U5 Blood Glucose
General Aspects of Altered Glucose Function
Hormonal Control of Glucose, Fat, and Protein Metabolism
Introduction to Metabolism
Glucose, fatty acids, amino acids, and other substances serve as fuel to meet the body's energy needs.
The liver plays a crucial role in managing the fuel supply, working in coordination with hormones from the endocrine pancreas
Key Metabolic Tissues and Substances
Adipose tissue
Skeletal muscle
Glycogen
Proteins
Blood glucose
Triglyceride storage
Amino acids
Glucose Metabolism
Importance of Glucose
The brain and nervous system primarily depend on glucose as their energy source.
The brain cannot synthesize or store glucose beyond a few minutes, necessitating a continuous supply from circulation.
Normal fasting blood glucose (FBG) levels: 70-100 mg/dL
After meals, blood glucose (BG) levels increase, prompting insulin secretion:
Approximately 2/3 of glucose ingested exceeds metabolic needs, which is then either stored in the liver as glycogen or converted to fat when glycogen stores are full
Regulation of Blood Glucose Levels
When BG drops below necessary physiological levels (e.g., between meals), glycogen is broken down through glycogenolysis, releasing glucose and helping to maintain BG levels.
The liver also synthesizes glucose through gluconeogenesis from amino acids, glycerol, and lactic acid during fasting or when glycogen stores are diminished:
Generated glucose can be released into circulation or stored as glycogen
Fat Metabolism
Overview of Fat Storage and Use
Efficiency: Fat is the most efficient form of stored fuel, providing 9 kcal/g, compared to 4 kcal/g for carbohydrates and proteins.
Most body cells (except the brain, nervous tissue, and red blood cells) can utilize fatty acids for energy alongside glucose.
The liver conducts most of the initial breakdown of fatty acids, especially during heavy energy demands.
A small portion of fatty acids is used for the liver's energy needs; the rest is converted into ketones and released into the blood.
Physiological scenarios, like fasting or diabetes, can lead to high ketone release, leading to ketoacidosis
Protein Metabolism
Role of Proteins in the Body
Proteins are critical for forming and maintaining all body structures; amino acids are the building blocks.
Only a limited amount of amino acids can be stored; excess amino acids get converted to fatty acids, ketones, or glucose for storage and fuel.
Since fatty acids cannot convert to glucose directly, proteins must break down, providing amino acids as substrates for gluconeogenesis during metabolic stress
Glucose-Regulating Hormones
The Pancreas
The pancreas is both an endocrine (hormone-producing) and exocrine (digestive enzyme-producing) gland.
Located behind the stomach between the spleen and the duodenum.
Islets of Langerhans: Contain four cell types that secrete hormones:
Alpha cells → produce glucagon
Beta cells → produce insulin and amylin
Delta cells → produce gastrin and somatostatin
F (or) PP cells → secrete pancreatic polypeptide to stimulate gastric secretion and antagonize cholecystokinin
These hormones work synergistically to regulate carbohydrate, fat, and protein metabolism
Blood Flow and Hormone Secretion
Pancreatic islets constitute only 1% of the pancreatic mass but receive 10% of the pancreatic blood flow
Insulin
Production and Function
Beta cells synthesize insulin from proinsulin, and its secretion is regulated by chemical, hormonal, and neural factors.
Insulin circulates freely in the plasma, unbound to carriers.
Actions of Insulin:
Primarily functions in the liver, muscle, and adipose tissue.
Little insulin is lost unchanged in urine.
Promotes glucose uptake and storage as glycogen.
Prevents breakdown of fats and glycogen.
Increases protein synthesis and inhibits gluconeogenesis
Properties of Insulin:
Water-soluble protein hormone that facilitates intracellular transport of potassium, phosphate, and magnesium.
An anabolic hormone promoting synthesis of proteins, carbohydrates, lipids, and nucleic acids.
Secretion Dynamics:
Increased with rising blood glucose levels, amino acids, and gastrointestinal hormones, and when beta cells are stimulated by parasympathetic mechanisms.
Decreases when:
Blood glucose is low (hypoglycemia).
High insulin levels (negative feedback on beta cells).
Sympathetic stimulation of alpha cells.
Inhibition by prostaglandin (PGE2) (Mefford, 2024, pp. 1261-1263).
Glucagon
Overview
Produced by pancreatic alpha cells and some gastrointestinal cells.
Acts as an insulin antagonist, primarily in the liver, lowering blood glucose levels.
Stimulates glycogenolysis and gluconeogenesis.
Secretion is stimulated by:
Amino acid-rich (protein) meals.
Low blood glucose levels or sympathetic stimulation.
Inhibited when glucose levels are elevated.
Also stimulates lipolysis, promoting a ketogenic effect due to increased free fatty acid metabolism in the liver
Somatostatin, Amylin, and Gut-Derived Hormones
Somatostatin
Produced by delta cells of the pancreas, essential for carbohydrate, fat, and protein metabolism.
Regulates alpha and beta cell functions by inhibiting insulin, glucagon, and pancreatic polypeptide secretion.
Different from hypothalamic somatostatin, which inhibits growth hormone (GH) and thyroid-stimulating hormone (TSH).
Amylin
A peptide hormone co-secreted with insulin by beta cells.
Regulates blood glucose by delaying nutrient uptake and suppressing glucagon secretion post-meals.
Provides satiety and may cause hyperglycemia if aggregated; contributes to beta cell loss in type 2 diabetes mellitus (T2DM)
Incretin Effect
Gut-derived hormones create an incretin effect, promoting glucose-dependent insulin secretion, inhibiting glucagon synthesis, and delaying gastric emptying.
Enhance beta-cell mass and replenish insulin stores
Counterregulatory Hormones
Overview
Include catecholamines, growth hormone, and glucocorticoids.
Work together with glucagon, functioning against insulin's storage effects during fasting, exercise, or when glucose intake is limited
Epinephrine
Role in Metabolism
A catecholamine from the adrenal medulla that maintains blood glucose during stress.
Inhibits insulin release while promoting glucose breakdown in muscle cells (muscle glycogen does not enter the bloodstream; muscles use it to conserve blood glucose for brain needs).
Major effects include:
Inducing glycogenolysis in the liver, leading to significant glucose release into circulation.
Activating lipolysis in adipose cells, increasing fatty acid availability (Mefford, 2024, p. 1263).
Growth Hormone
Metabolic Effects
A counterregulatory hormone that influences multiple metabolic pathways:
Increases cellular protein synthesis.
Mobilizes fatty acids from fat stores.
Antagonizes insulin effects.
Elevated during stress (e.g., surgery, trauma), exercise, and throughout childhood and puberty, decreasing with age.
Chronic hypersecretion can lead to glucose intolerance (Mefford, 2024, pp. 1263-1264).
Glucocorticoid Hormones
Functionality
Originating in the adrenal cortex, these hormones increase blood glucose (BG) levels.
Essential during fasting and starvation periods.
Stimulated by hypoglycemia.
Enhance gluconeogenesis in the liver, increasing hepatic glucose production.
Suppress the inflammatory response (Mefford, 2024, p. 1264).
Diabetes Mellitus and the Metabolic Syndrome
Definition and Impact
Diabetes mellitus (DM): A group of metabolic diseases characterized by hyperglycemia due to insulin secretion, action defects, or both.
Affects all age groups:
Estimated 7.3 million undiagnosed individuals in the US.
Disproportionately affects certain ethnic groups (Indigenous, Blacks, Latin Americans).
Leading cause of coronary heart disease, stroke, chronic kidney disease, and blindness; ranks eighth in US mortality (
Incidence and Classification of DM
DM is defined as impaired metabolism of carbohydrates, proteins, and fats due to insulin imbalances.
Key contributing factors:
Reduced insulin secretion.
Decreased glucose utilization.
Increased glucose production.
Individuals with uncontrolled DM can't transport glucose to cells, leading to cellular starvation and increased breakdown of fats and proteins for energy.
Types of DM:
Prediabetes: BG elevated but not diagnostic of DM.
Type 1 Diabetes Mellitus (T1DM): Autoimmune destruction of insulin-producing pancreatic beta cells, leading to absolute insulin deficiency.
Type 2 Diabetes Mellitus (T2DM): Associated with insulin resistance and progressive decline in pancreatic insulin secretion.
Gestational Diabetes (GDM): Occurs primarily during pregnancy.
Diabetes due to other causes.
Statistics on Diabetes Prevalence
According to 2024 CDC data:
38.4 million individuals (~11.6% of the US population) diagnosed with DM:
5% have T1DM; most have T2DM.
Diagnosed: 29.7 million (29.4 million adults).
Undiagnosed estimate: 8.7 million.
T1DM prevalent in children, incidence of T2DM on the rise, especially in specific minority groups (Allen, 2023, p. 702; CDC, 2024; Mefford, 2024, p. 1264).
Testing for Diagnosis and Management of DM
Screening Recommendations
Consider screening for all individuals aged 45 and older and those at risk including:
Clinically obese individuals.
First-degree relatives with DM.
Members of high-risk groups.
Individuals with hypertension or hyperlipidemia.
Those diagnosed with GDM.
Individuals who birthed macrosomic infants.
Those with previous prediabetes test results (Mefford, 2024, pp. 1264-1265).
Diagnostic Laboratory Tests
Diagnosis confirmed through tests measuring blood glucose levels:
Blood glucose measurements, urinary glucose, and ketones tests help manage DM.
Criteria for Diagnosing Diabetes (Chart 41)
Fasting Plasma Glucose (FPG) ≥ 126 mg/dL (7.0 mmol/L)
Fasting defined as no caloric intake for at least 8 hours.
2-Hour Plasma Glucose (2-h PG) ≥ 200 mg/dL (11.1 mmol/L) during Oral Glucose Tolerance Test (OGTT).
Hemoglobin A1C ≥ 6.5% (48 mmol/L), using a standardized laboratory method; repeat testing for confirmation without unequivocal hyperglycemia.
Random Plasma Glucose ≥ 200 mg/dL (11.1 mmol/L) in presence of classic hyperglycemic symptoms (American Diabetes Association [ADA], 2024).
Blood Tests for Diabetes Management
Types of Blood Tests
Various blood tests useful for diagnosis and management:
Fasting Blood Glucose (FBG): no food for 8 hours
Normal: < 100 mg/dL
Prediabetes: 100-125 mg/dL
DM diagnosis: ≥ 126 mg/dL.
Follow-up needed for elevated levels.
Random Blood Glucose Test: Done without regard to last meal, elevated ≥ 200 mg/dL indicates DM.
Oral Glucose Tolerance Test (OGTT):
Measure body's ability to remove glucose from blood after 75 g glucose at designated intervals; 2-hour result:
< 140 mg/dL: Normal.
140-199 mg/dL: Prediabetes.
≥ 200 mg/dL: Diabetes (Mefford, 2024, p. 1265).
Glycated Hemoglobin Testing (Hgb A1C):
Reflects average blood glucose levels over RBC lifespan→ 120 days
Measures the amount of RBC that have been glycated→ glucose molecule that has bound to it
Hgb A1C ≥ 6.5% suggests diabetes.
Capillary Whole Blood Glucose Monitoring: Rapid means to monitor BG using whole blood; noted laboratory tests yield 10-15% higher plasma results.
Continuous Glucose Monitoring: Gaining acceptance, advantages include reducing painful draws and better care guidance.
Urine Tests in Diabetes Management
Urine Testing Insights
Urine tests for glucose (glycosuria) indicate exceeded renal reabsorption thresholds, typically accompanying hyperglycemia.
Urine glucose testing has become mostly obsolete due to blood glucose monitoring ease.
Ketonuria testing via urine remains significant for T1DM management
Classification and Pathophysiology of Diabetes Mellitus
Classification Insights
ADA classification for DM includes:
Prediabetes: Diagnostic term for elevated BG not meeting DM criteria.
Type 1 DM (T1DM): Immune-mediated destruction of pancreatic beta cells.
Type 2 DM (T2DM): Features insulin resistance with metabolic syndrome manifestations present.
Gestational Diabetes Mellitus (GDM): Occurs mainly during pregnancy.
Other Etiologies: Includes secondary diabetes causes (Mefford, 2024, p. 1266).
Understanding Prediabetes
Defined when BG is elevated without yet fulfilling DM criteria.
Commonly detected in at-risk T2DM individuals.
Lifestyle changes can reverse prediabetes progression (Mefford, 2024, p. 1266).
Overview of Type 1 Diabetes Mellitus (T1DM)
T1DM represents approximately 10% of diabetes cases.
Immune-mediated (self) destruction of pancreatic beta cells leads to absolute insulin deficiency.
Presents as a catabolic disorder with heightened BG levels and utilization of fats and proteins for energy.
Prone to ketoacidosis due to lack of insulin (Mefford, 2024, p. 1266).
Understanding Type 2 Diabetes Mellitus (T2DM)
T2DM accounts for around 90% of diabetes cases—incidence increasing steadily since 1940.
Characterized by relative insulin deficiency rather than absolute deficiency.
Associated with various risk factors, such as advancing age, obesity, and family history
Metabolic Abnormalities in Type 2 Diabetes Mellitus
1) Insulin resistance: The hallmark of T2DM, noting ineffective insulin action—contributing to hyperglycemia.
2) Abnormal insulin secretion and elevated hepatic glucose production.
This state involves a progressive beta-cell function decline (Mefford, 2024, pp. 1266-1268).
Insulin Resistance and the Metabolic Syndrome
Overview of Metabolic Abnormalities
Insulin resistance contributes not just to T2DM but related to other metabolic issues, termed the insulin resistance syndrome or metabolic syndrome (Mefford, 2024, pp. 1268-1269).
Key metabolic issues include:
Obesity
Dyslipidemia: Elevated triglycerides and lower HDL.
Hypertension and systemic inflammation.
Obesity is a significant factor that exacerbates insulin resistance, with increased health risks observed particularly for central or abdominal (apple shape) obesity versus lower (pear) obesity (Mefford, 2024, pp. 1268-1269).
Clinical Manifestations and Laboratory Abnormalities
Characteristics include central obesity, elevated fasting/postprandial glucose, insulin resistance, hyperinsulinemia, and various comorbidities (Mefford, 2024, pp. 1268-1269).
Gestational Diabetes
Characteristics
Defined as any degree of glucose intolerance occurring during pregnancy, particularly in the second and third trimesters.
GDM complicates roughly 7% of pregnancies.
Associated with increased risk for Type 2 diabetes and complications later in life.
Universal screening is recommended, but remains controversial (Mefford, 2024, pp. 1268-1269).
Diabetes Due to Other Etiologies
Etiological Factors
A minor fraction of diabetes cases result from conditions like pancreatic disease, endocrine disorders (e.g., acromegaly, Cushing syndrome), or secondary diabetes due to medication or other factors (Mefford, 2024, p. 1269).
Clinical Manifestations of Diabetes Mellitus
Symptomatology
Onset of symptoms can be rapid (T1DM) or insidious (T2DM) with many individuals undiagnosed for years.
Common symptoms referred to as the "three polys":
Polyuria: Excessive urination due to glucose excretion after renal threshold is surpassed.
Polydipsia: Excessive thirst due to cellular dehydration from hyperglycemia.
Polyphagia: Excessive hunger primarily in T1DM due to cellular starvation.
Additional Symptoms
T1DM: May include weight loss and diabetic ketoacidosis (DKA) as initial presentations.
T2DM: Often features chronic skin infections, blurred vision, fatigue, and general malaise (Mefford, 2024, p. 1269).
Complications of Diabetes Mellitus
Acute Complications
Major Acute Complications
Diabetic ketoacidosis (DKA), hyperosmolar hyperglycemic state (HHS), and hypoglycemia are critical and potentially life-threatening issues requiring prompt recognition and treatment.
ED Visits: DKA accounts for ~175,000 visits annually; HHS is less frequent, composing approximately 9.5% of hyperglycemic ED visits (Mefford, 2024, p. 1270).
Diabetic Ketoacidosis (DKA)
Develops due to absolute or relative insulin deficiency, increased insulin counterregulatory hormones.
Common in T1DM patients during onset or as a disease complication.
Metabolic derangements include hyperglycemia, ketosis, and acidosis leading to symptoms ranging from polyuria, polydipsia, and dehydration to potentially coma (Mefford, 2024, pp. 1270-1271).
Hyperosmolar Hyperglycemic State (HHS)
Typically arises from inadequate diabetes management. Characterized by less insulin deficiency compared to DKA, leading to substantial dehydration yet absent ketoacidosis
Increased risk for infections, sepsis, and venous thrombosis
Hypoglycemia
Recognized as BG < 70 mg/dL, often in insulin-treated diabetes.
Symptoms relate to CNS effects from glucose deprivation and activation of SNS
tachycardiac, anxiety, headache, and confusion
common after heavy exercise in type 1 DM
Diabetes Complications Related to Counterregulatory Mechanisms
Somogyi Effect
A cyclical pattern of hyperglycemia following insulin-induced hypoglycemia due to hormonal counter-regulation
Dawn Phenomenon
An increase in fasting blood glucose due to circadian hormone rhythms, not associated with hypoglycemic episodes
Chronic Complications of Diabetes Mellitus
Chronic Complication Overview
Include microvasculature disorders (neuropathies, nephropathies, retinopathies) and macrovascular complications (coronary artery disease, cerebrovascular accidents)
Microvascular Damage and Advanced Glycation End Products (AGEs)
AGEs are indicated in vascular damage linked with glycemic control in diabetes
Macrovascular Complications Risk Factors
Include risk markers of atherosclerosis, hypertension, and other systemic conditions prevalent in DM patients. They contribute significantly to morbidity and mortality
key risk factors→ elevated fibrinogen levels and hyperinsulinemia
Diabetic Foot Ulcers
Common and can escalate to severe infections or amputations due to neuropathy and poor vascular health (Mefford, 2024, p. 1274).
Susceptibility to Infections
Elevated risks in diabetic patients stem from impaired sensory perception, reduced blood supply, hypoxia, and impaired immune response (Mefford, 2024, p. 1274).