Module 2 The Endocrine System

Self-Check

After a review of the lesson, complete the following multiple choice questions. Check your answers. Discuss with your instructor any concepts that you do not understand.

1. All of the following statements about hormones are correct except
   
   
   1. They are produced by endocrine glands
   2. They travel to target cells in the body
   3. They are carried by the circulatory system
   4. They are used to communicate between different organisms
      
      
2. The hypothalamus controls the anterior pituitary by means of
   
   
   1. tropic hormones carried by nerve cells
   2. nervous stimulation by the sympathetic nervous system
   3. releasing hormones in the bloodstream
   4. both nervous and hormonal stimulation
      
      
3. All of the following statements about the hypothalamus are correct except
   
   
   1. It functions as an endocrine gland
   2. It is part of the central nervous system
   3. It is subject to negative feedback.
   4. Its neurosecretory cells terminate in the anterior pituitary
      
      
4. Which of the following glands is controlled directly by the hypothalamus or central nervous system and not the anterior pituitary?
   
   
   1. pancreas
   2. adrenal medulla
   3. adrenal cortex
   4. posterior pituitary
      
      
5. In humans, the nervous and endocrine systems are similar in that both
   
   
   1. secrete chemical messages
   2. operate at the voluntary and involuntary level
   3. use highly specialized pathways
   4. respond very rapidly to stimuli
      
      
6. The main difference between the endocrine and nervous system is that only the endocrine system
   
   
   1. secretes chemical messengers
   2. is regulated by negative feedback
   3. depends on specialized neurosecretory cells
   4. relies completely on the circulatory system for transport
      
      
7. Compared with the response to a nerve impulse, the response to a hormone is usually
   
   
   1. shorter in duration and more widespread in effect
   2. shorter in duration and less widespread in effect
   3. longer in duration and more widespread in effect
   4. longer in duration and less widespread in effect

Lesson Summary

Inside your body, an action-packed medical emergency room drama is played out every minute of your life. If you were to photograph your blood and the nearby cells, you would see an incredible amount of ordered activity. For example, if you were to view thyroxine molecules being carried by the bloodstream and then persistently attaching themselves to muscle cells, you would see glycogen molecules being stimulated to change to glucose, mitochondria going into high gear and belting out ATP, and the blood warming up. This is the action of the endocrine system. However, it does not act alone it interacts with the nervous system to coordinate and integrate its activities. The release of those thyroxine molecules was stimulated by the release of thyroid stimulating hormone from the anterior pituitary, which was in turn regulated by the releasing hormones from the hypothalamus, an important coordinating centre in the brain. High levels of thyroxine shut down the releasing hormones and TSH by negative feedback.

The nervous system operates like our telephone system, whereas the endocrine system works more like our postal system. The nervous system regulates the activity of muscles and glands through electrochemical impulses in specific neural pathways that travel to them in milliseconds. The endocrine system influences cells by means of hormones carried by the blood. There is a lag period of seconds, minutes, sometimes days, or even years before the target tissue responds. Hormones target a broader range of cells than nerves do and they have widespread and diverse effects. The major processes controlled by hormones include reproduction (Unit B), growth and development (of the body and nervous system), reaction of the body to stress, maintenance of ion concentrations (sodium, calcium), water and nutrient (glucose) levels, and regulation of metabolism and energy balance.

Both systems include responses regulated by negative feedback. Epinephrine and norepinephrine are common to both systems. Nervous tissue, such as that in the posterior pituitary, the adrenal gland, and the hypothalamus secretes hormones. Some hormones influence the normal development and function of the nervous system (thyroxine and human growth hormone). Some processes cannot be regulated without both systems working together: homeostasis depends upon both systems. When this balance is disrupted, medical technologies developed by scientists, such as synthetic insulin, thyroxine, and ADH pills, glucose monitors, insulin pens, various surgeries and radiation treatments are used to re-establish it.