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Blood Glucose Homeostasis
Transcript of Blood Glucose Homeostasis
What is the purpose of the system?
Why do we need glucose?
Glucose is a carbohydrate sugar and is a major nutrient that humans require to survive. Every cell in your body requires a constant supply of glucose, because it is one of the major fuels the body uses as a source of energy. Glucose molecules are broken down within cells in order to produce adenosine triphosphate (ATP) molecules, energy-rich molecules that power numerous cellular processes
Why is glucose so important for some cells?
Some cells rely purely on glucose to produce ATP, as they cannot use other molecules such as fats or amino acids to produce ATP.
Why is blood glucose homeostasis important then?
The purpose of maintaining blood glucose levels is so that your body’s cells get a constant supply of glucose so they can carry out essential life processes such as respiration. Glucose molecules are delivered to cells by the circulating blood, so it is essential that blood glucose levels be maintained at relatively constant levels to ensure a constant supply of glucose to cells.
Significance of the system
It is important that blood glucose levels are maintained within fairly strict limits, between 4-8mmol/L, as the cells in the brain and central nervous system cannot make glucose or store more than a few minutes supply. They need a constant supply to function properly and carry out essential life processes such as respiration. Also, it is furthermore important because some tissues cannot use fats or amino acids to produce ATP; these almost exclusively rely on glucose to produce ATP and cannot use anything else.
Why does blood glucose need to be maintained?
Blood glucose needs to maintained within fairly strict limits because problems will result if those levels get too low below 4mmol/L (hypoglycaemia), or too high above 13 mmol/L (hyperglycaemia).
How are blood glucose levels maintained
In a healthy person, blood glucose levels are restored to normal levels primarily through the actions of two pancreatic hormones, insulin and glucagon. These are negative feedback systems and are coordinated by the brain, and specifically, the hypothalamus.
How does the system respond to an increase in blood glucose levels?
If blood glucose levels rise after eating, the beta cells (receptors) in the pancreas respond by secreting insulin (effector). Insulin first travels to the liver through the portal vein, and provide a feedback signal that tells the liver to stop releasing glucose into the blood stream (shuts down hepatic glucose production). It instead tells it to start storing glucose as glycogen. Insulin then travels to the rest of the tissues in the body through the blood stream, and signals to muscle and fats cells to tell them to also take up glucose and store it as glycogen or fat.
Why does blood glucose homeostasis advantage us?
In normal humans, having internal systems that manage and maintain blood glucose levels is a huge adaptive advantage, as it means that we have flexibility around when we eat, as we do not have to eat as regularly. If we did not have these internal systems, we would not have the ability to store glucose in the form of glycogen, which could later be used by cells as energy for life processes. We would have to be constantly eating glucose rich foods to supply our body with enough glucose to supply cells with energy in the form of ATP for essential life processes such as respiration. We would also be at constant risk of hyperglycemia and hypoglycemia, which can pose serious health risks. Without Alpha and Beta cells in the pancreas releasing glucagon and insulin to maintain blood glucose levels, we would have to control and try to maintain our blood glucose through our diet, which would be extremely challenging and ineffective.
The overall effect of this is that insulin produces a feedback mechanism that ensures blood glucose levels are rapidly lowered back to normal levels. They also ensure that blood glucose levels don’t fall too low when blood glucose levels fall back to fasting levels, as the pancreatic B-cells stop secreting insulin.
How does the system respond to an decrease in blood glucose levels?
If blood glucose levels fall to low, for example when you in a fasting state (not eating), alpha cells (receptors) in the pancreas release glucagon (effector). This works mainly in the liver to release glucose into the bloodstream, either by breaking down stores of glycogen (glycogenolysis) or by making glucose from other nutrients via gluconeogenesis.
These effects collectively cause an increase in blood glucose levels back to normal levels. When glucose levels are back to normal, glucagon release from the pancreatic alpha cells is blocked, which prevents blood glucose levels from rising too high and preserves stores of glucose in the liver.
Thus, blood glucose homeostasis is regulated by the constant oscillation between the releases of insulin as blood levels rise, and the release of glucagon as blood glucose levels fall, by alpha and beta cells in the pancreas.
The breakdown of glucose homeostasis
There are some exceptions to when the body can not carry out blood glucose homeostasis. This is the case for people who have diabetes
What is diabetes?
Diabetes is a metabolic disease in which causes high levels of blood glucose.
Type 1 & 2 diabetes
Type 1 diabetes is a form of diabetes where the pancreas does not produce enough insulin. This results from the autoimmune destruction of insulin producing beta cells of the pancreas and results in the body’s inability to maintain blood glucose levels. Beta cells in pancreas are being attacked by body's own cells and therefore can't produce insulin to take sugar out of the blood stream. Despite eating lots of food, the body shows signs of starvation. It can also lead to symptoms such as frequent urination, increased thirst, hunger, and weigh loss. Type 1 diabetes results from internal forces and is linked to person’s genetics; people who most get type one diabetes are normally healthy when onset occurs.
Type 2 diabetes is a form of diabetes where the body does not respond to the insulin that is produced (insulin resistance). Diet related insulin release is so large and frequent that receptor cells have become less sensitive to insulin. This insulin resistance results in less sugar being removed from the blood. Type 2 diabetes is normally caused from external forces and is linked to living an unhealthy lifestyle and obesity. Again, it can lead to symptoms such as frequent urination, increased thirst, hunger, and weigh loss, but can also mean the body is prone to infection or sickness.
Why does this lead to a breakdown of the blood glucose homeostasis system?
In a normal person, insulin first travels to the liver through the portal vein, and provides a feedback signal that tells the liver to stop releasing glucose into the blood stream (shuts down hepatic glucose production). It instead tells it to start storing glucose as glycogen. Insulin then travels to the rest of the tissues in the body through the blood stream, and signals to muscle and fats cells to tell them to also take up glucose and store it as glycogen or fat.
However, in a diabetic, the pancreas cannot or does not produce enough insulin (type 1), or does not recognize that insulin is present (type 2). This causes a breakdown of the blood glucose homeostasis system, and results in diabetics having high blood glucose levels. Because the body does not produce or recognize that insulin in present, when blood glucose levels rise in a diabetic, insulin does not tell the liver to stop releasing glucose into the blood stream. On top of this, the liver does not start storing glucose as glycogen, and muscle and fat cells do not start to take up glucose and store it as glycogen or fat. Without insulin, the body isn't able to utilize glucose for fuel. This means that the body cannot carry out essential life functions, such as respiration, as there is not enough glucose in the stored form of glycogen for the body to use and convert into energy.
Therefore, both type 1 & 2 diabetes require regular doses of insulin to be injected into the body throughout the day to ensure that the body knows to start storing glucose as glycogen when glucose levels start to rise. Without insulin, the kidney becomes unable to retain the amount of glucose present, and glucose starts to overflow into the urine, the body’s response to the high blood glucose levels.
By Liam McDonald
Components of the system
Brain - Hypothalamus
Pancreas - Alpha & Beta Cells
Why is this damaging?
Low blood glucose levels (hypoglycemia) can produce a variety of symptoms resulting from an inadequate supply of glucose to the brain. This can cause the impairment of essential life functions and over time can increase the risk of cardiovascular disease . Effects can include serious issues such as seizures, unconsciousness, and sometimes permanent brain damage or death.
High blood glucose levels (hyperglycemia) can also cause serious damage and can produce a very wide variety of serious complications over a period of years, including blurred vision, brain damage, kidney damage, cardiovascular damage, and can put you into a coma.
Both cause sometimes serious problems to a persons health and can pose serious risks if not treated in time.
This is why it is essential that diabetes inject themselves with insulin, as without insulin, diabetics would have to constantly eating to maintain blood glucose levels, as they have little stores of glucose in the stored form of glycogen. Before insulin was used as treatment for diabetes, this would be essential to their survival as cells need a constant supply of glucose for essential life processes. Insulin now aids the body in maintaining constant blood glucose levels, which is a huge adaptive advantage as it gives flexibility in when they can eat and prevents health problems associated with high blood glucose levels
Adaptive significance of insulin for diabetics