Homeostasis - Types of control, Diabetes, Feedback Loops

Type 1-2 diabetes, negative/positive feedback loops, controlling internal temp./blood glucose levels

Homeostasis

The body’s physiological ability to control its internal environment to ensure its stability in response to fluctuations in external or internal conditions.

Examples of homeostatic control in the body:

1. Internal body temp. (37 degrees Celsius)

2. Blood glucose levels

Negative feedback loop

A negative feedback loop is a mechanism where a variable triggers a counteracting response to return to a set point. - MOST HOMEOSTATIC PROCESSES

Positive feedback loop

A mechanism that intensifies a variable instead of counteracting it. This pushes levels out of normal ranges and is not typically used for homeostasis (e.g., childbirth).

Regulation of blood glucose levels

• Stimulus 1: Eating meals increases blood glucose levels, providing fuel for cellular respiration.

• Stimulus 2: Hours after eating or during fasting, blood glucose levels drop, potentially limiting cellular respiration.

Insulin and Decreasing High Blood Glucose Levels

• Stimulus: A meal increases blood glucose levels.

• Control: The pancreas (β cells) detects the high blood glucose.

• Response: β cells produce and release the peptide hormone insulin.

• Effector: Insulin signals target cells (liver, muscle) to take up glucose from the bloodstream.

• Action: Excess glucose is stored as glycogen in the liver.

• Result: Blood glucose levels return to the normal range.

Glucagon and increasing low blood glucose levels

• Stimulus: Hours after a meal or during fasting, blood glucose levels decrease.

• Control: The pancreas (α cells) detects the low blood glucose.

• Response: α cells produce and release the hormone glucagon.

• Effector: Glucagon signals the liver.

• Action: The liver breaks down stored glycogen into glucose.

• Result: Glucose is released into the bloodstream, increasing blood glucose levels back to normal.

Diabetes - type 1

• Cause: Autoimmune destruction of the insulin-producing β cells in the pancreas. This is a genetic predisposition.

• Mechanism: The immune system mistakenly attacks and destroys β cells, leading to little to no insulin production. Antibodies target β cells (often referred to as "friendly fire").

• Consequence: High blood sugar (hyperglycemia) because glucagon activity is normal, but the lack of insulin prevents glucose uptake and storage. The liver does not store glucose as glycogen.

• Treatment: Insulin injections to replace the missing hormone and blood pressure monitoring.

Diabetes - type 2

• Cause: Insulin resistance, where target cells become less responsive to insulin due to chronic high glucose levels (often linked to diet and exercise habits).

• Mechanism: Beta cells initially function normally and produce insulin, but the body's cell receptors for insulin are damaged or less sensitive. The liver also has impaired glycogen storage.

• Consequence: High blood glucose levels due to the body's inability to effectively use or store glucose.

glycogen/glucagon

• Glucagon: A peptide hormone produced by the pancreas (αα cells) that increases blood glucose levels.

• Glycogen: A polysaccharide stored in the liver and muscles, serving as a readily available source of glucose.