Glucose Flashcards
Where does energy come from?
- From the oxidation of organic compounds (CHO’s, amino acids, lipids)
- CHO’s are major source from food
What are the 4 classifications of CHO’s?
- Size of base carbon chain
- Stereochemistry (3D arrangement)
- “D” or “L” configurations (most human sugars are “D”) - Location of C=O functional group
- # of sugar units
Classification of # of sugars
- Disaccharides (2 sugar units)
- Oligosaccharides (2-10 sugar units)
- Polysaccharides (>10 sugar units; most common is starch)
Describe reducing substances
- They must contain a free/active ketone or aldehyde groups
- All monosaccharides and many disaccharides
- Non-reducing sugar: sucrose
What is the chemical formula and molecular weight of glucose?
- C6H12O6
- MW= 180g
Where does glucose come from?
- Breakdown of CHO’s from diet
- Body stores (glycogen)
- Endogenous synth (fr. proteins, lipids)
How does glucose metabolism work?
- Most ingested CHO’s are polymers that cannot be absorbed
- Salivary and pancreatic amylase digests disaccharides
How/where are CHO’s digested?
- Intestinal mucosa (Maltase-glucose; sucrase-glucose+fructose; lactase- glucose+galactose)
- Mono’s absorbed by gut, hepatic portal vein supplies liver
- Glucose (β-D-gluc.) is only CHO used for energy or stored as glycogen.
How is glucose metabolized?
- Body converts gluc to CO2+H2O to produce ATP
- 1st step; use ATP and hexokinase to convert gluc in the cell to G6P
- Metabolized in 3 pathways
1. Embden-Meyerhof
2. Hexose monophosphate shunt
3. Glycogenesis
Describe the Embden-Meyerhof pathway
- Principle path for gluc oxidation
- Aerobic: glycolysis produces pyruvate = 2ATP in cytosol
- Anaerobic: pyruvic acid goes to lactate (glycolysis)
- Substrates other than gluc can enter this pathway (lipids and proteins)
What is gluconeogenesis?
The formation of substrates that can be converted to glucose from non-CHO sources
What is glycolysis?
The metabolism of gluc to pyruvate or lactate for energy production
- Anaerobic energy production less efficient
What is lipogenesis?
Conversion of CHO’s to fatty acids
Describe the hexose monophosphate shunt
- G6P detours from glycolytic pathway
- Allows pentoses to enter glycolytic path
- Resulting NADPH has reducing power- protects RBC’s from oxidative and free radical damage
Describe glycogenesis pathway
- In several tissues, mostly liver and muscles
- Liver synths G6P from glycogen to glycolytic path
- Liver also converts G6P to glucose via G6-phosphatase to maintain gluc level in bloodstream
- Muscle cells; no G6P, gluc only catabolized to G6P or stored as glycogen
What is the body’s response to a low plasma glucose?
- Liver uses; glycogenolysis (glycogen broken down into gluc), gluconeogenesis (gluc generated from non-CHO’s)
- During short fast: glycogenolysis from liver
- Fast>1 day: gluconeogensis (lowers glycogen stores)
What is/does insulin do?
- From β cells of islet of Langerhans
- Only released with plasma gluc is increased (hypoglycemic agent)
- Increases movement of gluc into tissue cells
- Increases glycogenesis, lipogenesis and glycolysis
Inhibits glycogenolysis
What is/does glucagon do?
- Primary hperglycemic agent
- From α cells of islet
- Released during stress and fasting
- Increases plasma gluc via glycogenolysis in liver and gluconeogenesis
What other hormones increase plasma glucose?
From adrenal gland
Epinephrine (fr. medulla)
- Released in stress, inhibits insulin secretion, promotes lipolysis
Cortisol (glucocorticoid)
- Stimulated by ATCH and stress, conserves energy for the brain
What other hormones increase plasma glucose?
From anterior pituitary
GH (Growth hormone)
- Released due to decreased blood gluc/inhibited when increased, decreases gluc entry to cells (anti-insulin), increases lipolysis and hepatic gluconeogenesis
ACTH (adrenocorticotropic hormone)
- Released due to decreased blood cortisol, stims cortisol realease
What other hormones increase plasma glucose?
Thyroid gland
TSH (pituitary)
- Stimulates thyroxine (T4) release
- glycogenolysis, gluconeogenesis, increases intestinal absorption of gluc
What other hormones increase plasma glucose?
Pancreas
Somatostatin (inhibits gastric secretion and somatotropin release)
- From δ cells of islet
- Inhibits insulin, TSH, glucagon and GH
Glucose reference ranges
Blood:
AC: 3.9-5.5
R: 3.9-11.0
Critical: ≤2.5 ≥25
24hr urine: <2.8
Renal threshold: 8.9-10.0
Describe hyperglycemia as it relates to diabetes
- Impaired fasting gluc
- Impaired gluc tolerance
- Diabetes mellitus; Inappropriate hyperglycemia due to defects in insulin secretion/action
