Introduction
According to nutritionists, humans are known to consume a greater percentage of meals rich in carbohydrates compared to other classes of food. Common examples include: rice, bread, milk, ice cream, cookies, etc.
In my previous articles, I pinpointed the importance of glucose (as the main precursor) in carbohydrate metabolism. However, for glucose to act as precursor, it must first be taken up by cells.
Importance of glucose uptake
Glucose uptake is very essential to skeletal muscle, cardiac muscle, and adipose tissues. This is because it's the best fuel for muscles and tissues. The skeletal muscles comprises of the main framework that supports and protect the body. Cardiac muscles trigger the pumping and circulation of blood. At the same time, adipose tissues supplies the body with fat.
With that in mind, imagine a situation whereby an individual suffers from glucose uptake deficiency. It therefore means that the entire human body processes are directly affected too.
Glucose transporters
After a carbohydrate meal, glucose accumulates in the blood. Glucose uptake from the blood is mediated by glucose transporters (GLUT 1 to 4). However, the one we'll focus on is GLUT 4 which is the main glucose transporter in the cells of skeletal muscle, cardiac muscle, and adipose tissues.
It is worthy of note that, GLUT 4 is sequestered in small intracellular vesicles and moves into the plasma membrane only in response to an insulin signal. This therefore means that, if there's no signal from insulin, GLUT 4 will not move to perform its function (glucose uptake).
Mechanism of insulin signaling
By User Meiquer, wikicommons, cc BY - SA 3.0
"Insulin is excreted from the pancreas, and circulates in blood before binding to an insulin receptor expressed on the surfaces of adipocytes (fat cells) and myocytes (muscle cells)". Source
Once insulin binds to its receptor, this in turn starts many protein activation cascades. These include: translocation of GLUT 4 to the plasma membrane, influx of glucose and glycolysis synthesis.
In response to elevated blood glucose, pancreatic β-cells must cause normal release of insulin. Unfortunately, individuals with type 1 diabetes mellitus (also called insulin-dependent diabetes) have very few β-cells, and thus cannot release sufficient insulin that could enable glucose uptake by cells of skeletal muscle, heart, or adipose tissue. This leads to abnormal high level of glucose in blood (a condition known as hyperglycemia).
Since the cells are unable to take up glucose; muscle and fat tissues use the fatty acids (of stored triacylglycerol) as their principal fuel. Acetyl coA derived from the breakdown of this fatty acids in the liver is converted to ketone bodies. These ketone bodies (acetoacetate and β-hydroxybutyrate) are carried to other tissues to be used as fuel; this can lead to ketoacidosis.
References
Glucose uptake
Glucose transporters
Ketone bodies
Nelson, D. and Cox, M. (2011). Principle of Biochemistry, 5th edition. New York: W. H. Freeman and company, page 539.
Image source
All images are from wikicommons licensed under creative commons and eligible for commercial use.
I would like to point out something:
You've mentioned glucose as an essential energy source for cardiac muscle. This might be a wrong information. In a Biochemistry textbook written by Jeremy M. Berg, John L Tymoczko and Lubert Stryer, it was stated that:
Maybe you should get your fact straight.
Thanks for reading and also for the contribution. But I want to correct an impression you just made. In science, one man's work cannot overrule another if his work isn't supported by other scientists.
The fact i stated there is being confirmed by so many scientists and researchers, so a single textbook doesn't prove it wrong. However, I'm grateful you pointed me to it, I'll have to read more on it. Thanks once again.
Well, it would be unreasonable to quote 50 texts just to give you an idea, isn't it? If there is other literature which proved that cardiac muscles use glucose more than acetoacetate, you can state your references and reading materials. It would be better for a STEM-related article anyway. Sometimes a single textbook is capable of changing the view of hundreds. Whatever that has been proved in the past doesn't mean it is still true now. It's how knowledge expanded. Do your reading and let me know if you found something valid.
No problem
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Thanks boss