Carbohydrates Overview and Classification

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Questions and Answers

What is the primary function of gluconeogenesis?

Formation of new glucose from non-carbohydrate sources (correct)

Storage of glucose in the liver

Decomposition of fat into fatty acids

Conversion of carbohydrates to fatty acids

Which hormone primarily decreases blood glucose levels?

Glucagon

Insulin (correct)

Cortisol

Epinephrine

In which type of diabetes is there an autoimmune destruction of islet beta cells?

Type 2 Diabetes

Secondary Diabetes

Type 1 Diabetes (correct)

Gestational Diabetes

What process is responsible for the quick release of glucose into the blood?

Glycogenolysis Signup and view all the answers

Which hormone increases blood glucose by stimulating glycogenolysis, gluconeogenesis, and lipolysis?

Glucagon Signup and view all the answers

What is a common diagnostic criterion for diabetes regarding fasting blood glucose levels?

<blockquote> 126 mg/dL </blockquote> Signup and view all the answers

Which type of diabetes is characterized by insulin resistance and is typically seen in adults?

Type 2 Diabetes Signup and view all the answers

What is the fasting glucose range that defines prediabetes?

100-125 mg/dL Signup and view all the answers

Which of the following is NOT a potential outcome of untreated galactosemia?

Congenital heart disease Signup and view all the answers

During the Glucose Tolerance Test (GTT), which result indicates a diagnosis of gestational diabetes?

1 hour > 180 mg/dL Signup and view all the answers

In cases of hypoglycemia, which hormone is primarily responsible for raising blood glucose levels?

Glucagon Signup and view all the answers

What is the laboratory finding that indicates hypoglycemia?

Plasma glucose level below 60 mg/dL Signup and view all the answers

What type of carbohydrate metabolism is compromised in galactosemia due to the deficiency of galactose-1-phosphate uridyltransferase?

Lactose to glucose conversion Signup and view all the answers

What is the reference range for serum/plasma glucose?

74-100 mg/dL Signup and view all the answers

What is a significant relationship between whole blood glucose measurements and serum/plasma glucose?

Whole blood measurements are usually 10-15% lower than serum/plasma Signup and view all the answers

In the testing for gestational diabetes, what is the critical measurement taken upon fasting?

Fasting > 92 mg/dL Signup and view all the answers

Failure to thrive in a patient with galactosemia is primarily due to what factor?

Inability to metabolize galactose Signup and view all the answers

What classification of carbohydrate includes starch, glycogen, and cellulose based on sugar units?

Polysaccharides Signup and view all the answers

Which stage of carbohydrate metabolism involves the breakdown of glycogen to glucose?

Glycogenolysis Signup and view all the answers

During glycolysis, glucose is converted into which of the following end products?

Lactate or pyruvate Signup and view all the answers

In carbohydrate metabolism, which hormone is primarily responsible for lowering blood glucose levels?

Insulin Signup and view all the answers

What type of diabetes is characterized by the body’s inability to produce insulin?

Type 1 Diabetes Signup and view all the answers

Study Notes

Carbohydrates

Carbohydrates are compounds that provide chemical energy to cells
They are primarily sugars and starches
Carbohydrates are a primary energy source for the brain, erythrocytes, and retinal cells
Carbohydrates contain carbon (C), hydrogen (H), and oxygen (O)
"-ose" suffix signifies a sugar
Classification is based on:
- Number of sugar units (monosaccharides, disaccharides, oligosaccharides, polysaccharides)
- Size of the base carbon chain (trioses, tetroses, pentoses, hexoses)
- Location of the carbonyl group (aldehyde or ketone)
- Stereochemistry of the compound

Classification of Carbohydrates

Trioses - 3 carbons
Tetroses - 4 carbons
Pentoses - 5 carbons (e.g., DNA)
Hexoses - 6 carbons (e.g., glucose)
Aldose: carbonyl group at the end (aldehyde group)
Ketose: carbonyl group in the middle (ketone group)

Number of Sugar Units

Monosaccharides: one sugar unit (e.g., glucose, fructose, galactose)
Disaccharides: two sugar units (e.g., maltose, lactose, sucrose)
Oligosaccharides: 3-10 sugar units
Polysaccharides: >10 sugar units (e.g., starch, glycogen, cellulose)

Chemical Properties of Carbohydrates

Reducing carbohydrates: contain ketone or aldehyde groups (e.g., glucose, maltose)
Non-reducing carbohydrates: do not contain ketone or aldehyde groups (e.g., sucrose)

Carbohydrate Metabolism

Begins in the mouth with salivary amylase breaking down polysaccharides
Monosaccharides are absorbed by the gut and transported to the liver
Glucose is the only carbohydrate directly used for energy or stored as glycogen
Pathways of glucose metabolism:
- Liver and muscle glycogen storage
- Conversion to amino acids and proteins
- Conversion to fats
Ultimate goal is metabolism to CO2 and H2O

Glucose Breakdown

Glycolysis: Conversion of glucose to lactate or pyruvate, providing energy
Glycogenesis: Conversion of glucose to glycogen for storage (primarily in liver and muscle)
Glycogenolysis: Breakdown of glycogen to glucose when blood glucose levels are low

Glucose Formation

Gluconeogenesis: Formation of new glucose from non-carbohydrate sources (e.g., amino acids, glycerol, fatty acids)
Occurs primarily in the liver
Important in starvation and weight loss
Protects the body, especially the brain

Carbohydrate Metabolism (Lipolysis, Lipogenesis)

Lipogenesis: Conversion of carbohydrates to fatty acids, Excess glucose is stored as fat
Lipolysis: Decomposition of fat

Regulation of Plasma Glucose

Glycogenolysis: Releases glucose into the blood (quick response)
Gluconeogenesis, and lipolysis: Longer response, Release glucose into the blood
Glycogenesis: Liver stores glucose
Insulin decreases glucose levels
Glucagon increases glucose levels
Epinephrine and Cortisol increase glucose levels
ACTH increases glucose levels

Hormones Affecting Glucose Levels

Insulin: Decreases blood glucose by facilitating glucose entry into cells and promoting glycolysis
Glucagon: Increases blood glucose by stimulating glycogenolysis and gluconeogenesis
Epinephrine and Cortisol: Increase blood glucose by stimulating glycogenolysis, gluconeogenesis, and lipolysis
Adrenocorticotropic Hormone (ACTH): Increases blood glucose by stimulating the adrenal cortex to release cortisol

Other Hormones Affecting Glucose Levels

TSH (thyroid-stimulating hormone): Increases glucose absorption from intestines
Somatostatin: Inhibits insulin, thus increasing glucose

Types of Diabetes

Type 1 Diabetes: Insulin-dependent diabetes mellitus (IDDM), autoimmune destruction of islet beta cells, usually in children and adolescents
Type 2 Diabetes: Non-insulin-dependent diabetes mellitus (NIDDM), insulin resistance, usually in adults, related to obesity, lack of exercise, diet, and genetic factors
Secondary Diabetes: due to other conditions such as genetic defects, pancreatic disease, endocrinopathies or drug-induced
Gestational Diabetes (GDM): glucose intolerance during pregnancy, usually resolves after delivery but increases risk of later diabetes

Diabetes Diagnosis Criteria

Symptoms of diabetes plus random plasma glucose >200 mg/dL
Fast blood glucose >126 mg/dL
2-Hour glucose > 200 mg/dL during an oral glucose tolerance test (OGTT)
Hemoglobin A1c (HbA1c) > 6.5%, Confirmed on repeat measurement

Prediabetes

Fasting glucose between 100-125mg/dL
2-hr GTT results between 140-199mg/dL
HbA1c between 5.7-6.4%

GDM testing

Moms screened at weeks 24-28
2-hr GTT, fasting, 1 hour, and 2 hours after 75-g glucose load
Diagnosis: Fasting >92mg/dl, 1 hour >180mg/dl, and 2 hour >153mg/dl

Hypoglycemia

Plasma glucose level falls below 60 mg/dL
Release of glucagon, epinephrine, cortisol, and growth hormone
Treatment varies with cause (small, frequent meals, low in carbs, high in protein)

Lab Findings for Hypoglycemia

Low plasma glucose levels

Glucose

Insulin level
Galactosemia
Caused by a deficiency in galactose-1-phosphate uridyltransferase
Results in the inability to convert galactose to glucose or lactose to glucose
Symptoms: failure to thrive, mental retardation, cataracts, and death

Laboratory Testing Considerations for Glucose

Reference values depend on various factors, including the type of specimen, how it was collected
Reference range for glucose (serum/plasma): 74-100 mg/dL. Whole blood is 65-95mg/dl
Specimen collection methods (serum, plasma, whole blood)
Results are 10-15% lower for whole blood than serum/plasma due to dilution by cells

Glucose - Specimen Collection and Testing

CSF specimens: Analyzed ASAP; 60-70% of current blood glucose level
24-hour urine: A small amount of glucose is lost daily (<500 mg/24 hr).

Preservation

Perform testing <1hr
Separate plasma from cells <1hr
Refrigerate (slows down glucose utilization by cells).

Additive

Sodium fluoride inhibits glycolysis

Anticoagulant

Potassium oxalate

Enzymatic methods

Glucose Oxidase or Hexokinase
Fasting Glucose Levels

FBS (Fasting Blood Sugar)

Most frequently ordered screening test for glucose metabolism
Fasting values of >126 mg/dL indicate diabetes
FBS should be repeated on another day to confirm diagnosis
Borderline diabetes may have a normal FBS; needs a challenge test to show abnormality.

Glucose Tolerance Test (GTT)

Purpose: diagnose hyperglycemia/diabetes and evaluate symptoms of hypoglycemia
Phlebotomist responsibilities
Ensure consistency of tubes and specimen type
Venipuncture or dermal puncture: Monitor patient.

Oral Glucose Tolerance Test (OGTT)and results

Blood glucose level drawn before drinking glucose drink
Glucose drink given
Blood glucose level drawn again 2 hours later
Glucose levels should return to normal levels after 2 hours
If glucose levels are higher than 200 mg/dL, a fasting or random glucose level is needed to diagnose diabetes.

Glycosylated Hemoglobin (HbA1c)

Glucose attaches non-enzymatically to hemoglobin molecules
Provides a time-averaged glucose reading reflecting the mean daily blood glucose levels over the previous 2-3 months
Advantages: reflects time-averaged glucose, not subject to temporary variability, doesn't need fasting
Influenced by: Red blood cell lifespan, sickle cell disease, hemolytic diseases,

HbA1c Testing, Specimen and Methods

Specimen: EDTA whole blood

Ketones

Produced in the liver from stored lipids
Metabolic byproducts of fatty acid breakdown.
Include acetone, acetoacetic acid, and β-hydroxybutyric acid (78%)
Increased in conditions like carbohydrate deprivation, starvation, fasting, prolonged vomiting
Increased in diabetes
Tested in fresh serum or urine

(Micro)albuminuria

Early sign of nephropathy (kidney damage) due to diabetes
Caused by progressive changes in the kidneys
Microalbumin to creatinine ratio of >30 mg/g is diagnostic
Should be confirmed over a period of 3-6 months
Random or timed collections (24-hour or 4-hour)

Lactose Tolerance Test

Used to assess lactose malabsorption or lactase deficiency.
Patients given a lactose load, breath samples collected at timed intervals, and increased hydrogen levels indicate a diagnosis

Glucose and HbA1C Decision Levels

Fasting glucose
Two-hour oral glucose tolerance
HbA1c

Lipids and Lipoproteins

Lipids are essential for body function, including fatty acids, triglycerides, phospholipids, and cholesterol/cholesteryl esters.
Lipoproteins: Chylomicrons, VLDL, LDL, and HDL are lipoproteins varying in size, density, lipid content, and associated apolipoproteins (Apo)
Apolipoproteins (Apo) such as Apo A-I, Apo B, Apo B-100, Apo B-48, Apo CII, Apo D, and Apo E have specific functions and origins.
Lipid metabolism: absorption, exogenous pathways (dietary lipids), endogenous pathways (liver-derived lipids), reverse cholesterol transport
Factors impacting cholesterol levels must be identified
Methods for cholesterol and triglyceride measurement, specimen choice, and potential interfering substances are crucial.
Metabolic syndrome criteria and significance need to be understood.
Atherosclerotic plaque formation: a complex process that needs to be defined.
Clinical conditions: Dyslipidemia, hyperlipoproteinemia, hypercholesterolemia, hypertriglyceridemia, and hypolipoproteinemia
Clinical conditions: Arteriosclerosis and xanthoma

Friedewald formula

Calculation and limitations for clinical settings
Non-HDL cholesterol clinical significance

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Description

This quiz covers the fundamental concepts of carbohydrates, including their structure, classification based on sugar units and carbon chains, and their significance as an energy source. Explore different types of carbohydrates like monosaccharides, disaccharides, and polysaccharides in this informative quiz.