More physiology — communication, circulation, immunity

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The body as communications and control network

Chemical and electrochemical communications between regions and organs of the body take place constantly.

We have seen feedback processes which control certain reactions,

  • allosteric binding of reaction products;
  • control of lactose-digestion enzymes;
  • blood sugar levels controlled by insulin and glucagon;

as well as direct communication of muscle-control signals by the ANS.

We can anticipate the next chapter, on neuroscience, and see communications at work in other ways:

  • conveying sensory data input to the brain;
  • control of body functions by the central and peripheral nervous systems.

In addition to these two communication methods (chemical feedback and nervous-system control), another important system exists – hormones, the subject of which constitutes what has long been called the endocrine system (ES), although it is now known that hormones are also produced elsewhere.

The nervous system (NS) receives information from sensory organs dispersed throughout the body and in turn transmits information outwards, such as to a particular muscle-cell. Communication takes place at speeds on the order of 100 meters/second and so can reach any part of the body in less than 0.01 seconds. The effect of the output, such as a muscular contraction, lasts only a short time, so the action is specific, fast and short-term.

Compared to this, communication by the endocrine system is slow and less specific, but durable. Endocrine communication takes place through the transmission of chemical messengers called hormones. Hormones are chemicals which are synthesized by tissues which may exist in specific organs called glands or in tissues or organs which also have other functions, like the pancreas.

Hormones travel through the blood until they encounter cells with special receptors which match the hormone. Any such cell may be affected. What happens then depends on the hormone and on the receiving cell. Hormones influence many bodily functions at different levels.

One may imagine a metaphor based on modern telecommunications and good ol’ radio. If the nervous system is a high-speed point-to-point link, then the hormonal system is a low-speed broadcast from a point to any stations which may be tuned to that frequency.

Another metaphor is more anthropomorphic. Chemicals which permit communication are like messengers and that is what they are often called. We will meet a number of them.

The ES and the NS work together to optimize functioning of body processes.

We will look at the following subjects:

The endocrine system — hormones

The human circulatory system

The immune system

The lymphatic system

Then we will move on to neuroscience — soon.