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Biochem2 wk8- Integration + control of metabolism

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winniesmith1's version from 2017-03-27 20:56

Section 1

Question Answer
What is absorptive stateperiod when GI tract is full
What is post-absorptive stateperiod beyond absorptive state until next meal
A fasted individual is in which statepost-absorptive state
When is the absorptive state typically most pronouncedAfter the longest fast i.e. breakfast time
What happens after you eat breakfast1st meal of the day= most dramatic changes. 1st process= digestion. 2nd= Absorption. Blood glucose changes are therefore not immediate. Levels will begin to rise-15 mins after ingestion and peak between 30-60 mins ("typical" values)
What does bolus meana small rounded mass of a substance, especially of chewed food at the moment of swallowing.
What factors affect gastric emptying/absorption ratesize of bolus, complex CHO content, simple sugar content (GI) and fibre content.
How does fibre content affect gastric emptyingSoluble fibre will slow down gastric emptying. Insoluble fibre promotes transition of material through digestive tract.
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Section 2

Question Answer
How does the endocrine system respond to post meal blood glucose increaseBody changes focus from Glucose production → storage. Insulin release from pre-formed stores (rapid response). Synthesis and release of insulin if prolonged high glucose levels (pancreas; b cells). Plasma insulin conc ↑. Glucagon release (α cells of pancreas) is suppressed by insulin and other hormones (e.g. amylin) (paracrine) Plasma glucagon concentration ↓ Changes in hormone levels enable the body to control [blood glucose]
(*CHO in the liver post meal*) Why is the liver subjected to the largest changes in blood glucose?Hepatic Portal Vein (HPV): Vessel that moves blood from GI tract to the liver. The portal vein is not a true vein in that it does not drain into the heart. Function is are to supply metabolic substrates to the liver and to ensure that ingested substances are first processed by the liver before entering normal circulation. (Protection against toxins). Therefore sees blood from intestine before any other part of the body.
*Which glucose transporter mediates influx of glucose into the liver GLUT-2. 10-15 Km(substrate)mm (glucose, galactose & fructose)- liver, pancreas B cells, kidney, enterocytes.
*Which enzyme becomes inhibited?Glycogen phosphorylase. Catalyses conversion of glycogen to glucose-1-phosphate. Cleavage at the alpha(1-4) glycosidic linkages of glycogen.
*What will inhibiting glycogen phosphorylase do to glucose levelsReduce it. Glucose-6-phosphate is an inhibitor of glycogen phophorylase and G6-P levels are high when blood glucose is high.
*Which enzyme becomes activated?Glucose synthase.
*What does glucose synthase doElongation of glycogen chain at C4 position by adding glucose, activated by glucose-6-phosphate. Leads to elevated intracellular glucose-6-phosphate.
*Which ratio is also important in this enzyme control of metabolic substrate storage/productionInsulin/Glucagon. Insulin effects promote glucose conversion to glycogen and stop glucose production. Glucagon promotes conversion of glycogen to glucose.
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Section 3

Question Answer
(*CHO in the liver post meal*) What other metabolic process would we expect to be inhibitedgluconeogenesis
What is gluconeogenesisSynthesis of glucose from non-CHO sources.
Why is gluconeogenesis requiredTo ensure release of glucose into the blood during post-absorptive state to supply tissues with needed energy substrate.
What are the main gluconeogenic substratesLactate Glycerol “Glucogenic” amino acids (Mainly alanine and glutamine).
What gluconeogenic pathways occur in adipose tissueTG hydrolysis. Product = glycerol.
What gluconeogenic pathways occur in skeletal muscleLactic acid generation
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Section 4

Question Answer
What happens to glucose levels 1-2 hours post meal glucose release from liver falls dramatically (reaching almost zero). This limits the rise in blood glucose conc. In addition, liver continues to take up glucose (via GLUT-2) from the blood arriving via the hepatic portal vein. (These 2 actions combine to ensure blood glucose in maintained within desired range.
CHO in other tissues post meal- what happens to glucose uptake by skeletal muscle and adipose tissueIncreased
How do skeletal muscles/adipose tissue increase glucose uptake post mealincreased GLUT4 numbers on cell membranes. In addition, fat mobilisation is reduced: lowers the plasma conc. of non-esterified fatty acids (NEFA)- promoting metabolism of glucose. (changes causes by insulin).
What are changes in post prandial CHO metabolism mediated byGlucose- Lactate- Insulin/Glucagon
Lactate production and subsequent increase in blood lactate concentration always follows ingestion of a meal- Why?Immediately after a meal HPV glucose is high. Liver cannot take up all of this glucose. Glucose that is not taken up by the liver reaches muscles and adipose tissue. Some will be taken up (GLUT-1 & 4) and be converted into lactate (anaerobic metabolism). Lactate circulates in blood back to liver. Lactate is converted into glycogen.
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