Homeostasis and Diabetes Mellitus: Anatomy & Physiology Study Notes

Homeostasis and Its Disruption

Introduction to Homeostasis

Homeostasis refers to the body's ability to maintain a stable internal environment despite changes in external conditions. This process is essential for optimal physiological performance and survival.

• Definition: Homeostasis is the regulation of internal conditions such as temperature, pH, and glucose levels.

• Importance: Proper alignment of physiological, psychological, and environmental factors is necessary for peak performance and adaptation.

• Examples: Thermoregulation, blood glucose regulation, and fluid balance.

Diabetes Mellitus: A Case Study in Homeostatic Failure

Overview of Diabetes Mellitus

Diabetes mellitus is a chronic metabolic disorder characterized by elevated blood glucose levels due to defects in insulin secretion, insulin action, or both. It serves as a key example of what happens when homeostasis is disrupted.

• Definition: Diabetes mellitus is marked by persistent hyperglycemia (high blood sugar).

• Prevalence: Affects millions worldwide; in Canada, about 9% of the population has diabetes, with an additional 5-8 million having pre-diabetes.

• Economic Impact: Direct costs in Canada are estimated at $9-13 billion per year.

• Complications: Affects all organ systems and can lead to cardiovascular disease, kidney failure, and nerve damage.

Types of Diabetes Mellitus

Diabetes mellitus is classified into several types based on etiology and pathophysiology.

• Type 1 Diabetes Mellitus: Caused by autoimmune destruction of pancreatic beta cells, resulting in little or no insulin production.

• Type 2 Diabetes Mellitus: Characterized by insulin resistance and relative insulin deficiency; most common form.

• Gestational Diabetes: Occurs during pregnancy due to hormonal changes causing insulin resistance.

• Other Types: Secondary diabetes due to other diseases or medications.

Diagnostic Criteria for Diabetes Mellitus

Diagnosis is based on blood glucose measurements under fasting and post-glucose load conditions.

• Fasting Plasma Glucose: > 7.0 mmol/L (> 125 mg/dL) indicates diabetes.

• Oral Glucose Tolerance Test (OGTT): 2-hour plasma glucose > 11 mmol/L (> 200 mg/dL) confirms diabetes.

• Impaired Fasting Glucose: 5.5 – 6.9 mmol/L (100–125 mg/dL) is considered pre-diabetes.

Key Equation:

$\text{Fasting Plasma Glucose} \geq 7.0\ \text{mmol/L}$ $\text{2-hour OGTT Plasma Glucose} \geq 11.0\ \text{mmol/L}$

Symptoms and Pathophysiology

Diabetes mellitus presents with a range of symptoms due to elevated blood glucose and altered fluid balance.

• Polyuria: Increased urine output due to osmotic diuresis.

• Polydipsia: Excessive thirst resulting from fluid loss.

• Weight Loss: Due to loss of glucose and calories in urine.

• Additional info: Chronic hyperglycemia can damage blood vessels, nerves, and organs.

Pre-Diabetes and Related Conditions

Pre-diabetes is a state of impaired glucose regulation that increases the risk of developing type 2 diabetes.

• Impaired Fasting Glucose (IFG): Fasting blood glucose between 5.5 – 6.9 mmol/L (100–125 mg/dL).

• Impaired Glucose Tolerance (IGT): Elevated blood glucose after a glucose load, but not high enough for diabetes diagnosis.

• Diabetes Insipidus: A separate condition characterized by excessive urine output due to antidiuretic hormone deficiency; not related to blood glucose.

Prevalence of Diabetes: Demographic Data

Prevalence by Race/Ethnicity and Age

Diabetes prevalence varies by demographic factors, including age, sex, and ethnicity.

Group	Percentage with Diabetes
White American	8.4%
Hispanic American	11.8%
Asian American	8.4%
Native American	14.2%
American Indian (Arizona)	33.5%

Additional info: Prevalence increases with age and is higher in certain ethnic groups due to genetic and lifestyle factors.

Summary Table: Diagnostic Criteria for Diabetes Mellitus

Test	Normal	Pre-Diabetes	Diabetes
Fasting Plasma Glucose	< 5.5 mmol/L	5.5 – 6.9 mmol/L	> 7.0 mmol/L
2-hour OGTT	< 7.8 mmol/L	7.8 – 11.0 mmol/L	> 11.0 mmol/L

Key Terms and Definitions

• Homeostasis: Maintenance of stable internal conditions.

• Diabetes Mellitus: Chronic disease of high blood glucose due to insulin issues.

• Insulin: Hormone produced by pancreatic beta cells that lowers blood glucose.

• Hyperglycemia: Elevated blood glucose levels.

• Pre-Diabetes: Intermediate state of abnormal glucose regulation.

• Diabetes Insipidus: Disorder of water balance, unrelated to glucose.