Module 2 Lesson 7 - 5

Lesson Summary

Inside your body, an action-packed medical emergency room drama is occurs 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, you would see 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. Then, you would see mitochondria going into high gear and belting out ATP, and the blood warming. 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 regulated by the releasing hormones from the hypothalamus, an important coordinating centre in the brain. High levels of thyroxine stop the releasing hormones and TSH by negative feedback.

The nervous system operates similar to e-mail, and the endocrine system works more similar to snail mail. 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. A lag period of seconds, minutes, sometimes days, or even years occurs 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) as well as 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, ADH pills, glucose monitors, insulin pens, various surgeries, and radiation treatments, can re-establish it.