Chapter 7 Carbohydrates PDF

Carbohydrates Chapter 7 Preamble PowerPoints are a general overview and are provided to help students take notes over the video lecture ONLY. PowerPoints DO NOT cover the details needed for the Unit exam Each student is responsible for READING the TEXTBOOK for details to answer the UNIT...

Carbohydrates Chapter 7 Preamble PowerPoints are a general overview and are provided to help students take notes over the video lecture ONLY. PowerPoints DO NOT cover the details needed for the Unit exam Each student is responsible for READING the TEXTBOOK for details to answer the UNIT OBJECTIVES Unit Objectives are your study guide (not this PowerPoint) Test questions cover the details of UNIT OBJECTIVES found only in your Textbook! Introduction Carbohydrates Most abundant organic molecules found in nature Stored in the liver as glycogen Serve as our primary source of food and energy Biochemistry of Carbohydrates (1) Carbohydrates Group of organic compounds including sugars, glycogen, and starches that contain only carbon, oxygen, and hydrogen Can be classified using four criteria: Number of carbons in the chain Size of the carbon chain Location of the carbonyl (CO) group Stereoisomers Trioses Have three carbons Smallest carbohydrates Tetroses, pentoses, and hexoses with four, five, and six carbons, respectively. Glucose is a hexose. Biochemistry of Carbohydrates (2) Aldehyde Molecule containing the carbonyl group at the end of the carbon chain (first or last carbon) Monosaccharide is called an aldose. Ketone Molecule containing the functional group on an internal carbon Monosaccharide is called a ketose. Biochemistry of Carbohydrates (3) Stereoisomers Molecules that have the same empirical or chemical formula but have mirror image structural formulas. Also used to describe monosaccharides. D or dextro and L or levo isomers refer to the position of the hydroxyl group on the carbon atom next to the last (bottom) CH2OH group Most sugars in the body are D isomers. Biochemistry of Carbohydrates (4) Stereoisomers Glucose (α and β) based on the position of the –OH group on the anomeric carbon (C1), which is the C atom bonded to an OH group and an O. Biochemistry of Carbohydrates (5) Disaccharides Formed by the interaction of two monosaccharides with the loss of a water molecule. Three of the most common are: Maltose Two glucose molecules Lactose Glucose and galactose Sucrose Glucose and fructose Polysaccharides Group of complex carbohydrates composed of more than 20 monosaccharides Usually insoluble in water Most common polysaccharides are starch, glycogen, and cellulose, which contain 25- 2500 glucose units. Carbohydrate Metabolism (1) Salivary amylase Catabolizes polysaccharides to intermediate-sized glucosans called “limit dextrins” and maltose Pancreatic amylase Completes digestion of starch and glycogen to limit dextrins and maltose Intestinal mucosa Secretes disaccharidases to digest maltose, lactose, and sucrose to monosaccharides Liver Monosaccharides are converted to glucose and utilized for energy. Carbohydrate Metabolism (2) Carbohydrates are channeled into four pathways: Converted to liver glycogen and stored Metabolized completely to CO2 and H20 to provide immediate energy Converted to keto acids, amino acids, and proteins Converted to fats (triglycerides) and stored in adipose tissue Embden-Meyerhoff pathway Results in the glycolysis of glucose into pyruvate or lactate Can occur with or without oxygen Principal means of energy production in humans Hexose monophosphate shunt pathway (HMP shunt) Oxidizes glucose to ribose and CO2 Glucose Metabolism Glycogenesis Conversion of glucose to glycogen for storage Glycogenolysis Involves the breakdown of glycogen to form glucose and other intermediate products Process that regulates glucose levels between meals Gluconeogenesis Formation of glucose from noncarbohydrate sources such as amino acids, glycerol, or lactate Occurs during long-term fasting Glycolysis Conversion of glucose or other hexoses into 3-C molecules (lactate or pyruvate) Hormone Regulation (1) Insulin Most important hormone Only hormone that lowers blood glucose levels when they are elevated A group of counterregulatory hormones, including glucagon, increases levels when blood glucose concentrations are too low Occurs during fasting or between meals. Table 7.1 Principal Glucose Regulatory Hormones Hormone Gland Principal Effects Insulin β cells, islets of Langerhans- increases glycolysis, glycogenesis, and lipogenesis Pancreas decreases glycogenolysis and gluconeogenesis Glucagon α cells, islets of Langerhans- increases glycogenolysis, gluconeogenesis, lipolysis Pancreas decreases glycolysis, glycogenesis, and lipogenesis Epinephrine Adrenal medulla increases glycogenolysis, gluconeogenesis, lipolysis decreases insulin (glucose uptake) Glucocorticoids Adrenal cortex increases glycogenolysis, gluconeogenesis, lipolysis (Cortisol) decreases insulin (glucose uptake) Adrenocorticotropic Anterior pituitary increases glycogenolysis, gluconeogenesis, lipolysis hormone (A CT H) decreases insulin (glucose uptake) Growth hormone Anterior pituitary increases glycogenolysis, gluconeogenesis, lipolysis decreases insulin (glucose uptake) Thyroxine, Thyroid increases glycogenolysis, gluconeogenesis Triiodothyronine Somatostatin δ cells, islets of Langerhans- Inhibits secretion of glucagon and insulin Pancreas Hormone Regulation (2) Insulin Produced by the β (beta) cells of the islets of Langerhans in the pancreas Hypoglycemic hormone Allows glucose to move into muscle and adipose cells Stimulates glycolysis, glycogenesis, and lipogenesis Synthesized from a precursor called proinsulin Hormone Regulation (3) Counterregulatory Hormones Glucagon Pancreatic hormone Produced by the a cells of the islets of Langerhans A hyperglycemic agent Stimulated by a decrease in glucose Inhibits glycolysis, glycogenesis, and lipogenesis Epinephrine Stimulated in the “fight or flight” syndrome Glucocorticoids, primarily cortisol, Secreted by the cortex in response to adrenocorticotropic hormone Adrenocorticotropic (ACTH) and growth hormones Antagonistic to insulin Thyroxine (T4) and triiodothyronine (T3) Stimulated by thyroid stimulating hormone (TSH) Clinical Significance (1) Diabetes mellitus (D M) Common disorder Seventh leading cause of death in the United States Primary cause of blindness and end-stage renal disease A group of diseases characterized by hyperglycemia due to defects in insulin production, insulin action, or both. The ADA classifies diabetes mellitus into four categories: Type 1 Type 2 Other (secondary diabetes mellitus) Gestational Clinical Significance (2) Diabetes mellitus (DM) Type 1 Immune-mediated diabetes Insulin-dependent diabetes mellitus (IDDM) Caused by destruction of the β cells of the islets of Langerhans in the pancreas Absolute insulin deficiency Signs and Symptoms (3Ps) Polydipsia: excessive thirst Polyuria: increased secretion and discharge of urine Polyphagia: increased appetite, eating large amounts of food Clinical Significance (3) Type 1 diabetes mellitus Accounts for about 5 to 10% of diabetics. Most commonly diagnosed in childhood and adoles- cence, Cellular-mediated auto-immune response attacks the β cells of the islets of Langerhans Leads to insulinopenia Type 1 diabetics Prone to other autoimmune diseases Associated with the inheritance of particular human leukocyte antigen (H L A) alleles Prone to go into ketosis when glucose levels are out of control More likely to go into diabetic ketoacidosis (D K A) Clinical Significance (4) Type 2 diabetes mellitus Most common and milder form Accounts for 90 to 95% of diabetics Insulin resistance and dyslipidemia Risk factor for cardiovascular disease Diet and exercise are very important determinants in the pathogenesis. Hyperosmolar hyperglycemic state (HHS) Most commonly occurs in patients with type 2 diabetes with a concurrent acute febrile illness that leads to a reduced fluid intake Characteristics are: Insidious (gradual) onset Not necessarily insulin dependent Not ketosis prone Box 7-2 Risk Factors for Type 2 Diabetes Age > 45 years Overweight (BMI > 25 kg/m2)* or Weight >120% of desirable body weight Family history of diabetes (i.e., parents or siblings with diabetes) Habitual physical inactivity Race/ethnicity: Hispanic, Native American, African American, Pacific Islander Previously identified I F G or I G T History of G D M or delivery of a baby weighing 79 lb Hypertension (> 140/90 in adults) H D L cholesterol …35 mg/dL and/or a triglyceride levelÚ250 mg/dL Polycystic ovary syndrome History of vascular disease *A Basal metabolic index (BMI) may not be correct for all ethnic groups Clinical Significance (5) Increased risk for a number of life-threatening health problems Heart disease is the leading cause of death in diabetics. High blood pressure is present in about 73% of diabetics. Heart disease and strokes occur two to four times more frequently. Forty-four percent of new cases of end-stage renal disease are associated with diabetes. Nervous system damage is present in 60 to 70% of diabetics. Complications of Diabetes Mellitus Heart disease and strokes Diabetic retinopathy End-stage renal disease Nervous system damage (e.g., peripheral neuritis) Susceptibility to infections (amputation of lower limbs) Clinical Significance (7) Diabetes mellitus (DM) Gestational Gestational diabetes (GDM) is associated with pregnancy. Diagnosed when abnormal glucose concentrations are discovered for the first time during pregnancy. Occurs in 1 to 5% of pregnancies due to metabolic and hormonal changes Most women revert to normal glucose metabolism after delivery. High probability (30 to 60%) that a woman with gestational diabetes will develop diabetes later in life. Box 7-4 Low Risk for Gestational Diabetes Age 6.5 This should be performed in a laboratory using a method N G S P (National Glycohemoglobin Standardization Program) certified and standardized to the D C C T assay.* Or FPG > 126 mg/dL (7.0mmol/L). Fasting is defined as no caloric intake for at least 8 hrs. Or 2 hour postload glucose > 200 mg/dL (11.1 mmol/L) during during an OGTT. The test should be performed as described by the World Health Organization (WHO), using a glucose load containing the equivalent of 75 g anhydrous glucose dissolved in water.* Or In a patient with classic symptoms of hyperglycemia or hyperglycemic crisis, a random plasma glucose > 200 mg/dL (11.1 mmol/L) *In the absence of unequivocal hyperglycemia, criteria 1-3 should be confirmed by repeat testing. Clinical Significance (12 of 16) Impaired Glucose Tolerance (IGT) and Impaired Fasting Glucose (IFG) – Defined as having a fasting plasma glucose (FPG) > 100 mg/dl but < 126 mg/dL Oral glucose tolerance test (OGTT) – 2-hour values are >140 mg/dL but 126 mg/dL 2-Hour Postload Glucose (O G T T) – Normal: 2-hour postload glucose 200 mg/dL (must be confirmed) Source: American Diabetes Association. Standards of medical care in diabetes-2016 American Diabetes Association (January 2016) (Supplement 1) : S13-S17 Clinical Significance (13 of 16) Hypoglycemia Abnormally low plasma glucose level Below 50 mg/dL in men Below 45 mg/dL in women Diagnose using Whipple’s Triad 1. Signs and symptoms of hypoglycemia 2. Documentation of low plasma glucose at the time patient is experiencing the signs and symptoms 3. Alleviation of symptoms with the ingestion of glucose and an increase in plasma glucose Clinical Significance (13 of 16) Types of Hypoglycemia Drug-induced hypoglycemia Accounts for over 50% of patients who are hospitalized for hypoglycemia Fasting hypoglycemia Diagnosed with a glucose level