Why cells need glucose

In addition, by burning the protein in the cell, it is, in fact, slowly killing the cell. This can lead to a wide range of problems. In the short-term, high blood sugar can lead to anything from confusion to coma or death. Even slightly high blood sugar can lead to longer-term problems that can include liver or kidney damage, which in turn contributes to high blood pressure and heart disease.

A balanced diet, exercise and medication can protect the body from blood sugar issues. The team of proivders at Alrington Family Practice are dedicated to helping you face the challenge of diabetes. From diagnosis to management, they can help you maintain a healthy lifestyle. Call our office at or use our online booking tool to schedule an appointment at our office in Arlington, Massachusetts.

If all the talk of vaccines has left you in need of a refresher on which vaccinations babies need to stay healthy, check out this post for an up-to-date list. So how should you react? Muscle cells use fatty acids, glucose, and amino acids as energy sources. Most cells use glucose for ATP synthesis, but there are other fuel molecules equally important for maintaining the body's equilibrium or homeostasis. Indeed, although the oxidation pathways of fatty acids, amino acids, and glucose begin differently, these mechanisms ultimately converge onto a common pathway, the TCA cycle, occurring within the mitochondria Figure 1.

As mentioned earlier, the ATP yield obtained from lipid oxidation is over twice the amount obtained from carbohydrates and amino acids. So why don't all cells simply use lipids as fuel? In fact, many different cells do oxidize fatty acids for ATP production Figure 2. Skeletal muscle cells also oxidize lipids.

Indeed, fatty acids are the main source of energy in skeletal muscle during rest and mild-intensity exercise. As exercise intensity increases, glucose oxidation surpasses fatty acid oxidation. Other secondary factors that influence the substrate of choice for muscle include exercise duration, gender, and training status. Another tissue that utilizes fatty acids in high amount is adipose tissue. Since adipose tissue is the storehouse of body fat, one might conclude that, during fasting, the source of fatty acids for adipose tissue cells is their own stock.

Skeletal muscle and adipose tissue cells also utilize glucose in significant proportions, but only at the absorptive stage - that is, right after a regular meal. Other organs that use primarily fatty acid oxidation are the kidney and the liver. The cortex cells of the kidneys need a constant supply of energy for continual blood filtration, and so does the liver to accomplish its important biosynthetic functions.

Despite their massive use as fuels, fatty acids are oxidized only in the mitochondria. But not all human cells possess mitochondria! Although that may sound strange, human red blood cells are the most common cells lacking mitochondria. Other examples include tissues of the eyes, such as the lens, which is almost totally devoid of mitochondria; and the outer segment of the retina, which contains the photosensitive pigment.

You may have already guessed that these cells and tissues then must produce ATP by metabolizing glucose only. In these situations, glucose is degraded to pyruvate, which is then promptly converted to lactate Figure 2. This process is called lactic acid fermentation.

Although not highly metabolically active, red blood cells are abundant, resulting in the continual uptake of glucose molecules from the bloodstream. Additionally, there are cells that, despite having mitochondria, rely almost exclusively on lactic acid fermentation for ATP production. This is the case for renal medulla cells, whose oxygenated blood supply is not adequate to accomplish oxidative phosphorylation. Finally, what if the availability of fatty acids to cells changes?

The blood-brain barrier provides a good example. In most physiological situations, the blood-brain barrier prevents the access of lipids to the cells of the central nervous system CNS. Therefore, CNS cells also rely solely on glucose as fuel molecules Figure 2.

In prolonged fasting, however, ketone bodies released in the blood by liver cells as part of the continual metabolization of fatty acids are used as fuels for ATP production by CNS cells. In both situations and unlike red blood cells, however, CNS cells are extremely metabolically active and do have mitochondria.

Thus, they are able to fully oxidize glucose, generating greater amounts of ATP. Indeed, the daily consumption of nerve cells is about g of glucose equivalent, which corresponds to an input of about kilocalories 1, kilojoules. However, most remaining cell types in the human body have mitochondria, adequate oxygen supply, and access to all three fuel molecules.

Which fuel, then, is preferentially used by each of these cells? Virtually all cells are able to take up and utilize glucose. What regulates the rate of glucose uptake is primarily the concentration of glucose in the blood. Glucose enters cells via specific transporters GLUTs located in the cell membrane. There are several types of GLUTs, varying in their location tissue specificity and in their affinity for glucose.

Adipose and skeletal muscle tissues have GLUT4, a type of GLUT which is present in the plasma membrane only when blood glucose concentration is high e. The presence of this type of transporter in the membrane increases the rate of glucose uptake by twenty- to thirtyfold in both tissues, increasing the amount of glucose available for oxidation.

Therefore, after meals glucose is the primary source of energy for adipose tissue and skeletal muscle. The breakdown of glucose, in addition to contributing to ATP synthesis, generates compounds that can be used for biosynthetic purposes.

So the choice of glucose as the primary oxidized substrate is very important for cells that can grow and divide fast. Examples of these cell types include white blood cells, stem cells , and some epithelial cells. A similar phenomenon occurs in cancer cells, where increased glucose utilization is required as a source of energy and to support the increased rate of cell proliferation.

Interestingly, across a tumor mass, interior cells may experience fluctuations in oxygen tension that in turn limit nutrient oxidation and become an important aspect for tumor survival.

In addition, the increased glucose utilization generates high amounts of lactate, which creates an acidic environment and facilitates tumor invasion. Another factor that dramatically affects the metabolism is the nutritional status of the individual — for instance, during fasting or fed states.

After a carbohydrate-rich meal, blood glucose concentration rises sharply and a massive amount of glucose is taken up by hepatocytes by means of GLUT2. This type of transporter has very low affinity for glucose and is effective only when glucose concentration is high.

Thus, during the fed state the liver responds directly to blood glucose levels by increasing its rate of glucose uptake. These amino acids are taken up by the liver and converted into glucose, as described earlier. This is a dire situation that occurs only in cases of severe over-training or starvation. When individuals die of starvation or anorexia, it is often loss of protein from the heart muscle that leads to death.

Regulation of blood glucose. Your blood glucose is maintained within a fairly narrow range 80 to mg glucose per ml blood. Your blood glucose level is maintained by two hormones secreted by your pancreas: insulin and glucagon. Your pancreas is a large gland behind your stomach. Hormones are chemical message between different cells in your body that coordinate their activities.

When levels of glucose in your blood are high, the protein hormone insulin is secreted by certain cells in your pancreas. Insulins binds to receptor proteins in membranes of muscle and adipose cells. Insulin causes these cells to increase their uptake of glucose from the blood and its conversion to glycogen or fat.

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