The body needs energy to function. This energy must be obtained from food, processed and metabolised so it is ready for the cells to use. Glucose, a sugar molecule, makes up the most important energy source. The brain alone uses 20% of the glucose produced by the body.
Like many other factors, blood glucose must be maintained at the correct levels for everything to function as it should. Blood glucose and blood sugar are the same thing, so we’ll use ‘glucose’ going forward. The two main hormones oppose each other to maintain the balance of blood glucose.
Important Definitions
Glucose: a small sugar molecule the body uses for energy to function.
Glycogen: a long branched molecule, made up of glucose molecules. It acts as storage of energy for later use, mainly in the liver and skeletal muscles.
Glycogenolysis: the breakdown of glycogen into glucose.
Glycogenesis: the creation of glycogen from glucose. Don’t mix these two up!
Gluconeogenesis: the process of making glucose from non-carbohydrate sources such as fats and proteins.
Hypoglycaemia: low blood glucose.
Hyperglycaemia: high blood glucose. Don’t mix these two up, check your prefixes!
Insulin: The Anabolic Hormone
The hormone insulin controls anabolism: the storage and utilisation of energy. Insulin secretion takes place in the beta-cells of the islets of Langerhands, within the pancreas. It promotes glucose uptake from the blood into the body cells. It also promotes glycogenesis and fat generation, in other words, the storage of energy.
High blood glucose levels stimulate insulin secretion by the pancreas, with the aim of reducing blood glucose to normal again. For this reason, insulin follows a cycle where it is released shortly after a meal to store away the energy from food.
Most people have heard of diabetes mellitus, an endocrine disease involving insulin function. There are two main types of diabetes mellitus, which I am specifying because there is another kind of diabetes that is less well known, diabetes insipidus. So, let’s look at the details of diabetes mellitus.
Type 1 Diabetes Mellitus
An autoimmune condition, the immune system attacks the beta-cells in the pancreatic islets. Insulin production is halted or massively reduced, which is why T1 diabetics need to inject insulin regularly to manage their blood glucose. The result is excessively high blood glucose.
Type 2 Diabetes Mellitus
This form is much more complex and still not completely understood. Various risk factors contribute to reduction of beta-cells and insulin resistance. The cells don’t respond to insulin like they should and take up glucose from the blood. Increased glucagon secretion, unresponsive to blood glucose, could also be a factor.
The end result is a persistent hyperglycaemia which results in the symptoms of diabetes. We’ll cover the details of this later.
Glucagon: The Catabolic Hormone
Glucagon opposes insulin, counteracting all of its effects. The alpha-cells of the pancreatic islets produce glucagon in response to low blood glucose. Glucagon raises blood glucose and fatty acids, stimulates glycogenolysis and gluconeogenesis. In other words, taking glucose out of storage and making more of it.
Excessive glucagon levels contributes a lot to the development of hyperglycaemic ketoacidosis in undiagnosed or poorly managed type 1 diabetics. Ketoacidosis (DKA) becomes a diabetic coma if untreated and is life-threatening.
The Effects of Hyperglycaemia
An excessively high blood glucose impacts almost all of the body in some way. The main symptoms of diabetes mellitus include the triad of polyphagia, polydipsia and polyuria. Polyphagia means increased appetite or eating more than normal. Polydipsia means increased thirst or drinking more than normal. Polyuria means producing more urine than normal, referring to volume rather than frequency. That said, a higher volume of urine will typically increase the frequency of urination.
Other symptoms include vision changes, fatigue, weight changes, poor wound healing, neuropathy (tingling in legs and feet), recurrent infections, coma and seizures.
As mentioned before, ketoacidosis is a life-threatening complication of persistently high blood glucose levels. When the cells can’t use glucose, they produce ketone bodies to make energy from instead. These ketones make the blood more acidic and cause damage. Some people can smell the ketones, usually described as a ‘fruity’ smell or like nail polish. I personally can’t smell ketones very well.
Other diseases cause hyperglycaemia including other endocrine disorders, sepsis and brain pathology. Certain medications also affect blood glucose, particularly certain steroids, beta-blockers, statins and antipsychotics.
Stress impacts blood glucose, as the physiology of stress prepares the body for fight or flight, including making energy available. Stress induced hyperglycaemia matters a lot in cats, because they show extreme changes in blood glucose when stressed. For this reason, diagnosing diabetes mellitus in cats is not straightforward.
Most cats are stressed simply visiting the vet, especially if a blood sample is taken, so one high glucose result in a cat means nothing. Further testing needs to be done to confirm a diagnosis of diabetes.
The Effects of Hypoglycaemia
Hypoglycaemia is more immediately life-threatening than hyperglycaemia. Symptoms of low blood sugar include headaches, confusion, light-headedness, heart palpitations, anxiety, nausea and tremors. Severely low blood sugar causes seizures, loss of consciousness and even death.
The brain relies on glucose for energy, with no other option available to the cells. Hence the neurological symptoms and risk of seizures and brain damage.
Excessive insulin causes hypoglycaemia, whether it is an accidental overdose, not eating after taking insulin, being injected with insulin when not diabetic or an insulinoma. Insulinomas are tumours of the pancreatic islet cells and while benign, they produce insulin in an uncontrolled way.
Adrenal disease like Addison’s disease (hypoadrenocorticism), sepsis (glucose stores are used up) and other serious illnesses can cause low blood sugar too. Alcohol consumption, fasting and intense exercise, especially if diabetic will risk hypoglycaemia. Starvation, including eating disorders and neglect as well.
Xylitol, the artificial sweetener, causes a rapid release of insulin in dogs. This results in hypoglycaemia and liver damage. Xylitol only affects dogs in this manner, but it is a common ingredient in gum, mints, peanut butter, medications, supplements, sunscreen, toiletries and cosmetics. Dog owners, beware because xylitol toxicity is an emergency and needs rapid treatment.
Thanks for reading! April’s themes will be the physical impact of mental health problems on Mondays, and cats on Fridays for our Creature Features! Subscribe for updates when new posts are live. See you soon!
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