TutorChase logo
AQA A-Level Biology Notes

6.7.2 Blood Glucose Control in the Human Body

Introduction to Blood Glucose Regulation

Blood glucose, or blood sugar, is a key energy source for the human body. Its regulation is crucial for the functioning of various organs, especially the brain. The primary hormones involved in this regulation are insulin and glucagon, both produced by the pancreas.

Insulin: The Key to Lowering Blood Glucose

  • Role: Insulin's primary function is to lower blood glucose levels. It acts as a key, allowing glucose to enter cells.
  • Production: Beta cells in the pancreatic islets produce insulin.
  • Mechanism of Action:
    • Enhances glucose uptake by cells, particularly muscle and liver cells, for energy production or storage.
    • Promotes glycogenesis, where excess glucose is converted into glycogen.
    • Inhibits glycogenolysis (breakdown of glycogen) and gluconeogenesis (production of new glucose), preventing excessive glucose in the bloodstream.
Mechanism of insulin function

Image courtesy of designua

Glucagon: The Balancing Hormone

  • Role: Glucagon counteracts the action of insulin, raising blood glucose levels when they fall too low.
  • Production: Alpha cells in the pancreatic islets produce glucagon.
  • Mechanism of Action:
    • Stimulates the liver to convert stored glycogen back into glucose (glycogenolysis).
    • Promotes gluconeogenesis, ensuring a steady glucose supply during fasting or low intake periods.

Diabetes Mellitus: Disruption in Glucose Homeostasis

Diabetes mellitus is a group of diseases characterized by poor blood glucose regulation, leading to chronic hyperglycaemia.

Type I Diabetes: Insulin-Dependent Diabetes

  • Causes: An autoimmune response destroys beta cells in the pancreas, reducing insulin production.
  • Symptoms: Increased thirst and urination, unexplained weight loss, fatigue, vision problems.
  • Management:
    • Lifelong insulin therapy to replace the hormone the body can't produce.
    • Regular blood glucose monitoring to guide insulin dosing.
    • Dietary management to regulate carbohydrate intake.
    • Regular physical activity to enhance insulin sensitivity and glucose uptake.
Type 1 Diabetes-lower amount of insulin production in a diabetic patient.

Image courtesy of scientificanimations.

Type II Diabetes: Non-Insulin-Dependent Diabetes

  • Causes: Insulin resistance develops, where cells do not respond effectively to insulin. Often linked to obesity and genetic factors.
  • Symptoms: Often similar to Type I but can include frequent infections and slow healing.
  • Management:
    • Lifestyle modifications such as diet and exercise to manage weight and improve insulin sensitivity.
    • Oral hypoglycaemic agents to increase insulin production or action.
    • Insulin therapy in more advanced stages.
Illustration of normal Blood Sugar absorption vs. insulin resistance in Type 2 Diabetes

Image courtesy of scientificanimations.

The Physiology of Blood Glucose Regulation

The regulation of blood glucose is a dynamic process involving both hormonal and cellular responses.

  • Postprandial State (After Eating): The digestive system breaks down carbohydrates into glucose, absorbed into the bloodstream. This rise in blood glucose levels triggers insulin secretion, facilitating glucose uptake by cells.
  • Fasting State: When blood glucose levels drop, glucagon is secreted, prompting the liver to release stored glucose.

Glycogenesis and Glycogenolysis

  • Glycogenesis: Insulin promotes the conversion of glucose to glycogen for storage in the liver and muscle tissues.
  • Glycogenolysis: In response to glucagon, liver cells break down glycogen into glucose, releasing it into the bloodstream.

Gluconeogenesis

  • Occurs mainly in the liver and to a lesser extent in the kidneys.
  • Glucagon and cortisol stimulate this process to maintain blood glucose levels during prolonged fasting or stress.

Hormonal Interplay and Feedback Mechanisms

The pancreas, liver, and other organs work together, using feedback mechanisms to regulate blood glucose levels. Insulin and glucagon secretion are regulated by the blood glucose levels they help control, creating a feedback loop for homeostasis.

Role of Insulin and Glucagon in blood glucose regulation

Image courtesy of Carogonz11

Implications of Blood Glucose Dysregulation

  • Short-Term Effects: Hypoglycaemia (low blood sugar) can cause dizziness, confusion, and fainting. Hyperglycaemia (high blood sugar) can lead to dehydration, frequent urination, and fatigue.
  • Long-Term Complications: Prolonged dysregulation in diabetes can lead to serious health issues like cardiovascular disease, nerve damage, kidney failure, and eye problems.

Conclusion

Understanding blood glucose control is not only fundamental for students studying A-level biology but also essential for general health awareness. This knowledge forms the basis for understanding more complex metabolic pathways and disease processes. It illustrates the intricate balance the body maintains to ensure proper functioning. For students, grasping these concepts will aid in their academic journey and foster a deeper appreciation for the complexities of human physiology.

FAQ

Stress and the release of adrenaline (epinephrine) have a significant impact on blood glucose levels. Under stress, the body prepares for a 'fight or flight' response, which necessitates an immediate source of energy. Adrenaline, a hormone released by the adrenal glands, plays a key role in this process. It stimulates glycogenolysis in the liver and muscle tissue, rapidly increasing the amount of glucose in the bloodstream. Additionally, adrenaline inhibits insulin secretion and enhances glucagon release, further contributing to increased blood glucose levels. This process ensures that the body has enough energy to respond to the stressful situation. Chronic stress can lead to prolonged elevation of adrenaline levels, contributing to sustained high blood glucose levels, which can be problematic, particularly for individuals with impaired glucose regulation, such as those with diabetes.

The Somogyi effect is a phenomenon in diabetes management where a rapid decrease in blood glucose levels during the night leads to a rebound hyperglycaemia in the morning. This effect is often a response to excessive insulin administration or insufficient evening carbohydrate intake. The body reacts to the hypoglycaemia (low blood sugar) by releasing counter-regulatory hormones such as glucagon, adrenaline, cortisol, and growth hormone, which increase blood glucose levels. This counter-regulatory response often overshoots, leading to high blood glucose levels in the morning, known as rebound hyperglycaemia. Understanding and identifying the Somogyi effect is crucial for individuals with diabetes, as it requires adjusting insulin doses or meal planning to prevent these nocturnal hypoglycaemic episodes and subsequent morning hyperglycaemia.

Physical exercise has a significant influence on blood glucose levels in individuals with diabetes and is an essential component of diabetes management. Exercise increases insulin sensitivity, meaning that cells are better able to use available insulin to take up glucose from the blood. This can lead to a decrease in blood glucose levels during and after physical activity. For individuals taking insulin or insulin-stimulating medications, this increased glucose uptake can result in hypoglycaemia (low blood sugar levels). Therefore, it's important for diabetics to monitor their blood glucose levels before, during, and after exercise. They may need to adjust their insulin doses or consume carbohydrates before or during exercise to maintain stable blood glucose levels. Additionally, the type, intensity, and duration of exercise can affect how the body uses glucose, so these factors should be considered in diabetes management plans. It is advisable for diabetics to consult healthcare professionals to develop an exercise regime that safely fits their individual health needs and glucose management goals.

Liver and muscle cells play significant roles in glucose regulation, acting as the primary sites for glucose storage and utilisation. The liver is pivotal in maintaining blood glucose levels, particularly during fasting. It stores glucose in the form of glycogen through a process called glycogenesis, predominantly under the influence of insulin. During periods of low blood glucose, the liver converts glycogen back into glucose (glycogenolysis) and releases it into the bloodstream. The liver also participates in gluconeogenesis, producing glucose from non-carbohydrate sources, especially during prolonged fasting or intense exercise. Muscle cells, on the other hand, store glycogen for their own energy needs. Under the action of insulin, muscle cells uptake glucose from the blood and convert it to glycogen. During physical activity, muscle cells break down this glycogen to produce energy. The ability of liver and muscle cells to store and release glucose as needed is fundamental to preventing extreme fluctuations in blood glucose levels.

The body detects changes in blood glucose levels through specialized cells in the pancreas, particularly the alpha and beta cells in the islets of Langerhans. These cells act as glucose sensors. Beta cells, which produce insulin, are stimulated by high levels of glucose in the bloodstream. They respond by secreting insulin, which lowers blood glucose levels by increasing cellular uptake of glucose and stimulating glycogenesis. Conversely, when blood glucose levels are low, alpha cells are activated to secrete glucagon, which increases blood glucose levels by promoting glycogenolysis and gluconeogenesis. This detection and response mechanism is crucial for maintaining glucose homeostasis and involves complex biochemical pathways. The precise mechanism involves glucose entering the beta cells through specific transporters, leading to metabolic changes that trigger insulin release. Similarly, a decrease in intracellular glucose in alpha cells diminishes inhibition of glucagon release, facilitating its secretion.

Practice Questions

Explain how insulin and glucagon work antagonistically to regulate blood glucose levels.

Insulin and glucagon are crucial hormones in the regulation of blood glucose levels, functioning antagonistically to maintain homeostasis. Insulin, produced by the pancreatic beta cells, lowers blood glucose levels by facilitating the uptake of glucose into cells, especially liver and muscle cells, and by promoting glycogenesis, the conversion of glucose into glycogen for storage. Conversely, glucagon, secreted by alpha cells, increases blood glucose levels during periods of fasting or low glucose intake. It does this by stimulating glycogenolysis, the breakdown of glycogen into glucose in the liver, and gluconeogenesis, the production of glucose from non-carbohydrate sources. This interplay between insulin and glucagon ensures stable blood glucose levels, crucial for the body's energy balance.

Describe the main differences between Type I and Type II diabetes, focusing on causes, symptoms, and management.

Type I diabetes, also known as insulin-dependent diabetes, is caused by an autoimmune destruction of pancreatic beta cells, leading to a lack of insulin production. Its symptoms include increased thirst, frequent urination, unexplained weight loss, and fatigue. Management involves daily insulin injections or the use of an insulin pump, coupled with regular blood glucose monitoring and lifestyle adjustments. On the other hand, Type II diabetes, non-insulin-dependent, results from insulin resistance and a relative decline in insulin production. Its symptoms develop more gradually and include increased thirst, frequent urination, blurred vision, and slow wound healing. Management focuses on lifestyle changes like diet and exercise, oral medications to improve insulin sensitivity or stimulate insulin production, and in some cases, insulin therapy. Both conditions require careful management to prevent complications.

Hire a tutor

Please fill out the form and we'll find a tutor for you.

1/2
Your details
Alternatively contact us via
WhatsApp, Phone Call, or Email