & Huether, 2017).  The negative feedback mechanism is the instrument used by the hypothalamus to regulate secretions from the adenohypophysis, while the adenohypophysis adjusts the secretions of its target glands, which in turn alters the activity of the target tissues (Patton & Thibodeau, 2013).  The hypothalamus releases hormones that have inhibiting effects on the adenohypophysis. Some of those hormones include the growth hormone-releasing hormone (GHRH), growth hormone-inhibiting hormone (GHIH), corticotropin-releasing hormone (CRH) and the Gonadotropin-releasing hormone (GnRH) (McCance & Huether, 2017). 

Additional endocrine components 

• pineal gland 
• thyroid and parathyroid glands 
• pancreas 
• thymus 
• adrenal glands 
• ovaries (in females) 
• placenta (during pregnancy) 
• testicles (in males) 

References

Mallya, M., & Ogilvy-Stuart, A. L. (2018). 2: Thyrotrophic hormones. Best Practice & Research Clinical

Endocrinology & Metabolism, 32(SI: Hormones in milk - Part II), 17-25. doi:10.1016/j.beem.2017.10.006

McCance, K. L., & Huether, S. E. (2017). Pathophysiology: the biologic basis for disease in
adults and children. St. Louis, MO: Elsevier.

Patton, K. T., & Thibodeau, G. A. (2013). Anatomy & physiology. St. Louis, MO: Mosby/Elsevier.