External Sphincter of Man,
That’s What!

I guess there may be the slightest interest in what I, [Cerebrl], am up to. You know, the guy that runs this little blog. Well, I have been busy with school. Yes, school. Well, that and being politically active, developing a website (paid project that is, yea!), working for an after (urban) school program and trying to get back into working out. At the moment, I am taking microbiology, and human physiology in a short summer semester. If you are interested, here is what I had to write about this week for physiology:

External Sphincter of Man

1. Red and white muscle fibers differ in appearance due to the purpose that they serve. Red, or slow twitch muscle fiber’s purpose is for sustained, relatively lengthy use, or repetitive contractions without premature fatigue. They are commonly referred to as the endurance muscle because of their use in endurance type activities (ie. biking, running, swimming). To be capable of this type of use, these muscle fibers have a higher amount of mitochondria, the cellular organelle responsible for aerobic energy production (creation of ATP); and to supply the aerobic, or oxygen needs of these mitochondria, these muscle fibers have a rich capillary supply to deliver the oxygen to the muscle, as well as an abundant amount of myoglobin. Myoglobin is a muscle’s way of storing oxygen for use at a later time. The abundance of mitochondria and myoglobin is what gives the muscle a red appearance. This type of muscle does have a ownside, and that is it contracts more slowly, relative to its counterpart, white muscle fibers, and cannot generate a high amount of force due to their thinness. When high amounts of force are needed quickly, red muscle fiber’s design starts to fail due to the body’s inability to rapidly supply oxygen to the needed fibers, due to their use of fat, a slower energy source, as a fuel and their relative thinness.

White, or fast twitch fibers are quite the opposite to red fibers. These fibers are for powerful, quick activities and fatigue rapidly. They are white due to the lack of the oxygenated pathways for energy — mitochondria and myoglobin. These muscles utilize a more anaerobic environment for energy and are twice the thickness of red fibers. What they lack in mitochondria and myoglobin the make up for in glycogen stores. Glycogen is a polysaccharide, or long chain of sugars, that serves as a quick available source of energy. The production of energy used is the glycolytic pathway, an anaerobic production of energy by the use of glycogen reserves, and has two downsides: limited energy reserves, and a by product that causes quick muscle fatigue, lactic acid.

The rationale for the author’s hypothesis is that the external anal sphincter has a responsibility of sustaining a continuous contraction to hold the feces within the body. The design of red muscle fiber seemed to fit as it would not fatigue, and fail to hold this contraction. White muscle fiber would not “suit the bill” as the need for a powerful, short contraction seemed counterintuitive. What the author’s discovered partially reinforced their hypothesis. They discovered through a histological exam of the external anal sphincter that there is a combination of the two muscle types, white and red muscle fibers.

2. The muscles that EMG recordings were measured were the external anal sphincter, the gluteus maximus, or butt muscles, and occasionally from the abdominal muscles (external oblique and rectus abdominis). All muscles were voluntary. To test this, the authors used an enema retention test (the holding of liquid in the colon) to measure the activity and the voluntary control of the anal sphincter and found that it was indeed voluntary. This creates a increased desire to release these contents, but because the subjects were told to retain the fluid, they had to voluntarily contract the sphincter. This powerful contraction was similar to the voluntary contractions that were asked of the subjects separate from this test. So, if the sphincter was an involuntary muscle, the subjects would have emptied the fluid from the colon, due to this increase in desire, and not had a conscious choose to do so.

3. The “resting tone” that was discussed in the author’s paper was referring to a partial contraction even while the subject was not consciously contracting or aware of his sphincter or while the subject was at rest. The authors measured this “resting tone” while the subjects were asleep to remove any conscious awareness of the sphincter and its measuring. They noticed that, although minimal, there was still a slight partial activity or contraction of the muscle. I would say that this seems quite reasonable due to our need to prevent defecation during sleep, relaxation or any other inconvenient time.

4. As subjects increased their intra-abdominal pressure the authors noticed a variation in activity in the external anal sphincter. When the subjects were asked to laugh, talk/shout, lift weights they noticed an compensatory increase in the muscles activity or tone. When the subjects were asked to give a maximal expiratory effort, or strain hard, there was an increase in activity of the sphincter causing the sphincter to close up as to prevent an accidental defecation. I feel this is functionally important due to basic physics. As one increases pressure within the abdomen, more pressure will be applied to all organs, and the colon would not be an exception. This extra pressure on the colon and the excrement that it contains could cause accidental defecation, so the anal sphincter increases its activity to compensate for this pressure.

5. During the author’s examination of the external anal sphincter during sleep, they found that this muscle does minimize the amount of contraction. This minimal contract, though very minimal, was always present, but what was also noticed was at any point during the sleep the subject was disturbed, there was an increase in contraction. Unfortunately, there are no figures for these measurements, but they did go on to say that they believed that the internal anal sphincter was responsible for the closure of the sphincter as well, but they had no data to support the claim due to the difficulty of measurement. This seemingly redundant system should be all that is needed to hold in any fecal matter during activity, rest, sleep or coughing.

Wow, that was sexy! Well, this is what I have to go through if I am going to get into medical school. Nothing like having to study the human anus.