Wednesday, October 29, 2008

Metabolism V: Aerobic Metabolism vs. Anaerobic Metabolism

This will be a quick post comparing aerobic and anaerobic metabolism. Aerobic metabolism refers to metabolism that requires oxygen and anerobic metabolism refers to metabolism that does not require oxygen.

Aerobic glucose metabolism (aerobic glycolysis) is the most common form of glucose metabolism in our bodies. Fat metabolism also falls into the aerobic glycolysis pathway; thus, fat metabolism requires oxygen also.

Anaerobic glucose metabolism (anaerobic glycolysis) occurs in oxygen deprived cells and cells which cannot preform aerobic glycolysis (e.g. red blood cells). A byproduct of anaerobic glycolysis is lactic acid, which we will discuss more in a later post.

Aerobic glycolysis generates almost 10 times as much energy as anaerobic glycolysis. This is the principle reason we die if we don't have enough oxygen.

Next time, I will talk about how metabolism plays a role in exercise.

Metabolism IV: The Role of the Liver

The liver has a number of different purposes within the body. One of its key functions is to maintain metabolic nutrient levels in the blood. When blood sugar is high, the liver stores glucose. When blood sugar is low, the liver releases glucose from these glucose stores. The liver can also convert some fats and proteins into glucose, which it releases into the blood stream.

The next post will compare aerobic vs. anaerobic metabolism.

Sunday, October 19, 2008

Metabolism Part III: How and Why Our Bodies Use Fat

Our bodies use fat for energy for two main reasons.

The first reason is cyclic. We use fat for energy because when we have an abundance of energy, such as after we have had a meal, we store the excess carbs and proteins as fat. We convert the excess carbs and proteins into fat for storage because fat is a very efficient storage medium. One hundred calories of fat has less mass and volume than one hundred calories of carbohydrate.

The second reason is that the brain uses primarily glucose as its fuel source. The brain does not use fat as an energy source because fat cannot cross the blood brain barrier. Since the brain is kind of important, when blood glucose levels are not high, other cells in the body switch fuel sources from blood glucose to fat. Thus, the blood glucose is saved for the brain.

As a side note, during starvation, when blood glucose levels drop, the brain can use ketone bodies as a secondary fuel source. Ketone bodies are derived from fatty acids. However, even during starvation, the brain gets at least 25% of its energy from glucose.

In my next post, I will discuss the liver's role in maintaining blood glucose levels.

Saturday, October 18, 2008

Metabolism Part II: Regulation

In part one of my discussion about metabolism I discussed the different fuel sources. In part two, I will discuss metabolic regulation, starting with hormones. Hormones are biological compounds made in one part of a body to control another part of the body. The two main hormones that regulate metabolism are insulin and glucagon.

Insulin is secreted from the pancreas and signals muscle cells and fat cells to get their energy from blood glucose. Insulin also signals fat cells to convert excess blood sugar into fat and muscle cells to store excess blood glucose as glycogen (Don't know what glycogen is? Don't worry, glycogen will be discussed later).

Glucagon, which is also secreted from the pancreas, signals actions that oppose insulin. Glucagon inhibits fat and glycogen production. Glucagon signals muscle cells and fat cells to get their energy from stored fat. Thus, glucagon promotes fat breakdown (lipolysis).

There are other hormones that regulate metabolism. They all work similarly to glucagon and oppose the actions of insulin. However, I will not be discussing them here because they go beyond the scope of my talk about metabolism.

Insulin AND glucagon are ALWAYS present in your blood (assuming you're health, i.e. not a Type 1 diabetic). Their effect on your metabolism are dependent on their relative ratio. If you have more insulin than glucagon in your blood, then your body is probably making fat. If you have less insulin than glucagon in your blood, then your body is probably burning fat.

As you can imagine, immediately after a meal, your pancreas secretes more insulin. Your body wants to get its energy from the recently consumed sugars instead of its own energy stores (your fat). However, when you haven't eaten for a while, your pancreas secretes glucagon. This is because it wants your muscle and fat cells to get their energy from your fat stores, not your blood sugar. I'll discuss why in my next post.

Thursday, October 16, 2008

Metabolism Part I: Fuel Sources

We're learning about metabolism this week. Personally, I find the subject interesting because understanding metabolism can put a lot of fad diets and workout myths to rest. I've looked up information regarding these workout myths before, but never found a single source of information that discussed them.

Remember, I'm learning about metabolism for the first time right now and we are learning just a BRIEF overview of metabolism right now. That is to say, the concepts I am describing in the next few posts have been simplified and gloss over the true complexity of our metabolism.

This first post will describe fuel sources. Our bodies need energy. In our bodies, energy is ATP, a molecule that is used to power many cellular reactions. ATP can come from carbohydrates, proteins, and fats.

Sugars are carbohydrates. There are several different kinds of sugar, but the main one that is discussed with regards to metabolism is glucose. The process of turning sugars into ATP is called glycolysis. Glycolysis can occur with or without oxygen. However, more ATP are generated when glycolysis occurs with oxygen because one of the products of glycolysis can go onto generate further ATP when oxygen is present.

Fats are made up of fatty acids and a molecule called glycerol. Glycerol can be converted to glucose and make ATP through glycolysis. Fatty acids can make ATP through a different process called beta oxidation. Beta oxidation requires oxygen.

We generally do not want our bodies to use protein as a fuel source because proteins have many other tasks in our body. Proteins are responsible for cell stability, building muscles, and many other tasks. However, some proteins can be transformed into glucose and generate energy through glycolysis. Other proteins can generate ATP through the oxygen dependent path discussed with carbohydrates.

Next, I'll discuss hormones.

Sunday, October 12, 2008

Exercise: Taking Your Health Into Your Own Hands

When you see a doctor because you are ill, your doctor will provide you with a list of suggestions to help make you healthy again. These suggestions can range from taking antibiotics to fight an infection, to icing a sprained elbow. One common suggestion on every list, regardless of the illness, is exercise. Even if you have a torn ligament or broken bone, your doctor will suggest that you, in time, exercise the injured body part.

In family practice, I was interviewing a patient who had migraines. These migraines were excruciating and he said he would do anything to stop them from happening. He told me that the migraines came on after bouts of insomnia. He was also pre-hypertensive, which means his blood pressure is slightly higher than it should be. Now, considering exercise can help reduce blood pressure, and regular exercise can help regulate your sleeping cycle, I asked about the patient's current exercise regime. Turns out that he does not exercise, at all. It turned out that my preceptor (the doctor who runs the practice) had suggested exercise to this patient in the past, many times, without success. This patient would rather try a boatload of different pills than exercise 3 times a week.

The sad part is that this is not an uncommon occurrence among patients. Many patients do not exercise regularly, even when their chief health complaint may be solved by regular exercise. People would rather take medication with all kinds of scary side effects than jog around the block a couple times a week. Even more frightening, I say this living on the west coast, where we supposedly have a healthier style of living than our fellow Canadians living on the east coast.

Considering the economic slowdown we are facing, I wonder how many health care tax dollars could be better used elsewhere if people would just exercise more often.

Saturday, October 4, 2008

First Year Med Student vs. Instructor

If you've ever been to university, or talked to anyone who has gone to university, you have probably heard about the keeners who try to show off their knowledge by attempting to outsmart their professor. This can vary from asking an on-topic question from an article that was just published the day before to asking a question that is completely unrelated to the subject of the course. The bottom line is, the keener never looks smart; in fact, the person asking these questions are often privately despised by most of the class an often the professor too. On the bright side, hating the keener brings everyone else together, so really, they help to unite a class.

Now, the behaviour I just mentioned generally occurs in third or fourth year, when the undergraduate students have a good fundamental understanding about the area they are studying. Many of these keeners are in fact smart (academically, not socially), and if they are keeners in biology, they often find their way into medical school. The problem is, at this point, they've developed this keener behavior and they cannot stop trying to show off how smart they are. However, what they don't seem to grasp is that they are first years again, not third years who understand the fundamentals. This can lead to a beautiful moment if you have a professor who is not willing to be patient with this kind of immaturity.

Scenario 1

Keener 1: "Question, I see the thymus gland is located on the chest wall, this is different than in a fish, why is that?"

Professor: "Get a life (whispering to himself)...I'm sorry, I'm not a marine biologist, nor do I study evolution. In fact, I'm pretty sure I introduced myself as a medical doctor at the beginning of the lecture."

Note, whispering to yourself is not effective when you are presenting to a class of 300 student and thus, you have a microphone stuck to the side of your head.

Scenario 2

Professor: "Now, can anyone tell me what would make you suspect a pregnant woman is carrying a fetus with a tracheoesophageal fistula (a condition wherein your food pipe, the esophagus, is not a single pipe, but instead is interconnected with your wind pipe, the trachea)?

Keener 2: "Use an ultrasound?"

Professor: "evil laugh...Without using any technology...this is the art of medicine folks, we can't always rely on our toys!"

...nobody knows...

Professor: "If the mother's belly is larger than you'd expect, this would lead me to suspect there is amniotic fluid (fluid in the placenta that surrounds the fetus, it contains fetal waste and also nourishes the fetus too...yeh I know, gross!) buildup, and that is a sign the fetus has a tracheoesophageal fistula!" (because the fetus is not absorbing the amniotic fluid because it cannot swallow it properly)

Keener 3: Trying to prove how smart she is by proving the professor is wrong "Um...obviously you still need an ultrasound because the stomach would also be bigger if the mother was having twins!" self satisfied grin

Professor: "No. You can palpate to see how many fetuses the mother is carrying. Want to try again? Seriously, I can do this all day.

First year med students need to realize they don't know anything compared to their profs...asking questions is great. You are at school to learn. However, trying to show off is arrogant and pointless. It wastes EVERYone's time, including your own!

Friday, October 3, 2008

More Efficient Doctors = Bad For More Vulnerable Populations

As first year med students, we have a class called Doctor, Patient, and Society. The main goal of this class is to discuss social and ethical issues facing doctors and what their role is with their patient, in a community, and in society at large.

The other day we were talking about vulnerable populations. The focus of the lecture was a discussion about sub groups of patients that are more general than an average patient. Examples are immigrants, poor patients, and children.

An interesting issue that was brought up was that the government is demanding doctors see more patients per hour than before. On the surface, this seems like a decent idea because Canada is facing a doctor shortage; thus, getting each existing doctor to see more patients helps reduce this problem. However, making doctors see more patients per hour turns out to have negative consequences for immigrant populations. Immigrants, who don't speak english fluently, have a much harder time communicating with their physician. Thus, it takes much longer for a doctor to see an immigrant for a regular visit. In order for doctor's to see more patients in a shorter period of time, they need to see patients who can present their problems quickly. That kind of patient is usually a person who is well educated and fluent in english.

In order to help the majority, the minorities suffer. It's unfortunate that sometimes vulnerable populations just become more vulnerable, even when we are trying to help.