Carbohydrates Overview and Metabolism

Carbohydrates Objectives

• Students will be able to classify carbohydrates into groups.
• Students will be able to discuss the metabolism of carbohydrates in the body, including the hormones involved.
• Students will be able to differentiate between different types of diabetes based on clinical and laboratory findings according to the ADA.

Carbohydrates

• Carbohydrates are a major food source for energy, primarily stored in the liver and muscle as glycogen.
• Diseases related to carbohydrates are classified into hyperglycemia and hypoglycemia.
• Carbohydrates are derivatives of aldehyde or ketone, based on the location of the carboxyl group.
• Carbohydrates are composed of monosaccharides, disaccharides, oligosaccharides, and polysaccharides.

Carbohydrates-Glucose

• Glucose is the only carbohydrate directly used for energy and stored as glycogen with the help of insulin.
• All sugar molecules must be digested into glucose, a monosaccharide.

General Description of Carbohydrates

• Carbohydrates are compounds containing carbon (C), hydrogen (H), and oxygen (O).
• The general formula for carbohydrates is Cx(H2O)y.
• All carbohydrates contain C=O and -OH functional groups.
• The classification of carbohydrates is based on four structural properties: the size of the base carbon chain, the location of the CO function group, the number of sugar units, and the stereochemistry.

Carbohydrate Classification

• Carbohydrates can be grouped based on the number of carbons in the molecule (e.g., trioses, tetroses, pentoses, hexoses).
• Glucose and fructose are examples of hexoses.

Carbohydrate Stereochemistry

• Mirror image forms (D and L) are based on the position of the -OH group on the chiral carbon.
• D-sugars have the -OH group on the right side of the chiral carbon.
• L-sugars have the -OH group on the left side of the chiral carbon.

Chemical Properties of Carbohydrates

• Some carbohydrates act as reducing agents—these can reduce other compounds.
• Non-reducing carbohydrates lack the aldehyde or ketone group.

Classification based on number of units

• Monosaccharides
• Disaccharides
• Oligosaccharides
• Polysaccharides

Monosaccharides

• Simple sugars that cannot be further hydrolyzed.
• May contain three to six carbons.
• Common examples include glucose, fructose, and galactose.

Glucose

• The primary energy source for humans.
• Central to carbohydrate metabolism.

Fructose

• Also known as fruit sugar
• Component of sucrose.

Galactose

• Glucose precursor, converted into glucose for bodily functions.
• Galactosemia is a deficiency in processing galactose.

Others (Ribose and Deoxyribose)

• Important pentose sugars.

Question 1

• Glucose is the only monosaccharide directly used by cells for energy.

Question 2

• Hydrolysis of lactose by lactase yields glucose and galactose.

Question 3

• Starch is hydrolyzed by amylase to produce maltose.

Glucose Metabolism

• Glucose is absorbed and can enter three metabolic pathways.
• The ultimate goal is conversion of glucose to CO2 and H20.

Hormone Regulation

• Hormones regulate the entry and fate of glucose within the body.

Pancreas

• Two functionally different tissue types exist:
• Endocrine (hormone-releasing): Includes the islets of Langerhans containing four cell types releasing insulin, glucagon, gastrin, somatostatin.
• Exocrine (enzyme-secreting)

Pancreatic Disorders

• Major diseases include diabetes mellitus (DM), islet cell tumors, acute/chronic pancreatitis, pancreatic cancer, and cystic fibrosis.

Hormones Regulating Glucose Metabolism

• Glucagon
• ACTH (Adrenocorticotropic hormone)
• Growth Hormone
• Cortisol
• Human Placental Lactogen
• Epinephrine (adrenaline)
• Thyroxine (T4)
• Insulin
• Somatostatin

Insulin

• Primary hormone for glucose entry into cells.
• Synthesized by Beta cells of the islets of Langerhans.

Glucagon

• Primarily responsible for increasing blood glucose.
• Synthesized by alpha cells of the islets of Langerhans.

Epinephrine

• Produced by the adrenal medulla, increases bloodglucose during stress.

Cortisol

• Produced by the adrenal cortex. Increases blood glucose through mechanisms including gluconeogenesis and lipolysis.

Growth Hormone

• Produced by the anterior pituitary gland, increases blood glucose.

Thyroxine (T4)

• Produced by the thyroid gland, increases blood glucose.

Somatostatin

• Acts like insulin, inhibits insulin, glucagon, and growth hormone.

ACTH

• Enhances cortisol release and fatty acid release, promotes gluconeogenesis.

Human Placental Lactogen

• Increases during pregnancy, and functions to increase gluconeogenesis, and promote insulin resistance.

Hyperglycemia

• An increase in blood glucose concentration that is toxic to beta cells.

Characteristics of uncontrolled hyperglycemia

• Polyuria, ketonuria and glycosuria are seen in uncontrolled hyperglycemia.

Diabetes Classification

• Type I (insulin deficiency): Typically autoimmune-mediated.
• Type II (insulin resistance): More common and often related to lifestyle and genetics.
• Gestational: Develops during pregnancy.
• Other specific types: caused by other factors.

Risk Factors for Diabetes

• Obesity
• Family history
• History of Gestational diabetes (GDM)
• High-risk race/ethnicity
• Hypertension
• Low HDL cholesterol
• Elevated triglycerides

Metabolic Syndrome

• Collection of factors related to increased risk for diabetes and heart disease.

Type 2 Diabetes Classification

• Prediabetes
• Diabetes

Complications of Diabetes Mellitus

• Nephropathy (Kidney disease)
• Neuropathy (nerve damage)
• Retinopathy (eye disease)
• Cardiovascular disease

Laboratory Findings in Hyperglycemia

• Increased glucose in plasma and urine
• Presence of ketones in serum and urine
• Decreased blood and urine pH (acidosis)
• Electrolyte imbalance

Diabetes Insipidus (DI)

• Serum osmolality decreases.
• Urine osmolality decreases.

SIADH (Syndrome of Inappropriate Antidiuretic Hormone)

• Serum osmolality decreases
• Urine osmolality increases

Tests for Long-term Diabetes Complications

• Serum BUN (Blood Urea Nitrogen)
• Serum creatinine
• Urine albumin
• Lipids

Recommended Tests for Diabetes (Annually)

• Blood glucose
• HbA1c
• Microalbumin
• Estimated Glomerular Filtration Rate (eGFR)
• POCT

Gestational Diabetes Mellitus (GDM)

• Diabetes onset during pregnancy due to metabolic and hormonal changes.
• Usually resolves after pregnancy but increases risk of later-onset Type 2 diabetes.

Gestational Diabetes Mellitus Characteristics

• Insulin resistance, decreased insulin secretion.
• Higher prevalence among obese women, older women, those with previous GDM, and certain ethnic groups.

Hypoglycemia

• Imbalance between glucose production and utilization.
• Can be life-threatening if glucose levels fall to dangerously low levels.

Fasting Hypoglycemia

• Hypoglycemia occurring after fasting
• May be caused by tumors (insulinomas), hepatic dysfunction, glucocorticoid deficiency, or sepsis

Lactose intolerance

• A marked decrease in intestinal lactase leads to impaired lactose hydrolysis..
• The buildup of lactose leads to discomfort, cramping and diarrhea.

Galactosemia

• Defects in galactose metabolism result in elevated galactose (in plasma).
• A serious complication, requiring a diet restricted of galactose.

Glycogen Storage Diseases

• Inherited disorders related to glycogen metabolism.

Diagnostic tests for Glucose Metabolic Alterations

• Fasting Blood Sugar (FBS)
• Postprandial Blood Sugar (2 hours after meal)
• Oral glucose tolerance test(OGTT)
• HbA1c
• POCT
• Ketone tests
• Microalbuminuria
• Glycomarkblood Test
• Fructosamine Assay
• C-Peptide test