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Metabolism and Nutrition

Metabolism and Nutrition. Carbohydrates. Lactate Fructose Glucose Sorbitol. Lactate. Produced primarily by the placenta Energy source for oxidative metabolism Gluconeogenesis Does not occur in the fetal liver Lactate levels in fetus versus mother Higher in fetus than mother

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Metabolism and Nutrition

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  1. Metabolism and Nutrition

  2. Carbohydrates • Lactate • Fructose • Glucose • Sorbitol

  3. Lactate • Produced primarily by the placenta • Energy source for oxidative metabolism • Gluconeogenesis • Does not occur in the fetal liver • Lactate levels in fetus versus mother • Higher in fetus than mother • Levels fall postnatally to adult levels by 24 hrs

  4. Glucose • Maternal levels greater than fetal levels • Newborn concentrations increase rapidly to adult levels • Extremely low levels are peculiarity of those species with high fetal fructose • Low blood glucose concentrations prior to birth are partly a hypoglycemic effect of fructose

  5. Glucose - Calves • Postnatal levels • 3x higher than fetal levels • 1 day old levels are 2x adult levels • Postnatal increase due to • Spiking cortisol • Decrease in fructose concentration • Increased activity of gluconeogenic enzymes

  6. Glucose • Postnatally there are increased concentrations of • Glucose 6-phosphatase • Hexose bisphosphatase • Pyruvate carboxylase • Phosphopyruvate carboxylase appears and increases during the first day of life

  7. Fructose • Site of synthesis is placenta • Placenta is permeable to • Sucrose • Sorbose • Maltose • Lactose • Fructose • Impermeable from dam to fetus

  8. Fructose • Greater thermogenic effect • Very effective precursor for fatty acid synthesis and triglyceride synthesis • Excreted after birth without being utilized • May play a role in energy metabolism in young neonates

  9. Metabolism of Fructose • Glucose Sorbitol Fructose • Glucose Sorbitol • Sorbitol Fructose • Sorbitol Glucose NADPH DEPENDENT Aldose reductase NAD+ DEPENDENT Ketose reductase and sorbital dehydrogenase in fetal liver Aldose reductase in the liver, muscle and seminal vesicles

  10. Fructose and Sorbitol • Fructose and sorbitol are able to bypass the early steps in glycolysis • Phosphofructokinase • Sorbitol and fructose can be converted to the following by three pathways: • Glucose • Glycogen • Lipids • Or enter the TCA cycle

  11. TCA Cycle Review

  12. One Pathway of Sorbitol and Fructose glycolytic pathway • DHAP G3P Pyruvate • Pyruvate • Acetyl CoA • DHAP=dihydroxyacetone phosphate • G3P= glyceraldehyde-3-phosphate isomerization Lactic acid (anerobic conditions) TCA cycle as acetyl CoA (aerobic conditions) Energy via respiratory chain Used as substrate for lipid synthesis

  13. 2nd Pathway • DHAP G3P • G3P provides glycerol backbone of synthesized triacyglycerols, phospholipids and other lipids Reduction

  14. 3rd Pathway • DHAP can be condensed with G3P by aldose to yield fructose-1,6,-diphosphate leading to glucose and glycogen

  15. Intestinal Absorption • Sorbitol is absorbed by passive diffusion • Glucose is actively transported • Fructose transport • Partially active and carrier mediated • Does not compete for the glucose-galactose system • Rate of intestinal absorption is intermediate to glucose and galactose, but is utilized more rapidly in the tissues • Absorption is enhanced by the presence of glucose • A diet high in fructose • Shift in site of lipid synthesis • Adipose tissue to liver

  16. Intestinal Absorption • Sorbitol • Rate of intestinal absorption is 1/3 of that of glucose • May be due to its laxative effect in calves • It is metabolized in single pass through the liver • Very low levels are found in blood or urine

  17. Lipids • Triglycerides and cholesterol • Major components of plasma lipids that circulate as lipoprotein particles • Fetal calves • Very low levels of cholesterol and high density lipoproteins relative to maternal levels

  18. Maternal Versus Fetal Levels of Main Metabolic Substrates

  19. Ruminants vs Monogastrics • Nutrition and metabolism differ between ruminants and monogastrics • Some metabolic activities in calves and lambs are more similar to those of a mongastric newborn than to that of an adult ruminant • Blood metabolites of neonates and/or preruminant calves differ from mature ruminants due to the immaturity of various organs and rates and/or appearance of specific enzymatic activities

  20. Ruminants vs Monogastrics • Blood glucose concentrations in calves during the first several weeks of life are similar to humans • Mature bovines have lower blood glucose • Glucose levels increase after birth in the calf • Glucose levels further increase after milk is ingested • By twelve weeks of age glucose levels decrease • Decrease in glucose correlates to the maturity of the calf and increased microbial environment of the rumen

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