Vol. 3, No. 7
Within the body of man and most animals, God has created a group of organs that causes a uniquely animal characteristic, that of movement. The more than 600 muscles in our body allow, among other things, graceful movements, movement of food and even cause our passage into this physical world at birth. Let's examine how movement is made possible by the muscles of our bodies.
There are three distinct types of muscles: the skeletal muscles, the cardiac muscle and smooth muscles. Each of these has been designed with a very specific type of makeup that allows them to function in very different ways. The overall functions of the muscle system include movement, heat production, stabilization of body position and protection.
The skeletal muscles are also called voluntary or striated muscle. This refers to how they are controlled and how they look under microscopic examination. Basically, they attach to bones and cause the skeletal system to move. They are controlled by direct signals of the brain when we want to move in a certain way. They contain two very distinct types of proteins -- one thick and one thin. This arrangement causes a striped appearance, giving it the name striated muscle. These muscles can produce some tremendous forces, as in the case of "hysterical strength" where humans have done superhuman feats. This is probably possible because the muscle filaments all function at the same time, instead of alternating on and off.
The smooth muscles are also called involuntary or visceral muscles. This refers again to how they are controlled and look. These muscles are found in organs such as the digestive system, eyes, urinary system and many other places where we have muscles that are controlled by our autonomic nervous system. They operate as they are needed and are controlled by nerve impulses from the organs to the brain and turned on and off. Our food is moved through the digestive system without our thinking about it.
The cardiac muscle is that muscle which is found only in the heart. These muscles are self-exciting as they have their own electrical impulse system. Our heart must pump blood every minute, hour and day of our lives for us to remain alive and yet it still finds time to rest for about half of our lives.
The muscle system is indeed a wonderfully coordinated system controlled by the brain. It takes the signals from the central nervous system that allows us to get all of the muscles moving together to make coordinated movement possible. As we watch a baby learning to walk, we are seeing the brain and muscles learning to communicate back and forth. It will take much trial and error before everything is "fine tuned" just right and the baby takes off walking.
As we use our muscles, they increase in size as more fibers are added to the muscle. This process is called hypertrophy. When we do not use the muscle, it will remove muscle fibers and decrease in size or atrophy. This allows us not to carry around muscles that we are not going to need for the rest of our lives. As we increase our physical activity, we will begin to grow the needed muscle for our activity. The inspired apostle Paul indicated that physically we would grow when we made an effort, just like we would in our spiritual lives. Sometimes athletes say, "No pain, no gain." This reflects that we must physically move our muscles in order to get stronger.
Our bodies are indeed "the temple of God." We should make every effort to keep that temple in the best physical condition so that it can be used by God for service to him.
The digestive system of our bodies is a very central part of our daily lives. We give it much attention, especially as mealtime rolls around. Hunger is indeed one of the most powerful human needs. People who hunger and thirst will indeed make every effort possible to fill those needs, including some very extreme measures, even resorting to murder. When Esau was hungry, he was willing to sell his birthright for a bowl of porridge. That may be why Jesus used this very symbolism to teach how we should desire his Word, "Blessed are those who hunger and thirst after righteousness, for they shall be filled" (Matthew 5:6).
While we might know that we need to eat regularly and enjoy doing so, we generally know very little about this amazing creation in our bodies. Let's examine some of the basics of how the organs of this system, which are more than thirty feet in length, function to supply the cells of the body wit the materials necessary to keep them alive. This involves some very intricate activities. We are very familiar with the function of the tongue and taste buds, as they make eating the enjoyable activity it is. Once our food has been chewed and tasted, it is swallowed as a "bolus" or ball of food. The esophagus is a muscular organ that pushes our food to the stomach. If we were standing on our heads or even in zero gravity like space, we could still swallow. Once into the stomach, the major actions of the digestive system begin -- that of breaking down the food into smaller pieces.
The stomach is a "J-shaped" organ whose function is primarily to store our food. Food will stay in the stomach about four to six hours and be released very slowly into the small intestine. The stomach does digest some proteins that are in the food. It does this with a chemical called pepsin. This chemical is very strong and will digest a piece of meat very quickly. This chemical is produced by the cells of the stomach, and that would be digested by the pepsin, if it were active. But the Lord designed the cells to produce the pepsin in an inactive form called pepsinogen. When this is released into the stomach, the hydrochloric acid in the stomach activates it. The hydrochloric acid is produced in a similar fashion and causes the acid base balance of the stomach to be very acidic, having a pH of about 1.0. The stomach is lined with a thick mucous that prevents these dangerous chemicals from getting against the cells lining the stomach. The stomach has purse string muscles that close the openings into and out of it. If these do not work correctly, then we have acidic juices splashing back into the esophagus, producing the experience of "heartburn" or releasing the partially digested foods too soon into the first part of the small intestine.
The small intestine is the real workhorse of the digestive system. This is where most of the digestive and absorption is done. There are three parts to this section of the digestive system. They are the duodenum, jejunum and the ilium. The duodenum is where many other digestive juices are produced. This is where the sugars, carbohydrates and the rest of the proteins are digested or broken down into smaller pieces that can be absorbed into the bloodstream and then reassembled by the cells to build our bodies. To digest our food requires the secretions of the liver, pancreas and intestines to break down everything we need to stay alive. After breakdown, the materials are absorbed by the two remaining parts of the small intestine. These parts have special finger-like projections called microvilli. This increases the surface area of the intestines hundreds of times, allowing for more food absorption. At the end of the small intestine is another purse string valve that controls the passage of unabsorbed food into the large intestine or colon.
The large intestine is mainly for the storage of undigested food and for the re-absorption of water which was added to the food to keep it in a semisolid condition so it would flow. At the beginning of the large intestine is the structure known as the appendix. Evolutionary biologists say that this is a vestigial organ or one left over from our earlier evolutionary development when our ancestors ate leaves and plants more commonly. They believe that because the appendix has no function in the adult that it is unused. But they are wrong. In the baby, the appendix is very involved in the control of bacteria in the digestive system. It contains a lot of tissue, called lymphoid tissue, that fights bacteria. As the baby grows and its immune system becomes fully developed, then, the appendix, like the tonsils in the upper digestive tract, can be removed without a noticeable loss of function. But, it is not a vestigial organ as many want to believe.
The digestive system ends with the undigested food being utilized by bacteria known as E. coli that live in the large intestine. This bacteria breaks down the plant material, uses it for food and then releases the chemical we call vitamin K, which we absorb for our use. This very important relationship is critical to the existence of both, but these guests can sometimes present us with an unwelcome problem of intestinal gas which they release.
We can see, then, that the digestive system is an amazingly complex set of organs -- that all functions together to provide us with the necessary nutrients for life. With any one part not doing its job properly, the whole system becomes much less effective.
"I will praise the Lord for I am fearfully and wonderfully made."