Endocrine system

The Endocrine System is a chemical messenger system comprising feedback loops of hormones released by internal glands of an organism directly into the circulatory system, regulating distant target organs. In humans, the major endocrine glands are the thyroid gland and the adrenal glands. In vertebrates, the hypothalamus is the neural control center for all endocrine systems. 

The human endocrine system consists of several systems that operate via feedback loops. Several important feedback systems are mediated via the hypothalamus and pituitary. 

Endocrine glands are glands of the endocrine system that secrete their products, hormones, directly into interstitial spaces and then absorbed into blood rather than through a duct. The major glands of the endocrine system include the pineal gland, pituitary gland, pancreas, ovaries, testes, thyroid gland, parathyroid gland, hypothalamus and adrenal glands. The hypothalamus and pituitary gland are neuroendocrine organs. 

There are many types of cells that comprise the endocrine system and these cells typically make up larger tissues and organs that function within and outside of the endocrine system. 


What is the endocrine system composed of? 

  • Glands that produce hormones that regulate metabolism, growth, development, tissue function, sleep and mood. 



  • Chemicals produced in one part of the organism that affects another. 


What do endocrine glands do? 

  • Release hormones (chemical messengers) into the blood. 


What do hormones do? 

  • Deliver messages throughout the body. 


Target cells.. 

  • ..have receptors for particular hormones. 


If a cell doesn’t have a receptor for a particular hormone.. 

  • ..that hormone has no effect on that particular system. 


2 types of glands: 

  • endocrine glands  
  • exocrine glands 


What do exocrine glands do? 

  • Produce and release non-hormonal secretions through ducts. 


What are ducts? 

  • Small, tubelike structures 


Exocrine secretions: 

  • Sweat, tears, digestive enzymes 


Endocrine glands include: 

      – hypothalamus  

      – pituitary gland  

      – pineal gland  

      – thymus 

      – thyroid 

      – parathyroid  

      – pancreas 

      – adrenal glands  

      – ovaries (females) 

      – testes (males) 



  • found in brain  
  • makes hormones that control and are stored in pituitary gland  
  • link between CNS and endocrine system 
  • controls body temperature, thirst, and hunger 


        Pituitary gland 

  • found in brain  
  • master gland  
  • produces hormones that regulate many of the other endocrine glands and some organs 


        Pineal gland 

  • found in brain 
  • releases melatonin, which is involved in sleep cycles 



  • found in chest 
  • stimulates immune response by producing T-cells (lymphasites: a type of white blood cell) 
  • also part of lymphatic system 



  • found in neck region  
  • regulates metabolism 



  • humans usually have 4 parathyroid glands 
  • found in back of thyroid 
  • controls calcium 



  • mid-section by stomach 
  • regulates blood sugar  
  • both endocrine and exocrine gland  
  • failure results in diabetes(type 1: no insulin, type 2: hard time regulating) 


        Adrenal glands (also known as suprarenal glands) 

  • found on top of kidneys  
  • produce adrenaline (response to stress) 
  • produce steroids aldosterone and cortisol 
  • helps body respond to stress 



  • found in pelvic region  
  • releases estrogen to develop secondary sex characteristics  
  • eggs develop 
  • produces hormones that prepare uterus for fetus 



  • found in pelvic region 
  • releases testosterone to develop secondary sex characteristics  
  • responsible for sperm development 



Adrenaline (also known as epinephrine) is a hormone of adrenal glands: 

– helps respond to stress (fight-or-flight response) by increasing blood flow to muscles, output of the heart, pupil dilation response, and blood sugar level.  

– causes increased heart rate 



Aldosterone, the main mineral corticoid hormone, is a steroid hormone. It is essential for sodium conservation in the kidney, salivary glands, sweat glands and colon. It plays a central role in the homeostatic regulation of blood pressure, plasma sodium (Na+), and potassium (K+) levels.  



Cortisol is a steroid hormone, in the glucocorticoid class of hormones. In the early fasting state, cortisol stimulates gluconeogenesis (the formation of glucose), and activates antistress and anti-inflammatory pathways. When used as a medication, it is known as hydrocortisone.