Biochemistry of Glucose Metabolism

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Questions and Answers

What is the initial product formed from glucose in the metabolism pathways described?

Lactate

Pyruvate

Fructose

Glucose-6-phosphate (correct)

Which enzyme is responsible for converting glucose to glucose-6-phosphate?

Lactase

Amylase

Maltase

Hexokinase (correct)

During anaerobic glycolysis, what is glucose ultimately converted to?

Pyruvate and lactate (correct)

Oxygen

Glucose-6-phosphate

Fructose

Which of the following pathways is NOT mentioned as a metabolic pathway for glucose?

Krebs Cycle Signup and view all the answers

What role does salivary amylase play in the digestion of carbohydrates?

Hydrolyzes starch and glycogen to dextrins Signup and view all the answers

What is the recommended timeframe for separating a serum specimen from cells?

Within 30 minutes Signup and view all the answers

What should be added if the serum specimen is delayed beyond the recommended separation time?

Sodium fluoride Signup and view all the answers

What is the maximum recommended adult dose of glucose for testing?

75g Signup and view all the answers

How long should a patient fast before obtaining FBG?

8 to 10 hours Signup and view all the answers

What substance allows a whole blood sample to avoid glycolysis for up to 48 hours when refrigerated?

Sodium fluoride Signup and view all the answers

Which method employs cuprous ions for glucose measurement?

Folin Wu method Signup and view all the answers

What is the consequence of delaying the separation of a serum specimen beyond 30 minutes?

Increase in glucose levels Signup and view all the answers

What is NOT recommended regarding glucose testing for pregnant patients?

Avoiding routine glucose screening Signup and view all the answers

What is the threshold for diagnosing diabetes using HbA1C?

6.5% Signup and view all the answers

At what fasting plasma glucose level is diabetes typically diagnosed?

<blockquote> 95 mg/dL </blockquote> Signup and view all the answers

Which of the following glucose levels corresponds to hypoglycemia symptoms?

50 to 55 mg/dL Signup and view all the answers

What should be the plasma glucose level 1 hour after a meal for it to be considered normal?

< 180 mg/dL Signup and view all the answers

How is fasting plasma glucose also referred to?

Fasting blood sugar Signup and view all the answers

What is the recommended screening period for all nondiabetic pregnant women for GDM?

24 to 28 weeks Signup and view all the answers

What is classified as postabsorptive hypoglycemia?

Insulinoma associated Signup and view all the answers

What is the recommended threshold for 2-hour plasma glucose testing?

≥ 155 mg/dL Signup and view all the answers

Which hormone is directly responsible for stimulating the adrenal cortex to release cortisol?

ACTH Signup and view all the answers

What is the primary mechanism by which thyroxine increases plasma glucose levels?

Increased glycogenolysis and gluconeogenesis Signup and view all the answers

How is Type 1 diabetes characterized in terms of insulin production?

Absolute deficiency due to autoimmune destruction of pancreatic β-cells Signup and view all the answers

Which type of diabetes is associated with gestational diabetes mellitus (GDM)?

Type 2 diabetes Signup and view all the answers

Which antibodies are commonly associated with Type 1 diabetes?

Glutamic acid decarboxylase autoantibodies (GADA) Signup and view all the answers

What is the effect of somatostatin on insulin?

Inhibits insulin secretion Signup and view all the answers

Which of the following is NOT a characteristic of Type 1 diabetes?

Insulin resistance Signup and view all the answers

Which process increases the level of glucose in the blood during times of fasting?

Glycogenolysis Signup and view all the answers

Which of the following best describes the characteristics of Type 2 Diabetes?

Non-insulin dependent with relative insulin deficiency Signup and view all the answers

Which complication is specifically associated with microvascular problems in diabetes?

Retinopathy Signup and view all the answers

What is the primary management strategy for Latent Autoimmune Diabetes of Adulthood (LADA)?

Parenteral administration of insulin Signup and view all the answers

Which of the following factors is not considered a risk factor for Type 2 Diabetes?

High levels of physical fitness Signup and view all the answers

Idiopathic Type 1 Diabetes is characterized by which of the following features?

Requires insulin replacement therapy Signup and view all the answers

Which hormone is increased in Cushing's Syndrome and can affect blood glucose levels?

Cortisol Signup and view all the answers

Which of the following statements about insulin action in Type 2 Diabetes is correct?

There is a relative insulin deficiency with resistance Signup and view all the answers

What is the result of using hypoglycemic agents such as metformin?

It regulates blood sugar levels Signup and view all the answers

Dilantin and Pentamidine are drugs that lead to which specific diabetes-related issue?

Receptor abnormalities Signup and view all the answers

Which symptom is commonly associated with hypoglycemia?

Mental confusion Signup and view all the answers

How does Type 2 Diabetes primarily differ from Type 1 Diabetes?

Type 2 is non-insulin dependent Signup and view all the answers

Which of the following is a potential complication of diabetes that affects the nervous system?

Neuropathy Signup and view all the answers

What unique aspect characterizes the onset of Type 1 diabetes in adults?

Less aggressive autoimmune destruction over time Signup and view all the answers

Which genetic syndrome is associated with Type 2 Diabetes?

Down syndrome Signup and view all the answers

Study Notes

Fate of Glucose

Most ingested carbohydrates are polymers like starch and glycogen
Salivary and pancreatic amylases digest polymers into dextrins and disaccharides
Maltase hydrolyzes disaccharides to monosaccharides
- Sucrose to glucose and fructose
- Lactose to glucose and galactose
Monosaccharides are absorbed by the gut and transported to the liver via the hepatic portal venous blood supply
3 possible metabolic pathways for absorbed glucose:
- Glucose converted to glucose-6-phosphate using ATP (enzyme: hexokinase)
- Embden-Meyerhof pathway
- Hexose Monophosphate Shunt
- Glycogenesis

Embden-Meyerhof Pathway for Anaerobic Glycolysis

Glycolysis is the conversion of glucose to pyruvate and lactate
Anaerobic glycolysis occurs when oxygen is not a concern

Diabetes Mellitus

A group of metabolic diseases characterized by hyperglycemia, resulting from defects in insulin secretion, insulin action, or both
Two main types:
- Type 1
- Type 2
New categories of diabetes (ADA/WHO):
- Type 1 diabetes
- Type 2 diabetes
- Other specific types of diabetes
- Gestational diabetes mellitus (GDM)

Type 1 Diabetes

Insulin-dependent diabetes mellitus (IDDM), juvenile-onset diabetes mellitus, brittle diabetes, ketosis-prone diabetes
Result of cellular-mediated autoimmune destruction of the beta cells of the pancreas leading to an absolute deficiency of insulin secretion
Antibodies associated with type 1:
- Islet cell autoantibodies (ICA)
- Insulin autoantibodies (IAA)
- Glutamic acid decarboxylase autoantibodies (GADA)
- Tyrosine phosphatase IA-2 and IA2B autoantibodies
- Zinc transporter 8 antibody (ZnT8)
Constitutes only 5% to 10% of all diabetes cases
Risk factors:
- Genetic, autoimmune, environmental

Type 2 Diabetes

Non-insulin-dependent diabetes mellitus (NIDDM), maturity onset or adult type DM, stable diabetes, ketosis-resistant diabetes, receptor-deficient DM
A result of an individual’s resistance to insulin with an insulin secretory defect (relative insulin deficiency)
Constitutes the majority of diabetes cases
Characteristics:
- Usually more gradual symptom onset
- Insulin independence (initially)
- Ketoacidosis uncommon
Risk factors:
- Genetic, obesity, sedentary lifestyle, race/ethnicity, PCOS, dyslipidemia, hypertension
Complications:
- Macrovascular and microvascular
Uses hypoglycemic agents to regulate blood sugar level (e.g., metformin)

Other Specific Types of Diabetes

Associated with secondary conditions:
- Genetic defects of beta cell function or insulin action
- Pancreatic disease or injury
- Endocrine disease
  - Example conditions: Cushing’s syndrome, pheochromocytoma
- Drug or chemical-induced receptor abnormalities
  - Example drugs: Dilantin, Pentamidine, Thiazides
- Other genetic syndromes
  - Example: Down syndrome

Criteria for Testing and Diagnosis of Diabetes Mellitus

HbA1c ≥ 6.5% using a method that is NGSP certified and standardized to the DCCT assay
- HbA1c also known as glycosylated hemoglobin
Fasting plasma glucose also known as fasting blood sugar
Random plasma glucose also known as random blood sugar

Criteria for Testing and Diagnosis of Gestational Diabetes Mellitus

International Association of the Diabetes and Pregnancy Study Groups recommend screening for all nondiabetic pregnant women at 24 to 28 weeks of gestation

Hypoglycemia

65 to 70 mg/dL (3.6 to 3.9 mmol/L) - glucagon and other glycemic factors are released
50 to 55 mg/dL (2.8 to 3.1 mmol/L) - observable symptoms of hypoglycemia appear
Classification:
- Postabsorptive (fasting) - associated with insulinoma

Glucose Measurement Methods

Alkaline Copper Tartrate + Heat -> Cuprous Ions
a. Folin Wu Method
- Cuprous Ions -> Phosphomolybdate -> Phosphomolybdic Acid or Phosphomolybdenum Blue
- This is a colorimetric measurement

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Description

Explore the intricate processes involved in glucose metabolism, including digestion and conversion pathways. This quiz covers the enzymatic breakdown of carbohydrates, glycolysis, and the implications of diabetes mellitus. Test your understanding of these critical biochemical concepts.